Air sealing attic: materials and fire safety
I’m a homeowner thinking to do some DIY air-sealing in the attic. I was preparing to use caulk on narrow gaps (top plates), and spray foam on larger gaps (penetrations for cables, plumbing vent stack, etc). Not being a pro, I was going to just stay away from anything thermally hot, like the furnace vent.
Then I noticed that many spray foams meant for the homeowner have surprisingly low ignition temperatures – generally at 240 deg F. Even the orange fireblock stuff is down at 240 F, for many brands. This ignition temperature is lower than many other materials in the attic, which means the foam may be the first thing to ignite up there. And seeing some videos online, many common DIY foams can propagate a flame pretty well, too.
So I started second-guessing my plan. I got a quote from a pro for the job, and they use a foam with an ignition temperature around 450 F, so that seems better at least. On the other hand, the estimator said they’d use this foam around the furnace vent, too. Is that allowed?
I’d like to err on the side of fire safety, so any advice on what materials to use? Should I use caulk where possible, instead of foam? Getting trickier, per residential codes (this is a townhome with adjacent neighbors) do I need thermal or ignition barriers around the foam? If I did, that would seem to negate the convenience of using spray foam in the first place. There will be fiberglass insulation over these areas.
To be clear, I am not talking about fires that occur during or shortly after application due to incorrect application techniques.