Using rigid foam to insulate below floor in a way that meets fire code
joecap5
| Posted in Energy, Heating & Insulation on
Hello,
I need to improve the insulation below my floor along the exterior walls.
Currently there is fiberglass insulation but because of the achetecture of my raised range the are drafts.
I want to use some rigid foam insulation to block of the drafts but want to make sure it meets fire code. Rigid foam exposed to living space would not meet code.
I would be installing the insulation above the drop ceiling on my lower floor.
I don’t know if a drop ceiling is considered enough of a fire barrier though or if I would need to put up some sheet rock in front of it.
Would anyone know?
Thanks
Replies
Not saying there are none, but I have never seen a residential drop ceiling assembly that is fire rated. More then likely yours is not. The way to find out would be to pop a tile off and look at the back. If rated, you will see it stamped on the back.
I would say that if your concern is the draft, foam would do a better job at sealing air movement. It is possible to accomplish with rigid insulation and caulking but I would rarely opt for that option.
Dry wall
Drywall and similar plaster products have a 30 minute fire rating for every half inch thickness.
Two sheets, skim coated provide just over a one hour fire wall.
There is fire-rated riged, but it's probably hard to find.
I'm not sure to meet code if I necessarily need something that is fire rated to be a barrier. The code says something to the effect of foam can't be open to living space. Not sure if the drop ceiling is considered closing it off from living space.
There is no circumstance where protecting foam from fire is more important than when the foam is placed on the ceiling.
Nor is there any dopped ceiling that is, by itself, an adequate fire barrier.
The most common way to protect foam is with drywall, at least 5/8" thick, fastened with screws into something solid every 6", with the seams mudded & taped.
In practice, this means covering the ceiling with foam board, then fastening lath or hat channel atop the foam board -making sure the lath is attached to the rafters above the ceiling. Mount the drywall to the lath.
Do it right, and the lath can support your drop ceiling.
So- why bother?
I cannot emphasize enough them fire hazard posed by even "fire resistant' foam. The stuff heats up, ignites, falls from the ceiling, and then burns like rocket fuel on the floor. This behaviour is NOT evaluated by the fire resistance tests. It also generates massive amounts of very irritating smoke as it burns.