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Community and Q&A

Fire-Retardant Paint for Garage

Renovations102 | Posted in Building Code Questions on

Hi folks,

Does anyone know if DC315 application is code in NH for rim joists, exposed garage ceilings, etc.? I had my rim joists sprayed w/ 3″ of closed cell this week & the salesperson stated theĀ  product does not smell & I can be home.

The crew showed up w/ no fans (even though I was assured they would have them for ventilation), so I had to turn them away. In talking w/ them, one guy said “It will stink really bad for several days, & it’s not even code here anymore, if I were you, I wouldn’t even have it applied.”

I have read the closed cell burning is not as big a concern as it is made out to be…

I don’t want to have any toxic product sprayed if there is little to no benefit & if it is not required…


I also saw this:

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  1. Expert Member
    BILL WICHERS | | #1

    I doubt very much any fire retardent paint is going to be acceptable as a fire barrier in a garage. A garage is supposed to have 5/8" drywall for fire protection (assuming this is an attached garage), and I'm not aware of a fire retardent coating that can meet that level of protection.

    Rim joists are sometimes an exception, with some exposed foam being permissable by code. If you want a simple "no smell" level of fire protection for the rim joist, get a back or two of Safe n' Sound mineral wool batts, and cut those to cover the foam in the rim joist. Mineral wool is usually capable of supporting itself when stuffed between joists like this, so you don't need any glue or support wires, and mineral wool itself is a fire rated material. Mineral wool doesn't offgas, either.


  2. Renovations102 | | #2

    Thanks Bill,

    I was thinking the same thing on the Rockwool. IF it's current nh code to cover the rim foam, that is likely what I'll do.

    Side issue, I think a lot of states also allow 23/32" osb on a garage ceiling & common wall as a fire barrier or 5/8" drywall as you stated...

    1. Expert Member
      BILL WICHERS | | #3

      I'm not aware of OSB being suitable as a fire barrier on a garage, I've never seen that. I wouldn't trust it myself regardless. Drywall is considered to be a non-combustible material, OSB is not -- OSB will burn. What is often done in a garage is to just mud and tape the drywall, but not to fully finish it to save money. I would at least prime it though -- unprimed drywall will yellow in a short period of time, and then it looks crummy.


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