Thermal barriers and spray foam
regarding the requirement of thermal barriers over spray foam insulation in walls – does the barrier need to be in contact with the foam or can there be an air space? specifically, i am retrofitting an old school building to be apartments, it has thick brick walls with no insulation so we are going to frame a steel stud wall inside the wall with about 1.5″ gap between the wall and spray about 2-2.5″ of closed cell foam to at least R-13.3 per IECC for mass wall buildings – there will be about a 2″ gap between the face of the foam and the sheetrock – is there any issue with that? walls are about 9′ tall and extend from floor to deck above
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If there is an air space between the thermal barrier at foam there is usually a requirement for fire stops & fire blocking at some interval to impede vertical fire spread, but the thermal barrier need not be in contact with the foam. Local codes often vary on the firestop requirements.
Installing sprayed cellulose in the steel framing would usually meet that firestop requirement, but may still require a fireblocks between floors depending on how your local code officials interpret it. This was discussed a bit in this older thread:
https://www.greenbuildingadvisor.com/question/what-fireblocking-is-required-in-double-stud-walls-filled-with-dense-pack-cellulose
ok, thanks - the floor and floor deck above are concrete slab so fireblocking shouldn't be an issue, for some reason i thought i had read years ago that the thermal barrier had to be in contact, but i saw nothing in the code that says that.....it makes sense though
Here is what the 2018 IRC says:
"R316.4 Thermal barrier.
Unless otherwise allowed in Section R316.5, foam plastic shall be separated from the
interior of a building by an approved thermal barrier of not less than 1/2-inch (12.7 mm)
gypsum wallboard, 23/32-inch (18.2 mm) wood structural panel or a material that is tested
in accordance with and meets the acceptance criteria of both the Temperature
Transmission Fire Test and the Integrity Fire Test of NFPA 275."
I take this to mean that as long as your thermal barrier separates the spray foam from the building interior, you are good to go. Essentially, the code is saying: If there is a fire inside the building, we want some material to hold off the fire getting to the spray foam.
Peter