Spray foam optimal or does another solution exist?
We are doing a renovation on a room that was an addition to our house that was never conditioned and never had a vapor barrier in the crawl space and also bringing the flooring to house height level and then removing the sliding door which currently separates the room from the house. When the previous owners built this addition many corners were cut, e.g. no gasket or seal on rim joist area, cantilevered floor that had no insulation and was completely open for critters to crawl in, etc. Ceiling is a non vented cathedral ceiling and did not have enough insulation to meet code for a non vented design. We’ve demo’ed out all existing drywall and fiberglass insulation as the original plan was to blow in closed cell spray foam. I’m confident the foam would result in a very tight envelope and structure and result in a comfortable assembly.
However I’m having second thoughts after reading horror stories where spray foam was not installed correctly and there is then persistent off gassing for years on end. We have two small children at 1 and 3 so I am being very cautious as isocyanates and some of the other voc’s are very bad for developing bodies. I know I won’t be able to replicate the insulation and air sealing that foam would give with other methods, however I’m wondering if another method would be good enough.
The other method I’m contemplating is to caulk each stud bay, e.g. stud to osb sheating, caulk basically any intersection and then either caulk or can spray foam the rim joist area. Then use Roxul batts to insulate. R15 for 2×4 walls and R30 for the cathedral ceiling. This would result in way more labor. Might be cheaper but would take way more of my time. It looks like Roxul recommends a poly vapor barrier on the interior side over the insulation, is that correct? If so should it also be done on the ceiling and is R30 enough? House is located in a suburb of Denver, CO. Climate zone 5b. I would also consider dense packed cellulose for the walls but I don’t think it would be good enough for the ceiling.
Thoughts? Am I being rational or overly cautious? I’m just putting this out there as I’ve flip flopped on the decision too many times.
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Replies
Todd,
If you want to seal leaks between your wall sheathing and your studs, you might want to consider the use of sprayable caulk: Air Sealing With Sprayable Caulk.
It's also possible to establish an air barrier at the drywall layer; for more information on this approach, see Airtight Drywall.
Thank you Martin. I have read the sprayable caulk article already and find it to be a nice solution. Kind of a middle ground in between typical batt only insulation and spray foam. I have interestingly had a very difficult time finding anyone in the Denver area who does this. I have concentrated on the Eco Seal product though. I'll have to look into that more thoroughly. It would certainly be much more time effective. Is R30 enough for an unvented cathedral ceiling? Roxul R30 batts is what I'm considering but could be swayed.
I find the airtight drywall assembly to make a lot of sense but I feel that it would be moot if I cannot control air movement through the rim joint. Would sprayable caulk work here also?
Thanks.
Todd,
Q. "Is R-30 enough for an unvented cathedral ceiling?"
A. You are in Climate Zone 5, so the answer is no. The building code calls for a minimum of R-49 ceiling insulation in your climate zone. For information on ways you can achieve R-49 in a cathedral ceiling, see How to Build an Insulated Cathedral Ceiling.
Installing polyethylene sheeting or foam with foil/vinyl facers on the interior side of an unvented cathedral ceiling it creates a moisture trap- DON'T DO IT! Use a variable-permeance smart vapor retarder such as Certainteed MemBrain or Intello Plus instead of poly sheeting. For the unvented ceiling this is critical, but it's also a good idea for the 2x4 walls.
R15 in 2x4 framing doesn't meet code either- you need R5 continous insulation thermally breaking the studs to get there. If you have room to add 1.5" of unfaced Type-II EPS between the drywall and the studs & rock wool you'll meet code, and the EPS would have about 1.8-2 perms of vapor retardency toward the interior, which is low enough for wintertime moisture control at the sheathing in your climate zone (as long as it's air tight.) If you've already sprung for a roll of smart vapor retarder for the ceiling, putting it between the foam & studs is fine, caulking it at the edges to the framing for air-tightness.
Dense packed cellulose would be good for both the walls and ceiling. The R value would be slightly lower than with rock wool, but the fit would be nearly-perfect, and the cellulose would also share the moisture burden with the structural wood. You'd still need to use a smart vapor retarder (on the ceiling anyway.)
If you have the headroom for continuous foam on the unvented ceiling, you could put up to 3" of unfaced Type-II EPS up there without creating a moisture trap. As will the walls it's still a good idea to use the smart vapor retarder as an air barrier behind the foam, since foam changes dimensions slightly with the seasons and over time, which makes sealing seams of sheet foam a less robust long term air-barrier.
If you can't find it locally, you can get 8' x 100' MemBrain online at Menards (a midwestern retailer- the nearest one to you is in Cheyenne WY) for about a C-note + shipping: https://www.menards.com/main/paint/drop-cloths-plastic-sheeting/poly-film/8-x-100-membrain-smart-vapor-retarder-air-barrier-film/p-1902435-c-8188.htm
Intello Plus can be had at 475 High Performance Building Supply: http://foursevenfive.com/product/intello-plus/
The Intello product is a bit more vapor-tight than MemBrain, but that's not a big deal unless you intend to keep the interior above 35% RH in winter (which would require either a very tight house or active humidification in Denver' high-dry climate.)
Dana,
Thank you for the very detailed answer. The info on the smart vapor retarder is great.
I have also thought of doing EPS over the stud wall as well and then attaching the drywall with long screws or potentially furring strips if needed but I lean towards the former and researched here elsewhere.
To hit code for the 2x4 framed wall it sounds like SPF wouldn't be compliant either as the studs would still be thermal bridges. Is that correct? We've only been at this house for 6 months which was built in 1982. There is also a well done (to my knowledge) addition over the garage in 2002 so the rest of the structure is not insulated to todays levels although it is built with 2x6 walls and and the original foundation has foam around the perimeter, not sure if it is under the slab. The design is a nice passive solar one that will need help with summer shade but does great in the winter.
I have performed a fairly comprehensive level 1 sealing of the attics by using LED retrofit kits and sealing them for the 36 can lights and then sealing any other penetration. That has helped remarkably. I used ECO Bond caulk btw and was impressed. Nice to have no smell with it.
I have attached pics of the room in question.
One nice thing about this room regarding spray foam is that it is right now not open to the house. It is separated by a sliding glass door. I would further seal this with heavy plastic and good tape and open all windows in the room. I can give the room multiple weeks fully open and before drywall to let the foam fully cure, off gas, etc. Even a month would be fine with us. Wiring for the house does pass through into the basement through this room but i have sealed those penetrations with canned foam.
We were scheduled to have this done last Monday but Denver has been cold and snowy and so after reading about foam temp requirements and then substrate temp requirements I canceled the foam job.
It might be pertinent to add that we just had a new roof put on with GAF Tiger Paw used as the underlayment.