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Air sealing rim joist spaces, does code require a fire resistant barrier over it?

pizza's picture


I'm air sealing rim joist spaces in my basement with 2" thick XPS pink foam in each cavity-does code require me to cover it with fire resist barrier (like a piece of drywall) over it?

None of the literature I've seen describing this ever says to cover it with a fire barrier like drywall, including the literature I've read and downloaded here on FHB or in a book a bought from Taunton Press on energy saving projects.

I know it's required when your insulating an entire basement wall with it.


Air sealing a rim joist (post #207367, reply #1 of 6)

Can anybody help with this question?

In the basement, probably (post #207367, reply #3 of 6)

In the basement, probably not. But the best solution is to call your local building department and ask. Codes vary regionally.

Andy Engel

Never try to teach a pig to sing. It wastes your time and annoys the pig.

I would suggest checking your (post #207367, reply #2 of 6)

I would suggest checking your local building code.  Often books and magazines won't include things like this since it will be different depending on local municipalities.  For what it's worth every time I have foamed a box header in both Ontario and Manitoba we have always covered it with drywall. 

Rim joist air sealing (post #207367, reply #4 of 6)

Thanks Andy. I'll give them a call.

Rim joist sealing (post #207367, reply #6 of 6)

Was looking at my old posts and wanted to reply by saying I called my local township code enforcement and they said yes I do need to cover each piece of foam with a layer of drywall. They even suggest to make it easier by using fiberglass batts instead of the foam but I will use the foam because of what I've read here on FHB that foam and a can of great stuff is a better way to go. Thanks 

Air sealing rim joist spaces (post #207367, reply #5 of 6)

I agree that the answer you get will depend on where you are.  I our area, covering rigid foam in rim joist bays is not required.  The rationale is this is a very limited square footage of foam, not an entire wall which no one in their right mind would leave unprotected.  


Duluth, MN

On the end of Lake Superior