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!
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Ted's Energy Tips 
Hi Ted, we’re building a second story addition in our house in the Cincinnati area (very cold right now). Roof is built with 2×12 rafters for the cathedral ceilings. The architect spec’d insulation baffles, R-30 fiberglass insulation and vapor barrier. Ceilings will be drywall. Roof has full ridge vent and the soffits arw vented. I finished installing the unfaced insulation and 6 mil vapor barrier recently. Drywalled the first bedroom and the following day saw a wet spot on the drywall. Upon investigating, I discovered condensation between the insulation and the baffles. Most of the condensation has been on the north facing side of the roof. Any help you can offer would be greatly appreciated!
Was the drywall job finished everywhere by the point you saw the condensation spot? That moisture had to have gotten in there somehow from the interior of the house. The baffles got cold and the water condensed on them and dripped down.
Is it possible that moisture built up on the baffles after you insulated but before you closed up the ceiling?
The key thing is to keep air from the interior of your home (which is relatively high moisture content) out of that cavity. If you keep getting condensation even after you’ve closed up the cathedral ceiling and it’s had a chance to dry out, there’s got to be some other way humidity from the interior is getting in there.
The first room is the only one that has been drywalled. There were several day between the time that the insulation was done and the plastic vapor barrier was put up so I would guess that’s plenty of time for the moisture buildup. Is the 6 mil plastic on its own enough to keep out the moisture or does the drywall need to be in place as well?
The plastic will make a huge difference, as long as it’s sealed well. But if every seam isn’t taped air tight, all bets are off. Just remember that any air that can travel into the cavity is carrying that moisture. The equivalent of a 1 square inch hole transfers more than 100x as much moisture into the area as would go through drywall.
Hi Ted, we live in an older home and recently noticed a significant increase in dust and dust bunnies around the home. We change our furnace filter every season and maintain the furnace. Any thoughts?
https://polldaddy.com/js/rating/rating.jsTed,
I had an HVAC system replaced 6 months ago and now since we are using the heat when needed in the cold morning, the air smells very musty when the a/c kicks on in the afternoon. We don’t notice the musty smell with the heat running, only when the a/c is running. The musty smell comes from all of the vents and it smells musty to me if I sniff the return air vent duct with the filter removed. I have 2 HVAC units in this attic space and the one that wasn’t replaced doesn’t blow musty air at all.
Prior to replacing the HVAC system we had zero trouble with musty air. The ductwork is 9 yrs old. I’ve had the techician out to inspect the unit and he claims he can’t find a reason for the musty smell.
Do you have any suggestions?
Thanks!
Bill
My first thought is that the drain pan for the AC isn’t flowing well and moldy water is in there, but if your HVAC tech checked it out and didn’t detect that, maybe not. Then again, if he didn’t do a thorough inspection, he wouldn’t have seen it. Especially if you can smell it when you sniff the return duct. This happened to my system last year and it wasn’t obvious until the drain pan overflowed and leaked on my ceiling!
There could also be mold in the drain pan even if it is draining properly. Then when the condensate from the AC splashes down into the pan, it could release the odors.
I live in the Northeast. Builder put up T&G wood on cathedral ceiling with no sheetrock. Insulated with fiberglass batts. Ventillated with styrofoam channels on underside of roof, ridge vent at top and Soffit strip vents on bottom. Also have 10 recessed fixtures. Finally, the roof and ceiling wrap around a chimney. I think the design violates every rule in your book. I am going to rip the ceiling all out this year and start over. New plan:
1. Use foil backed closed cell foam to create a 2″ airgap below roof plywood. Seal edges with tape.
2. spray foam 2 – 3″ on the hard foam between the rafters.
3. Sheetrock ceiling. Tape seams. Paint with water impermeable paint.
4. Apply a rubber tape to the sheet rock where the rafters are.
5. Re-install T&G wood, nailing through the rubber tape to insure a good seal.
6. Install recessed lighting cans that are completely sealed and insulation tolerance. Spray foam all around them.
7. I don’t know what to do around the chimney. I think it has its own moisture problems. I.e. I think it carries moisture from above and emits its into the cavity between the roofing and the insulation. Lots of condensation in the bays that surround this chimney. Maybe I need to waterproof the brick in that cavity, like with a Drylock paint.
8. Question: How do I treat the black mold on underside of rafters? Bleach solution? Special mold treatment? Replace everything?
Thanks for your advice.
I’ll tell you, these builders should be forced to live in the houses they build and pay for the eventual repair costs. It’s unconscionable.
First, a couple comments on the solution.
1. Please don’t use tape. The adhesive will quickly give out. If you spray foam it, just jam the foam board into place and foam right over it.
3. Between sheetrock and a couple coats of standard latex paint, you’ll be in good shape.
6. Consider low-profile LED fixtures. They’ve come a long way, are airtight and you’ll never have to worry about replacing bulbs.
7. Chimneys are tough. What’s probably happening is the masonry transmits the cold very effectively so that the cavities around it get super cold, leading to more condensation. Some stone is highly moisture permeable which can wick water. Your best bet might be to just foam it where it’s exposed into the cavities. That will keep the cold and moisture out of the cavities. As long as the flashing is good, you should be in good shape.
7a. You might be restricted from doing this by building code. Even though chimneys have ample spacing to prevent heating (otherwise the roof would catch fire, right?) some jurisdictions force you to have certain gaps around chimneys, allowing for only fireproof materials like sheet metal and rock-wool insulation.
8. Simple warm soap water is highly effective on mold. It’s a best kept secret. People all say bleach it, but soap breaks down the mold and it washes away. Chemistry in action!
Good luck on your project. I’m very glad to hear that you’re going to do it right. You’re doing a huge service for the next owner of your home!
https://polldaddy.com/js/rating/rating.jsI have a bonus room that has a faint odor. It smells like osb/a little sweet. The smell stays in the bonus room no other room unless the AC sucks it down the steps to the return. I sealed the bathroom up there. Sealed the bonus room and turned off the AC and heater. It smells Only in the bonus room above the garage. Doesn’t smell like the attic. Doesn’t smell like the stale closet. It’s like something is off gassing. But it’s a newer house. 3 years old and it has smelled the same day one. Hot or cold doesn’t seem to affect it. When you walk-in the room it smells 10% bad and 90% ok. So it’s faint. We never use the room. I removed everything from it. Drilled holes in some walls in bath. Nothing. Pulled carpet back and drilled hole in floor 1 spot. Nothing. All smells like attic. But not what I’m smelling in the bonus room. No smell in the garage either. So air is off and nothing in there. What do I do.
Could you be getting some odor migrating up there from the garage? Often odors can migrate up through the walls and floors to emerge in bonus rooms of these sorts.
I’m glad you mentioned that it doesn’t change with temperature since off gassing is usually highly temperature dependent.
Garage smells can be tricky because the garage gets flushed out every time you open the garage door whereas the air in the bonus room is fairly stagnant. So I wouldn’t rule out something in the garage. The trick is that most air movement is from low to high in a building (like a chimney) so it’s possible for odors to start in the garage and float upstairs.
The other thing is that the odors could be lingering in there because the air never circulates to flush out odors. So any off gassing that occurred could have ‘tainted’ carpeting and other building materials in there. I would wait until spring and then open it up at every opportunity (assuming that it has windows?) so that you can flush it with fresh air and try to get rid of odors. At the same time, clean the carpets and anything else that might have captured odors. It might take weeks of flushing, but if it’s worth a try given everything you’ve described.
I left it for a year open and still can smell the smell. I then closed it up and found it’s coming. From the bonus room. The garage I keep shut for weeks and I go in from the house and it doesn’t smell like it. I do have a gas hot water heater. But it doesn’t smell like gas. If it was off gassing after 3’years it would be gone. What does wet insulation smell like ?
To me it has to be producing the smell. Like wet insulation or hot water heater or mold. It never gets less or more smelly.
That’s useful info. I agree, it sounds like it’s coming from something in that room.
I’ve never known insulation to smell sweet. Usually it’s either like paper (if it’s cellulose) or moldy, and those are distinctive odors.
Sweet smells are associated with anti-freeze, which you say it can’t be. There are a couple of other things that give rise to that type of odor.
Sometimes these types of smells can come from animals. Someone reported wasp nests leaving a sweet odor. But you’d think that would disappear over several years.
Sometimes the odors like this are electrical, caused by heating wires. But again, given your description, this seems unlikely.
Can you identify the odor more precisely than just “sweet”? Does it remind you of anything?
Maybe sweet is a bad word to use. It’s not stale like a closet. Because the closet in the room smells like a closet. It smells to me like sawdust/attic with a little twist. So I can smell the smell. Then open the attic and it’s different.
These odor issues can be maddening.
A good cleaning of the carpet (do you have carpet?) with a baking soda wash can be a good way to suck up odors that might be embedded in it. Here’s an explainer: https://www.wikihow.com/Deodorize-Carpet-With-Baking-Soda
Here’s a couple other articles that might be of use to people having odor problems:
https://www.treehugger.com/green-home/10-surprising-sources-gassing-your-home-and-what-you-should-do-about-it.html
https://www.doityourself.com/stry/osb-vs-particleboard
https://polldaddy.com/js/rating/rating.jsI am building a gabled addition off of my house. It will have a cathedral ceiling in the center and have attics on the far side and on the side that connects to the house. The house is vented using opposing gable vents. I will vent the cathedral and far addition attic using ridge and soffit vents.
How should I vent the section of roof/attic thy connects to the house? There wont be adequate soffit length on that part of roof to use it for venting.
Should I just cut a hole in the current roof allowing the air to come inside that part of the addition attic? Add a turbine too ?
Please email me if you need pics. I need a answer quick as I’m in the process of sheathing. Thanks!
Depending on your climate, and the construction of your ceiling, ventilation of cathedral ceilings can be unnecessary.
If you have built the ceiling properly airtight, without recessed lights out other holes, then there’s minimal moisture that gets in there. People often pack these tight with cellulose insulation.
If you haven’t built it tight, for example, all the folks who have cathedral ceilings with no vapor retarder and have a wood tongue and groove ceiling, then all bets are off.
https://polldaddy.com/js/rating/rating.jsHello Ted,
In reading your info regarding condensation freezing/thawing behind drywall of cathedral ceilings, it seems pretty clear that is the issue I have in my home. How do I locate a building scientist locally (I’m just north of Chicago, IL) to troubleshoot?
Thanks for your help and for your tips.
In your area, there should be some some great energy specialists/building scientists. Start by looking for energy auditors and building science professionals with experience in dealing with moisture problems.
I found this company in the Chicago area that trains and certifies building science professionals. If you give them a call, either they could help or they could point you to someone in your area who is experienced in solving moisture problems:
https://www.priorityenergy.com/service-group/building-science-professionals
Excellent! Thank you very much for this info.
https://polldaddy.com/js/rating/rating.jsHi Ted, I sent you this through Facebook messenger and am putting it here as well so you receive it. Thanks! Hi Ted, we just read your article about condensation in vaulted ceilings. We think we may be dealing with just sadly! We’re in Upper Bucks County and we’re wondering if you do home visits or know someone we can hire who knows about all this stuff? We want to know what we’re dealing with before trying to fix it. We assumed it was a roof leak but now after reading your article we think it’s what you talked about…
Hi Jeff, thanks for getting in touch.
While I am not currently taking on paid clients, I would be happy to try to help you deal with the issue. Unfortunately, I’m currently out of the state for an extended period.
Perhaps describe the issue, when and where it occurs and I’ll work on helping you diagnose the issue. Then, when a contractor does come out, you can give them some direction and you’ll have a better sense of whether they’re steering you in the right direction.
In our area, there are a few contractors who I’ve worked with who are trustworthy and have had green and healthy building training.
Dave Lawler, Lawler Construction in Doylestown
Tom Wells, TGW Construction in Yardley
David Redner, Redner Home Renovations in Warrington
Thanks so much Ted! I’ll take some pictures and write up a description soon.
Hi Ted,
Our house is basically a series of three peaks in a row. The two side peaks are drywalled cathedral ceilings and we don’t seem to have issues with them. The middle peak is the largest and is also a cathedral ceiling, but is tongue and groove wood, and doesn’t appear to have drywall underneath. There are 7 can lights in it as well. There is a ridge vent, and there are soffit vents, but because the center peak actually meets the other two peaks, there is a very limited amount of soffit on the center peak. There are de-icing cables along mos of the valleys of the roof, which seem to be working. The issue is, that inside in the central peak ceiling, there are numerous stains as you can see in the pictures, and even though we haven’t seen dripping, it has happened because we discovered stains on the cushion of a chair from dripping from the ceiling in the last few days. Also, you can see there is staining on the wall in one place from where the ceiling meets the wall. We assumed it must be leaking in the roof, which is 15 years old, but after reading your blog we’re thinking it is just moisture going through the ceiling and condensing and dripping back down. What are your thoughts?
Thanks!!
From your description and the photos, it definitely sounds like condensation drips. That construction is very tough to remedy without a lot of work and expense. But the alternative is worse given the cost of replacing a roof!
If it were my ceiling, id do two things. First, I’d replace the bulbs in the recessed lights with LED retrofit bulbs. These can be sealed airtight to the ceiling. If you’re lucky, the moisture is getting into the cavities from the lights and this will do the trick.
If there is nothing behind the wood, then you can try to have someone carefully caulk every seam. This might work but it’s risky. It might not stop the condensation and just hide the leaks by redirecting the water down the ceiling to somewhere else.
If it were mine, I’d sandwich a layer of foil faced poly iso foam and a new inner wood layer.
Hi Ted,
Thanks for your below answer! Quick question, are you saying to remove the wood ceiling, put a layer of wood then the poly iso foam then the wood ceiling back up?
What are your thoughts about removing the can lights and wood ceiling and drywalling the ceiling, or removing the lights and drywalling over the wood ceiling? Thanks again!
Sorry, I was quickly typing on my phone before a movie 😉
I’m thinking the easiest solution is to screw right to the existing wood then put whatever aesthetic surface you want right over that. It’s a lot easier than ripping off the entire ceiling and starting from scratch. They’d just use longer nails/screws to screw the new surface on since they have to go through the foam.
You can drywall right over the wood as well, though it’s always nice to be able to add R-value cheaply in the process. With cathedral ceilings, usually the fiberglass in the cavity gives you a comparatively low R-value. The foam provides more plus gives what’s called a “thermal break” so the rafters have some insulation as well. The net result would be tight and warm.
Finally, as far as the cans go, you could close them off and surface mount lights (track lights etc.) or you could go with the LED retrofits which can be sealed perfectly. I’d use a thin layer of caulk to seal it to the ceiling, making sure to get dimmable fixtures and a warm color temperature (2700k). With the long life of these fixtures, you should never have to change a bulb again.
Thanks so much for all your help Ted! Lots of food for thought!
Ted,
I hope this message finds you well! What is your opinion on insulated metal duct work? Should you insulate it, or leave it to radiate some of it’s heat/cool to help condition the space it is in? In my situation it is a basement and insulated crawlspace.
Also, the aforementioned crawlspace is an addition that abuts the basement. Should I drill large holes or remove sections of the abutted rim joists to help connect the air of the crawlspace to the basement? I had planned on bringing a duct into the crawlspace to supply conditioned air, but if I open it up to the basement, would that supply enough conditioned air, or would I need a dedicated duct? The crawl is only about 300 cubic feet, so I wouldn’t need that much conditioned air. 4″ duct I’m guessing.
Thank you!
Andy
Hey Andy, good to hear from you again! It’s bitterly cold out here. Sure glad we sprung for excellent windows!
On to your question regarding insulated metal ducts. I personally prefer to insulate them even in conditioned spaces because I want as much heat as possible to go to the desired rooms. I’ve found that even well insulated, there’s enough losses from furnaces/boilers to keep most basements warmer.
For the crawlspace – you really just want a little air flow to keep the air and moisture from stagnating and building up in there. A small, 4″ duct blowing in there would be fine. Most don’t even use a return because there’s enough natural leakage to allow the air to flow.
I wouldn’t trust just letting natural airflow through small openings to do the trick. It could work, but better to have controlled flow rather than random.
Hope that helps 🙂
I’m in Michigan and it’s bitterly cold here also. 0 with wind chills in the -20’s. And yes, as always you are much help. Can I just pop a duct through the rim joist into the crawl, or should I run it around the perimeter to the furthest outside wall?
Andy
If you use a supply and return, you’d want them on opposite sides of the space. You could get away with an inlet for the duct on one side and a hole used as the return on another interior spot along the rim joist if you can space them apart. If they’re too close, the air will pretty much just flow from one to the other and you might be better off just allowing the air to flow in and out through cracks.
OTOH, it would be best if you did as you said and ran a duct through the space and had it blow the conditioned air into a distant corner so as to give the best air flow through the space. Use your judgement given the size of the space (tiny you say) vs. the amount of effort required.
https://polldaddy.com/js/rating/rating.jsHi Ted, Your info about the crawl space seems to address my concerns too. I have a converted summer bungaloo (tiny 504 sq ft) on Long Island which serves my needs very well with the exception of a very cold floor in winter. I wanted to blow-in insulate but the space is only 18″ high enclosed with cinder blocks & just 2 small air vents. No one can get under there to cover the ground with plastic. When we first converted it we raised the floor with 2×3’s using the oak floor as a sub-floor, & filled the space with regular pink insulation. This was a DIY job, we didn’t think of the crawl-space at that time. We also insulated the attic floor with the same pink, covered that with plywood, & recently added an attic opening bunting.
The thing is this; an Energy Expert wants to come in & blanket insulate(?) the attic walls & ceiling. I’m afraid of wood rot up there if its too enclosed. The original toung-in-groove wood is still in place on my roof so it’s old stuff he would be playing with. Also he is not addressing the cold floor in any way other than carpeting. I need a second opinion. What do you think?
Hmm, that’s a challenge. I’ve worked in tight crawlspaces but never that low! You’re right, that would be impossible. One thing you could, which might sound a little wacky but would give you much warmer floors, is to lay 1″ XPS board foam as if it’s a complete floor. You could then put 1/2″ plywood over that then carpet it. The downside is that you lose 2+” of height (not a big deal) and doors would have to be cut back to give clearance (which wouldn’t even work for the entry door) so that would require some clever carpentry.
Barring that, then thick carpet padding and wall-to-wall carpet is your best bet.
For the attic, if the attic is insulation does encapsulate the attic then the attic space should be brought into the heated space of the house by supplying a small amount of heated airflow through the space. It wouldn’t have to be kept at 70F, but a small duct supplying air (if you even have a forced air heating system) would help keep you out of trouble.
https://polldaddy.com/js/rating/rating.jsHi Ted,
I am hopeful you can help with what seems to be a pretty common setup.
We have a 1.5 store house (.5 is upstairs with an unfinished attic space). We also have an unfinished daylight basement (one wall full concrete, two walls step down concrete with framing, and one wall all wood framing). The outside of the home is all stone and brick. The basement has no appliances or HVAC other than a tankless water heater. We live in climate zone 3A.
The builder put R-19 batt insulation in the ceiling. We are beginning to think about finishing the basement and did a ton of research that suggested insulating the walls and rim joists would be better even if we didn’t finish the basement to make it more a part of the living space. We choose to do a ROXUL product in the walls and rim joists. During this process, I pulled down some of the R-19 insulation as it was in the way of the rim joists. I notices some areas where the sheeting above was moist. This seems to be around areas where there are interior walls or other areas that get a good bit of heat (under the fireplace, shower, bathroom, etc.)
I discussed this with my builder and he said “this is how everyone does it”. It is not in my DNA to just ignore moisture on floor sheeting.
My assumption is that with the basement temp (50 degrees even on a 20 degree day outside) is that the hot air above is causing the cold side of the floor to release moisture.
My assumption is that we need to add HVAC to the basement. Thoughts on other options or corrections to my thoughts?
Thanks for your time!
Steve
I’m with you – always pay attention to moisture. What your builder may not be aware of is that moisture problems destroy more homes than any other cause except for fire. I equate detecting moisture to smelling smoke. Might not kill you immediately, but left unchecked, it can be devastating.
To get to the specifics – the area you found the moisture – was that just near the rim joists as opposed to under the more central part of the basement? I ask since the rim joists are cold areas, so the floor above the insulation could still be quite chilly – enough to cause condensation formation. Then, the batts, if faced could be trapping that moisture between themselves and the floor, allowing the moisture to build up.
Condensation won’t form on warmer areas unless the moisture levels are extreme. But if they were that high, you’d probably have mold all over the basement.
Do you have a normal subfloor (usually plywood sheets) between the basement and first floor? Some older homes just have the floorboards laid over the joists. If you have a subfloor, then it’s unlikely that there’s enough moisture drive from the main living space to go down through the floor and into the basement. if you don’t, then moisture could very easily move between the floor boards and down to the basement. So your specific construction is very important.
As you noted, it’s typically considered best practice these days to make the basement part of the conditioned space of the house in order to minimize the chance of these types of moisture issues. But again, it depends on specifics. If it’s an old house with dirt floors and tons of moisture coming up from the ground, well, bringing that mess into the house envelope might not be so great. But assuming a normal construction, I’d do what you say – insulate rim joists and get some air flow to flush out the moisture and warm the basement somewhat.
One final note – it’s not usually a good idea to insulate rim joists with moisture permeable insulation like Roxul. This has led to moisture passing through the insulation and condensing on the cold rim joist. This happens repeatedly over time and rots it out. Much better to use a couple inches of blue-board (extruded polyurethane insulation) cut to fit then caulked into the rim joists. It’s a labor intensive job but worth it.
Here’s a how-to on this: https://www.familyhandyman.com/basement/insulate-basement-rim-joists/view-all/
Cheers,
-Ted
Thank you Ted for the quick reply. A couple of follow ups to help with the specifics.
House was constructed in 2017, so brand new. Plywood floors with a mixture of hardwood and carpet throughout the main level.
The moisture is in a variety of spots. Much of it is close to the outside rim joist, but some is in the center as well. Most of it seems to be around seams in the plywood as well as where walls would be above. It is very sporadic and not everywhere.
May not matter, but basement has 11 foot ceilings.
Concrete foundation is not yet insulated. None of the rooms will be finished that have exposed concrete. The outside foundation does have a mat over the spray on material.
Humidity in the room is currently at 52% and 50 degrees. There is a de-humidifier that runs. Could that be pulling moisture from upstairs.
Good tip on the 2 inch foam. I will definitely go that route.
Would love any further thoughts.
Thanks,
Steve
Thanks for the added info. That is interesting. I wonder if the joist bays where you’re experiencing the moisture are leaky (air leaks). If cold air flowed through those bays, between the floor and the insulation, then, wherever you have elevated moisture, like at floor cracks, you’d have a higher chance of condensation. Just a guess, but I can’t think of other reasons why this might be occurring. You might want to just stick your hand in there to see if it feels cold compared to other bays where you’re not getting moisture.
Humidity levels sound perfectly normal. Typically moisture, like hot air, rises up, so it’s rare for air/moisture to get sucked down into the basement unless there’s a strong source of air flowing out from the basement (i.e. like a clothing dryer or furnace). But it doesn’t sound like that’s the case, so the moisture is something of a mystery. I’m going to put my money on just cold air flowing through and a bit of excess moisture slipping between cracks.
One question on the rigid foam. is it acceptable to use a thinner rigid foam (.5 -1 inch) and then put rock wool over it for additional r value? May be a “cheap-skate” question, but I was curious.
Thanks!
Not a good idea. The rockwool will insulate the board foam allowing the inner surface to get cold. This would become a condensation magnet.
Insulation Question:
I am thinking of putting rigid, closed cell polyethylene insulation to cover 2 basement windows and on top of the trap door, which is the only entrance/exit to the basement. Guess it would have to be sealed/caulked on to be effective(?) Would I need to put the insulation on the bottom of the trap door to be effective? This basement is quite cold.
Also, thinking of putting some in my unused fireplace opening, and then sealed it with window insulation shrink kit. Currently have the 1″ white rigid panel insulation jammed in, but not sealed.
Would these things be worth doing? Your thoughts greatly appreciated!
I am in cold climate–NE Ohio area.
Insulation like that can work well. For the windows, you want to seal it well around the edges so that moisture doesn’t get trapped in that space because it will condense and freeze on the window. Then thaw and drip onto the wood. Over time, this will rot out the window frame. But if you’re careful, the problem should be minimized.
On the trap door, the insulation can be on either side. You might want to use a good compressible weatherstrip (it’s called D-profile) around the perimeter to seal it without having to do anything drastic to the door.
Lots of people do the fireplace opening like that. If you want to use the fireplace periodically, you could instead get a “chimney pillow/balloon”. This goes into the opening of the chimney and inflates so it’s relatively easy to install and remove. If you’re never going to use the fireplace, then you might seal it more permanently like you described.
These things wouldn’t take much effort and would certainly help reduce drafts and energy loss.
https://polldaddy.com/js/rating/rating.jsI have a two story small beach house we live in full time. The heat pump has a air handler that draws cold air from under the house. Our upstairs bedroom is constantly dusty. We have high humidity most of the time at the beach. I checked the floor vents and they seem to be dusty. I have my system checked yearly so I assume my ducts are sealed correctly . What can I do to reduce the dust? Thank you
you say it draws cold air from under the house, do you mean the air handler is mounted down there and the ductwork is under the house?
I would suggest that you not assume anything. I’ve seen numerous systems that are professionally maintained that had ducts disconnected from the main trunk line, leading to huge amounts of impurities and cold air getting sucked into the system. since the source of the dust is most likely that space under the house I would look for leaks in the air return section of the system. Start at the air handler and make sure that the filter port is tightly sealed. and especially check the ductwork that leads back into the air handler. often this is not sealed at all, allowing a lot of air to get pulled in around the cracks.
I am remodeling my kitchen which is made from cement block I put two by fours flat against the inside wall and insulated between them with 1 inch fRigid Styrofoam I do not have enough room to put the 2 x 4‘s the other way so I had to lay them flat against the cement block and secure them I noticed when it got cold in the single digits outside temperature there is ice forming behind the 1 inch Styrofoam the other portion of the wall that I did not insulated does not have this moisture and ice what can I do to prevent that ice from getting between the block and the Styrofoam someone told me to just drywall it and it will go away but I am worried if it does not the ice and moisture will eventually turn into a mold problem behind the insulation even the metal outlet boxes that I attached to the cement block have Moisture drops in them that doesn’t sound good to me I would think the bare cement block walls would have More moisture on them than the insulated wall but it is exact opposite
When you don’t have insulation, the warmth from the heated interior gets directly to the block wall, keeping it at a higher temperature than the insulated section. That’s exactly what the insulation does – it prevents heat loss by keeping the cold on the block side and the heat on the inside.
Water condenses on colder surfaces, so that’s why you’re seeing frost on the block behind the insulation.
If you haven’t yet put up drywall, then any moisture inside the house will go directly to those cold walls and condense. Once you seal the walls up, you won’t have this problem as long as there’s no way for air from the inside to get to the block.
The trick is going to be those outlet boxes. Air will get into the wall through the outlets and around the covers. If you want to avoid problems you either have to forego outlets or come up with a way of mounting them on the surface so that you can insulate behind them. However, you should consult your building code enforcement official to ensure that you’re allowed to do this.
The other thing to consider is the type of insulation. Since you only have 1-1/2″ of space, you should consider foil faced poly-iso foam board which gives almost R-7 per inch AND serves as a vapor retarder. Normal white Styrofoam is highly moisture permeable and has a poor R-value.
Do you absolutely not have more interior space to build the wall in? Given that you’ve had to lay the 2×4’s thin way, you might also consider laying sheets of poly-iso foam over the 2×4’s (picture drywalling with foam). Even 1/2″ will have considerable benefits since the 2×4’s have poor R-value and will transfer a lot of cold into the wall. So much so that it could cause moisture problems on the inside of your drywall. If you add this 1/2″ across the 2×4’s and the 1-1/2″ in the spaces in-between, you’ll have about R-10, which is pretty good given that construction. And you’ll have much better chance of avoiding any sort of moisture issues.
It still won’t help your outlet issues. I’m afraid I can’t help you there other than what I said – mount the boxes on the surface of the drywall. I’m sure you could come up with an aesthetically pleasing way of doing this in a kitchen. For example:
https://www.legrand.us/wiremold/at-home/surge-protection-and-power-strips/pm-plugmold-multi-outlet-strips.aspx
Also, check out these products:
https://www.menards.com/main/mouldings/surface-mount-raceways/c-9801.htm
Good luck and stay warm!
Hello Ted,
I’m hoping you can provide some advice.
I’m in NJ and the house is 17 years old. The insulation is not so good . One room is ice cold in winter and very warm in summer, not sure if the insulation even was installed behind the wall . The room is on the second floor above the kitchen. The kitchen extends further than the room by several feet. The outside wall is a kind of a knee wall under the window sill with a height of 2 ft. I would like to find a way to insulate this wall. It would be quite impossible to get into the space behind the wall to install the batts even if we remove the sheetrock because it is too small to crawl inside to do it . What would be the best approach to insulate the wall in the room ? Not sure if spraying foam will work either , because of possible condensation , vent control . I used infrared test device and the temperature on the floor is about 48 , the thermostat in the house is set for 70 degrees. ( it is 20F outside now ) .
Thank you,
Lynda
It might be that cold air is getting into the floor cavity between the kitchen ceiling and the room above. When you use an infrared/thermal imaging system, it’s amazing what you can see as it tells the story clearly. I’ve seen a number of homes with this problem where there is an opening right from the side of the house into those floor cavities. It’s hidden by siding, but the cold air can run right through it.
Since you’ve got an IR thermometer, you can scan the floor temperature and map out the problem. Maybe use a piece of chalk or blue painter’s tape to mark the floor where it’s cold. if the entire thing is cold, that’s a big problem. But chances are that you’ll find channels of cold, corresponding to the space between the floor joists. If it runs from the wall and across the floor, you might even be able to trace the channel from one side of the house to the other.
If it is this, then the best solution is to figure out how to access that exterior wall where the cold is getting in. This could be a real pain, requiring pulling off siding. An alternative that could be much easier would be to cut an access in the kitchen ceiling if it’s drywall. That’s really easy to cut and repair. You’d want to trace temperatures in the kitchen ceiling in the same way to trace exactly where the cold is getting in.
Your actual question was about insulating the wall. Did your IR thermometer show this wall as very cold too? If this is very cold too then you would want to cut out the sheetrock and insulate. It sounds like a mess, but any decent carpenter could cut it out easily, insulate it and replace the sheetrock good as new, as long as the wall has a normal paint job that could be redone.
In addition to bad insulation and/or air infiltration through the floor cavity, you might just not be getting enough heat to that room. Often, upstairs rooms have poor ducting of heat from the furnace, leading to a much colder room. If you have heating vents in the room, you should ensure that you’re getting enough airflow and that the air is as warm as it is to other rooms. It could be that a metal duct is running between the floor joists where it’s cold, which would really cool off the heating air!
So many possible issues. Best to really figure out the source of the cold so you can fix the right thing.
Good luck. It’s going to be cold for a while the next couple of weeks!
Hi Ted , Thank you for your reply. I forgot to mention the wall temperature is around 50F . I suspect the batts either fall out or never been installed properly. It was always cold in this room .
I checked the ceiling temperature on the first floor under knee wall space as you recommended. There are some voids possibly around the joists , where the temperature 10 degrees lower than is surrounding space.
When you said that the carpenter could cut the sheetrock and insulate the space behind the wall , did you mean spraying foam through the cut ? Is it somehow possible to install batts behind the wall from inside even if it would require to remove all sheeetrock? Or any other solution ? I have some concerns about spraying foam, that is could cause a mildew ( north wall) or be a fire hazard if vent covered with foam ?
Thank you ,
Lynda.
I am thinking that they could cut an access at the floor level up the wall. Then they could inspect what’s going on with air leaks and missing insulation. Once they see that, they should recommend a strategy for improvement.
You typically want the insulation right against the inner wall and directly above the lower floor ceiling. They could either spray foam or use batts.
Thank you for your help!
you’re very welcome. Happy New Year!
one last thought, if they do cut out the drywall, you may wonder what to do on the last piece that they replace when patching the wall. the best thing might be for them to glue a 2in thick piece of polyiso board foam on to the back of the last sheet of drywall so that you’ll have good insulation behind that last piece. or, of course they could just fit a batt insulation into the cavity, but that would run the risk of having it fall out when putting in the drywall. So my preference is to glue sheet foam on to things like attic hatches and patches like this.
Thank you so much ! It is exactly what I wanted to know.
https://polldaddy.com/js/rating/rating.jsTed
I could use your advice. I have a 2 story home built in 1950 on a cement slab, 2800 sq ft zone 5. Poor insulation. HVAC system and ducts in attic along front of house. The rest of the 2 story is finished. House is very drafty and furnace pushes very hard, I assume I’m losing effiecency of the hvac because the space is not conditioned. I’m nervous about spray foam and have had all kinds of crazy quotes for closed cell foam and ceiling the entire attic. I was thinking about closing off just the furnace area about 10’x30′ and ceiling that area. Then blowing in more insulation above the garage and other area not sealed off. I cannot get access to the floor, so I would blow some insulation above the upstairs rooms.
You have a number of possible options. I always like to approach these things in a way that will maximize the benefits with the least amount of disruption and cost.
With a really leaky house, any system would be working hard so that sounds like the priority before doing anything dramatic in the attic.
The other thing is that it could just be bad/leaky ducts. It might be easier to insulate/seal the ducts and make sure the system isn’t sucking in cold air (like through the filter port). A few things like this could easily increase efficiency 25%.
What I’d really suggest is that you get a good energy auditor to come in to look at your house and system asking them the same questions. A few hundred dollars spent now on expert consultation could save you thousands in costs to re-insulate which might not even solve your problems.
Your last thought about closing in the area where the furnace is could work very well, but it could also “starve” the furnace of combustion air depending on the design of the furnace. Some furnaces just take combustion air from the space in which they’re installed. Others have a fresh air intake that supplies the combustion air. You have to be extremely careful about changing the environment around the furnace unless you know exactly what’s going on.
https://polldaddy.com/js/rating/rating.jsI recently bought a cement block building in which the walls or sweating a lot on The inside as the temperature went down on the outside I put 1 inch Styrofoam on the interior walls and anchored two by fours flat against the wall one and a half inch thick because that’s all the room I have to work with on the inside the 2 x 4‘s or getting wet and underneath the foam there is a lot of moisture if I put a vapor barrier on the outside walls with 2 inch Styrofoam will that help eliminate the sweating of the walls on the inside this is an all above ground structure with a concrete floor
Yep, that will happen. Cold walls are like the windows in your bathroom – they provide the perfect opportunity for condensation.
The moisture is inside the building, not coming through from the outside.
Ideally, you’d insulate only the exterior of the block and keep the interior exposed. This would keep the block warm enough to avoid the condensation you’re seeing. Since you’ve already insulated inside, the exterior insulation will still help because that will keep the block and interior of the foam from getting so cold.
Use the dense foam-board (blueboard or pinkboard). The white foam is much more prone to breaking down and doesn’t provide as much insulation for the 2″ that you’ll be using.
Thank you for your help I am going to insulate the outside before I drywall the inside to make sure the moisture disappears I’m worried about mold underneath The one inch insulation on the inside and the 2 x 4’s rotting from the moisture I hope it works
Sounds like a good plan. Best not to trap in moisture when possible.
Hi. I’ve just put on an addition. Brand new poured basement one wall stick built the second floor has 2×6 walls with faced r 19 insulation and the outside is just sheeted with tyvek for now no siding on yet. My problem is that I’m getting moisture and frost on the inside of the sheathing and backside if insulation. How do I stop this? The house is kept at 70 degrees and the inside humidity is right around 40. I’m out of ideas and don’t wanna continue to drywall till I know if this is okay.
Hey Kris,
How long since you poured the basement? It can take a long time for all the moisture to come out and for it to fully cure. You can test this easily by taping down a sheet of plastic on the concrete floor. Maybe 2’x2′. This will trap moisture under the plastic so it’s visible. If you get condensation on the plastic in the first day, then you can imagine how much moisture that it’s dumping into the air.
Just to make sure I understand. Are you saying that there’s no sheetrock so you can pull back the insulation and see the inside of the sheathing? If that’s the case, then you’re almost certainly going to see frost because there’s nothing stopping moisture from getting from the house to that freezing cold sheathing. Even if the humidity is 40% at 70 degrees, that moisture will condense on a surface that is just 50F.
The danger now is that you’ll trap moisture in the walls. I would definitely want to put something on those walls to stop more moisture from getting from the house onto that cold sheathing. But, short of rock, it’s going to be tough because moisture will find way in there if the walls aren’t air-tight, so even putting up plastic on the interior probably won’t be enough to really stop moisture from getting in there.
I’m thinking, sheetrock ASAP and hope that the dry outdoor air will be enough to suck the moisture out of the outer wall. But before you put the siding on, pull off some of the sheathing to make sure there’s not still moisture in there. I know that’s a PITA but you’re in a bind now. Especially in the winter when the moisture will really want to condense in there.
Hi Ted. Yes that’s correct there’s no drywall up yet. So I should probably make sure walls are dried up then drywall asap? I will definitely try the plastic on my basement floor and the basement has been poured since September but I never started heating the addition till November
Yep, I’d get them buttoned up soon. Hopefully they’ll dry out. It’s going to be tough with the cold weather, but hopefully you can make it work.
The south facing walls will dry much sooner if you get sun on them since that will greatly reduce the condensation risk in them during the day. You might Drywall those first if they do dry out.
https://polldaddy.com/js/rating/rating.jsI️ raised my second floor ceilings basically all the way to the peek and I️ was just wondering what should I️ do about the vents in the side of the house and how do I️ properly insulate the ceilings now
so as I understand it, you’ve turned them into cathedral ceilings. As such you need to treat them as is detailed in various articles about cathedral ceilings.
you would either close off vents and insulate the full cavities above the new ceilings and below the roof or you would leave the vents open so the air can flow above the insulation and below the roof and out ridge vents at the top. either method can work depending upon how it’s been submitted but the safest is to have good vents and allow air to flow above the insulation and below the roof.
https://polldaddy.com/js/rating/rating.jsHi Ted – I was just up in my attic and noticed the switch on the air handler seems to be off. Is this a summer/winter thing or should it remain on att all times? Judy in New York
I’m afraid I don’t know. Most air handlers don’t have switches. Could it be for a UV lamp or humidifier? You may have to ask the person who services your system.
https://polldaddy.com/js/rating/rating.jsHI Ted, we have a 2 story colonial with a gambrel roof in the northeast. A few years ago, we listened to an insulation contractor and added 8 inches of blown cellulose on top of the pre-existing pink fiberglass insulation.
We love that we utilize much less oil in our forced hot air furnace, but the humidity in the attic gets very high in the colder months… about 30-80% higher than outside! We have lots of ventilation: the original gable vents, we added soffit and ridge vents, and even added some Levanco under-shingle vents. The attic’s temperature stays aligned with the outside temperature.
One insulation contractor believes that the cellulose feels damp because it has been absorbing moisture from the air in the attic and moisture from stack-effect air coming up through air gaps. He wants to remove the cellulose and fiberglass batts, air seal everything, and blow in loose fiberglass. He’d also spray foam the basement’s rim joists to slow down the stack effect. All of this will disrupt our house, damage our finished-basement’s walls, and cost a lot of money! Another contractor says that this is hogwash and I should do nothing.
Will doing all this work solve our humidity problem?
Will this work simply move it to a different area like the walls?
Can heat from ducts running on the exterior wall be dumping hot humid air through the soffit baffles and into the attic?
Should we consider going back to how the house originally was, with the thin 6″ insulation batts and lower RValue?
I’d really appreciate your thoughts before this becomes a real problem. Any advice would be GREATLY appreciated.
Thank you!
Honestly, the first contractor’s solution sounds more like the right approach. There’s clearly a lot of air from the interior getting into that area if the humidity levels are so high in spite of good ventilation.
It’s hard to say where the moisture is coming from and that assessment need to be made. As you suggested, if you’ve got ducts in those walls, it’s quite possible that they’re leaky and blowing lots of air through the cavity and into the attic. That would be really bad but would also be easy to determine using a thermal (IR) imaging system.
If I were in your shoes, I’d hire an energy consultant with a thermal imaging camera to look at the space and see if they can locate any specific big air leaks. If there are big leaks, those can be addressed directly with much less disruption than tearing everything up and starting from scratch. OTOH, if they just find a diffuse leakage, then you may have no choice other than pulling out the existing insulation and air-sealing.
Now that we’ve got colder weather, you should be able to inspect the space to see if any humidity is building up. After cold nights, you’ll be able to see frost on the exterior walls/under the roof if the humidity is very high.
Another thing to consider is that the humidity is coming through your attic access door. That’s quite common. All the ventilation in the attic space could actually suck air from the interior space into the attic, leading to high humidity.
Thank you so much, Ted. We have a very nice attic hatch cover, made out of 4 inches of aluminum-backed styrofoam. The contractors are here right now, ripping up the drywall in the basement so they can seal the sill area, and in sucking out all of the cellulose in the attic. Tomorrow they will air seal around the wall cavities and everywhere else.
I don’t want to go through all of this effort for nothing so I am trying to thing through everything as much as possible… My bathrooms are all lined up against the exterior wall. My fans have been installed properly, but is it possible that moisture from the showers can work its way through the bathroom’s wall cavity and into the soffit, dumping into the attic?
any help is appreciated!
Chris
There’s often a lot of moisture that can get up there because there’s just so much moisture in bathrooms during showers. Sometimes the moisture will just go right past the fan because the hole is so large and they don’t seal it. As you said, moisture can also go up through the wall cavities, though it needs a way to get into the cavities. However, I did a job where a family had a nasty moisture problem above their bathrooms and I foam sealed the top of the wall framing (where exposed in the attic) because the drywall didn’t connect to it, leaving huge gaps. The moisture just flowed right up and led to a ton of mold right above those areas.
Usually, the signs of moisture will be directly above where it’s escaping from the house into the attic, so it just takes a little detective work to find likely sources. Another common problem area is where the vent stack (the pipe that goes up the wall and out the roof) goes through the wall. I never see those giant holes sealed.
Any chance you make housecalls? 🙂 I don’t think the air sealing did much to help the situation and we are still battling this issue
https://polldaddy.com/js/rating/rating.jsHi Ted, I have a bit of an unusual insulation situation. I have existing an 1×6 wood ceiling that is remaining and exposed in the interior of my house. Then black roofing paper on the outside of the 1×6 so you can’t see thru the cracks and above it a new 2×10 roof structure . I was set to insulate above the 1×6’s in the 2×10 roof with fiberglass bat. However that would leave air gaps under the bats just above the 1×6’s rather then an air gap above the insulation just under the roof , where I will have some low profile vents cut in for air flow. One of the insulation contractors said he wants to put in loose fill under a bib. as he said there shouldn’t be a gap above the inside roof but rather on the roof side of the insulation.he architect said” R30 batts with foil face face up. It would be stapled to top of rafters before plywood is placed. Fiber glass insulation doesn’t need extra area for air flow, but you have enough space in design for flow because the 2×10 rafters are lifted above existing roof to join top of PSL bond beams around the perimeter and to allow electrician to run conduit.” totally different info. Not sure who if any of them are right. I hope this is a clear question. Thank you for any info you can share to help.
Question – what’s your climate like? Are you in a hot-humid climate like down south? Or a colder, northern climate?
The general rule is vapor barriers should go toward the warmer surface because that’s where the “push” from moisture comes from. Let me clarify – in a northern climate, in the winter, it’s cold and dry outside and warm and humid inside, so the moisture is trying to move from inside the house to outside. That’s why the vapor barrier would go close to the ceiling – to stop moisture as soon as it can.
OTOH, in hot, humid climates, the moisture is outside the house trying to get in, so you put the vapor barrier close to the roof, to stop the moisture from getting further in towards the inside of the house. Hope that’s clear.
So, if you’re in a colder climate, then, if I’m reading it right, the architect is wrong. Putting a foil face (which is a perfect vapor barrier) up, towards the roof, would be creating a perfect situation for condensation to form since the foil will block the moisture from inside the house. The foil will be cold in winter since it’s exposed to the roof. Moisture will want to condense on the foil then drip back down into the insulation.
I think you could put the insulation above the 1×6’s as you describe it. The cavity between the roofing paper and the 1×6 ceiling planks will be warm since it’s exposed to the inside of the house. The insulation above it will be fine. Just imagine if the 1×6 ceiling wasn’t in place, then you’d just have an exposed beam ceiling. You wouldn’t have to fill that with insulation – insulation above would be fine. The ventilation should be on the cold side of the insulation, below the roof (in northern climates). So I think your intuition, as you’ve described it in the first part of your message, should be fine. Just keep an inch or more of an air gap between the insulation and the actual roof so that moisture can flush out naturally.
Thank you for responding. I am actually in Venice Beach in Southern California. So a warm Climate. I have heard two very different things from Insulation contractors and a 3rd from the Architect. 1- plain fiberglass bats no foil cut and placed in between the new rafter bays That would leave a gap below the insulation towards the inside of the house. The architect has a similar way. But with foil facing up. The 3rd is using a bid and loose fill to pack the insulation in leaving little or no gaps close to the inside of the house and a gap closer to the roof. I was planning to have some low profile vents on the roof. Thank you again
okay, so warm but not extremely swampy like Florida. and chilly spells but not so much to cause major condensation risks. I think most current building scientists would suggest foregoing the vapor barrier. I would think the primaries saying that you’re looking for is to avoid baking in the Summer sun which means as much insulation R-value as you can get in there. I would still avoid direct contact with either surface. but wouldn’t really worry about the airspace directly above your ceiling.
Thank you for posting this! We had a contractor insulate leaving an airgap between the roof & the top of the insulation. Since we are just getting ready to put up T&G ceiling wood, we were wondering if 6 mil should go up against the insulation before the wood. It looks like a yes from you. We asked the insulation contractor and they said no. We live in the Pacific Northwest
The Pacific Northwest can be a tough climate with it’s high rain and general humidity. The good thing is you typically don’t have the extreme temperatures seen in other regions, so condensation is less of a concern.
Putting up a vapor retarder just behind the T&G ceiling is little different than having a sheetrock ceiling. Since the insulation goes beyond that, the plastic stays warm, like the inside of the house, minimizing the possibility of condensation. It also greatly minimizes energy loss from air flow between the T&G.
If your builder is concerned about trapping moisture, you could use Tyvek (taped at the seams) which would stop the air flow and the vast majority of the moisture movement but still allow some moisture transfer, whereas the poly acts as an almost complete moisture barrier. You might ask him what his reasoning is.
Hi, I use forced air to heat and cool my place and I noticed that air comes out of my intake (or return) vent when it is windy outside. Does this mean that my ducts have leaks? Thank you.
Just to be clear, I notice that air comes out of my return vent when the system is off and it is windy outside.
Typically, the answer is yes, this would indicate that you have leaks.
There are times when cold air will “drop” out of the return vent. Since cold air is denser and heavier, if the air in the ducts gets cold, it will create a draft. Just like sitting in front of a cold, but totally air-tight, window, you can feel the cold air flow.
However, based on your description, since it increases with windy conditions, it is highly likely that you have significant air leaks.
If you feel how much cold air comes out of different vents, both returns and supplies, you may be able to find the closest vent to the largest leak. If it’s just your return, then it might be something as simple as the air filter slot on the air handler (is this in your attic?). Many times I’ve seen the filter slot open wide to the attic, allowing all sorts of cold/hot air and dust into the system. If your system is like that, then you can just put tape over the slot after replacing the filter.
If the air handler is in the attic, then it’s worth checking it for air-tightness. You can caulk or tape with foil tape after cleaning seams around the air handler. That can make a big difference to efficiency and hence your utility bills.
Hi, thank you for your response. It was very helpful.
HI Ted! Thanks for having such an informative site! I am about to do some insulation work on a 1920 farmhouse and wanted to get some opinions. It’s a 2 story 2400 (ish) sq foot farmhouse with a stone foundation, metal roof and wooden (poplar) exterior walls covered in vinyl, and oak beadboard for the inside walls and ceilings (no sheetrock or plaster except in the kitchen and bathrooms which are additions, and there is sheetrock over the wood in the living room and downstairs bedroom. There is no basement, but a crawlspace under the house with stacked rock foundation. The floors are also Oak with no subfloor. I’ve been in the house for 6 years. The walls are pretty tight, (someone blew foam into at least some of them). However the floors and ceilings are quite drafty. I’m planning to spray foam the attic floor – that seems pretty obvious. My questions revolve around the crawlspace. The stone foundation is currently quite open. There is some fiberglass insulation under the floors and it’s molding and falling down. – that clearly has to come out. The mold is not severe, and the space without the insulation might be OK as is, though I do see some mold on the wooden walls, which is not acceptable. The stone foundation and wall supports are quite irregular, so sealing the foundation off completely seems daunting if not impossible. It has been suggested to me to put plastic down over dirt, and spray foam on the underside of the floor, but leave the foundation walls mostly open for venting. Does this sound like the correct approach?
Given your construction, you have to be really careful about moisture buildup in the house that would seep through the leaky walls and ceiling and cause problems. Having no sheetrock and just wall boards is asking for trouble as you tighten up the house. That’s one of the unintended consequences of making an older home more energy efficient. As it was originally, the home was built “leaky”. What this means is that during the winter, the cold, dry air would flush out the interior humidity, making it much less likely to build up inside the walls and ceiling. As you tighten the home, the humidity inside increases, making these issues more of a concern. So please keep this in mind.
That being said, for your crawlspace, definitely – seal the underside of the floor so all the ground moisture doesn’t rise up through the floor and into the house. Plus, adding plastic over the dirt is and important part of the solution. Note – there’s a correct way of doing that so it’s effective. You want two layers of plastic with seams staggered and taped so there’s no way for water to come up. The plastic should also go up the walls a bit. If you have someone spray-foam the underside of the floor, have them foam the plastic to the wall so that it forms a permanent seal. If it’s really tight, you’ll probably even find pools of water under the plastic when you’re done. That’s fine – it means all that water isn’t entering your home. However, if it’s extreme, you may want to have an automatic sump installed at the low point so that the water will periodically get pumped out.
Ted,
I am working on a 14×14 room addition on a crawlspace. The floor joists are 2×10 and there is approximately 15″ below the bottom of the joists. The entire space has been sealed with 2″ rigid foam on the floor, walls, and in the rim joists. Upon your recommendation, I am going to bring some conditioned air into the space via a 4″ duct. I’ve decided to use insulated flex duct as I’m not really worried about air flow to the space. Should I hang the duct from the bottom of the joists, or would it be ok to just lay on the floor. Also, do you think I need a boot and register on the end, or could I just leave it as open duct?
Much thanks in advance!
I would tend to want to hang it from the joists in order to protect it. You might also want to put 1/4″ metal screen on the end to keep the rodents out.
I can’t see any need for a boot and register, but don’t quote me on that. There may be some code compliance reason for that.