If you have any questions you want answered, feel free to drop me a note. If you’ve got a question, chances are, there are lots of others out there with the same question. So ask away!
Note: all comments are moderated unless I’ve approved one of your previous comments. Almost everybody gets thrown off by this, but I moderate comments to avoid spammers. The downside of this is that you won’t see your comments post until I’ve had a chance to review and approve them. Sometimes this can take days (sorry!) Thanks for your patience.
Great site, it’s been a wealth of information for me. We recently moved into an 80s log home outside of Portland, OR, with, you guessed it, a beautiful tongue and groove cathedral ceiling and an old metal roof. All was well until the the temperature dropped below freezing and the ceiling started dripping, even when it was dry outside. I’ve read your suggestions, and had all kinds of ideas tossed around by roofers, but the latest was a new one that I hadn’t see as an example here, but just might work. I’m hoping to get your input!
The existing roof is on block foam and wooden spacers, with no ventilation. The roofer I’m considering wants to remove everything down to the tongue and groove, and then ice and water shield the entire thing, top to bottom. Sounds good so far. This is where it gets interesting. He does a lot of metal buildings, and wants to cover the ice and water shield with a 3 or 4″ laminated fiberglass insulation blanket (so plastic wrapped fiberglass) typical in those applications, and then lay the 12″ 24ga standing seam metal panels directly onto the fiberglass blanket. His plan is to skip any wood supports, and instead screw through the blanket directly into the tongue and groove. In a way, this is a lot like an unventilated foamed construction, but less labor-intensive. He swears this is a solid approach and has done it before.
What do you think? We had two periods of ice dams last year with big snows, so that’s one concern (assuming the insulation proposed is only ~R-10). I’m also wondering if laying the panels on unsupported insulation will be an issue over time, or if moisture will collect in the plastic surrounding the insulation. The most expensive risk would be rotting the T&G ceiling, but I’m hoping the ice and water shield will prevent that. He’s assured me he won’t shoot any fasteners through the ceiling into the interior of the house, which I’ll put in the contract. We’re in a tight spot and need to do something before the fall rains arrive!
Would love to hear your input.
Thanks again for the great site,
Thanks Dave. Appreciate the feedback.
From your description, the current situation is very likely due to the moisture inside the house going up through the T&G ceiling and condensing/freezing on the underside of the roof. Quite a bit of ice can form which will then melt over time leading to substantial “drips”. The most surefire solution to this is to block the passage of moisture through the T&G and into the cavity above it. The “easy” way to do this is pulling off the existing roof (sounds like they are suggesting doing this anyway) and putting a layer of board foam (XPS or foil faced PolyIso) directly behind the T&G. Then, have high density spray foam applied to the back of the foam board. Once you’ve taken these steps, you can fill the rest of the cavity with an insulation of your choice, like fiberglass, etc. However, if you’re going through the first two steps, you may as well just add more spray foam. 1″ of XPS plus 2″ of spray foam would give you about R-20.
If you do this, then you can use whatever method your builder wants for the roof above it. Best to use a ventilated roof so you have all your bases covered. However, with the combination of foam board and spray foam, your ceiling should be virtually moisture-proof.
Note – you’re probably wondering “why the foam board and spray foam?” The foam board provides cost effective R-Value per inch of thickness and greatly reduces moisture leakage through the T&G. However, by itself, it wouldn’t be air-tight, which is critical. The layer of spray foam over it makes it completely air-tight. Block the air and you block the lion’s share of the moisture transfer.
The other reason is that if you just spray foam to the back of the T&G, it will “glue” it in place making it near impossible to remove if you need to. There’s also a chance that the spray foam would ooze between any cracks in the T&G, which will make it ugly because foam is next to impossible to clean.
Thanks for the quick reply, Ted!
A challenge I should have specified is that the only wood on the outside face of our T&G are the firring strips the existing corrugated metal roof is attached to. Ours is a log home, with exposed log purlins holding up the T&G from the inside. Based on how rotten the washers are on the roof screws, and the fact that many of the screws spin in place, I’m assuming the firring strips are rotten and coming off in the roof removal. We’d then be looking at a vast, flat expanse of outward facing T&G, nothing else.
I’m really hoping to avoid the cost, roof weight, height, and thermal bridging that would come with adding 2×4 or 2×6 purlins on top of the T&G to create a cavity that we could fill with spray foam. If we wanted to create a typical vented cathedral roof, we’d also need to sheath, provide air gaps, and install soffit vents, which is a huge project compared to doing a thinner “hot” roof, which I’m hoping we can get away with?
A roofer who was out yesterday suggested a similar approach to the one I first mentioned, laying out ice and water shield across the entire expanse of T&G as the first step, and then in his case nailing down 1″ polyiso, and then laying the standing seam roof panels directly on the foam and fastening them through the foam to the T&G. No purlins, no extra wood on the roof, but only R6. He also said taping or filling gaps between polyiso sheets was unnecessary. It’s possible I could go up to 2″, or two layers of overlapping 1″. With the ice and water shield across the entire T&G, I’d have stopped the moisture transfer from inside the house to the outside, correct? Then it’s a matter of reducing the radiant/conductive heating from the T&G with whatever insulation approach we use to the point that it doesn’t heat/cool the air trapped between the insulation and the back of the metal roof panels to the point of condensing, right?
I like your idea of spray foam, but again I’m hoping to avoid framing a whole roof cavity on top of my flat T&G.
So between the two approaches (ice & water/polyiso/roof panels and ice & water/pvc backed fiberglass roll/roof panels), which do you think will fair best?
The way I see it, the polyiso will maintain it’s thickness and R value, but leave slight air volumes under the metal roof panels that may become condensation sites, as well as the uncertainty of the foam’s performance over time and the potential for air gaps between foam panels. The fiberglass approach will have a minimal R value (R2? R4?) once it’s compressed by the roof panels, but would effectively conform 100% to the back side of each panel, reducing the air volume where moisture could accumulate.
A possible third option could be 1″ or 2″ polyiso with 2″ (or 1″?) laminated fiberglass, which might combine the best of both systems? But if my stack up is T&G, ice and water, polyiso, pvc-backed fiberglass (with the pvc in contact with the polyiso), and then metal roof panels, will I trap moisture in the polyiso layer between the ice and water and pvc? Or will I have excluded airflow enough that it’s a non-issue?
Or at a higher level, do I need to abandon this thin, hot roof idea and vastly increase the scope to build a traditional roof plenum? Really hoping that’s not the case, as we’re pumping money into this house at an alarming rate!
Thanks again for taking the time to help us out!
Ah, I see…
Ok, the ice and water shield across the T&G should provide an airtight moisture barrier. That itself should eliminate most of the issues you’re having, as you’ve figured out.
The fiberglass is going to work exactly the opposite of what you described. Compressed against the surface, it will hold any moisture in direct contact with the roof and can lead to bad roof rot. Much better to have an air gap between the polyiso and the roof. The double layer with seams staggered is a method recommended by the building science people. Even if the chance of moisture getting past the ice and water shield is low, it’s not zero, so the extra protection of dual layers is worth it.
I understand you’re talking about encapsulated fiberglass, but in that position, you don’t really want more vapor barriers. I think you’d be much better off with a thicker layer of polyiso. Two 1″ sheets gives you a pretty good R-value in a compact package. Thicker is better. You’ll just have to decide how much space you’re willing to use.
Anything along these lines should be vastly better than what you’ve got now (which sounds like it’s probably all rotten). Personally, I’d prefer to have a little air gap between the top surface of the insulation and the underside of the roof. Most recommend 1″+
Whatever you do, keep it airtight inside and structurally sound on the roof side.
Sorry to insert this reply out of sequence, but I didn’t see a reply button lower down. New developments! One of the roofers pulled up a section of the existing metal roof, and we found that on top of the tongue and groove there are 2×4 battens running horizontally, with 4×8 foil faced polyiso fully filling the gaps in between. The foam in the small section we pulled up looked okay. The roofer now wants to remove the existing metal, pave over the entire foam and batten assembly with ice and water shield, and lay down reflectix (metal faced bubble insulation) and then the new standing seam metal panels directly on top, fastened to the battens.
The issue I see is that the current roof assembly is T&G, then “black plastic moisture barrier” (haven’t visually confirmed this, but it’s in the drawings), then the foam/batten layer. If we go with his plan, the roof will be T&G / black plastic / polyiso / ice and water shield / reflectix / metal panels. Since the black plastic is clearly compromised, it seems like the moist air from inside the house is going to go up into the air spaces between the black plastic and the ice and water shield and get stuck there, no? We don’t have room to spray foam on top of the foam board as you suggested, unless we add a lot more volume to the roof assembly.
Seems like there’s a risk of insulation/batten rot, as well as a chance that condensation will form on the sticky side of the ice and water shield where there are gaps between foam sheets or battens, if we take this approach, no?
It’s a ton more work to pull everything off to the T&G, and there’s the risk of breaking up the polyiso, which I’d like to re-use, but it seems like putting the ice and water shield directly onto the back of T&G would be the better build. What do you think? Could we get away with following the roofers suggestion to just hide everything with ice and water? Would certainly save a good chunk of time and money.
Thanks again for all your help!
I agree with your analysis. It sounds like a whole lot of vapor barriers that would be very risky for trapping moisture. You typically only want one vapor barrier in any construction like that. It appears that you would need more analysis before proceeding. If it were my house, I would carefully cut out some of the T&G where you have observed the dripping so that you can inspect what is happening above it. It may turn out that there is just a small area where the vapor barrier above the T&G is ripped and allowing moisture to go through. I would be particularly suspicious of any places that there might be light fixtures, ceiling fans, or other electrical boxes cut through the barrier. Those always prove problematic.
Hi again Ted!
Was hoping I had this sorted, but trying to keep costs down, get this roof on before the rainy season, and keep the chosen contractor in good spirits has got me into a corner. Your suggestion to have a engineer come out would be ideal, but I can’t pull that off and keep things on track, unfortunately.
I’m hoping to get your feedback on what I hope is the last iteration of what our roof will look like. To refresh, the existing room if a is cathedral T&G ceiling, followed by black plastic vapor barrier, horizontal 2×4 battens with Polyiso sheets in between, and then corrugated metal on top, fastened directly to the battens.
The roofer doesn’t want to tear up the battens and foam, so the current plan is to fill in any gaps between the foam sheets and the battens with spray foam, but not spray any additional foam on top. That will leave us with a level surface with the top of the battens even with the top of the foam sheet. Then he wants to cover the entire roof in ice and water (adhered directly across the foam and battens), and then, because he’s a big fan of Reflectix, lay that down between the ice and water and the new standing seam metal panels. I realize this is a non-traditional use for reflectix, more akin to a commercial roof, but he swears by it. Aside from a little added cost, I don’t see that it will do anything harmful, so I’m willing to do this if he warrants the whole thing.
So in this scenario, the new roof will have an old black plastic air barrier on the back of the T&G, and then a (hopefully) air tight layer of ~2″ polyiso with the edges foamed, then ice and water, followed by reflectix and metal panels. Our main goal is avoiding rot and condensation, not final R value. I realize that there are multiple air barriers in this system, but effectively all of the system is an air barrier at this point, no? Plastic sheet, sealed foam, ice and water, reflectix, all in a full-contact sandwich. Every layer is an air barrier, and in full contact, so is that okay? Seems pretty similar to just filling the whole volume 100% with spray foam, no? And now at least the ice and water is close to the metal panels, which should keep any condensation from making it’s way back to the T&G.
Would love to send you a few photos, but don’t see a way to do that….
Thanks again for all your help!
Thanks for the memory refresh on the planned design!
Your proposal sounds good to me. As long as you do a good job air sealing, the chance of condensation on either side of the structure seems minimal. Plus, if you ever get a roof leak, the water will run down the Reflectix or water shield and out at the soffits rather than into your house 🙂
Thanks Ted! Really appreciate your help with my project. Job starts in two days!
Hi Ted, I bet you were hoping this one was all wrapped up!
Tear off began on my roof today, and they found that much of the polyiso is compromised and will need to be replaced. Under the polyiso they found 30# felt, in good shape, which was a surprise. The original plans called out a plastic moisture barrier, which is what we based our plan on. I’m assuming there is no additional moisture barrier under the felt, but I’ve asked the roofers to check.
I’m now faced with the cost of replacing 1,800 sqft of polyiso, but am also wondering if the felt is a sufficient air barrier against moisture from inside the home passing through the T&G and into the unventilated roof space? I could incur even more expense and have them tear off the felt and replace it with ice and water….
So the two approaches to consider are now…
1.) Original T&G, old felt, new 2″ polyiso between old 2×2 battens and foamed around the edges, new ice and water, new reflectix, and then new standing seam panels
1.) Original T&G, new ice and water, new 2″ polyiso between old 2×2 battens and foamed around the edges, new ice and water, new reflectix, and then new standing seam panels
Knowing that option 2 may increase my cost by $5,000-$10,000, what would you advise?
Really hoping this is it!
Thanks as always,
Oh, that’s a shame. Felt paper actually is an interesting material. It is highly vapor permeable In some situations and less permeable in others depending upon humidity levels. in normal roofing applications this is a good thing because it allows the water vapor to go out slowly through the roof while not allowing water through. However, whomever did the installation under your tongue and groove ceiling didn’t understand this. They probably thought it was a good vapor barrier. Instead they inadvertently used a product that allows water vapor to pass through which is why the poly iso was compromised. In this type of application a simple plastic vapor barrier or the durable ice and water shield that you suggested would be much better. If the original installer had used blue board or pink board insulation, they wouldn’t of had a problem because those are XPS Which is much more moisture tolerant than poly iso.
If they are going through all this trouble, it really would be easiest to spray foam directly to the back of the felt paper so you don’t have to tear everything up. The spray foam will provide a good vapor barrier right behind the felt paper eliminating the moisture issues. Depending upon how bad the poly iso is, you might be able to just spray foam directly over the back of that. Some moisture would get into the poly iso but since you have additional insulation (spray foam) on the back of it, it would minimize the chance of condensation inside the poly iso which would allow the poly iso to safely give up its moisture back into the living space. It really depends how badly moisture saturated the poly iso is.
Hi Ted, thanks for the speedy reply! I don’t think blowing foam will be an option on our timeline, unfortunately. Assuming we’re going with rigid foam, should we use XPS instead of Polyiso. In this ice and water sandwich situation, will one perform better than the other? The contractor just bought some polyiso, but I’m wondering if that was the best choice. Mostly I’m curious about moisture issues over time, as well as blowing agent released into the essentially sealed cavity. The polyiso is blown with pentane. Not sure if that poses an explosion risk if captured in a sealed envelope. Never heard or a roof blowing up, but the idea crossed my mind…. Thanks!
With the ice and water shield, I’d be less worried about moisture getting to the polyiso. The natural moisture in the cavity will likely just mirror the moisture levels in the outdoor air, even if it’s sealed somewhat. The situation where there is an issue was with a tongue and groove ceiling and so a lot of moisture was able to work its way up into the polyiso. I can’t comment on outgassing. My guess is that most of that occurs early on in the life after the panels are formed, but who knows. I don’t know enough chemistry but I have to imagine if there was some sort of flammability/explosion risk that we would have heard about it by now, lol.
Hi Ted, project is underway, and I must admit, a bit terrifying. I’m in need of your advice again! The polyiso they’re finding is shot, so they’re replacing all of it with new foil faced poyiso. The 30# felt that was between the T&G and original polyiso looks good, except over the eves where there was no insulation at all. In the compromised areas, they placed ice and water over the felt to better protect the polyiso they’re adding there to support the roof deck, but without removing the horizontal wood battens that separate the polyiso sheets first. Ran it right up and over it all. Interesting approach, but it made me wonder if we should do that everywhere?
Side note, the roofer didn’t want to tear up all the battens and original 30# felt, due to the sequence he’s using to progress across the roof daily without leaving it open at night (we have lot’s of overnight dew this time of year).
That said, he may entertain adding ice and water on top of the 30# felt and battens everywhere, as he did over the eve. Basically making a sandwich of the polyiso with ice and water on both sides. So…. Original T&G, old felt, old 2×2 battens, ice and water covering everything listed prior, new 2″ polyiso, then ice and water again, over the entire flat surface, reflectix, and then the standing seam panels. One funky sandwich, to be certain.
Would this be better than the current plan, that is the above without the bonus inner layer of ice and water covering the battens and old felt?
What’s not clear to me is if the layer of ice and water over the felt and battens with be a benefit or a liability. On one hand, it won’t let any interior moisture contact the poyiso, but on the other hand, if any moisture from outside makes it into the insulation cavity, it will literally be encapsulated, since the the two layers of ice and water in this approach lay directly on top of each other as they pass over the battens, making a seal.
Skipping the interior ice and water layer would at least could allow some drying back toward the inside of the house through the felt, yes? But it could also let moisture through the other way. I’m at a loss as to whether this is a good or bad thing. Will the fate that the polyiso is foil faced mean that some moisture in the felt is irrelevant for the insulation? And will the fact that the the entire outside surface of the polyiso is now going to be covered with ice and water in all scenarios (unlike the original roof build) dissuade moisture from even venturing into the insulation cavity, since there’s no airflow out of the cavity on the roofing side?
A couple new details learned this weekend in case they’re relevant: (1) there are a small number of gaps in the T&G where you can actually glimpse the back of the original felt, probably due to the house shifting over time (log home with log purlins); (2) we can’t spray foam the edges of the polyiso sheet because it’s already a force-fit between the battens.
Thanks again, as always! You’re helping me keep my sanity! Will definitely be hitting up that donation button : )
Hi Dave. Is the existing polyiso the stuff with the felt-like coating on it? If so, I can see how that would have absorbed all the moisture from inside the house. The foil faced should minimize that.
In your construction, I’d be a lot more concerned about the moisture from inside than from the outside. The inside moisture is continuously trying to get up there and any moisture that you “trap”, should be done on the warm side (i.e. as close to the inside of the house as possible). That moisture will stay as vapor. If you put the ice and water shield on top of the insulation, that will trap moisture on the “cold side” where the vapor can condense into liquid water – no good. The foil faced poly iso will help a lot to reduce the vapor that escapes the house but I’d be a lot more comfortable if the ice and water shield was on the warm side of the polyiso.
p.s. got the donation – thanks so much! keep the questions coming!
Thanks for the quick reply, Ted! The donation was well-earned with your infinite patience!
The original foam that was removed was foil faced, both sides, like the stuff going in. Somewhere between 20 and 40 years old. The facing didn’t have a date code, but it also didn’t have a web site either (if we dare date it by the invent of the modern internet ; ) ) It was mostly intact, except the ridge cap stuff, just darkened around the edges, brittle, and chewed on by mice. (Any idea if mice have a taste for ice and water shield??)
The plan, currently being executed, is to have ice and water on the outer face of the polyiso, between it and the metal roof panels, as the secondary water barrier. Since the roof is only ~R12, it seemed like there would be a high likelihood of condensation forming under the metal panels due to the “warm” insulation heating outside air trapped between it and the back of the metal panels on a cold day, which would then seep down onto the insulation. Or at least that’s what we surmised…
What to do you think about adding the intermediate layer of ice and water between the old felt and the polyiso, assuming we’re keeping the outer ice and water layer? Sounded like you were in favor of that in your last comment, if I understood correctly?
Do you see any issues trapping the old felt under that intermediate ice and water layer? Presumably the felt is only moisture permeable directly through the surface (through micropores?) and not permeable laterally, from a vapor perspective, so it should just sit there basically inert, if the ice and water is bonded to it, no?
I could probably get the contractor to add this scope for $4k, whereas he wanted $10k to tear off everything and lay down ice and water without the battens and then add new battens (that was his “not going to do it” price, I think). The only weirdness is trapping the battens, but other than being odd, and making a bit of a puzzle for a future roofer, I don’t see any real issues, do you?
Thanks as always!
This is a tough call. Given the construction, an air and moisture barrier directly above the T&G ceiling and below any insulation is a necessity. I don’t see a problem with the existing felt.
I’m not a fan of putting another layer of rubber on the other side, however I understand the need for some water barrier below the metal roof. Ideally, one would want an air space above the polyiso so that any moisture could flush out like a normal insulated roof, with insulation, ventilated air channel then roofing. If that’s not a possibility, then the rubber sandwich around the polyiso if done securely, would be very similar to the layers of aluminum on the polyiso. I don’t see that as a deal breaker.
I read one of your articles from 2019 regarding tongue and groove ceilings. Our house was built in the 1980’s and we bought it 12 years ago. In September 2019, we hired a contractor to change out our skylights, roof and siding. Long story short, he did a horrible job, and we had to fire him mid project. After he started to change out the roof, we started to get this small dark brown drips throughout the house wherever there is tongue and groove ceiling. We also notices occasional drips on the ceiling. We also now have a horrible stink bug problem. I am wondering if the changing of the roof with the tongue and groove ceiling has created a water vapor issue. Additionally, if there is that space in the roof, can it be lending itself for the stinkbug entrance?
Lastly, our electric usage has also risen significantly; so curious if there is something that potentially wasn’t done that could have made the roof less energy efficient, causing us to utilize more climate control?
Thank you for taking the time to read through this.
I’m sorry to hear about your home’s issues, it sounds like a real headache!
If I’m understanding correctly, your home already had tongue and groove ceilings and the contractor worked on the roof/siding and skylights?
Did you have any other work done on your home or did anything else change with the heating/cooling systems? The issues that you’re having might be related to the work but it could be coincidental.
An important question is – what time of year or during what weather conditions is the dripping the worst? Cold or hot weather? Humid or dry outside? That would help track down the problem a lot.
You note that the drips are occurring throughout the house, so I’m assuming that there are some areas where the ceilings weren’t touched.
Normally, the roof really shouldn’t have any effect on the inside of the house. However, there are things they could have done to the roof that could have caused issues. For example, if they took off the roof sheathing as well as shingles, they could have done things inside the roof cavity that affected you interior climate. They also could have done something with the roof underlayment that could have effects. For example, if the original roof was “tight” they might have ripped it off during the roofing job and done an inferior job with the new roof. Alternatively, it’s possible that it was leaky before and they used “ice and water shield”, which is common nowadays. This is a thick rubber mat that sticks on the roof. It’s essentially moisture impermeable and makes the roof completely tight. It’s conceivable that that would have increased the moisture level inside the house. So there are a lot of possibilities depending on exactly what was done.
It’s also possible that unrelated issues are causing the problem. For example, if your heating system has a whole-house humidifier, it might not have been in operation before and an HVAC tech could have cleaned it and turned it on, greatly raising the humidity levels inside the house. This could also increase your electricity usage as some of these system are tied in to your hot water lines.
It could even be something as seemingly unrelated as getting more house plants. The moisture evaporating from the house plants can lead to indoor humidity issues. And, houseplants can also lead to big sinkbug issues. I had this exact issue in my home. When stinkbugs first appeared in my area, we had huge numbers in the house. My wife finally figured that they must be living in our large potted plants and we (sadly) got rid of the plants. Now we get a few stinkbugs but vastly fewer than we used to get.
Feel free to send me more details and we can keep trying to pinpoint your issue.
just read your blog on cathedral ceilings and mold and insulation. i wanted to drop my plan here and see what you think.
i have my ceiling split into 3rds. 1 flat ceiling, 1 cathedral ceiling, and 1 flat ceiling that then of course has 2 gable inside walls for the great room that need insulated vertically. we used 5/8″ drywall and installed furring strips nailed to the bottom of the trusses since our trusses are 2′ on center and i didnt want the drywall to sag overtime even though its rated for 2′ on center. we installed the furring strips at 16″ on center which really locked the trusses together and the drywall is very stiff now. we live in Ohio and only an R49 is needed but we want to do an R60 hence the 16″ on center furring strips for more weight that can be carried with no drywall sag over time.
all of my LED lights dont require a recessed box and can come in contact with insulation but i bought those Tenmat rockwool insulation covers that i put over the LED lights so they can be replaced one day and not get insulation everywhere and all boxes for fans etc. i spray foamed the Tenmat to the drywall, i also spray foamed the drywall edges, corners, wire penetrations, plumbing vents etc etc. i believe i sealed about 80% of the ceiling as tight as i can get! the only spots not sealed are the long edges of the drywall where they are screwed to the furring strips length wise. i was hoping taping and mudding all edges of drywall will help stop air flow and we will use an approved class 2 vapor retarder ceiling paint.
my other plan was to use closed cell spray foam on the drywall and inner gable end walls to vapor barrier everything and get a 100% tight ceiling. my issue is 1.) the cathedral ceiling at the top plate will be hard to get into and spray since it gets tight in there and 2.) im worried about the closed cell spray foam getting under the trusses where the furring strips have the drywall 5/8″ lower. im worried when the foam expands it could push the drywall down as it expands in that gapped location.
im also worried about the venting of the cathedral ceiling part. we did porches in this location front and rear so we dont have soffit venting here because on the other side of the roof decking is the inside of the porch attic. if i blow in my R60 cellulose in the cathedral parts the R value will not be an R60 and it’ll be smooshed between the drywall and the roof decking. the max that area has is about 8″ tall. on all the flat ceilings we have soffit vents with plastic air channels so we do have a lot of intake and ridge vent air flow for the main house attic. the porches will also have there own soffits and ridge venting but the part of the porch thats over the main house attic will be completely sealed off unless i cut holes in that sheathing and the porch and house attics will share the same air. after reading your blog im worried about no air flow and the insulation being in the cathedral ceiling parts and again at the ends it touching the roof decking even though this roof decking is under another roof that of the porch roof above it.
PS i have a youtube channel and this video will be posted 2/12/22 addressing these concerns. id love feedback. thanks scott.
I’m going to check out your videos and get back to you after I get a full image of what you’re doing. Looks like a great set of videos.
Hi-not sure how to use this forum but you are so smart! I have a 1930 small cabin and don’t think there was ever insulation. Someone bootlegged a small triangle room above our living room…. and we took it out because we didn’t need that room – low ceilings and just useless. After taking it out our living room opened up to beautiful cathedral like ceilings. Our former contractor stiffed cheap insulation in the cathedral ceiling between all the rafters right up against the actual bottom of the roof (that appears to be plywood held up with flat wood slats across)… without any ventilation. I wish I could drop a photo.
He left the job due to car accident. Then I started to research the insulation cathedral ceiling concern and I’m worried about condensation since the insulation is up against the roof…. So before we close up the ceiling with shiplap…. I am now told we can do spray foam. I think there are no soffit vents.
I read your article that high density sprayed polyurethane foam creates an air-impervious barrier and is also very effective at slowing vapor movement when applied at adequate thicknesses (greater than about 2 inches)… can I send you a photo?
My fear is what if it is not air tight? It’s such an old house I bet nothing is air tight in that roof… Would this make it air tight and then we don’t have to worry?
Or if we left it with no Insulation will we still have a condensation issue?
Thanks Elizabeth. The foam should work great and will seal it up, as you surmised. If you hire a foam company, they should advise you as to whether or not they’d recommend removing the insulation that’s already stuffed in there. Specifics depend on your local climate and building codes.
Good luck with your project. Glad you’re doing your research!
Hope this message finds you and your family well and you’re staying cool, if you’re experiencing the 90-degree heat wave we’re getting here in Michigan. That just so happens to be the reason for my message. I know in winter we want to keep the attic space as close to the outdoor temperature as possible to prevent ice dams, condensation, etc. But in summer, I think it would be beneficial to keep the attic space as cool as possible, to try and keep that heat from trying to radiate down through the ceiling into the conditioned space. Is there any benefit in insulating the gable end walls to aid in this? I know it’s not a large swatch of square footage, but every little bit helps?
Best Regards, Andy
The lion’s share is radiating down from the roof because of solar heat gain so I would guess that adding a radiant barrier under the roof would be much more effective than adding insulation to the gables. That’s the one use of radiant barriers that really makes sense because it actually works remarkably well.
Hi, would Sika Pro select r-matte 3 (1/2″) work as a radiant barrier if attached to the underside of the rafters? I have a gable end, single story house with apx 12″ of blown in insulation and a ridge vent. I live 60 miles north of Houston, Tx so usually do not use much heat. I do have a 4 ton central A/C with an 80k btu propane furnace. Access to the outer sides (lower portion of the attic) would make a roll product difficult to install. I could do the first 8 ft with foam board and then use a roll (maybe perforated) product after that? Would moisture build up be an issue?
Rick Hirsch Hirsweet Aussies Rick’s Southwest Mercantile
Hey Rick, as long as you don’t seal up the entire attic and let air flow, it should continue to let the moisture flush out. Using a section of radiant board under the rafters would be great. They also have perforated radiant barrier foil for the rest where access is better. I used this stuff in my own garage attic and it has been great.
Merry Christmas and pre-Happy New Year! I hope this email finds you and your family healthy, wealthy, and well!
I understand the importance of air sealing an attic and the usual offenders: recessed cans, electrical boxes, wires through top plates, etc. But I also see some people recommending to spray foam/air seal the top of any partition wall plates where they contact the rafters/ceiling joists. This I don’t understand as those junctions will almost always be covered by joint tape, drywall mud, and paint. What are your thoughts in regards to sealing those junctions?
Radiant barrier is actually something I hadn’t thought of that may make a lot of sense! I’ve been debating on insulating the attic in my garage. It’s an open truss ceiling, no drywall or insulation currently. I’d like the insulation, but also don’t want to lose my access to overhead storage and access, not that I have a lot of weight bearing up there since they are trusses.
Glad to help!
I bought the brand new home in Oct 2018. Recently I found moisture issue on the OSB sheathing in the North eastern exterior wall which has the moisture level from 35% to 50% during winter months and which seems to be really high. In the attic the same North eastern exterior OSB sheathing is dry. The other exterior walls are normal and they don’t have any moisture issue in the OSB sheathing. My home is wrapped with Tyvek and has Vinyl siding. The inside humidity during winter months are between 28% to 32%. I checked for water and sewer pipes leak and there is no issues with them. These moisture issue is happening only in the North eastern exterior wall during winter months and disappear in summer months. The drywall inside the home on North eastern wall does not have any issues. Can you please let me know your thoughts on that.
How did you find the moisture in that wall? The sheathing wouldn’t be exposed unless you pulled the siding and Tyvek. Also, how did you measure the moisture in the sheathing? Just asking because I want to understand the problem more before proposing any possible answers.
There is sewer pipes in the north eastern exterior wall that started rattling (sounds like dripping) during winter months when using hot water. So I opened the drywall of the North eastern exterior wall to check for sewer leak and thus I found the moisture in the OSB sheathing after opening the drywall and removing the installation. I did the home inspection recently to get a better understanding of the moisture issue and the inspector brought moisture pin meter reader, depth moisture meter and thermal camera through which he measure the moisture level on the OSB sheathing from the inside of the home. I got the full inspection report and I am happy to send to you if you want to have a look at it.
Ah, very good.
So the pipes run through the cavity of that wall. My guess is that air is flowing into the wall cavity alongside the pipes. That air is carrying moisture from the house into the wall. The moisture then condenses or freezes inside the wall since the sheathing is very cold.
Can you follow the pipe down the wall to the hole it comes through from below (at floor level)? You should seal the opening around the pipe with canned spray foam if you can. You want to make sure no air flows up through that hole. You might also be able to figure out where the pipe comes into the wall down below, like up from a basement, and seal any other openings around the pipe.
This is my best guess as to what is causing the moisture problem from what you have described.
Sure will we get those holes sealed using foam. Just curious if this moisture issue is caused due to condensation, then is it normal to have the level of moisture of 35% to 50% on the OSB sheathing? Also the moisture issue is not just in that stud cavity alone but I found the moisture issue is present in the entire north eastern wall of length 40Ft.
That Is extremely high moisture if that is the actual moisture content of the wood. If the entire wall is that moisture level, it’ll be important to find out how the air is getting inside of the wall. Is it possible that the stud cavities are open at the bottom allowing air from the basement for example to flow up through the walls?
I am not sure about the stud cavities in the basement. I do have the finished basement and will definitely look at them to see if they are open. Also want to let you know one more thing. There are 4 HVAC vents that are going through the same north eastern wall to my upper floor. The HVAC vents seems to be insulated really good on the backside and those are not touching the OSB sheathing. By any chance the heat produce from the HVAC vent might cause this moisture issue in the entire north eastern wall?
That is quite likely the source. The air going through those ducts Is carrying your moisture from the house into those cold walls. Any air leaking out of the duct will be a problem. Since most HVAC contractors do not seal the ducts well, almost all of them will leak. It is a bad building practice to run ducts through exterior walls. I’m assuming these are sheet-metal ducts and not one piece plastic insulated ducts. The one piece ones are long runs of continuous material so they will not leak but it is rare for them to be used in wall cavities like this because they are round and they don’t fit without crushing them So builders will use oval sheet metal ducts that are meant to run through walls. Unfortunately, if that is your problem, the only solution is to cut out the sheet rock to get access to the ducts and then seal them tightly using mastic. Tape is no Good because the adhesive will fail overtime and then you’ll be stuck with the same problem again. This calls for a permanent solution.
Yes as you mentioned we have the oval sheet metal HVAC ducts installed for the entire home. Sure I will follow all of your suggestions. I really appreciate all your efforts and time for looking into my issues and providing good solutions.
I would suggest doing a little exploratory work we are one of the ducts runs through the wall. If you’re handy with sheet rock you can carefully cut out a section to examine the wall around that area. If the duct is leaking as we suspect then the moisture will be most built up near the seam where the pieces join together. Because of the heat moving through the duct you probably won’t see ice, just moisture buildup. Good luck!
Here is the update regarding the moisture issue in my home. Last week the siding and roofing contractor came to my home and pulled 2 vinyl siding on second floor and 2 on the first floor of the northeastern wall where I have a moisture issue. On that day, the outside temperature was around 50°F. We found water droplets behind the vinyl siding as well as on the top of the Tyvek. The OSB sheet outside was also wet. Since we didn’t pull all the vinyl siding on that day we don’t know where the water is coming from also where exactly the leak is. I have couple of questions as below.
Can water get behind vinyl siding?
Also can water pass through Tyvek?
Can I send the exterior pictures of my home to your email id tedinoue@Gmail.com? so that you can get a clear idea of it.
I wouldn’t worry about moisture on the exterior under these conditions. When the outside conditions go from very cold to warm, you are almost guaranteed to see condensation buildup because the walls are still colder than the outside air. However, if the same thing occurs without a big temperature increase, that would be more worrying.
Tyvek is designed to be moisture permeable. It allows water vapor to pass through but liquid water sheets off of it. If it were not, then it would trap moisture against the sheathing which could rot it out. Again, if you find water buildup behind the tyvek under normal weather conditions, that wouldn’t be good.
It’s ok for building materials to get wet from time to time as long as it dries out relatively quickly. It’s longer term wetting that leads to mold growth and rot.
Also, if the interior of those walls is wet, that wouldn’t be good. Water vapor can get in but it shouldn’t be condensing into liquid water in appreciable quantities. That can soak into the wood, saturating it and causing big problems.
Hi Ted. The dust in my condo has suddenly turned blue in color. Any idea what might be causing it? My HVAC system (air conditioner, air handler) were replaced just under 3 years ago and get an inspection/tuneup once a year. The air ducts were cleaned about a year and a half ago. I change the return filter every 2 months and I have HEPA-filter air purifiers that I change the filters every 6 months whether the “change filter” light is on or not. I have no water leaks and the humidity in the condo stays under 50%.
That’s pretty odd!
Any chance that the duct on the back of your dryer came off or developed a crack? It’s possible that it’s blowing lint into the house. Otherwise, that is really mysterious!
Love your articles as they are very informative and still trying to read and absorb all of them. I was hoping you can help me with a stubborn excessive moisture in my home that no one has been able to help me to figure out the real problem with the appropriate fix. My house was built in 1956 and has double sided paper with a small amount of what looks like fiberglass between on the attic floor. Previous owners then added fiberglass batted insulation on top of the old insulation with the foil side down – some places it is placed in the up position and I was told to flip those pieces so the foil is facing down on top of the old double sided paper(foil) insulation. I have two gable vents, a 1000 CFM attic fan(runs by humidity and temp) near the Ridge of the roof. The soffit vents where clogged so I replaced 10 of the 12. I think I am only getting at most 600 air through those 16×4 inch vents as the holes are really only 14×3 in. I was told getting more intake air in the attic will help to reduce the humidity in the house but I am not sure that is correct. The fan in the attic was set incorrectly at 30% humidity and ran constantly (I live in western pa). If I don’t have enough intake through the soffits and the fan was taking air from the house through the attic pull down steps (not sealed tightly), wouldn’t it pull the moisture and the house? I get it not very energy efficient. I put in a new french drain and gravel around the entire house foundation about 15 years ago as I was told the moisture was coming from the foundation walls. My walls are underground but there is no signs of wet brick in the garage or cellar areas. I recently sealed a number of air infiltration to reduce the high humidity in the basement. The air conditioner is a bit undersized as it turns out so it will not remove all humidity in the summer (house got to 72% humidity), but the worst part is the moisture in the winter. Currently, November 1, the house humidity is at 65% unless I open all the windows with the outside humidity at 50%, the humidity level is dropping to approximately 50% (matching the outside). One problem is my thermostat does not register the humidity in the house correctly. When my separate analog device is saying 65%, my thermostat is saying 45%. I know the 45% cannot be right because I can feel the humidity on my skin and my clothes in my closet and dresser and bedding is all wet to the touch.
I had one expert insulation man do a door blower test and it showed my windows are good but did find some areas that are open to the attic such as the bulk head in the kitchen and the stairwell ceiling leading to the basement. His solution was to have all the soffits changed to continuous ventilation soffits, install roof vents all across the roof (instead of a ridge vent), and he would seal the attic from the home space, slash the foil on the fiberglass insulaton and then blow in cellulose to an R49 (install baffles as well). He could also aeroseal the HVAC duct work for better efficiency. The other solution or maybe I have to do as well is to install a whole house dehumidify on the furnace. All of this is expensive but willing to do if it will work. I just cannot understand with how leaking my pull down attic steps are how the moisture is building in the house, no matter what the attic fan setting. At one time I had a ridge vent but I got mold in the attic so it was recommended that I use a fan and not a ridge vent to vent the attic. I feel like it is a fine mist in my house and with winter coming it is getting worse with using the furnace. I am cold as I am trying to let in cold drier air (but not always due to rain), but with windows closed and the furnace on the humidity won’t go down below 60%. Should I just install the whole house dehumidifier and then move to change the house soffits and then hire the other company to insulate the attic as well. Finding contractors to do this work is difficult and I did not want to purchase a dehumidifier, but I am not sure replacing the soffits and insulating and fixing the pull down attic steps will fix this issue.
Your ideas and help is appreciated. Please let me know if you need any additional information. The attic is really only insulated to about R25-30 and I have a number of pot lights in the living room which is the floor of the attic. My house is a one story old style mid-century modern house – two level roof – attic – can only crawl or kneel in the attic – Attic does have a plywood floor throughout – is this helping to cause the issues? I don’t have high humidity in the attic. Everything is ruined in the house and I need new furniture which may come this month or next. I really am at my wits end as I have been trying to solve this issue for over 15 years.
Thanks for your help.
Sorry for the long delay. You’re exactly right. The fan is likely sucking air and moisture from the house into the attic. If running continuously, that’s a big problem, especially during colder months. However, if you’re not having issues with attic moisture, even during winter, then don’t mess with the attic yet. Focus on the indoor humidity.
An undersized ac should dehumidify better than a larger unit. Also, it may be undersized because of the leaks in the house and the continuous attic fan running.
I would seal the high hats and the open areas to the attic. Aeroseal is also a good idea. The biggest moisture problems are usually associated with leaky ductwork. That would be my first job. That could solve all the problems.
Did they do a thorough inspection of the ducts? You need this before doing the aeroseal job or it could cause a huge sticky mess in the house! Did they do a duct blaster test? That should have pointed to any larger duct leaks.
So my main advice is to check the ducts and air handling system and seal them well. This is top priority.
Tightening the attic access can help quite a bit. I like the thick foam attic hatch covers by The Energy Guardian.
The moisture in the house is another matter I think.
Thanks Ted for your reply. The moisture in the house is the bigger problem than the moisture in the attic. The attic fan humidistat was set too low so I adjusted to 45% for the winter. This cut the run time on the attic fan. However, I am at 55% humidity in the house with temperatures at night in the forties. The company who recommended the Aeroseal did not do the duct test cause they said too expensive to run when people don’t get the Aeroseal. Why the sticky mess? I did a rudimentary duct test, turn furnace off, close all windows and run all bathroom and kitchen fans. I found more air coming from the return side not the supply side. This company says the Aeroseal is only run in the supply side and they only do what is visible on the return side. With a finished basement not much is accessible. Do you think I should rip open the basement to expose the duct work that won’t be Aerosealed? Also everyone is saying the problem is since not enough air is getting to the attic is why the moisture and heat is being held in the house. Seems like you are saying the moisture build up in the home is not from this issue? I am barely getting 300 NFA into the attic now. What should I look for in the company performing the Aeroseal- handle the return ductwork and the sticky mess you discussed. Thanks so much. I am willing to spend money to fix but would be very disappoint to spend so much money on new soffit and Facia and a new Ridge Vent and the problem not be solved. Thanks again for your help.
Unless there’s a big source of moisture inside the house, like humidifiers, lots of house plants, unvented shower bathrooms…, the interior moisture has to be coming from the outside. You’ve touched on the possible sources: basement moisture coming up and air leaks letting air and moisture in from outside. I don’t see how the attic ventilation issue could be causing the issue. Consider this – what happens when a house has no attic? By their logic, wouldn’t that trap in all the moisture?
55% humidity inside the house isn’t bad at all. I’d be surprised if my house dips below that except in the very cold winter when the air is exceptionally dry.
A professional duct test should cost a few hundred dollars in a typical house and is well worth it when you have these kinds of issues. However, it’s mainly a concern if the ducts run outside the conditioned space of your house, like through the attic. It can also happen when the builders used the wall cavities as “ducts”, especially for return air. Those wall cavities are often open in some way to the outside (attic or even through the siding) which can lead to huge losses and sucking in of large amounts of moisture.
When I used to test homes, I would turn the heat up to full blast (in the colder months) and then use my thermal camera to trace all the ducts. That showed me where they all run and gave a clue as to if they ran them through walls/ceilings instead of through ducts. It sounds like you did a good test and the return is in fact very leaky, so I’d look at that is your primary suspect.
Aeroseal is a glue based system. So if they screw up and try to seal ducts where there are no ducts, it just blows glue into the house. I had a client who had this unfortunate thing happen when the Aeroseal installer forgot to properly seal the supply register in the basement. Covered everything in the basement with a sticky mess! This is why it’s so important for them to check the pressure in the ducts before starting the blow. This is part of the process, so they shouldn’t have made this mistake, but nobody’s perfect…
Thanks Ted. I agree with you on the 55% humidity sounding not so bad but my clothes and bedding are wet and my skin feels wet. The duct work that goes through the garage (unconditioned space) for the bedrooms is covered by a finished ceiling or is covered in duct work insulation. Sounds like you are suggesting I rip open the basement to expose any issues with the return ducts in that area as a possible problem to the moisture in the main living area. I also have a chlorine smell in the living room, which is above the basement. My house is plaster not dry wall but without the lath. Also, I do have excess humidity on the ceilings and where an interior wall meets an exterior wall. Do you think fixing any air leaks, as you suggest is the suspected problem, take care of the peeling paint and moisture on the ceiling? How do you feel about a whole house dehumidifier? Is this something I should consider after all other possible issues are exhausted? My main believe is a dehumidifier should not be needed when a house is properly built. Just not sure where to spend the money to get to the root of the problem? Is this the order to get this house back to proper living where my clothes and bedding are not wet – Have my contractor back to perform the duct blaster test, Tear the basement apart to find anymore air leaks and redo, fix the ventilation in the attic, new windows (energy audit did not identify this as a problem but they are over 20 yrs old and feel leaky to me), dehumidifier as a last option. Sorry for so many questions but your experience and willingness to help has been invaluable to me to know which steps to take to get to the root of this issue.
I would not tear anything apart unless it is a last resort. The easiest way is to not destructively test Using a thermal camera. That should show if there are major leaks. If the inspector knows what they are doing there is a very clear thermal signature. Given the length of time that you have had issues, I think it is well worth getting a pro in there with a thermal camera and the necessary equipment. It might involve another blower door test and Duct blaster test, But that should give you a clear indication and save you having to rip open things unnecessarily. Especially plaster. My house is the same vintage and I would not do that unless absolutely necessary
I tried to post this last week and I’m not sure if it went through, so I’m going to try again. I apologize if you’ve already received it. I do have some new information in the last paragraph. Thank you for your help in advance.
I have a question about attic insulation. I have a cape cod house built in 1932. I want to mention that I live in Buffalo, NY so that you have a sense of the outdoor climate of the house. My attic has a bedroom in it creating the classic cape cod attic space of a box (the bedroom area) in a triangle (the attic space). So my attic space is two sections of knee walls, exterior walls, underside of roof and attic floor, along with a single triangle section above the bedroom ceiling of about three high feet to a roof peak. The attic presently has mineral wool batts on the exterior walls and underneath the roof on the inside of the attic areas, and most likely in the area above the bedroom ceiling. There is no insulation in the attic floor or on the knee walls.
I am getting a giant ice dam on the Northeast corner of my roof in the winter( the wind and weather usually comes across Lake Erie from the Southwest here), so my present insulation arrangement ( and ventilation) is clearly inadequate. In December, I am having insulation, to code R values, blow into the attic floor ( treated celluouse) along with fiberglass batts put down on the attic floor, and insulation put on the knee walls (blankets of some kind), and celluose blown in the area above the room ceiling on top of the mineral wool batts that we think are up there now. They will also cut in two gable vents on opposite exterior walls on each side of the attic that is composed of knees walls, underside of roof, attic floor and exterior walls. There are also already two gable vents on opposite exterior walls to each other in the area above the bedroom ceiling. There is a ridge vent in the area above the ceiling as well. ( I wish it wasn’t there because I think the gable vents would work better with out it, but there it is) There are no soffet vents anywhere.
My question is – once the new insulation is put in on the attic floor and the knee walls and the new gable vents cut in, is it necessary to remove the old insulation that is presently on the underside of the roof and the exterior walls? I have debated back and forth about this. The insulation company has said ‘There is no reason to remove the old insulation, except for aesthetic purposes”. My dad is a mechanical engineer who teaches thermodynamics, so I asked him. He thinks leaving the insulation is fine in the winter, but was concerned about the roof getting hotter in the summer and thus keeping the old insulation on the underside of the roof might wear out the roof tiles a little sooner. But, then he says it might not make that much difference and it would be Ok to leave the old insulation there. The roof is an Owen Corning architectural shingles roof about 2 years old. There are two issues to consider that I can think of – the temperature of the roof and also the temperature of the attic. Will leaving the old insulation in there make any difference to the heating and cooling of the attic in winter and summer? That is my main question.
Another way to say it – Am I better off removing the old insulation ( once the new insulation is in) or is it fine to just leave the old insulation where it is? Thanks so much for your help with this question! I have been thinking on it for months. I’d rather not remove the insulation at all ; it will be a very messy project so if I could leave it there without much disadvantage I would rather. But I want to know all the science of leaving it there or taking it out.
One final note – I’d be removing the insulation myself and it is a Philip Carey mineral wool from the 1940’s I think. I know that mineral wool itself does not contain asbestos, but I have read that some mineral wool from the 1940s might have asbestos added to it. I have never read however that mineral wool batts in residential homes from the 1940s has asbestos in it. So, in an abundance of caution, I had the mineral wool tested just to make sure there is no asbestos in it. The lab report came back and there is no asbestos detected. Great! So I just have to decide whether or not I want to remove it. Thanks for reading all of this!
Thanks for the question and details!
First, I wouldn’t worry about roof temperatures. In practice, the amount of “cooling” provided by exposing the underside of the roof is going to be minimal. There are many buildings that have insulated/non-ventilated roofs that work fine in hotter climates. Come to think of it, my roof is like that!
That said, there is a reason to remove the fiberglass from under the roof deck – potential condensation trapping.
Since you’re going to insulate the attic floor, the heat that was lost from the house up into the attic space before (which was also making your ice dams worse), was warming that attic space. Now that you’re going to be insulating much more, those attic spaces will be much colder. That’s the intention – less heat loss out of the living space.
However, any moisture that gets into the attic spaces is going to want to condense on the underside of the roof and the roofing nails. People often notice water dripping from the roofing nails poking through during the winter because nails are a great conductor of heat/cold. The ventilation you’re adding should help reduce this, but there’s still a chance.
If you leave the insulation in under the roof deck, you won’t see any of the condensation and it will be less likely to get flushed out by the ventilation. Hence the trapping of condensation between the insulation and the roof deck. Over the years, this can lead to premature failure of your roof (i.e. – it rots out).
Regarding your question about attic temperature – yes, the attics will get hotter during the summer if you pull the insulation from under the roof. But that’s a minor price to pay compared to risking a rotten roof! Plus, even though everybody does it, I strongly recommend against using those attic areas as storage areas. Mostly, they just become home to mice and present a fire hazard. Plus, the access doors into the attic allow moisture and heat to escape from the living space into the attic, which can accelerated the roof rot problems I mentioned. Regardless, you want to ensure that any access between the living space and the attic spaces is as air-tight as possible. A tightly fitting door with a gasket is highly recommended. I’ve seen to many pieces of plywood or drywall just placed into the hole, allowing huge heat loss and moisture problems.
Hope that helps!
Thanks so much for your thoughts! I see what you are saying – take the insulation off the underside of the roof so I can have a clear view of checking for condensation in the winter. With the new insulation, the attic will be colder than before and even with the new ventilation, it is good to check to see if any condensation would be an issue up there. Also, I’ll make sure that the two attic access doors are insulated as air tight as possible – I see how humidity from the living space can seep through any small cracks. Thanks again for your thoughts.
I have a question about attic insulation. I have a cape cod house built in 1932. I want to mention that I live in Buffalo, NY so that you have a sense of the outdoor climate of the house. My attic has a bedroom in it creating the classic cap cod attic space of a box (the bedroom area) in a triangle (the attic space). So my attic space is two sections of knee walls, exterior walls, underside of roof and attic floor, along with a single triangle section above the bedroom ceiling of about three high feet to a roof peak. The attic presently has mineral wool batts on the exterior walls and underneath the roof on the inside of the attic areas, and most likely in the area above the bedroom ceiling. There is no insulation in the attic floor or on the knee walls.
So, I am having insulation, to code R values, blow into the attic floor ( treated celluouse) along with fiberglass batts put down on the attic floor, and insulation put on the knee walls (blankets of some kind), and celluose blown in the area above the room ceiling on top of the mineral wool batts that we think are up there now. They will also cut in two gable vents on opposite exterior walls on each side of the attic that is composed of knees walls, underside of roof, attic floor and exterior walls. There are also already two gable vents on opposite exterior walls to each other in the area above the bedroom ceiling. There is a ridge vent in the area above the ceiling as well. ( I wish it wasn’t there because I think the ridge vents would work better with out it, but there it is) There are no soffet vents anywhere.
My question is – once the new insulation is put in on the attic floor and the knee walls and the new gable vents cut in, is it necessary to remove the old insulation that is on the underside of the roof and the exterior walls? I have debated back and forth about this. The insulation company has said ‘There is no reason to remove the old insulation, except for aesthetic purposes”. My dad is a mechanical engineer who teaches thermodynamics, so I asked him. He says leaving the insulation is fine in the winter, but was concerned about the roof getting hotter in the summer and thus keeping the old insulation on the underside of the roof might wear out the roof tiles a little sooner. The roof is an Owen Corning architectural shingles roof about 2 years old. There is the issue of the temperature of the roof and also the temperature of the attic. Will leaving the old insulation in there make any difference to the heating and cooling of the attic?
Am I better off removing the old insulation ( once the new insulation is in) or is it fine to just leave the old insulation where it is? Thanks so much for your help with this question! I have been thinking on it for months. I’d rather not remove the insulation at all ; it will be a very messy project so if I could leave it there without much disadvantage I would rather. But I want to know all the science of leaving it there or taking it out.
One final note – I’d be removing the insulation myself and it is a Philip Carey mineral wool. I know that mineral wool itself does not contain asbestos, but I have read that some mineral wool from the 1940s might have asbestos added to it. I have never read however that mineral wool batts in residential homes from the 1940s has asbestos in it. So, in an abundance of caution, I am having the mineral wool tested just to make sure there is no asbestos in it. I sent it off to a lab last week using a kit from Home Depot and am waiting for results. If it has asbestos in it, I am leaving it and not removing it. Thanks for reading all of this!
Working on adding additional insulation to my attic. I’m laying down an intial new layer of R19 and then a perpendicular layer of R30, so R49 in total. I live in Michigan, so I know they say between R49-R60 for my area, so I’m considering adding a third layer on top. But my question is, is there an R-level or thickness in which fiberglass insulation no longer provides any benefit, or the cost to effectiveness starts to become a negative, or other mitigating factors such as height or weight come in to play?
Best Holiday Wishes to you and your family!
There’s definitely diminishing returns. I haven’t heard of negatives other than cost/benefit.
I like the criss-cross method because that helps cover all the cracks and minimizes unintentional gaps that can dramatically reduce the effective R-value, especially at the rafters.
R-value is directly convertible to relative heat transfer, so R-10 = 1/10 = 10%. R-50 = 1/50 = 2%. So you can see, doubling from R-50 to R-100, while it reduces the heat loss by half, is only taking you from 2% to 1% overall loss. So in the grand scheme, going super-high hardly seems worth the effort for such small incremental improvements.
I found your blog to be very informative and wanted to ask a question, have you ever see faulty spray foam cause moisture and mold issues? We have a very severe moisture problem (and hence mold problem) in our house ever since we made our walk up attic a finished space about three years ago. The space has open cell spray foam and knee walls. No dehumidifiers in the attic and the bathroom fan vents through the attic out the roof. An old duct vent also sits in the bathroom and was not closed up by the last contractor going strait into the attic. Further more we have an encapsulated crawl space in the basement which is rather dry and has one of those EZ Breathe Ventilation Systems. The entire house is heated and cooled by Mitsubishi mini split systems. Upon inspection an energy audit company explained that the spray foam job was not done correctly and we have air leaks in in the section between the roof and the knee wall. We are looking into this further but I feel the moisture levels are so high that something else may be the cause. The moisture and mold is interestingly sitting in the stairwell wall cavities which we know due to air testing by our mold remediation company. Last year we had an HVAC, which sat behind the knee wall, over condensate and dump buckets of water into our walls. This was remediated and repaired or so we though until the mold smell came back this summer. We are trying desperately to pin point the root of the issue so that we can get everything fixed and don’t have this problem a 3rd time. Figured it would not hurt to ask here and see if anything immediately jumped out to you as the cause.
The higher humidity could be a side effect of the foam but not the fault of the foam per se. Because foam is so effective at air sealing the house, even with some imperfections it is much better at air ceiling than any other method of insulation. What happens is that if there are moisture issues in the house, a foam house is less forgiving because there is less air exchange with the outside. So any excess moisture in the house will be more likely to be trapped in. The big question is what is causing the excess moisture in the house in the first place. Since you are using a mini split, you may wish to run that in its dehumidify mode to pull the moisture out of the air. This may help to reduce the issue during times of high humidity. The other thing that is counterintuitive is you should not leave the house open in the morning because the humidity levels outside in the morning are extremely high and could be making the problem worse. I would just try running dehumidification constantly and keeping the house closed up to see if that helps enough.
Thank you so much for your answer! We cannot sort out the cause of the humidity, at least not yet. We switched all the mini-splits to dehumidify a few weeks back. We now have an industrial dehumidifier in our attic and every 3-4 hours it is still pumping out about 5 quarts of water and has been for over two weeks. We have a few specialists coming out in the next few days so hopefully we can locate an answer. In the meantime, your articles have been very informative!
Wow, that is a ton of humidity. Good luck
I’d be very interested to learn what they discover.
A continuation of my reply, now that I’ve had a chance to re-read your original question. I had a migraine and a fuzzy head when I sent my first reply.
You wrote: “An old duct vent also sits in the bathroom and was not closed up by the last contractor going strait into the attic.”
I’m not sure I understand this. What do you mean by “sits in the bathroom”?
I checked out the “EZ Breathe Ventilation System” and am dubious about this for a couple of reasons.
First, if it sucks air out of the crawlspace and vents it outside, that air has to be replaced by an equal amount of outdoor air, being drawn in somewhere. That outdoor air has all the moisture in it that’s outside, so this is no different than installing a fan blowing humid air into the house. This will almost definitely create moisture problems if it’s running all the time.
Keep in mind that humid air rises up through the house and collects at the highest points. Hence attic/upstairs rooms tend to be the ones that get loaded with moisture. The ventilation system may be removing humid air from the crawlspace but it’s sucking it in anywhere else it can come in.
If you want to do an experiment, turn off the EZ breathe system for a week or two and observe what happens in your house as far as moisture levels.
I have a curious question for you, but it’s a subject you’re an expert in: condensation. This summer I’ve been working on erecting one of the temporary carports that you see at Harbor Freight, Canadian Tire, and the like. ShelterLogic is another name brand of them. They’re basically a metal tube frame that a tarp is secured over. I reinforced mine with a wood sub-frame to stiffen it up and for when the tarp has served it’s purpose, I can sheath it in another material: corrugated metal, siding, etc.
My issue is there is a tremendous amount of condensation on the inside of the tarp and metal framework. I know it’s not airtight, and I don’t think there’s really a way to make them airtight. It is warmer inside the tent than the ambient air temperature, so I’m assuming the difference in temperature is what’s causing the condensation? This isn’t a few beads running down the sides, though. This is like someone sprayed the whole inside with a hose. If you take a broom and hit the ceiling it will rain on you. For the floor I put down plastic sheeting and then stone on top of that in hopes that it would keep ground moisture from rising up into the space. Do you think that this is from ground moisture? Should I put another tarp over the stone? Or is this just cooler air migrating into the tent and then condensing based on the change in temperature? What’s the best way to address this? A couple of vents on either end of the structure?
All the best, Andy
Before reading your entire post, the thing that came to mind was ground moisture. In order to get that much condensation, there’s got to be a massive source of moisture.
I have experience heavy metal objects in my garage getting covered with water when I leave the doors open on a humid day after a cold night when everything inside has cooled off. But given the extent of the moisture that’s accumulating, it really seems like a ground moisture issue.
I had a wet dirt crawl space under a condo that was rotting out the floor joists above the crawl space. To remedy, I used thick plastic sheeting with all seams overlapped by several feet and taped. Then I put another layer on top of that and did the same thing. Then, I used spray foam to glue and seal the plastic to the foundation walls. It was probably overkill but it stopped the moisture problem instantly. So much water was coming up through the ground that puddles would form under the plastic.
So that’s my best guess. I think you did the right thing, but you might just have to work extra hard to ensure that the plastic is completely water tight.
But, it still could just be so humid out that the air is saturated with moisture and that’s causing the issue. But then I would expect the entire outside of your house to be covered in moisture every morning too.
I did put heavy plastic sheeting under the stone that I laid and was careful not to punch too many holes in it, other than for the landscape stakes I used to hold it in place. I’m sure there’s always a chance that the stone has poked holes in it. I have noticed that every since I have placed the tarp over the structure that the stone has been a dark color, like it’s damp, compared to before I had the tarp over top, and it would dry out. I didn’t know if the stone was damp because of the condensation dripping on it, or if it was the source of the moisture. We have had lots of rain over the past couple weeks/month, so it’s 50/50 whether it’s humidity in the air, or from the ground.
Should I try to disperse the existing condensation on the walls and ceiling via squeegee, or would it rectify itself once I solve the ground moisture issue? Should I put a couple vents on the end walls?
It seems like there’s been constant condensation every since I put the tarp on: warm, cold, dry, raining, it’s always there.
That is the weird thing. It seems like you did the right stuff to protect against this happening.
It sounds like the stone is absorbing moisture from the air and holding it. Since it has more thermal mass, it will promote condensation formation then soak in the water, forming a reservoir. The water could then be coming out of the stones, getting trapped in the structure and exacerbating the condensation issue. Just a guess.
You might try laying plastic sheeting or tarps over the stones for a week to see if that makes a difference. Anything that can hold moisture in the structure should be eliminated
Fans can help a lot to flush out moisture and reduce condensation. Ideally, you’d put fans at either end of the structure, one blowing air in and a second flushing it out, to promote air movement through the structure. Then run them when it’s dry outside. But it’s a real battle during spring and fall when it can be so humid outside.
Let me know if you figure this one out. It’s something of a mystery why the condensation would be so bad.
As far as the squeegee, that would certainly speed the process. But if the condensation just comes right back, it would be a waste of time.
Thanks again, Ted!
I’m going to get a big tarp, maybe even big enough to double, and place it over the stone on the ground. I don’t have anything in there yet as I’ve still been working on it, and then noticed the condensation issue, so wanted to try and correct that first! I definitely don’t have anything in there that has any thermal mass: a fiberglass ladder and some sawhorses, some leftover lumber, etc.
I may try getting some vents or cold air returns and putting them at the top of the front and back end walls, just to try and promote cross ventilation.
I’ll let you know what seems to rectify the issue once I know!
Just wanted to update you on my outdoor tent-shed condensation issue. Over the weekend we experienced some pretty warm weather here in Michigan for November: high 50s-mid 60’s, 50% humidity. I had unzipped the front door/flap about a third of the way up on both sides. It isn’t flapping in the breeze, but it does have some gaps on either side at the zippers and promotes better airflow. Gusts of wind can push it back into the structure 8-10″ or so. As of last night, and this morning, all the condensation on the interior surfaces of the structure and frame had dissipated. I would estimate the front third of the stone on the ground within the structure had appeared to dry out and became lighter in color. I do have a tarp, but have not laid it on the ground yet. I realize the increased air flow is helping to dissipate the humidity, but I also can’t leave the structure open in inclement weather. I am now unsure if I have a ventilation or a ground water/humidity problem. Research continues.
If I had to guess at this point, I’d say it’s a ventilation issue. Take pretty much any space and close it up then drop the temperature and condensation will likely form. The positive thing is, during the colder months, the outside air holds much less moisture. Air leaking in will tend to draw out the moisture. And the structure will hold in heat, relative to the outdoor temperature. So I’d be surprised if you experience many problems for the near future.
Next spring, when it gets warmer and there’s more humidity, you’ll probably experience this again as the interior will be cooler than the outdoors. At that point, ventilate like you’ve been doing recently.
Thanks again for the advice! Like you said, I think I’ll be safe for the winter, since the air is so dry, and will readdress as necessary in the spring. I have seen that some people in travel trailers, RV’s, long-term camping/traveling, will use bubble wrap on their windows and they say that solves their condensation issue. In theory, I understand how it would work, but without air sealing I have to assume you still get some condensation behind the bubble wrap and I don’t know if that would cause mold or mildew problems long term.
I live in East Tennessee and have a house built in 1970. Lots of large trees around but the sun does hit my roof about midday for several hours. My living room has a vaulted ceiling and that room is the only room in the house that is above a crawlspace. The vaulted ceiling is painted sheetrock with wood beams that were covered and trimmed out with wood trim and paneling when the house was built. There are no recessed lights. I have had a terrible humidity problem in this room. Moisture seems to collect along the point of the ceiling along the beam and on the sheetrock At the peak. The moisture then leads to surface mold and a funky odor in the room. When I clean it it appears to be only on the surface and nothing feels soft or damaged. I recently had my crawlspace encapsulated with a dehumidifier and also had a new hvac system installed as well as new windows and doors. It seems to have helped somewhat but not entirely. Additionally, before the encapsulation and new hvac, there is one ac vent on a wall about 8 feet high and it would sweat and water would run down that wall. Then water would form on the opposite wall at the peak of the ceiling and run down that wall. So far that has not happened yet this summer but we are just getting started with the heat and humidity. This mainly all happens in the summer btw. Also, there is a ridge vent on this house which I don’t believe was common practice when it was built. I never got a chance to speak with the previous owner about whether or not she had this problem prior to the ridge vent and she has since passed. The portion of the house that has the vaulted ceiling has soffit vents as well as this ridge vent. The rest of the house has a gable vent on one end and the ridge vent. Another issue is when I get up there to clean the beam in the living room I notice little leaves and seeds stuck between the moldings. I’m thinking this ridge vent is causing this and wondering if it is the source of all my problems. Any insight you could give me would be greatly appreciated!
Hi Kip, sounds like there’s a lot of humidity around. Could be coming from the crawl space or just general humidity in the outdoor air. From the actions you’ve taken care of the crawlspace but it’s worth measuring the humidity level in there. You can get a humidity gauge from Amazon for about $10, so it’s worth getting a few. With what you’ve done, your crawlspace should be well below 60% humidity but it’s worth checking. If it’s high, then the mitigation efforts you’ve taken may have to be checked to ensure the encapsulation is complete.
I’d also measure the humidity at a couple spots in the living room. A few feet off the ground and up near where you’re getting the mold. The humid air in the house will rise, so it accumulates at vaulted ceilings. Any place it condenses will be colder than normal, as you found with the air conditioner vent. The cold air is chilling the vent and it’s acting like a dehumidifier by causing the moisture in the air to condense on the vent. It’s also cooling the ceiling where it’s blowing, causing the condensation to form in those areas.
If the humidity in the house is at normal levels, you shouldn’t get the condensation on the AC vent or ceiling, so the big question is where is the humidity coming from. There are a few possibilities…
First, you might be unintentionally letting moisture into your house by opening windows for fresh air. This time of year, allowing the fresh air in brings tons of moisture in with it. If you then close up the house and run the AC, all that moisture has to be removed from the air. But it will also condense exactly the way you’re seeing. The only solution is to keep the house closed up tightly when the humidity levels outside are high. One of those moisture gauges is useful to have outside so you can know when it’s safe to open the house up and when you should keep it closed. I wouldn’t open the house up if there’s more than 60% humidity outside as a rule of thumb.
If you aren’t opening the house for fresh air, the house could be very leaky. Windows, doors, other areas can let in copious amounts of humidity. You can tell some of this visually, and you’ll know where you have drafts during the winter. So that’s something to check.
Another very common area for humidity problems involves leaky ductwork for the HVAC system. Especially air return ducts, which suck air back towards the unit (everything on the filter side of the air handler). If there are any leaks, which there always are, they will suck in moisture from the outside. If those ducts run through the attic or other areas outside the enclosed area of the house, they will suck in outside moisture and distribute it throughout the house.
Given that this is an ongoing problem and there are several possible sources, it would be worth spending the money to have your home analyzed by an energy auditor who can do “blower door” and “duct blaster” tests and visually inspect the home for other issues. They should be able to pin-point the problem areas and suggest remediation methods. Without that, it’s going to be a lot of guesswork and you could spend thousands on contractors without getting anywhere.
sorry another question – we have already ‘painted TnG and it supposedly just started leaking, frankly I believe it was the previous owner who knew it and did not disclose but that is another fight he already screwed us on the roof around the chimney – anyway are you recommending to sheetrock OVER the T&G or demo and then sheetrock this will be our last address want it done right
As long as the moisture issue is caused by condensation rather than a roof leak, if it were my house, I would just sheetrock over the T&G. If you wanted to improve the ceiling insulation in the process, you could first screw a layer of PolyIiso foam board to the T&G, taping the seams. Then screw the sheetrock through the foam into the T&G. This would give you a near perfect moisture barrier and really improve the R-value of the ceiling.
Before doing any of that, again, if it were my house, I would cut out a section of the T&G and inspect the water damage in the ceiling and ensure that there aren’t bigger issues that need to be dealt with first.
Hey Ted, I tried to post this last week so I apologize if it’s a double post. I had some trouble logging in to post my question and I’m not sure if it actually went through or not.
I’m building a new house, ICF exterior walls, typical rafter roof system, unvented. This question is regarding the roof system. My original thought was I would put 2” of rigid foam above the rafters to reduce thermal bridging, then spray foam between the rafters. I’ve seen this done plenty but hadn’t looked at the details. All the details I can find show, from the inside to the outside, rafters, decking, foam board, then another layer of decking. Having to double up on decking would make this a no-go for me. I was wondering, since the second layer of decking has to be attached through the foam board anyway, is the first layer of decking absolutely required? Why could I not place foam board directly on the rafters, then decking over the foam board, with fasteners going through the foam board directly into the rafters? The only thing I could think of is that with the foam board not securely sandwiched between two layers of decking, maybe moisture could accumulate between the foam board and decking? That got me thinking even more, and I started wondering if instead of foam board, what if I just ran 2×4 purlins every 24” OC, which would space the decking off the rafters 1.5”, then when I spray-foamed from underneath, the foam would fill the cavity between the rafters and the decking. I realize there would still be thermal bridging wherever a purlins meets a rafter, but it seems like it would still be a good system. I would save on cost by omitting the foam board, and the additional amount of spray foam would be pretty small. I have not seen any examples of roofs being done this way, and I was wondering if there’s a reason why. Thanks.
I don’t know for sure, but I think the approach of: roof deck + foam board + another layer of wood is probably for structural reason. If you’ve got (for example) 2″ of foam board right on the rafters, then the screws that go through the roof sheathing have to pass through 2″ of non-structural foam. When there’s a shear force, i.e. a heavy snow load, the torque applied to the screws could cause the entire structure to slide down the rafters, breaking the screws.
However, even if you roof decking screwed right to the rafters, then foam, and then another layer, you’re going to have the same forces, unless maybe they figure that you’d use a lot more screws since you could screw to the first layer decking anywhere? You’d have to ask a structural engineer why it has to be built this way. Sorry I can’t be of more assistance but I wouldn’t want to advise you on something with such structural significance.
That said, my personal preference would be to put a layer of foam across the inner surface of the rafters. In this location, you’re not affecting the structural integrity at all and you’re putting up a layer that will greatly reduce moisture from getting to the roof deck.
Since you’re building new, how about SIP roofing panels? They’re designed for this and just drop in place for the roof. My dream house would be a timber frame SIP house built by this builder; https://hughloftingtimberframe.com/
I live in the Mid-Cape area of Cape Cod, Barnstable County, Massachusetts. I have a gambrel style home. The main house, 2″ by 4″ wood frame exterior walls, with a 2nd story was construct
Your professional expertise would be appreciued in the summer of 1976. An addition with a 2-car attached garage with apartment above was built in the summer of 1988. I have had Cape Cod Light Compact utilizing Rise Engineering as its energy subcontractor, has performed 3 Energy Audits over the last 10 years. In 1988 we added a central air conditioning system, Lennox ducted, serving the entire residence including the apartment area.
Our entire heating system is a Weil-McLain Gold boiler running on Number 2 home heating oil.
I am interested in utilizing a basement room, 4 poured concrete walls with a 4′ opening into the original poured concrete foundation basement with a walkout pass door.I was thinking of adding 2″ by 4″ fastened by mastic to the interior foundation and then drywalling same. This room has 2 basement casement Andersen windows that are installed below our wood deck and the room has a masonry fireplace with damper and 8″ by 8″ clay flue liner.
Can or should I insulate the interior walls with pink Owens-Corning wall insulation before adding drywall or leave space uninsulated. I run a Kenmore dehumidifier year round through my Air Conditioner air exchanger pump in the main basement.
Your professional expertise would be much appreciated by this retiree and planning to D-I-Y-ere.
I lived right down the road in Falmouth. Still have family there.
When your question came in, I was reading this article by coincidence. I would insulate it personally. Check out some of the advice in this article
Ted, I have the classic T&G ceiling construction: The roof is installed over the rafters. Fiberglass is shoved between the rafters. T&G boards are nailed to the rafters. I do have ridge vents but no soffit vents to speak of. I removed the ridge vents several years ago but encountered condensation problem so I reinstalled them. My issue is leakage. What is the best way to solve this problem and the most economical way? I am certain the best solution is not the most economical way but like to hear from you about the different options available. Thank you for your help.
Unfortunately, The best way would be to remove the ceiling material and put up something like drywall or you could probably get by with foam board as a base layer that is airtight. Then you would install the t&g boards over that as an aesthetic layer. Alternatively, you could drywall or foam board over the T&G boards and if desired for aesthetics install new T&G over that. Some people try to just have plastic sheeting underneath the T & G boards but that is prone to getting holes in it or having open seams that allow moisture to travel through so I don’t really like it as a solution. The most economical would be to simply drywall over the existing ceiling and then it would behave like any other cathedral ceiling.
I am about to redo my roof. Do you recommend:
1. Remove roof decking and existing insulation then cover with closed cell foam?
2. Remove 1 feet or so of decking at peak of roof, remove insulation, then packed space with high density cellulose?
3. Or any other methods you recommend.
That’s lucky, sort of 🙂
If it were my house, I would pull the roof decking and spray foam directly to the back of the T&G, though you might want to have a layer of something behind it so the foam doesn’t ooze through any cracks and ruin the appearance of the wood. It could be as simple as cardboard. Better would be a layer of poly-iso board foam. It could 1/2, just cut to go in the space, then foam over that. That will completely air seal and insulate the space really well. And, if the roof ever leaks, the water will mostly just drain down the foam and out the soffits.
Is the ridge vent still necessary after the closed cell foam insulation is put down? I can’t add enough soffit vents due to how the house is constructed. Thanks.
The ridge vent isn’t absolutely necessary much of the time, however inspectors can be pretty rigid about them, so I would probably have one regardless of the soffit venting situation. With the foam, you won’t have the adverse effects that sometimes arise with the ridge vent actually sucking air from inside the house. So the vent will give any residual moisture a chance to diffuse away.
Hi Ted, revisiting an old subject. This is your answer from Feb 17, 2021:
If it were my house, I would pull the roof decking and spray foam directly to the back of the T&G, though you might want to have a layer of something behind it so the foam doesn’t ooze through any cracks and ruin the appearance of the wood. It could be as simple as cardboard. Better would be a layer of poly-iso board foam. It could 1/2, just cut to go in the space, then foam over that. That will completely air seal and insulate the space really well. And, if the roof ever leaks, the water will mostly just drain down the foam and out the soffits.
My question is:
1. Do you recommend open or closed-cell foam insulation for this application?
2. Do I need to fill up the space completely all the way to the roof decking with foam?
Hi Keith, for this application I would definitely go with closed cell since the primary goal is moisture blocking. Open cell slows moisture but it’s still considered permeable. In some applications, that’s desirable but here, we want to completely stop moisture.
With closed cell, even an inch will block the water from going through, so the thickness is more dependent on how much R-value you want. Closed cell is about R-7 per inch, so a few inches provides as much insulation as a full cavity of fiberglass (assuming 2×8 rafters). If you go with poly-iso against the T&G, that provides about the same R per inch as closed cell foam, so you could do something like 2” poly-iso, then 2” spray foam, leaving a little air gap, that would work pretty well in most climates. For extremely cold climates, more insulation would be even better.
What is the best way to address attic/soffit venting when you add an addition for a room whose roof intersects the main roof perpendicularly, and you lose the soffit venting for the area that the addition now occupies. Assuming that you would not cut an opening in the existing roof to connect the roof systems of the old with the new, and take advantage of the soffit venting for the addition?
Also, do you know of any good information of calculators that deal with diminishing returns in regards to fiberglass insulation depth?
Hope you and your family are well! Finally starting to warm up a bit here in Michigan.
That’s a good question and I don’t know that there are really good solutions.
I have seen vents that install under the shingles that allow air into the roof cavity, so that’s viable. If it were my home, I’d personally probably just spray foam the underside of the roof deck if possible and not worry about it, but some code enforcement people might get persnickety about that.
Here’s the vent products that can provide air flow in these situations
I love this company’s products and used the ridge vent and soffit vents in my own home’s renovations.
Hi Ted, do you have any thoughts on supply & return vents in an unfinished basement? Most people seem to recommend closing them off perhaps depending on the season, but it makes me wonder if that would lead to moisture problems, or other issues.
Sorry if you’ve covered this, it seems basic but I couldn’t find anything.
Hi Andres, thanks for the question – that’s a good one. I should write an article on it.
As long as the basement is sealed off from the outside and is just an unfinished part of the house, I think allowing supply/return is beneficial. Here’s why…
If closed off, the basement will build up humidity. It’s naturally more humid than the house because of moisture coming through the slab and foundation walls. With the vents circulating, the main house air, which is warmer and should be lower humidity, will help flush out the cool, humid air from the basement. It will also keep the basement warmer and closer to the the temperature of the home. This is beneficial as it reduces the condensation potential in the basement.
This will naturally raise the humidity elsewhere in the house and also distribute whatever is in the basement air so I would encourage keeping the basement relatively clean and free of chemicals or at least make sure containers are well sealed.(lots of people keep nasty stuff in basements. I’m guilty of storing my paint down there.) You might want to install a replaceable filter on the return to minimize dust.
I hope you and your family are well! I’ve begun insulating my concrete basement walls with rigid xps. I have left a 1/2″ gap between the concrete floor and the bottom of the rigid foam. My initial plan was to fill this gap with expanding foam, but then I questioned that plan thinking what if I ever develop a leak in the concrete wall, I would want the water to be able to escape and be a visual representation that there’s a problem I need to address in that location. But my brain also says I should seal that gap to keep indoor conditioned air from getting in between the concrete and rigid foam and possibly condensing or causing other problems.
What do you think is my best plan of action for this specific issue?
Thanks in advance, Andy
I had to ask “WWJD”? That’s, “what would Joe Lstiburek do?”
Here’s his page on basement insulation. They seem to recommend a full wrapping of the foundation walls so that no air gets in to add to the condensation. I’ve always assumed that the foundation walls would be wet anyway because of moisture drive from the outside dirt. But when in doubt, follow Joe’s rules!
Me again! Thanks for your info on sealing the foam to the wall. I’m going to take your advice and seal the bottom of the rigid foam where it meets the basement floor. I’ve used a handheld temperate gun to take readings on different areas of the surface of the foam and noticed that the temperate would drop where there was an undulation in the concrete wall creating a small air pocket between the foam and wall. I’m assuming this is because air was migrating up from the floor and settling in these pockets.
Part two: I’m going to insulate my whole basement with the rigid foam. Only about half of my basement will be finished in the traditional sense of a studded wall, electrical ran through the studs, drywall, etc. The other half of the basement is more utilitarian: storage shelves: washer/dryer, furnace, water heater/softener, etc. I know that I cannot leave the foam exposed because it’s hazardous if there’s a fire, but I also don’t want to build a full wall with drywall in this area. I thought about building a stud wall on the flat, reducing the depth from 3.5″ to 1.5″ while still giving me a structure to easily fasten a covering. I could use your advice on what may be an appropriate covering for this area that more than likely will never be finished. I’ve toyed with the idea of either cement board or hardibacker, as they’re unaffected by water and moisture, but very heavy. Thought about faceless drywall or denshield too. I thought maybe polyiso, but it could be easily damaged, and since the walls will have to dry inward, I don’t want to trap any migrating moisture within the wall assembly. I’ve also though about the plastic polywall paneling that they install behind sinks and in wet areas, but I’m afraid that would behave the same as polyiso with no ability to pass moisture. Am I missing any good ideas that you can think of? Thanks for letting me borrow your big brain!
Good questions. I seen some people use 1×3 nailers with concrete screws through the foam, then attach drywall to that as the fire-stop. You could likely get by with thin drywall to cut down on the weight. I had no problem hanging bathroom drywall (with the anti-mold facing). I’m not sure if there’s standardized requirements for code regarding the wall material covering the foam. Might be worth contacting the local official to see what their requirements are.
Good luck with the project. Your basement should be noticeably more comfortable/efficient after that retrofit!
What is your opinion on flex duct vs metal duct. Obviously flex is pre-insulated and by name, flexible, which cuts down on elbows and by association, potential leaks, but that could be overcome with mastic and foil tape on a metal duct. And I have to think from a physics or air flow view, metal will beat flex every time. Is the only advantage of flex ease of installation, longer runs, less elbows, etc.? Kind of like the ventilation version of pex?
Secondly, in replacing existing duct work, if using metal, would you insulate it? My thought was that metal duct work obviously transfers heat well and radiates that heat to some degree. If I were to use metal duct work in my basement and crawlspace, would that heat radiation be enough to somewhat heat the space by proxy, or as supplementation so it wasn’t as cold, or I didn’t need to supply as many vents, which could affect flow throughout the other areas of the house, or even worst case, cause need to upsize my furnace? The basement and crawlspace will be totally encapsulated with rigid foam insulation. I was going to supply a duct and register just for the crawlspace, but if the nature of the metal duct running through the space would be enough to acclimate the crawlspace, that would save me time, trouble, air flow, etc.
In uninsulated spaces, like attics, I’ve found flex is very practical in my own home. As you noted, it’s insulated and one piece, so as long as you secure the ends well, you get no leaks. There are tables that show air flow resistance and you are absolutely correct – metal duct is superior. I just upsized the flex and made sure to use gradual curves. I think for most installations in attics, flex is better if done with a bit of care.
In semi-conditioned spaces, like you noted, metal ducts will radiate a fair amount of heat. It can be very significant, especially with air losses that almost all of these have. Plus, metal is easier to suspend from ceilings. With flex in hanging situations, you tend to get a wavy runs. So I like your logic – metal makes sense in those situations.
I’d suggest careful sealing of joints with “duct mastic”. It’s very sloppy but it’s the standard for the best quality/lowest leakage duct installations.
Happy Good Friday! I’m getting ready to finally close up the floor in my crawlspace, but before I do, and lose the access I have, I have a question. It’s a 14’x14’x2′ (to the bottom of the sub-floor) space with a single 6″ metal duct running through it supplying the room. It is totally encapsulated in 2″ rigid foam: floor, walls, rim joists, all seams air-sealed with expanding foam. Should I supply a 4″ duct supplying conditioned air to one of the outside corners of the crawlspace facing back towards the room, or do you think the heat radiation from the metal duct would be enough to keep the space conditioned?
Happy Easter to you and your family!
Best Regards, Andy
Happy Easter to you too. Let’s hope 2021 is a much better year than 2020!
A small supply duct would certainly help flush out “stale” air from the space and reduce the chances of undesirable moisture issues. You might want some sort of damper on it so you can control the amount of air-flow.
A small space like that is only ~400 cubic feet and you only need enough flow to flush it with enough air to exchange a couple volumes per hour. Let’s say 1000 cu.ft per hour or about 17 cubic feet per minute – about a quarter of a typical bath fan 🙂 You could probably get that with a two inch outlet on the 4″ duct. But it all depends on the conditions in the space and the air pressure in your ducts.
To summarize – a little air flow should be sufficient and is better than none.
Awesome! I know you always have the answers! I had planned on running 4” flex duct into the space with a damper at the main trunk. In the crawlspace I had planned on terminating to a 2×12” register boot. I really couldn’t find a better type of termination. And the crawlspace is sealed from the basement. Where is the flushed air going to go? I know I’ll end up pressurizing the crawlspace to some degree, which isn’t necessarily bad, but is there any downside to that?
The excess air will just find its way out through cracks and holes – there are always some 🙂
I’ve heard this method recommended many times by building science people and no one has mentioned any ill effects.
Yes, here’s another one for you. The floor joists in my crawlspace run perpendicular to the house joists, so as my 6” supply duct comes into the crawlspace, it runs into a 2×10 joist within 16” or less . My original plan was to head off one floor joist so I could use an elbow and create as gentle of an angle as I could until I transitioned under the joists. But what do you think about the heavy duty flexible metal duct that’s available? Would the air turbulence it creates with all those segments outweigh it’s convenience? I did see it’s available at my local home improvement store today in a 6” size which gave me the idea. I would attach a pic but wasn’t sure how.
I think I would use a normal metal duct elbow unless you had the space for a very gentle 90 turn for the flex duct (I’d imagine a circle with at least a 2′ radius).
OTOH, if you’re just talking about the little supply duct for the crawlspace, the airflow requirements are so low that most precautions can be ignored. Also, no need to run between the joists, just drop the duct down and support it under the joists with wide enough hangers so the duct isn’t crimped.
Here’s a couple of links that might be of use to anyone considering the details of running flex and the impact that bends, and crimps have to air flow
Click to access Thermaflex-Air-Flow-and-Air-Friction-Brochure.pdf
A second article talking about running flex
I hope this email finds you and your family healthy and well!
I’m working on the exterior of my home while the weather is nice and I would like to extend some of my overhangs, or build some awnings to cover my meters and air conditioner and to help keep rain and snow away from the foundation, provide some shade in the summer as well.
It would be better for me to set the framework for these awnings on the roof over the exterior wall to help carry load, but that is a bit more involved with tying in to the existing shingles and pitch. My thought was to mount a ledger to the wall under the existing overhang within the space above the windows. I probably have close to a foot between the top of the windows and the bottom of the overhang. My concern is I have ridge and soffit venting. I know that if your attic is properly air sealed you don’t need to worry as much about venting, but my concern is in the winter, snow and ice would accumulate on the awning/roof extensions and would more than likely block the gap between the underside of the existing overhang and the top of the awning. Depending on the weather and snow accumulation, it may even be able to grow and push up into the soffit, depending on snow melt and refreeze, etc.
Do you have any thoughts on how I could avoid this blockage that would more than likely come with winter other than lowering the attachment point of the awning, which I am limited by window-top anyway?
Always appreciate your insight!
Thanks again, Andy
That’s an interesting building question – never thought of that one before, but it’s certainly a good observation!
One options might be to build a ventilation channel using something like Cor-A-Vent (see this link: https://www.cor-a-vent.com/siding-vent-sv-3.cfm). That could go on the ledger board (so as to preserve the strength of the connection between the ledger and the wall). You’d have to leave an air gap so the air could move through the Cor-A-Vent and up to the soffits, and you might want to have some sort of “dam” to stop it from being snow covered.
Just a thought. Off-hand, I can’t think of any other way around this issue.
hi i just had windows installed and im freaking out because at the bottom corners where a nice wood frame is , if i push on the part closest to the window i can draw moisture/water onto my finger !! i think it starting to rot my wood framing. just on the bottom corners??? what is going ??
It’s common during cold weather for windows to have condensation on them, especially over night when the curtains are drawn. Even with high quality windows and good installation, I have to go around with a towel to soak up excess moisture on some mornings. Especially in my BR where the humidity is higher than other rooms and I have thermal shades on the windows.
If you’re experiencing too much moisture, and you have curtains or other window treatments, you should try leaving them open a bit at night to allow some of the warmer room air to warm the windows. This can help a little, but it won’t solve the problem.
It’s possible that you have other problems, but condensation is the most common winter moisture issue, so I’d start there.
One final suggestion, if you’re using humidifiers, use them less or not at all for a while to see if that reduces the problem. Humidifiers usually dump far too much moisture into the air, leading to mold growth, condensation, wood rot etc. If you must use a humidifier, keep the humidity level in the room below 50% during the winter. 40% is better.
I wrote earlier today about removing/replacing insulation that has rodent droppings.
I’ve been re-reading your older articles about air-sealing, and it sounds like the right thing to do.
But two more questions occurred to me:
1) I do not have bathroom fans to vent moist air. Should I install them (2 upstairs full baths). Your article said to vent through the roof.
2) My living room has a cathedral ceiling. In the attic, this is a sloped area. I emailed the rep I talked to, asking him if they air-seal and remove/replace the insulation in that sloped area.
Once I understand these two questions, I think I am ready to get this job done.
But as I said, I don’t want to solve one problem only to cause another!
Your articles have been very valuable!
I don’t see my original posting, so here’s a brief summary:
I had bats/squirrels in my attic a few years ago. I had a wildlife guy put an exclusion device to get the bats out, then he sealed around openings. I haven’t noticed any sound or activity since.
The attic insulation has droppings, plus the squirrels messed it up a bit.
I had a rep from a company to evaluate. He said they would remove the insulation/droppings (suited up, house area lined with plastic), vacuum up all droppings/debris, disinfect, air-seal gaps, install new R-30 insulation.
My original question was whether the air sealing would affect air flow or moisture in the house.
But then more questions occurred to me as I re-read some of your articles. I sounds like the air-sealing is a “go”. But I had further questions (post above) about the bath fans and I’m asking the rep about the cathedral ceiling area.
Thanks for your questions and notes 🙂
So, yes on air sealing the area under the insulation when you pull the insulation and clean out the attic.
Your question on bath fans is timely because it’s easier to do when the insulation is pulled. Make sure the bath fans are air sealed to the ceiling as well – that’s a huge source of moisture damage that almost everyone ignores. A little canned foam from the attic side around the perimeter of the fan box works great.
The duct from the fan should go straight up (or nearly so) to a vent hood mounted on the roof. This allows the fan to work efficiently (the less duct the less air resistance) and keeping it vertical reduces the chance of water building up inside the duct.
I’m not sure I understand about the cathedral ceiling. Are you saying that the cathedral ceiling is visible in the attic, like protruding through the floor sloping up? I’ve seen this type of construction a couple of times. If that’s the case, then yes, air seal any gaps (there shouldn’t be any unless you have recessed lights poking through the ceiling) and ensure good insulation covering it, just like you would do the floor of the attic.
Hope that covers it. My head is a little fuzzy today. Feel free to shoot over more questions.
The cathedral ceiling (or just a high ceiling) is above my living room, but below the attic, if that makes sense. About halfway across the living room, the ceiling slopes downward. So from the “normal” attic area, there is a section that slopes downward, which corresponds (as best I can tell) to the sloped area above my living room.
I emailed the attic guy about whether they remove/seal/replace insulation in that area. I hope to get a response.
I’ll also ask about the bath fan installation. I just re-read your article about it, and I was thinking just as you said, that it makes sense to do it when the insulation is removed. But I don’t know that I’ll be able to coordinate two jobs that way. I may be stuck doing it afterwards (I don’t want the installer to have to deal with the attic/rodent issues).
Would have been easier if the original builder had installed bathroom fans!
Thanks for your response!
I need your help. My exterior back wall is getting blister or bubbles in the paint but I dont have a leak. who do i need to hire to know if the house is having humidity problems? Thank you in advance.
Often, though not always, bubbles are indicative of moisture trying to force its way through from the other side. It can generate a lot of pressure which will literally blow the paint off the wall on the inside. It is possible that there is water or moisture behind that wall, which I guess means inside of the wall. Is this a sheetrock wall? One thing you can do very easily is take a sharp knife with a thin blade and carefully push it into the wall to see how much force it takes. If it goes in easily like butter then the drywall is probably saturated with moisture. If it resists and you can’t push the blade in without exerting a lot of force, then the drywall is not wet. This should be a minimally destructive test as it will just leave a small slice in the wall surface That could be easily repaired if it turns out to be nothing. If it does turn out to be wet, then that drywall will probably have to be cut out and replaced anyway.
It can be hard to find somebody who is good that specializes in tracking down moisture problems. If you Google “building science” and “moisture troubleshooting” in your area, you may have luck finding someone. I would suggest looking at a person or company’s website to see if they have information like mine on there or if they are just trying to sell a product. That should be a start. Feel free to ask more questions if you learn more about your situation and need some more tips.
Your blog has covered all of my questions. As an electrical contractor I see everyone doing just what you say and it sickens me that they get away with doing half the job wasting the clients money. I stand there looking like the a nit picker trying to make sure all of these items are done and I will stand by it to the end. You give my facts another point of meaning now as I will be able to show Clients I am not the only one who does it right. I will now be fixing up the air flow issues just in time for the winter your donation will come when my family sees how much you have helped!
I live in the San Francisco Bay Area peninsula area in an older home with a dirt crawl space, CAN lights in a vaulted ceiling, and fiberglass insulation between the ceiling and the roof. You describe exactly what I have experienced in the Springtime during the past several years. Water drips from the CAN lights onto the floor below the vaulted ceiling (when it is not raining outside and has not rained for many days). There is visible water damage to the ceiling that has accumulated over several seasons. I’d like to have a qualified professional assess my situation before contemplating repairs, but I am struggling to find the right person using the search terms you suggested. Can you recommend some one in the Bay Area who I can work with to better assess my situation and propose solutions? Thanks.
I’m afraid I missed your message when you first sent it sorry for the long delay. In the Bay area, there should be many options. You can look for people experienced in building science and moisture troubleshooting. A BPI certification is a good thing to look for. If possible find an independent company, not one that provides services like insulation or HVAC installation. I generally have been more impressed with specialists who focus on building science issues. They don’t have a vested interest in selling you something usually.
Your info is outstanding. I live in Oregon, where do I find a pro like you to do an analysis?
Thank you! There are a lot of good analysts out in the Northwest. You can try searching for “BPI certified” or “building science” or “home thermal imaging” for your area. The trick is finding people with experience and the right motivations. I typically suggest looking for independent people, not associated with an HVAC or insulation company. If you don’t have luck, email me with your town and I’ll try searching for someone promising.
It is great to have the info you provided. I am having water dripping from the light features in the ceiling. I also have fiberglass ceiling. Is there a way to fix the light features without redoing the entire ceiling? Will removing the moisture from the house (for example, seal the crawl space) help?
I live in San Mateo city, Bay area, California.
Water dripping from the ceiling light fixtures is definitely a big problem!
As you suggested, the first approach would be to greatly reduce the moisture in the house. I’d suggest buying a few of these inexpensive moisture monitors and placing them in a few locations in the house including the rooms where the light fixtures are dripping and the crawl space. This will give you better idea of the current humidity levels in the house and confirm your thought that the moisture is coming from the crawl space. It might be that the crawl space isn’t the source of the problem, which would save you a lot of effort. However, if your crawl space is noticeably wet, then you want to take care of that immediately. I had a townhouse with puddles on the floor from water seepage up from the ground! The previous owners never dealt with the moisture and it rotted out the floor joists under the kitchen to such an extent that the refrigerator was at risk of falling through the floor!
Given how much moisture is building up in your ceiling, it is very likely that damage has already been done inside the ceiling. The dripping water means that the wood is probably already saturated. Over time, this will lead to mold and rot. At the very least, I would consider replacing those light fixtures with sealed, flush mount LED fixtures. When installed tightly against the ceiling, these will greatly reduce additional moisture from entering the ceiling and will help to reduce additional damage. But ultimately, I think you’ll have to bite the bullet and cut out a section of the ceiling around the light to assess the extent of the moisture in the ceiling.
Here’s a link to a bunch of these humidity/temperature gauges at Amazon:
I’m having a problem with condensation on my ceilings and bricks of my chimney. I have vaulted ceilings and there isn’t anywhere for venting. I’m at my wits end with this problem and I don’t know where to go next. Is there a way I can talk directly to you or send pictures? Please help!
Sure -send me anything you’ve got to tedinoue@Gmail.com
The more details, the better. What the conditions are when it happens – outdoor temperature and weather conditions. Time of day. What was the day before like? And clear photos showing the area where the condensation occurs and the relative position in the room. It’s also useful to know where you live (city and state) so I can look up weather/temperature history.
I have a 1980’s atrium. Fully HVAC with humidistat and exhaust fan. If I dont manually adjust humidity exhaust almost daily and sometimes hourly, condensation forms in the house.
That probably means there’s missing insulation in the areas of condensation. Moisture rises and collects at the ceiling so that’s usually where the problems are worst.
Thanks for quick response. The atrium roof is glass and the house surrounds the atrium. It is a t & g, cathedral ceiling on house. Is there way to insulate around atrium from the inside? Its a one story house with asphalt shingles and a 3″ roof deck which in the 1980’s was good enough for insulation.
Is the condensation forming on the glass or somewhere else?
If it’s the glass, there’s nothing you can do other than reduce the humidity in the house or get more warm air movement up near the glass to try to keep it warmer.
If it’s on other surfaces, like the T&G ceiling, that can be more problematic. Again, any time you get condensation, the first thing is to review your home’s humidity. This can vary greatly from room to room depending on usage. For example, the humidity in my bedroom at night increases considerably because it’s sealed up and we’re breathing all night! Other examples are near showers, if the bathroom isn’t being vented adequately and in areas with lots of house plants that release a lot of moisture into the air.
If you’re using a humidifier, try not using it for a while and see how that changes things.
You can get little humidity meters from Amazon for cheap. If possible, put them close to the places where condensation is forming so you can see what the level is right there. Since the moist air rises, the humidity at the ceiling can be significantly higher than a few feet off the ground.
Here’s one example of the gauges I’m referring to
I have a 2-story property in Huntington Beach, California that was built in 1964. It was renovated in 2017. Starting last December, two sections of the property is showing excessive condensation and moisture accumulation. This condensation problem is mainly on the north facing areas. One area is on the first floor, and the other area is on the second floor, and these areas are not on top of each other. I am using a 50 pint dehumidifier and DampRid closet hangers to absorb the excess moisture continuously, but I want to know what is the cause of this so I can fix it. I greatly appreciate any feedback. Thank you.
Huntington Beach has a very mild climate, so it’s surprising that you’re having condensation problems.
What surfaces is the condensation forming on?
It’s common for people to develop condensation issues after a renovation due to the improved construction which makes a home “tighter.” The tightness is good, but that also means one has to be careful about uniform insulation and reducing interior humidity sources.
Condensation will form on the colder surfaces in a house. Often, that’s windows, which is almost unavoidable if there’s excess moisture in colder climates. In your climate, it’s less common.
I’d do a couple of things
1 – check for interior moisture sources. Most common is showers that aren’t properly vented. I always recommend checking the bath fan for good suction at the intake. Then, make sure the fan runs during the shower and for at least 15-30 minutes after you finish showering in order to remove the excess moisture.
2 – monitor the humidity in those rooms where condensation is occurring. You can get these on Amazon so cheaply – https://www.amazon.com/dp/B07QMZL448/
If you find the humidity in those rooms rises up past 60%, you know there’s too much moisture in the air under most circumstances. During the summer, it can be hard to keep it down.
I checked the daily humidity numbers for your area in December and they were very high – 60%-80% for many days. If you open the windows, especially at night or early morning when the humidity is very high, the house will fill with moisture which will condense easily. Unfortunately, that’s unavoidable. The humidity drops quickly as the day warms so you can flush out the extra humidity by opening up the house on non-humid days in the afternoon. But it can be a tough battle in your climate.
I’d start with those little humidity gauges placed throughout the house. See what the indoor humidity is like and if it is associated with any particular usage patterns, like opening windows or showering or cooking. Keep using dehumidifiers when the house is closed up, that might be your only solution during the colder months. During the summer, running the air conditioner will suck the moisture out of the air quickly.
Hope that helps.