What are the requirements for framing for a gas insert in an existing masonry fireplace? See the attached picture that shows the framed opening for the gas insert (circled in red). The insert will project about 5" outside of the existing firebox. My contractor insists that drywall all the way to the insert edge (the red box drawn on the picture) is ok. Is he correct or do we need to use non-combustible material like cement board? BTW, he is going to insulate with Rockwool between the studs. We were also planning to just paint the wall around the insert for a clean, modern look. Is it possible to paint over cement board or other non-combustible material? Is any special surface prep required?

Any advice would be much appreciated.

Framing for gas fireplace insert in existing masonry fireplace

  • You most certainly can paint cement board. However, you may not like the results since you'll see the texture of the cement board through the paint. You'd need to skim coat it with plaster if you want a smooth surface to paint.
    – FreeMan
    Sep 20 at 13:08

It depends on the gas insert. Many gas inserts are listed for contact so if it is your contractor would be correct. I don’t think the contractor would try and cheep out on this because a fire would be on his bond if he did not do it properly.


You must consult the manual for the insert you are planning to use, it will specify the required clearances to combustibles.


When I did mine, the installer insisted that I use fire rated drywall. As well, due to a wooden mantle above the fireplace, we had to add a metal deflector above the firebox to change the hot air flow up the face.

I would get the name and model of the fireplace you're having installed and read the installation instructions regarding clearances myself.

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