finishing basement rim joists

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Old 06-21-19, 08:14 AM
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Question finishing basement rim joists

Need some advise on finishing basement rim joists. I'm framing an unfinished basement (poured concrete walls) with foamboard, framing and fiberglass. I know the section between the new top plate and the top of the floor joist (about 8 inches high) has to be sealed for fire stop. One wall only has about 2 inches between the rim joist and the outside wall plate, so it can be sealed with 1 1/2" foamboard and 1/2" drywall. The other wall has about 8 inches between the concrete wall and the outside wall plate. Do I need to build a 2 X frame and drywall behind the top plate, or just add more fiberglass to fill the 8 inch void and build a 2 X drywall frame directly attached to the top plate ?

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Old 06-21-19, 08:22 AM
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I think you must mean wall sill plate... not top plate. Or are you actually framing walls down there?

Fire codes vary from place to place. Since your basement will be unfinished, I don't think they expect too much in the way of firestopping. What they do require is that any insulation used must be fire retardant, so plain foam cannot be left exposed. That's the only reason why they would require it to be covered with 1/2" drywall.

Alternatively, you could just use a fire rated foam such as 2" Thermax which is foil faced and does not need to be covered with 1/2" drywall.

If you are actually framing walls, the best method is usually to drywall a band around the ceiling first before putting your top plate up. That way the entire top of the wall, top of your foam, and any space behind is capped by drywall.

And things in Canada may differ from here in the US.
 
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