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markmm
fire resistance in interior wall

I have a framed interior 2x4 wall with concrete backer board(1/2in) on one side finished with drywall mud and kitchen base cabinet on other. On the concrete board side is a wood burning stove. If I fill the voids in the wall(between studs) with an expanding foam product from hardware store will these give greater fire resistance to the wall? Other ideas?

keith3267
Re: fire resistance in interior wall

Some, if not all, expanding foams give off toxic gasses like cyanide when they burn or get hot. I don't think I would do that behind a wood stove. Just make sure the top sill above the studs does not have any holes in it. If it has any plumbing or wire holes in it, then fill those with foam or caulk or stuff fiberglass in them very densely so the wall cavity does not become a chimney in case a fire was to get started.

If you use any insulation, use rockwool. But the most important thing is to make sure you have the proper clearances around the wood stove.

You could also treat the studs with a Sodium Borate solution. It greatly reduces the combustibility of wood. It is what gives cellulose insulation an acceptable fire rating.

markmm
Re: fire resistance in interior wall

How do you apply that to an existing wall, where do you get it? Thanks

markmm
Re: fire resistance in interior wall

I forgot to ask, does the concrete backer board have decent fire resistance?

junkout
Re: fire resistance in interior wall

concrete backer is fire proof yes but it transfers heat very well. to do it right you need to have a 1" air space between the concrete board and combustibles. with inlets at the bottom and vents at the top by doing this you can reduce the required clearances of you stove by 1/3. but no you should not insulate directly behind the backer board especially not with spray foam.

A. Spruce
Re: fire resistance in interior wall
junkout wrote:

concrete backer is fire proof yes but it transfers heat very well. to do it right you need to have a 1" air space between the concrete board and combustibles. with inlets at the bottom and vents at the top by doing this you can reduce the required clearances of you stove by 1/3. but no you should not insulate directly behind the backer board especially not with spray foam.

It is imperative that you check with your local building code office for requirements. As Junkout states, you must have a 1" separation between the backerboard and the combustible wall behind it, you can't just attack the backer board and tile directly to the wall. You will also have requirements for the footprint and hearth area of the stove. While you may not think this is important, it not only affects your safety, it affects your insurance coverage as well.

keith3267
Re: fire resistance in interior wall

Did not know it was a finished wall. Just make sure you have the proper clearances around your stove.

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