I'm cutting up Foamular 250 into 8"x14.5" rectangles to be installed as air blocking under my knee wall.
I also installed those (cheap) foam pipe covers over my heating pipes as a side project.
Just out of curiosity I took my BBQ lighter to a small wedge of each type of foam... boy they burn/melt FAST and with an acrid smell and smoke. The Foamular 250 def. had the worse smell and seemed to burn more easily than the pipe covering which seemed to melt away rather than burn.
I've seen warnings about keeping foams, like Great Stuff, away from sources of heat over 250*F (even after cured). And the foamular has a clear warning printed on it about needing to be covered by an appropriate ignition barrier.
Should I be worried about using the foamular as an air block? In my situation it is not being used as a fireblock/stop, just as an air stop. In addition the attic-side will be pressed against dense pack cellulose. I suppose any fire that makes it into the joist area would be one SERIOUS fire... but all the same, am I better off using wood for this? The reason I liked the idea of the foam was the 1) it acts as an insulator, 2) it is light weight, 3) it is cheap, 4) the most important reason, it's easy to trim and wedge into place. The perimeter of the foamular air blocks will be sealed with Great Stuff Pro Gap & Crack filler.
I was planning to box a few IC-rated recessed lights with the foamular, I wanted to 1) keep the cellulose away from the fixture, 2) be able to air seal around the fixture (it's an air-tite rated fixture, but I figure a second air sealing foundry is a good thing). I bought LED trims to fit in, so I don't imagine that high temps will be a big issue, but you never know, for example a short or something near by could throw a spark (despite being inside a metal box). Is it a bad idea to use the foam board in this manner?
I had been planning to air seal the attic side of my knee walls and first floor ceiling prior to putting up insulation. I am planning on spraying seams, penetrations, etc w/ Great Stuff Pro... I've seen videos of "pros" online that spray this stuff around like crazy, including on/over electric boxes. Is using Great Stuff in that manner OK, or am I risking it expanding into the box, or being a fire risk if a short occurred inside the box? Particularly with plastic Carlton boxes I feel like a real short in the box could potentially throw a spark thru the strain relief tabs that hold the romex. Maybe I'm just being overly concerned?
I get the JLC, one of the articles this month was on foam-related fires in Massachusetts... in those cases it seemed to be related to the foam catching fire on its own due to the extreme temps produced by the curing process when sprayed on too thick... but it still has me a bit worried :-/
The blown insulation contractors I hired will be here on Wed, so I need to make up my mind on what I'm doing and what materials I'm using, plus get it done
... I took Tue off work, so I will have the whole day to work on this.