Insulation, Radiant and Vapor Barriers - To Foam or Not to Foam

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GRob
10-16-05, 10:13 PM
I am residing my house. I plan on blowing in insulation and then will either wrap it w/Tyvek or put an additional 1/2" rigid foil-backed foam. On the outside I am planning on using either Hardiplank or Cedar Clapboard.

I thought the foam would provide for better in****ation, because it helps block heat/cold transfer through the 2x4 and blow insulation will not be perfect. However, will I be doing more harm by traping in moisture?

Thanks.

Concretemasonry
10-16-05, 10:29 PM
I don't think any foam nailed to the exterior of the house would be a vapor barrier if you did not tape the joints. If were to try to claim it was a vapor barrier for use elsewhere, you would get a lot of arguements saying it was not. It will definitely more than make up for the insulation void (thermal short circuit) created by the 2x4s.

I would still use the Tyvek over the foam since this would be a moisture barrier.

Dick