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.
Ted's Energy Tips 
https://polldaddy.com/js/rating/rating.jsTed,
Just finished building a studio over an old stand alone 2 car garage. It has a simple 7 degree pitched shed roof with rubber membrane. There are generous overhangs all around and plenty of soffit vents, straight shot from bottom to top. I’ve firred out the inside of the rafter bays with 1 1/2″ continuous strips (giving me 1 1/2″ vent space). Not including vent space i have 11″ to add insulation. Then add 3/4″ strapping over that and blueboard and plaster.
The plan was to put 1″ rigid foam xps as the venting baffle (and more R value) and then add regular fiberglass batt under that. In this scenario should the batt be faced or unfaced? I have been told faced but would this create a double vapor barrier? Should the baffles be air sealed?
There is no plumbing in the studio but it will be heated (mini split) and used a lot.
Thanks.
Sven (Cape Cod, MA)
Typically, you would want to put the most vapor impermeable layer (the foam board) closest to the living space – the logic being that it would block the moisture from getting into the cavity. Any residual moisture should be allowed to move through any other insulation and be flushed out with the venting. Putting it in reverse could be risky – even with a vapor barrier on fiberglass batts, you’re likely to get moisture migrating past the batts and into the cavity. Once that happens, the inside layer of the XPS will be somewhat cold and presents a condensation risk.
If you’re not living in the studio and generating lots of moisture from living activities (showering, house plants, etc.) then there’s probably minimal risk. However, to be on the safe side, I wouldn’t recommend the ceiling-fiberglass-XPS order. You’d be better off using more XPS and skipping the fiberglass.
Ted,
I just stumbled across this site, and I’m right in the middle of doing pretty close to what Sven suggested. It’s a cathedral ceiling. I have built 1.5″ vent chutes using half-inch xps (air sealed with spray foam). I’m putting R30 fiberglass bats underneath the vent chutes, which will compress (2×8 rafters) and de-rate to R25. Next, I’m installing a continuous layer of two inch xps. Finally, drywall. Should give me ~R38 for the whole assembly.
I used xps for the chutes because I understand that it’s somewhat vapor permeable. I used only half inch xps to maximize permeability. Reading your answer to Sven’s question, I think that what I’m doing qualifies as having the most vapor impermeable layer closest to the living space–the continuous layer of two inch xps. My thinking is, vapor will be able to diffuse out of the cavity (through .5 xps) faster than it can diffuse in (through 2″ xps). But, I would appreciate your thoughts on that.
In addition, a complication is that three rafter bays are blocked by skylights. Despite my mad googling skillz, I struggled to find an elegant solution to venting these bays. Most of the building science resources I read said, essentially, don’t have skylights. Some resources said that switching to a hot roof design is the only option (I’m not keen on that). A building inspection resource I read suggested venting around the skylights by drilling holes in the rafters, above and below the skylights, thereby creating a bypass.
I went with the holes–two 2″ holes in each rafter, 2″ below the top of the rafter, and 2″ apart. In the “bypass” rafter bay, I increased the chute depth to 4″ between the lower and upper sets of holes. (For the 4″ vent sections, I plan on adding two layers of 2″ xps between the rafter, in place of the fiberglass, because I’ve only got 4″ of space.)
I’d also appreciate any thoughts on this skylight solution.
As I mention, I just found your site. There’s some great information here–I’ll continue snooping around!
Many thanks.
As you’ve described, it sounds like a great ceiling – wish I had that in my cathedral ceiling!
There’s still going to be some risk of condensation, though minimal with the construction you’ve described. Even though slightly moisture permeable, the XPS will be a colder layer since it’s exposed directly to the vent. With all the insulation below it, the XPS will be much closer to outdoor temperature than indoor. Any moisture that gets into the cavity will tend to condense on the interior of the XPS.
Having said that, if your construction is solid, then there’s very little chance of moisture getting past the drywall and 2″ XPS. So unless you somehow get moisture into the cavity (roof leak or other means), you’ll probably be in good shape.
As for the skylights, given everything else you’ve done, I wouldn’t worry. People fret about it, but I’ve never noticed issues with them. The only issues I’ve found, hot roof or vented roof, is when people do stupid things like fill the ceiling with recessed lights, allowing moisture to flow unimpeded from the interior of the house right into the ceiling cavities.
Correction: Rafters are 2×10, not 2×8.
Many thanks, Ted. That gives me some comfort that I’m doing the right thing. I only want to do this once! 😃
https://polldaddy.com/js/rating/rating.jsDear Ted,
I have started renovation of my house and came to some problems.
House is made of 1.5 full brick(around 40cm) and there is inside wall insulation made of 5cm rockwool then vapor nylon and Gypsum board. That was done 35years ago. 10 years ago house got outside wall insulation called “demit” 5cm Styrofoam. Inside wall insulation was left inside.
Ceiling is made of concrete and we have 10cm of rockwool and below that to concrete surface is vapor nylon sheet.
There were massive temp loss before we puted insulation on the celling. We don’t have any mold problems.
The question is should I leave the inside wall insulation or remove it since house got outside insulation ? Some say that keeping the inside wall insulation you lose accumulation capacity of the wall so room heats faster but also cools faster.
Also if you have any tips they are more than welcome!
Thank you!
Marko
I think I see. This is an interesting question. Let me try to describe this for other readers and ensure that I understand your wall:
Your newly made wall structure has exterior insulation which makes the bricks inside the insulation, as well as a layer of rockwool then interior wall.
If you leave the rockwool, then the bricks will be in-between two layers of insulation, so less subject to changes in temperature. The mass of the bricks will hold temperature, so the inside of the house will “feel” less temperature swing.
If you remove the rockwool, then the bricks will be directly exposed to the interior temperature, but you will reduce the insulation of the wall overall.
From a purely physics perspective, the overall energy use must be greater without the insulation than with it. When it is cold, it takes more heat to overcome the interior heat escaping into the wall. The brick will add thermal mass in either case but when insulated, the thermal mass will be at a temperature in between the indoor temperature and outdoor temperature. Since insulated, the main thermal mass will be your wall board, so the heater or air conditioner will turn on and off more often in order to maintain a constant room temperature.
However, if it is uninsulated, the heater will have to run longer to bring the room up to temperature because it has to heat the wall board and the brick up to temperature and the overall energy use will be higher because there is less insulation. So if it were my house, I would leave the insulation in the wall. Also, removing the insulation would be a big pain, requiring cutting open all your walls!
Let me comment on the effect that people are talking about. If you are using minimal cooling during the summer, then when it is hot outside, the mass of the brick will take longer to heat up, and so you won’t need to turn on air conditioning until later in the day. If it doesn’t stay hot too long, then it might take all day for the brick to get warm, at which point the sun goes down and the brick cools off naturally with the night air. If your climate is just right, then you might not need any air conditioning.
However, if you have a period of hot weather, the bricks will get hot and hold that heat, radiating it into the house so you have to use air conditioning even after sunset to keep the house comfortable. Same in winter. Long periods of cold means the brick stays cold and it is hard for it to heat up to comfortable temperature. So without insulation, the walls always feel cold which makes it uncomfortable inside the room.
I know this is lots of information and confusing! The summary is – if you are in a moderate climate where the thermal mass of the brick holds the hot/cold so you don’t need air conditioning/heating, then having the brick uninsulated inside is better. But in more extreme climates, you want more insulation.
Thanks for reply.
Ted, thank you I have learned a lot. I plan on using a foam spacers the placing ridged ridged foam in the attic between the ceiling cavities with foil wrapped foam over over the cavities. I will not be able to foam over it all, but this should work well. I now have a question, the house is opened to the studs. How do you suggest insolating both the wooden cavities as well as insolating the basement brick surfaces? For the basement I was thinking of spraying with a foam kit, then placing a foam sheet, and then frame out with 2×4 ‘s then …? Any help to include telling me, my proposed approach is out to lunch would be helpful.
Thank you
Joe
Using the rigid between rafters and then a layer of foil faced insulation should work great. The foil is both a moisture barrier and a radiant barrier, which when shiny, can greatly increase the effective R-value for hot summer days. The attic space should be much more comfortable .
In the basement – I spent a lot on foam kits and sometimes they worked, and sometimes they didn’t. In the end, I would have been better off paying a pro to come out and spray. That said, that approach works wonderfully well. I had several clients who had wet basements and rotten walls that were conventionally installed with plastic fiberglass and 2×4’s. They ripped it out and did what you said and couldn’t be happier. The foam stopped the moisture. Then either a layer of board foam, or a thicker layer of foam spray, then framed out as normal works great. Be careful of any potential wood contact with wet surfaces, like the floor. You want a moisture barrier between the wood and concrete. Even pressure treated lumber is best to protect against too much moisture. That’s easily accomplished with rubber membrane material.
For the main house, be cautious about doing anything that prevents brick from drying. If the existing brick wall has an air gap that allows air to flow up the backside of the brick (facing the inside of the house), be sure to retain at least a 1″ air gap. If moisture builds up in the brick wall, you can have severe freeze-thaw damage. Personally, I’d consider using a 1″ spacer, then board foam in the cavity.
Also, be sure to check with local building code enforcement to see if they have any specific rules or suggestions so you don’t run afoul of anything.
I can put pacers against the brick and then foam, then the 2×4 stud wall with foam in-between the cavities without a problem if that is the better way to go. I have noticed two schools of though on the web on the subject. That is why I ask you, you come across as straight forward and honest. That means a lot to me, so thank you. Please confirm that the approach I have outlined in this paragraph is what you meant.
Thank you
Joe Ostaseski
Sounds good Joe. Just always remember to keep wood away from water and you’ll avoid most of the issues.
Hi Ted, I have a question. How do I air seal wall cavities?
I have true 2×4 walls on an 180’s home. To say that the home leaks would be an understatement. I am remodeling, so I have the opportunity to seal and insulate the exterior walls. My question is:
What is the best way to air seal a cavity.
Paint
Some sort of sprayable caulk
1/2 ridged foam board with caulk around the edges Something else
What is better, rockwool or fiberglase?
Lastly, do I need a vapor barrier in zone 5?
Outside or on the inside of the of the insulation?
If you’re doing a full remodel, I would pull off the exterior siding, if possible. Then run all the electric etc. that you want while you have easy access. Then have them spray foam with high density foam. This would provide the tightest, most durable solution, giving you a good R-value for the cavity and providing an intrinsic vapor barrier. With other solutions, you’re depending too much on the quality of the installation in order to avoid moisture issues in the cavity.
Hello Ted,
Just stumbled on this blog looking for information about insulating a 1952ish fixer upper bungalow.
The exterior sub siding is tongue and groove, with knots in the wood loose and falling out, etc.
The siding is raked cedar.
I have been gutting the sheetrock to wire and plumb and insulate, and also just to freshen up a very abused house.
Have been using foam spray to fill the gaps in the tongue and groove, electrical and plumbing raceways, and silicone on headers and around windows, etc. The insulation type I chose is mineral wool. Am using 5/8″ sheetrock, typical mud / tape followed by latex paint, except the bathroom, which is plaster and tile.
Is it ok to fill the “V” part of the tongue and groove with foam spray to slow and limit drafts? Or will this possibly cause moisture build up?
I live in the Pacific Northwest where there is a lot of moisture and mold problems. I typically run a de-humidifier during winter and transition seasons to keep the house moisture down to about 50 – 55 %
So far I have not putting vapor barrier / plastic as I thought the latex paint is not permeable to water.
Have only two bedrooms to go, so it’s pretty much done now, but will be insulating this week and will make a correction if I am doing this wrong.
Thanks for any help to know if was using wrong installation method, or to stop worrying that I’m ruining the house.
It sounds like the tongue & groove board is the exterior sheathing, where modern houses use plywood? So that’s your air barrier?
Where you live is a challenging environment with all the humidity drive from the outside in. I don’t believe sealing the T&G will harm anything and, like you said, will help to slow airflow into the cavity and your house. A sealed T&G would act like a continuous plywood sheathing, so if one works, so should the other. The only thing is, due to seasonal expansion/contraction of the boards, you may find that the foam detaches and you lose all your hard worked air sealing. Depends on how pliable the foam is. If it’s the softer stuff, it will probably last. If the hard stuff, that doesn’t give, so the seals may not last. Hard to say one way or another.
You might consider using a layer of board foam, cut to fit between the studs, pressed into the cavity near (but not in contact with) the T&G. This will give a better air seal and added insulation and water barrier. You could then put your mineral wool inside that to fill the rest of the cavity.
One warning if you go that route – since the board foam will stop trap from the inside, you want to follow the rule of no more R-value of permeable insulation (the mineral wool) than the board foam. So, roughly 1″ of board foam (R4 to R-6) vs. 1″-1.5″ of mineral wool (~R4/inch).
Finally, check with your local code enforcement officer to see what specific codes need to be followed for your area. You don’t want any trouble late in the game!
Hey Ted:
I have a question about insulating knee walls and attic roof lines in a cape house. We recently had a company install 2-inch Thermax boards along the roof line behind the knee walls. Not between the joists but over them. The boards run horizontally and they were fastened with screws, then tapped. Long story short, they did an Okay job. There are some gaps around the attic utility lights and the poly board is not a real tight fit against the wall where the attic ceiling and top of the knee wall meet.
I’m worried about air flow. Should this space be completely air tight or is a little air movement a good thing? In the summer when the space warms the air will try to enter the rooms that are cooled with central air, so I’m not too worried about humidity. In the winter when the attic is cold, this is when I’m worried about condensation and mold because the warm air will try to enter the attic behind the knee walls and get behind the foam boards.
Additionally, before this work was done I installed batts (a few years back) behind the knee walls and between the joists in the floorings. Should these be taken out or is it Okay if they stay in? The company said leave them because it will help with first floor of the house.
Your input is really appreciated. I can send you some pics if you would like.
Regards,
Tim
West Hartford, CT
Cold winters, Hot & Humid Summers
A couple photos would help though I think I have a good visualization of the construction.
To summarize:
Insulation board installed under the roof, across the rafters. Some gaps would allow air from the house to enter the roof cavity
Existing insulation on the floor and on the back of the knee wall
It sounds like there’s insulation on all the surfaces of the space behind the knee wall, which would create a cold, dead airspace. This raises red-flags – with insulation, more is not necessarily better.
Is there any ventilation from soffit to ridge behind the insulation board? Given the configuration you’re describing, I’d want there to be some outside air flowing through those channels to flush out moisture that can enter.
Since you have insulation on the knee wall and floor, this attic space will get minimal heat from the living space (that’s the purpose of the insulation, after all). As such, as you noted, it will be cold and any moisture that gets in there will suddenly chill and be prone to condensation. Without ventilation, that’s a concern.
The real question is – how air tight are the walls and ceiling between the living space and the attic space? You clearly have access into the space, so there’s a door or hole. Is this sealed tightly (doubtful)? Are there other holes that would allow air flow between the living space and this attic space? Even if you didn’t have the insulation on the knee wall and floor, I’d still be concerned about this.
I wouldn’t necessarily rip out any insulation, but I would strongly recommend sealing up any openings between the living space and this space – especially the access door. Good compressible weatherstrip:
works well as long as the door and jamb are flat and secured tightly.
You want to block out all the openings between the joists that run under the floor as in this picture:
Once you’ve done the air sealing and ventilation the best you can, you just want to monitor the space during cold weather to check for any signs of condensation. It may turn out things are fine and you don’t have to do anything radical. If you do discover condensation issues, then you’ll have to take more remedial actions.
Ted, thank you for the quick reply.
I’m sending some pics (don’t laugh). I did call the company and a manager is coming back so we can discuss the work that was completed.
What I learned about Cape houses is that it is best to insulate along the roof line to create a conditioned attic/knee wall. I have some duct work in there and I would like to maintain the storage space. The living space is currently hot in the Summer and Cold in the Winter. When I insulated the knee walls and floors with batts a few years ago it helped but it needed another approach. 2-inch Thermax board with reflective foil along the roof lines seemed like a better approach. More difficult, that is why I hired a company. The house does not have soffits and the area is vented with gables at the peaks of the house. The knee walls never went fully up to the attic roof line for ventilation purposes.
Another challenge of this attic is that it is located next to a loft that is above our garage. The garage loft is unheated and traps cold or hot air. Should this area within the attic also be covered with Thermax board. Now it is simply covered with batt insulation to reduce flow.
Long story short, if the house does not have soffits can this space be turned into an air tight area with foam board? I was under the impression that the boards are installed over the rafters to allow vertical airflow up into the attic space above the ceilings towards the gables. This will keep the roof cold in the winter (no ice dams) and block heat in the summer. FYI, the house does not have a ridge vent.
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Again, your advice is really appreciated.
Tim
EDITOR’S NOTE:
The following comment was posted from an anonymous account. Its content reads as if it’s coming from someone with an agenda to denigrate certain forms of insulation that have been shown to be effective and safe with very few complaints.
Original comment:
My experience with cellulose was absolutely negative. We stopped at the attic and did not dense pack walls. Rather, we paid 1.2k and then more, to have the attic vacuumed out and have cellulose removed. We used the lights off flash light test and positively observed incredible dust in our living environment after cellulose install, it ruined carpets even, creating a fine white mist that never left the living spaces. We did seal and use supposedly pro contractors and such. Safety claims of this product may not be accurate. We’re definitely against cellulose, our attic is not a substitute for material which otherwise belongs in a landfill. And we have the blue demin batts from home depot under the girls room in a crawl space area w/ 20m polly on floor and half way up walls. I’m currently researching to find information on this noxious smell now permeating this one room with demin batts below. Not sure if that’s just demin batts or may also be attributable to the fire retardant spray foam along joists and ridges, limited application. We will be pulling the denim batts out too, since in warmer temps it smells god awful and we all get headaches in this room. Boric acid is not the same as borax, although many claim it to be. It’s chemically different and FSC’s are not really necessary for insulation. We have a right to a chemical free living environment and this insulation project was a disaster. Regardless of safety claims, the claims made in this article simply can not be overlooked. http://www.huffingtonpost.com/entry/cellulose-insulation-is-it-lumber-liquidators-20_us_58cc0da5e4b07112b6472cf4 In my opinion, if cellulose is used, it must accompany total air sealing specifically to include air tight membranes or new boxes in each and every point of use electrical box along walls. Run a simple flash light test in the dark for particulates before and after. If you get an increase, the cellulose did more harm than good.
Hi Ted, I just purchased an old home with with a kitchen in an addition off the back. It has a pitched ceiling under the pitched roof that is not insulated and there’s only about 6″ space between the roof sheathing and the ceiling drywall. I think poking holes and blowing in insulation would be easiest but how do i address venting the area or do I even need to vent such a space. Thanks for your time. Really informative blog.
That’s a tricky one. I’d be leery of filling up the cavity with insulation, though I have seen that done before without ill effects. The safest way to deal with that is to build in the ceiling. You could add a 2-4 inches of poly-iso board foam directly to the ceiling, screwing nailers (1×3 boards) over the foam, through to the original ceiling rafters. Then, you screw new sheetrock to those nailers and you have a new, insulated ceiling, without worrying about that attic space above the ceiling. This also minimizes the chance of any moisture getting up into that space which could lead to mold/rot problems. Another nice feature is that, at the same time, you could run wiring in these convenient gaps between the sheetrock and the board foam, and then install flush-mount LED ceiling lights. If you’re in a sunny climate, that kitchen must get hot during the summer! Adding 4″ of Poly-iso would give you a real R-28, making the room much more comfortable. If you blow insulation in there, at the most you’ll get about R15, and even less if you consider thermal bridging caused by the heat transmitted through the rafters.
I know this seems like an extreme solution, but it’s actually one of the simplest and most effective. If you bore holes in the ceiling and blow in insulation in such a small space, it can be difficult to know that the insulation has adequately filled the space. An if you totally fill the space, like you might with dense-packed cellulose, you run the risk of trapping moisture in the insulation under the roof deck. While this can work (I have cathedral ceilings packed this way in my living room) it can be risky. Especially if you have or add recessed lighting or there are other routes for moisture to get into the ceiling cavities.
That method never crossed my mind. Thanks a bunch for the advise.
Hi Ted; I live in corner apartment 1 bedroom. I have been there since 12/03. I have been seeing the beams and nail coming thru the sheetrock and are all gray like mold. My land lord seems to think is from me burning candles. Not true. It has now spread the entire house in the bathroom and kitchen. He advises for me to paint over it….any suggestions I believe it is mold brick on the outside and sheetrock in the apartment. no insulation in between. Thank you
It’s common to see”shadows” of the beams behind the sheetrock. I had to diagnose this in a house once. What happens is that the wood beams cause the sheetrock to be slightly cooler than the surrounding area. This leads to an increased opportunity for condensation which traps dust and soot, hence the gray shadows. In the case I inspected, the occupant used oil lamps sometimes. Not doing anything wrong, but the lamps created a very fine soot that stuck to those areas. It was a very pronounced effect that baffled a lot of people and took a bit of sleuthing to figure out.
Ted,
We have a ceiling attic space where are 3 bedrooms are located. I measured and we has 13″ of blown-in insulation on the floor but no insulation between the ceiling joists or walls and there is a 7″ gap between the particle board wall section that separates the bedroom area from the garage. This upper area of our house is always hot is the summer and always cold in the winter(MN). So my thought was to put up batting insulation on the ceiling and walls and close the gap in particle board wall and insulate that as well. Its a 24′ x 24′ space 7′ high with 3-roof vents and soffit vents on one side, 7″ gap leading to the garage is on the other side which I believe is where all the heat and cold is coming from. Do see any issues with my plan?
You would probably benefit from having an energy auditor come in with a thermal camera so you could make sure that’s where the heat/cold is coming from before going through the trouble of doing the work. A lot of times, it turns out that it’s the HVAC system that’s at fault. Often these rooms are far from the heating/cooling system so little air gets to them through the long ductwork.
That is, assuming you’ve got a forced air heating system. Air conditioning certainly would be air through ducts.
As for your plan. If you’re talking about insulating the area of the attic above the already insulated floor, then that won’t help much. On the other hand, you mention a wall abutting the garage. If that wall isn’t insulated, it should be, as you want a tight layer of insulation as close to the walls/ceiling of the living space as possible.
I’m also not sure where this 7″ gap is on that wall. You’ve got the sheetrock of the bedroom wall facing the garage, and the wall studs. There should be insulation covering the backside of the bedroom wall that faces the garage. Are you saying there’s just an empty space there then the garage attic?
Sorry, it’s a bit confusing.
Ted,
I think you are correct on the HVAC system, It does not heat or cool up in that area very well. The gap in the attic separates the garage attic from the bedroom attic space. Unless it’s there for air flow, I’m guessing the builders didnt measure properly for that wall. I don’t think I will move forward with adding ceiling insulation in the attic everything I researched shows those areas non insulated. Thank you responding.
Hi Ted,
Hoping you can lend some guidance here. Please refer me to other posts on this subject if you have already answered.
The Situation: bought a lovely Victorian 3 years ago in the Northeast. There is loose cellulose blown in the attic right before we moved in which completely covers the floor. They installed a hatch over the pull down stairs in order to insulate that as well. I have had a few contractors look and they say yeah that looks fine. the house is big (4500 sq. feet on 3 floors) so they said they cannot do a blower door test. They advise that I get a smaller house or that I can do a better job of sealing up the basement. Seems like if the attic is poorly sealed then air is getting drawn up there and so the air will just continue to get sucked into the basement because of the negative pressure being created in the house. the basement does not seem especially drafty to me. I already have a natural gas powered steam heating system which would be extremely expensive to make more efficient so improving insulation is my best option to lower my bills.
Here is my issue. When I went up in the attic during a real cold snap I expected it to be pretty cold, it wasn’t. 10 degrees outside, 65 degrees in the bedrooms on 3rd floor and about 55 or 60 degrees in the attic. There are ridge vents and a couple other vents letting air out of attic. Shouldn’t it be colder up there if everything is well air sealed and insulated? I moved some of the insulation away and it appears there is still a plywood floor on at least part of the attic. Am wondering if it was too much work to remove the flooring and properly air seal so they just did not bother. How do I find a correct contractor or should I remove the current insulation myself so that I can at least see what I have?
I know it is a huge house and will never be super tight but it seems advisable to at least make sure the insulation system for the attic is working well.
Great observations.
You actually can do a blower door test, but it requires two of the normal sized blower door setups to do it accurately. However, for a home like that, you really don’t need it to be super-accurate. The main point is to depressurize the house during cold weather so that when you do a thermal scan, the cold air infiltration points are visible.
The insulation and the hatch cover should help since the attic hatch is a primary leakage point. It’ll be a real pain to visually inspect the attic with loose cellulose. The infrared thermal scan will tell the story much better, though I would wait to do that until it gets very chilly (normal daytime temperatures freezing of less is best).
As for the attic temperature, it depends. Try going up there first thing in the morning, before the sun has had a chance to warm it up. The solar heating factor can be tremendous. Most attics I’ve gone into have been surprisingly warm in spite of frigid outdoor temperatures.
With blown in cellulose, if deep enough (typically 15″+ inches on a recent job), it shouldn’t really matter too much if they got under the attic floor or not. As long as it’s all covered. Yes, it’s not perfect, but probably not terrible. Not like if insulated with batts.
A thermal scan will show any problems more accurately than anything else and allow you to focus right in on problem spots. That will save you a lot of time and money on remediation that might not be necessary.
thanks very much ted. I will try to find someone to do a blower door test with 2 units. it is getting colder now so we should be able to see some differences. I actually bought a thermal imaging add on for my android phone. it is a different camera lens which plugs in and does show some cool differences in relative temperatures.
I was thinking of getting the Android add-on but couldn’t rationalize it since I have a full-blown, albeit extremely bulky one. It’s great tech. You should be able to see quite a bit with yours when they’re running the blower doors.
Hello, we have a new build with cathedral ceilings. On the second floor we have a walk out porch. I had the house spray foamed. Just over the French doors that lead to the porch we have a portion of the bedroom ceiling that is not insulated that leads to a closed dormer that is completely spray foamed, all except the ceiling portion just above the doors. The house envelope is complete, we had an exterior weeping of water. Upon tearing the siding off we found a hidden wall cavity where theRe w as no spray foam. Builder says ceiling to the bedroom nets to be insulated and the a vent placed in the face of the dormer. The insulation company says no. They need to repay and file the void but not spray the ceiling as it would create a dead space within the envelope thus creating an area that could collect moisture. Who is correct? I tend to go with the insulation company…by the way the hose interior is all tongue and groove pine and cedar.
I’m having difficulty visualizing this but from the way you describe it, it sounds like the insulation contractor is more correct. As they said, if you create a dead air space, you can trap moisture and create serious problems. Plus, if the insulation contractor specifically tells you to do this and they do the work, then they will be responsible should their solution create any problems.
Conceptually, you want to insulate a continuous layer around the living space, and ventilate anything outside of the insulation so as to flush out moisture.
Sorry I can’t give you a more definitive answer, but it sounds complicated enough that the specifics would need to be addressed by someone there who knows the exact construction.
Thank you, possibly a better way of looking at it would be as a knee wall area that would be inaccessible from the interior of the house. The builder wants to insulate the floor and interior side wall and vent that room to the outdoors. The insulation contractor says no vent is need nor any insulation on the floor or interior wall as the knee wall area is inside of the envelope created when the home was spray foamed.
Oh, so the roof above that area is insulated? It seems like you could go either way in fact I might be more comfortable with what the Builder was saying insulating the new wall and the floor and ventilating the space. That wouldn’t be creating a dead air space as far as I can tell. So perhaps the insulation contractor has other concerns?
Insulation contractors concern is that the venting will break his capsulated area which currently gets radiant heat to it through the ceiling. If that areas floor is insulated and vented the cold air will cause conensation. The area we are talking may be 20 cubic ft. I have no issue heating it cost is so little. We live in the Upper Peninsula of Michigan. Basically builder would be make and insulated area and venting it, where the isolation contractor wants to spray foam the exterior wall where they missed originally and. The void area they are respraying was causing conensation as the cold air hit it causing the weeping of the water on the outside of the house.
Okay got it. Sounds like the insulation person knows what they’re doing.
I greatly appreciate the help, I wish I could have explained it better.
Not to worry, these are great discussions and we all learn from them.
Ted,
Thank you for the great information provided in your article. Your advice along with some other research has made me very nervous about adding additional insulation to my 1965 brick veneer home. I am currently remodeling the kitchen and removing wood paneling in the living room. Behind the wood paneling is a reflective foil insulation covering the wood studs, an empty stud cavity, an unwrapped/unsealed particle board, a 1in gap, and then the brick. I was thinking about removing the old foil insulation and installing some Kraft batts, but I am concerned about trapping moisture and causing stud rot or damage to the outside brick. I live on a lake in TN so moisture levels will be high and winters will be moderate. I will have to insulate around the copper pipes, but should I insulate the whole exterior wall or leave the aluminum foil insulation prior to adding drywall?
Thanks in advance for your advice.
Joe
Joe, if you’ve already stripped it to the studs, this would be an ideal time to add insulation. As you noted, the air gap behind the brick is necessary. From your description, it seems like you have a full stud cavity backed by particle board then the air gap then the bricks. If that’s the case, you could certainly add insulation into the stud cavity as that wouldn’t be interfering with the air gap. But perhaps I’m not understanding the exact construction you’re dealing with.
The other thing you can do is to use sheets of board foam applied to the inside of the studs, then re-sheetrock. The board foam is a good moisture barrier and has excellent r-value per inch if you use foil-faced poly-iso board. This would leave the cavities open as originally, which would minimize the chance of unintentionally altering the dynamics of the wall. This is my preferred method even though it adds some complexity since you have to mark stud locations on the sheet foam so you’ll know where to screw in the sheetrock. And of course you’d have to use extra long sheetrock screws since you’d be going through the insulation to reach the stud. You also have to consider window jambs which would need to be extended due to the new thicker wall structure.
Other than that, it’s an excellent way of insulating walls when you have them ripped apart already.
One warning since you mentioned pipes – the best strategy for pipes is to insulate behind them (between the pipe and the exterior wall) leaving the space between the indoors and the pipes uninsulated. This minimized the chance of the pipes freezing because the pipes get some of the heat from the living space. If you just insulate the pipes, then insulate the wall between the pipes and the living space, the pipes will be much more likely to freeze.
Hope this helps. If you need any clarification, don’t hesitate to ask.
Ted,
Thank you so much for this great information and the quick reply. All of your assumptions are correct about the wall construction. The poly-iso board is an approach I had not thought of. If I understand you correctly I would simply nail the poly board over the interior face of the studs making sure to mark them for drywall installation? I am not real crazy about adding the extra thickness and having to worry about making accommodations for every window and outlet. Could I trim the board to go between the studs (mounting flush with the face) and then use seam tape to attach the board to the face of the stud? A lot of work, but would this kill the moisture barrier or R factor? Any other materials that I should consider?
Lastly, thank you for the warning about the pipes I will be sure to insulate only the exterior side of the pipes…I am guessing with poly board or fiberglass? Should I encapsulate the copper water pipes with that foam pipe wrap insulation?
Thanks again,
Joe
Great! I agree, while superior, the interior foam can be a pain to implement. you can certainly go between the studs. Use a tight fit for the board. Very little moisture will get through painted sheetrock so that’s not a problem. If you insulate behind the pipes, no other insulation is helpful. But hot water pipes should be insulated with a good foam or rubber insulation just to reduce heat loss.
Great info. I will use some canned spray foam to seal any gaps. Last question: reflective foil side goes towards the exterior for a TN lake home?
Craig, it is always suspicious when homes that formerly had no problems suddenly develop issues. From your description, it sounds like there’s moisture buildup that’s causing the paint to come off and the potential mold growth.
Typically, adding insulation wouldn’t cause a problem like this because it would help to warm the ceiling which would reduce the chance of moisture buildup. On the other hand, it’s possible that the lack of insulation allowed the ceiling to stay warmer when the sun was out because more of the attic’s heat would radiate downward, heating the ceiling and causing moisture to evaporate more quickly.
Do you remember when the paint and black dots started appearing? Was it this winter?
Another question – do you have any moisture sources in your bedroom, like using a humidifier or plants? Or is the problem area near the bathroom where moisture from the shower could be coming into the bedroom?
The key is to reduce interior moisture and be diligent in flushing out moisture that may accumulate. I always advise people NOT to use humidifiers and to run bathroom vent fans for 20-30 minutes after taking a shower to flush out all the humidity. Also, verify that the bath fan is working by placing a sheet of paper up the the fan grille and seeing if it sucks onto the grill tightly, indicating good air flow.
If you don’t have a mold sensitivity, you should clean off the black dots from the ceiling using a soap-water solution. Many people will say bleach, but that’s dangerous to inhale and simple soap-water will dissolve mold and wash it right away. Be sure to thoroughly dry the area and monitor it over time to ensure it doesn’t come back.
Hi Ted,
Thanks for the quick response. This started shortly after the insulation went in and it was before winter. I don’t know what else to do. I had a painter friend come out and look at it. He said the paint is old and he would scrape and redo it for me.
I should mention that it is right above my sliding glass door. I would like to send you some pictures if possible to show you. The humidity does get kind of high in the house so I don’t know if that has something to do with it. Other than tearing out the insulation, I don’t know what else to do.
It’s possibly coincidental.
I wouldn’t do anything drastic like pulling the insulation before doing more observations over time.
If you friend can scrape and repaint, that will give you an opportunity to see how it progresses over time. In particular, I would look for any signs of condensation at that location.
You should also consider using a dehumidifier in the room. High humidity is rarely good for homes so if the humidity is noticeably high, dehumidification is called for. You want to keep the humidity between 40%-60%. Above 60% and you have ripe conditions for mold.
Hi Ted,
I live in San Francisco in a home that was built in 1928 with no insulation. I had the flat roof replaced about a year ago. During that time, I asked the roofer if he could install insulation which he did. There isn’t a lot of room between the ceiling and my roof, but he was able to put rolled in pink insulation R-30 I believe. Now, I am starting to see some black dots along the edge of my bedroom ceiling and the paint is starting to crack and peel where it wasn’t a problem before. I have asked the roofer and contractors and they said it is not from the insulation. They did say to control the humidity which is probably causing the issue. This wasn’t a problem before, but now I’m wondering maybe that’s why these older homes never had insulation so they could breathe.
Hi Ted.
I have an 1840’s farmhouse in NY that I’ve been working on for the past few years. I’m doing sort of a restore yet modernizing where possible. This year I plan on residing the house. I’ll be using all sides primed western red cedar to match the existing. If the South and West sides weren’t to the point of no return I would be scraping and painting. Anyway, I figured why not insulate the exterior walls while I’m at it and my main question is what to use. The house is timber frame with the studs mortised into the sills/beams, etc. and they are full dimension 2×4’s. There is no sheathing and I’m not going to add any, nor any insulation board as I’m not padding out the window trim, etc. Those have been getting restored and I’m getting pretty good at glazing sashes! My initial thought is to use Roxul batts and then a house wrap, forgoing any vapor retarder completely and letting any cavity moisture dry to the exterior through the wrap and siding since the wood will be sealed on the interior side. At the same time making sure to air seal any gaps, cracks or holes on the interior envelope with canned spray foam to slow down the vapor intrusion. First off, is this a good idea? I restored the plaster walls on the interior so installing a vapor retarder on the interior was never an option.
The other question would be that if this is a good idea, would the 1/2″ gap between the siding and insulation have a negative effect due to convection? And if this is not a good idea, I’d be grateful for a suggestion! I’ve been trying to really research all of this but cannot seem to find a real answer! Thanks!
To make sure I’m understanding what you’re describing – you’re removing and rehabbing the siding. While the siding is off, you’d like to insulate the walls, which are plaster inside. You don’t want to add exterior insulation as that will increase the thickness of the walls, necessitating extending the window jambs.
My first choice in your situation would be to foam in the walls with closed cell foam, spraying right to the back of the plaster interior and filling in the cavities. That would air seal and the walls, insulate them well and be water resistant.
You mention using batt insulation, like Roxul, with a layer of house wrap over that. You could certainly do that. The house wrap will be vapor permeable and will shed water that might get in behind the siding. If well taped at the seams, it would also do a pretty good job of minimizing the wind-wash that would compromise the insulation.
A small gap between the insulation and siding would be recommended to avoid water getting trapped between the insulation and siding which could rot it. If you use the house wrap across the studs, that will lock the Roxul in the cavities, then you’d use nailers to ensure a gap remains between the siding and the house wrap. You could also use a mesh drainage material. Here’s a great article that describes the details of a good rain-screen layer:
http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-rainscreens
Thanks Ted,
Just to have all facts, It will be all brand new cedar siding, sealed on all sides. But the rest you got spot on.
I love spray foam, did it to my kitchen cathedral ceiling, but for this project it’s not in the budget and doesn’t really work logistically for a spray foam contractor as it’s not like the building will be bare to just come and shoot. I will be doing the project myself over the course of probably many months little by little. So as the less expensive and DIY method I’ve decided on Roxul batts due to it’s moisture forgive ability, and mold resistance. Also it’s higher R-value and work ability than fiberglass.
Now I’m glad you’re ok on the roxul and housewrap plan but hear me out on the rain screen idea. Even strapping out the studs 1/4″ on top of the house wrap before the siding will again effect the depth of siding vs. the trim. Something I’m really trying to avoid. So, because the Roxul is only 3.5″ thick and therefore leaving a 1/2″ gap to the exterior of the true 2×4″ studs…could I “wrap” and staple the house wrap around each side of the studs by 1/2″, therefore creating a rain screen essentially inside the stud bays? I figure as long as the house wrap at the bottom of the house is then feathered out over the water table drip flashing like normal then all flow ok? I know it won’t be perfect, say at the second floor beams where the house wrap will be back flush with the siding for 8″ or so. But it’s better than no rain screen, right??? It will be a little tedious I’m sure but if I can sort of have my cake and eat it too then I’ll work for it.
Thanks,
Kayne
I get it, that’s a clever idea but sounds like too much work. Plus, all those staples in the house-wrap would provide a lot of opportunities for tears and water to get behind it.
How about this. Fill up the bays, do the house-wrap flush and use spacers for the siding except just below the trim. The slight difference would be minimally noticeable (probably). You could do a dry-run, just tacking up some of the siding to see how it would look before committing to that method.
HI Minh,
You definitely want to give each bath a fan and independent duct with as short a run as possible before terminating out a roof vent. The vents are easily installed by a qualified roofer and should last the life of your roof. The problem with sharing ducts is that this necessitates longer runs, which provides more air resistance meaning the fans work less effectively. Also, if you use one bath fan and not the other, there’s the chance of blowing stale air from one bathroom to the other.
The only time this doesn’t apply is if you have a single in-line fan, with a larger duct running through a single roof vent and a ‘Y’ to combine the inputs from vents in two bathroom ceilings. This can work quite well if properly installed and is much quieter since the fan is mounted in the attic instead of the bathroom ceiling.
The humidity levels are indeed troublesome. As you noted, you’re in a humid environment and that’s likely the cause of the very high humidity that you’re measuring inside. That can be really tricky because humidity at those levels can really saturate building materials and be a real mold breeding ground.
I generally wouldn’t recommend attic roof vent fans. I had one or two in my home when I bought it and was shocked by how much it drove up my electric bills. Natural venting should be all that’s necessary.
Got to run. Post more questions!
Ted,
In regards to bathroom fans, I also do not have one nor do I have any existing ducts running in the attic. My roof has quite a slope, and I think it will be harder to install through the attic, so I was looking into wall vents. Are there any known issues or cons vs. pros you can tell for wall vs. ceiling/attic fan/vent system one? What would prevent outside air from getting into the bathroom if I install a wall unit?
Thanks as always!
Are you thinking about the type of fan mounts right in the bathroom wall and go straight outside? If so that’s actually an ideal situation. Just mount it high up near the ceiling because humid air rises and will accumulate at the ceiling.
Hello Ted! We are going to be replacing radiant heat units that have been extremely expensive to heat our home and do not even keep it warm. We live in Kentucky. We were considering the fujitsu units until we read your article. What would you recommend instead?
Frankly, given the lousy support Fujitsu has given, I can’t recommend them to anybody any more.
At the current time, Mitsubishi is the vendor of choice. However, Mitsubishi has the same type of warranty – if it breaks, even under warranty, you pay the labor, which is often much more expensive than the parts.
Based on this, I would talk to your local certified installer and mention that you’re concerned about this warranty policy and see if they have any coverage that would pay for labor if the system goes down. Even if it’s a service contract, it would be worth it because it can cost $1000-$2000 to repair the units under warranty due to the labor intensive nature.
Ted, what is your overall opinion about radiant heating? I was actually researching it as a secondary source of heating for my house, but stumble across this comment. The primary source of my house heating is by steam radiators powered by heating oil, which is quite expensive 😦 I was surprised to read that WC Townsend said it was extremely expensive. Are there different types of radiant heating, maybe more modern ones that do not consume as much energy? Anyway, your thoughts on this matter are highly appreciated as always.
The trick is there are multiple types of radiant heating. One refers to those free-standing radiators that plug in your wall or are wired in to run totally by electricity. Those are efficient in the sense that they convert 100% of the electrical power into heat. However this is not cost effective in most places. The other type of radiant heat is the type where you have tubes under your floor that heat up the flooring. That provides a very comfortable Heat but it’s efficiency depends on the heat source for the water that circulates in the tubes. This can be from oil, gas, electricity Etc. So you have to research this specific details.
I hope that helps
We had a very slow leak in one of our mini-splits which resulted in a loss of cooling almost 2 years after the installation and well past their warranty. Our installer diagnosed the problem, repaired the leak and recharged the system at no charge to us, stating their installation was at fault. I was shocked and very thankful for the honesty. The moral here is check out your business and reviews before spending a chunk of money. Great service is priceless.
Ted, your website is incredible and scary in the way that good information can be.
My family just bought our first house after 30yrs in the US and so I’m admittedly not the smartest house owner around. I’m trying to learn though.
To the point: the top story of our home was cold compared to the rest, we consulted HVAC specialist; they used an infrared temp sensor-device and saw that the ceiling was very cold relative to the rest of the house. Peaking in the attic he discovered that the insulation was r15 where our region needs r37. Trying to save money, I bought put in atticat fiberglass insulation; around r37 worth. The problem is that I most likely blocked the soffit rafter vents. There weren’t any covers there, but I could see light from the outside coming in before I put the insulation in. I tried to put in some foam vent covers but the tight was so tight I couldn’t squeeze in. So I skipped that step. That was just this last week, so no mold yet. I’m just afraid of what I’ve done…
Should I get a pro and have them put in the rafter vents covers, or can I compensate somehow? Powered attic ventilator?
I appreciate your time.
-Minh Nguyen
Thanks!
It is indeed intimidating. When I bought my first house, I really knew nothing, and suffered because of it. It wasn’t until well into renovating our second home that I decided that it was necessary to become well educated in how homes and their mechanical systems “work.” It was shocking just how much misinformation our contractors gave us, and how authoritatively they spoke!
To make sure I understand, you added some fiberglass and probably covered some of the soffit air vents?
How else is the attic vented? Is there a ridge vent or vents at the gable ends of the attic?
Also, are there recessed lights or other holes in the ceiling of the upstairs rooms that would allow lots of moisture to move from the living space up to the attic?
Most importantly, are all the upstairs bathroom fans vented properly? Meaning, is there a sealed duct running from the bath fan to a vent on the roof?
You can double check to see if there’s moisture problems during the winter because they become very evident due to water condensing on the underside of the roof or even freezing on nails poking through (from shingles). If you don’t see any indication of moisture buildup, you’re probably safe for now. But I would suggest paying close attention to the situation for the next few weeks.
If you really filled in the area by the soffits with insulation and the insulation is tight against the underside of the roof, then I would suggest removing it from those areas because that can trap moisture against the roof and lead to wood rot. I understand what you mean by tight spaces because mine is like that too and it’s very difficult to get in those areas. Here’s a tip – get a small rake with a long handle. Then you can reach way down to where the soffits are and push the insulation away from those areas. Something like this could work well if you attached and extended handle to the existing one.You might be able to use a pool pole and just duct-tape the handle of the rake to it to give you a long reach.
Ted, I am incredibly appreciative. Thank you very much. Whenever the complexity of a house becomes headache inducing, I just try to be grateful to have a house at all. But anyways, thank you for your kindness and your time.
-minh
Hi Ted,
I see 3-4 ridge vents. No gable vents. I see 2 small grilled openings at the top of the roof.
No recessed lights.
There are no bathroom fans. We open the windows. The humidity in the room still rises 10% to about 75% after showers. I’m about to install bathroom exhaust fans and will vent them into the duct system. Regarding this matter; i’m confused on whether I should get an inline system or just the typical ceiling mounted one…
But no, there is not a sealed duct running from the bath fan to a vent on the roof. I take it this is far more desirable than running that bath fan to another duct which leads outside?
No mold or freezing in the attic but the humdity sensor is about 85% now; this is probably affected by recent rains and the fact that we’re 5minutes from the ocean. But still, 85% does not seem healthy.
I installed the soffit vents covers as per your instrucitons.
Still, regarding the high humidity, do you think it’s a wise choise to get a powered attic ventilator? And if so, can I just attach it to the grilled openings at the top of the roof?
Any suggestions you have on this matter would be much appreciated.
Thank you for your help.
Sincerely,
Minh Nguyen
Thank you for your quick response!
Hi, Ted,
I need an unbiased opinion. We have received 5 bids from contractors to replace our hvac heat pump system. We currently have 25 year old Trane 2.5 ton and 3 ton heat pumps and two air handlers heating a 1990, 4600sf, 2 story home. Our pumps are dying and our electrical bills are gigantic in the winter…$600 for December and January. We live in Washington State. We wanted to replace our 2 heat pump systems with one high quality heat pump, a 5 ton Bryant Evolution Extreme, with upstairs and downstairs zoning. It is not too difficult to combine the ductwork into one system, because our system has the air handlers with supply and return ducting all in one closet. It turns out that before the home was added on at both ends, the system had only one heat pump and air handler and the ductwork would have been one system. All of the load calculations have come in between 57,000 and 60,000 btuh which seems to lend itself well to a single 5 ton heat pump. Two contractors seem to think it would work well, one says he thinks it will work well, but we need to have a backup plan if it can’t meet our heating needs. Two others say that it needs to stay as 2 systems and would only bid it that way. One of the contractors (who didn’t supply heat load calculations but who has many great references) sells American Standard heat pumps and would not bid it as one system. He is adamant that two systems is the way it should be done. His cost is only $2,000 more for 2 systems than one of the 5 ton Bryant Evolution Extreme heat pumps. We’re looking down the road though and thinking we like the idea of one system when it comes to maintenance and repairs. We were thinking that if we seal our ductwork we could gain enough to give us the assurance that one 5 ton system would work here. Please share your opinion when you get a chance.
Clarification: $600 PER MONTH winter electric bills
If it were my home, I would stick with two systems. Zoning with a large system would lead it to be massively oversized when only one of the zones is operating, possibly causing significant comfort issues and poor dehumidification ability. Two, smaller systems would be more efficient and more comfortable, as well as better able to handle humidity. In addition, I prefer multiple smaller systems because if one does break down, at least you’ve got some heating/cooling ability.
Ultimately, when you make your choice, go with the contractor who comes with the best references and gives you the most confidence in their abilities to troubleshoot and support the system. In the long run, you’ll be happiest with a quality install and great service.
Ted
I love your web site. I’ve read almost everything you write. I have some questions regarding insulating cathedral ceilings in a rehab located located near Atlanta, GA. I have spent hours researching the best way to insulate my cathedral ceiling (to R30 or better). Almost all of the information that I can find deals with the wintertime issue of preventing warm, moist interior air from condensing somewhere in the roof system and causing damage and/or reducing energy efficiency. I can’t find anything that discusses what happens in the summer when the hot/humid air on the outside meets the colder air (from AC) on the inside. Do you know of any information that discusses roof insulation systems for hot/humid climates? I want to design an insulation system without using spray foam. Mostly because I’m wary of health issues. I am thinking of using one of the healthier materials like wool or denim along with some rigid foam to get the R value that I need. I like the idea of using rigid foam on the underside of the joists prior to drywall as part of the system. The project is a rehab with all old drywall and insulation removed back to the studs/rafters. Rafters are both 2×8 and 2×10 (in different rooms). The house has a metal roof with a ridge vent, but very poor (or non existent) soffit vents since the house has no eaves. Can you think of a way to insulate the ceiling that would use the ‘hot roof’ system using foam boards (XPS?) and/or wool batt insulation? If not a ‘hot roof’ system, do you have other suggestions or ideas for a design?
Thanks and Best Regards
Mike
Thanks, I appreciate the kind words!
Your question is great and right on point. Most of us worry about the cold climates, but the same problems can and do occur in hot humid climates. Florida is a good prototype where this type of issue rears its ugly head.
As you know, condensation occurs when moisture laden air comes in contact with a colder surface, causing the moisture in the air to condense into liquid water, so the trick in all climates is to prevent warm air from coming in contact with these colder surfaces.
The basic rule is to put your vapor retarders on the “warm side” of the insulation. So in a hot climate, you’d put the vapor retarder closer to the roof or outer walls to block the moisture from moving through the insulation and coming in contact with the inner, air conditioned walls and ceiling.
That said, since you mentioned using board foam, you’d put one or more layers of that directly under the roof. For best results, you’d seal the seams and the edges (caulk or canned foam) to minimize the amount of moisture that can sneak around the board foam and enter the ceiling cavity where the loose insulation is.
Here’s a couple references from people much smarter than me!
https://buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates
https://buildingscience.com/documents/insights/bsi-015-top-ten-dumb-things-to-do-in-the-south
https://buildingscience.com/documents/digests/bsd-107-understanding-ventilation-in-hot-humid-climates
https://buildingscience.com/documents/reports/rr-9904-unvented-cathedralized-attics-where-we-ve-been-and-where-we-re-going/view
https://buildingscience.com/documents/conference-papers/cp-1302-monitoring-two-unvented-roofs-air-permeable-insulation-climate
Hello,
Do you have any ideas on why new upvc double glazed windows (argon filled, with warm edge spacer and thicker profile than old ones) are giving off so much convection draught. The windows are definitely sealed up and close tightly. Of course I’ve done all the usual things like install blinds and long thermal curtains, but in my previous house with basic double glazing I had no need to go to extremes, in fact I just used lightweight curtains for privacy and there was no draught at all. Since moving to this new house, it’s been an absolute misery; not because it’s cold; British houses generally are, but the constant draughts make it difficult to be comfortable even with the heat blasting. I have done everything I can regarding draught proofing and insulation and have realised it is probably the constant waves of convection from the windows which is making the whole house draughty. I have never known this even in an old Victorian house with wooden windows and single glazing, so it is really strange as to what is going on with this house; the contant ‘moving air’ means it’s just like trying to heat a house with all the windows ajar! Any sort of feedback would be most welcome!
I have a 35 year old post & Beam home with a vaulted ceiling, at times I do have a moisture problem. I have about 14″ of cavity wth 2-6″ fiberglass bats. I’ve been told to add ventilation (there is none now) – I’ve been told not to ventilate but dense pack with cellulose- I was told to install rigid foam board on top of the existing decking & add new decking & shingles ( which I lean towards because the shingles need replacing anyway). The ceiling is 1×6 t&g so there is plenty of air leakage. I would appreciate your input. John
The critical component with a tongue-and-groove ceiling is to make sure there is a air / moisture barrier directly behind the boards so that moisture is prevented from entering the cavity. Without that barrier the moisture will pass up through the insulation whether it is cellulose or fiberglass and then come in contact with the cold roof deck where it will condense into liquid water and that’s where the problems really begin.
Rigid foam board on the top of the roof deck can help keep the roof deck slightly warmer reducing the chance for condensation however I would consider it a risky solution with the insulation inside the cavity as well because so little heat will get through that layer of insulation that the roof deck will still get very cold and you risk the same condensation problems.
hey ted , you have helped me in the past with heating / cooling questions and would like to pick your brain again. we had installed a central air system with heat pump for a vacation cottage to eliminate my antiquated oil burner system. so we have forced hot air that i leave on about 53 to prevent pipe freezing over winter . not sure if you remember the case. anyway, that is doing fine for doing the job but just recently had leak from water pump coupling that failed as far as i can tell. my questions are about radiant floor heating. we are on a slab and the way it looks my 3 bedrooms will need all new carpeting and my living room with laminate flooring looks to be ruined as well from about at least an inch or water on it for i dont know how long. i was planning to redo all flooring with tile to avoid ripping up wet carpet ever again . i thought this could also provide opportunity for nice radiant floor heating in winter weekends when i am there because the forced air heat in overhead registars makes me miss radiators . the air is clearly cooler down on the floor. not a disaster but maybe spend a little more now to make the home more comfortable and as you get older easier then constantly feeding my wood burning stove for heat on those cold weekends. is this a big job to put is 3 bedrooms and living room to use as needed, not main heat source or is it probably not worth it? kitchen /hallway is already tiled so have some concerns abouts it also raising height of floor in those rooms, possible tripping hazard? any thought . thanks again hope holidays went well bruce
Hey Ted,
First off – great info on the site! I live in a 1950’s townhouse that has a brick exterior and plaster walls with an air gap in between (as described in point #4 in your “How NOT to insulate your house” post). I’m working on adding some extra insulation to the attic and noticed that this gap extends all the way up, where I thought there would be a top plate.
Currently, there’s loose-fill insulation that covers the air gap along the outer walls of the house. Can this gap be left covered with insulation, should it be uncovered and open to the attic, or should I follow a different approach?
That’s always a tricky one. Often, these gaps run all the way down to the basement which is a problem because that draws relatively warm, moisture laden air from the basement and dumps that moisture onto the underside of the roof sheathing. This can then condense and rot out the roof. It can also cause ice dams by melting the snow on the roof above. In those cases, I usually like to see the gaps sealed in the basement but left open at the top which allows some “air flushing” but draws the air from the outside which poses less moisture/heat risks than basement air.
To answer your question – best to leave these gaps uncovered in the attic. For the most part, I don’t like messing with original construction techniques from that vintage if there haven’t been problems.
The one thing you could do is install vent chutes under the roof deck and blocking to prevent insulation from getting out to the soffit area and minimize the chance of the insulation trapping moisture against the roof. Here’s a great article covering this in detail.
I live in Rochester NY with pretty cold winters. My 2415 sq ft home is heated by a 7 year old Trane XL15 heat pump with a variable speed electric backup. We heat the home to 67 day, 69 evening and 61 sleeping. The heat pump does a good job down to temperatures in the upper teens. In other words the backup rarely comes on. From mid-teens down the backup kicks in more frequently with it running very often in the single digits. At the same time the heat pump is running continuously. I have received conflicting advice from our service techs as to whether on not I should be cutting the heat pump out at extreme temperatures. I would appreciate your advice.
Modern heat pumps are designed to work at cold temperatures and still do so more efficiently then the backup heat. The techs should have been able to look at the output curves and tell you this. Unfortunately, many are uninformed , and give out bad advice. So yes, keep on running your heat pump- it will supplement the electric heat more efficiently. Thanks for asking that question because I know a lot of people have the same one.