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s002wjh 01-30-2012 06:17 PM

rigid board and framing need gap?
when install framing over rigid foam that is against the concrete wall. do i need put a 1/2" or 1/4" gap between the foam? airflow or whatever purpose?

also when install rigid board to concrete. do i need leave a bit gap between board and floor? 1/2"

Gary in WA 01-30-2012 06:44 PM

No gap behind foam board, tight to concrete with proper adhesive:
Yes, 1/4" gap under f.b. to fill with canned foam.

Air-tight drywall;
Ask me about the ones you question; air-seal rims/add rigid foam board, fire-stop top plate and every 10' lineally, sill sealer under p.t. bottom plate, no poly, no paper faced cavity insulation, no water-resistant drywall, no foil-faced foam unless quantified.


joecaption 01-30-2012 06:46 PM

Leave a gap at the wall, no need for a gap at the floor.

s002wjh 01-30-2012 06:47 PM

sorry i didn't make clear, what i meant is gap between the Front of foam and Stud wall. and gap between foam and floor

for the fireblock, is that include 10' for the ceiling too(after furring the ceiling, there gonna be gaps between ceiling joist)? or 10" is only for vertical stud walls?

Gary in WA 01-30-2012 09:32 PM

I would not leave a gap at foam face/studs to help convective loops around the cavity insulation batts (unless cellulose or SPF). Fill the gap under the foam board at the slab with canned foam, you don't want any basement air getting to the concrete wall:

Fire-blocking the wall every horizontal 10' apart from slab to 2x filler between wall top plate and existing house mudsill plate (if full-height concrete):

Page 2:
You don't want the outlet fire in the wall getting to the floor joists cavity bays above. It will be blocked (confined) to 10 foot wide sections of wall by however tall they are.


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