Single vs. Two-Component Foam for Band Joist
BrunoF
| Posted in General Questions on
I have a fairly messy band joist between my attached garage and house with joists from both sides coming through. I was thinking to air seal and insulate it with closed cell spray foam rather than with caulk and fiberglass batts but which foam should I use…single component or two component?
thx.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Either will work. One-part spray foam is what I usually call "canned foam", and includes products like Dow's Great Stuff, Loctite's Tite Foam, OSI's Quad Foam, etc. Any of those will work fine for basic air sealing needs, and they're all commonly used for that purpose. There is also Kraken Bond's product, which is good for larger areas.
Two part spray foam includes the Dow FrothPak, other similar DIY kits, and the stuff installed by commercial contractors. You do get a more durable foam layer with this stuff, and it can cure properly in thicker layers, but it's lots more expensive. Depending on the size of the rim joist you're talking about here, one of the FrothPak kits may be a good fit here.
Note that you can't air seal with "fiberglass batts", because fiberglass is not an air barrier.
Bill
2 part foam will be ready for second layer in minutes depending on the environment, 1 part can be longer
1 part foams are generally not as fire resistant as some of the 2 part foams.
all of the 1 part "closed cell" foams ive seen are still only r4 to r5. but two parts reach 6-7.
I wouldn't consider any of the closed cell spray foams to actually be R7 in practice. That's marketing mumbo jump. R6 is much more realistic. I do agree with the rest of your comments, although I doubt there is a sufficient difference in fire resistance to really matter -- all these spray applied foam insulating products will burn in a big fire.
Bill
the fire related info is hard to dig through sometimes, but canned 1 part spray foam ignites at 200 something degrees while some 2 part products claim 600 degrees.
what that changes in reality is beyond me. but i imagine in either case that the fumes and smoke are gonna be pretty gnarly.
Yeah, I wouldn't want to breath the smoke from any of that stuff! The much lower ignition point is probably more of a concern than the overall flamability here: lower ignition points mean it takes more to get the material to START to burn, which is a Good Thing.
Bill