How to caulk or foam edges of rigid foam between studs? Best techniques? Foam gun?
What’s the best way to install rigid foam between studs?
Is there a good pictorial guide out there?
My application is a 1920’s home in California Climate Zone 3. The home has a failing brick basement wall with no remaining vapor barrier. The owner previously placed fiberglass, which of course failed miserably.
The goal here is to install 2″ rigid boards between the existing rough cut dimensional 2×4″ lumber. The question is what method?
* Cut tight
* Cut loose and foam with window & door foam
* Cut medium tight and caulk
* Something else?
The goal is a large gap by the bricks for hopefully drying out, and flush to the inside of the studs. This basement is used occasionally for sleeping by family members, and the owner wants the insulation restored for wintertime comfort.
Finances mean the brick can’t be removed and the wall properly sheathed for quite some time. Clearly this wall needs a complete re-do on the bricks.
Your thoughts on how to install rigid foam between studs?
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Replies
I like canned foam. It helps to cut the edges with a bevel so that the expanding foam forces the foam back into the cavity instead of away from it. Leave around a 3/8” to 1/2” or so gap all the way around the perimeter and fill it with canned foam. I prefer the loctite Titefoam for this if you expect any movement or thermal cycling since it seems to be a little more durable, but it does cost more.
Bill
Is there a foam gun compatible permanently "flexible" foam available? I have the great stuff foam gun, which I prefer to the cans.
Is the regular or window version better?
I like tremco's exoair flex
https://www.tremcosealants.com/markets/commercial/air-barrier-systems/transitions/tapes-and-foams/exoair-flex-foam/
And you can watch Big Matt do this method of you'd like a video explanation. https://youtu.be/ckJ_0TpkvK8
Consider using two part spray foam. With or without some rigid foam. Should form a more reliable seal that cut-n-cobble + canned foam.
The really small 12 board foot 2-part spray foam kits are good for this purpose. The key to making them last is to keep the cans warm while you're using the kit. Submerging the cans in warm water is a good way to accomplish this.
Bill
Before closing it all in it's worth fixing all of those obvious mortar gaps in the brick, and may even be worth a lime mortar parge. (Ask a mason to assess that.)
Is there enough space between the stud edges and masonry to slip in some foam board? A continuous layer of foam board isolating the wood from the brick will keep the moisture content of the wood better bounded, lowering the rot, fungus, and insect attack risk.
If there isn't any way to put foam board between the brick & framing,, installing spacers to keep the foam board 1/2" off the masonry is the next-best- an inch of air is a good capillary break, and provides a more than adequate drain space. (Even a quarter inch is good, but hard to maintain on uneven brick surfaces.)
To meet fire codes any vertical cavities need to have fire blocking, and this becomes more important with flammable insulation like foam board. Some locations require blocking only between floors, others require a second fire block midway up. Find out what's needed in your jurisdiction.
The 2-part foams only make sense if you're using it as insulation. It's unlikely that the basement would go through even a 12 board foot kit if only using it to seal the board foam.
The DIY closed cell foam kits are also some of the least-green insulation materials still legal to sell in the US (though still substantially better than XPS foam board), since they use HFC245fa as the blowing agent, a powerful greenhouse gas (almost 1000x CO2 @ 100 years). The choice of foam board matters too. The most-green would be 1lbs density foil faced polyiso, which has about half the CO2e footprint of (the more benign) HFO blown closed cell foam, making it comparable to rock wool or fiberglass, followed by EPS. A the extreme other end of the scale is XPS, which is blown with an HFC soup, the largest component of which is HFC134a at about 1400x CO2 @ 100 years. See:
https://materialspalette.org/wp-content/uploads/2018/08/CSMP-Insulation_090919-01.png
There is at least on DIY foam kit using HFO1234ze as the blowing agent, but it's for a 3lbs density foam, with ~50% more polymer per R than the HFC blown stuff. The higher polymer per R puts it in the same CO2e range as the HFC blown 2lbs foam, so it's not really any greener despite the low-impact blowing agent.