Insulating a rim joist

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Old 07-18-16, 08:34 PM
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Insulating a rim joist

I am currently working on finishing my basement in southern new jersey and i am currently at the point of insulating my rim joists. I have install 1 inch rigid foam board in all the cavities and used spray foam to seam all openings. I plan on putting up 1/2 inch drywall next. My question is: after the drywall is attached thru the foam board and into the joists can I then add 3 1/2 inches of unfaced fiberglass insulation for added r value without potentially causing a mold and/or condensation problem in the rim joist area?
 
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Old 07-19-16, 06:38 AM
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Adding 3.5" of fg should be fine as the 1" of rigid will keep the inside surface of the drywall above the dew point. Here is a related article: Calculating the Minimum Thickness of Rigid Foam Sheathing | GreenBuildingAdvisor.com

Bud
 
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Old 07-28-16, 02:44 PM
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So why not just put batt insulation after insulating rim joists with rigid foam and sealing all of the seams at edges? By insulating with rigid foam and sealing all cracks will create a vapor barrier in effect, batt insulation can go right up against rigid foam.
 
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Old 07-28-16, 02:57 PM
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Hi curious,
The question would be, would just batt insulation provide an acceptable ignition barrier to protect the rigid insulation. We know that 1/2" of drywall is accepted, but have not seen an opinion on using just fiberglass to cover the rigid. As always, ask local code officials as they have the final word.

Bud
 
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