Q&A: A Forum for Green Building Experts and Beginners

My house is spray foamed with open-cell Icynene on the roof deck as well as all walls. I have an HRVv for fresh air.

Everything's been good but I'm noticing now that the humidity in the attic starts out around 36% in the a.m. but gets up to 60-70% during the day then back down to 40-50% at night. The temp is always within 5% of the house temp. I'm not sure what to do.

There isn't any moisture sources in the attic. To make it more confusing is, there are two separate attics and both are doing the same thing.

Any help would be greatly appreciated. I don't know what to do.

My dream house will use double stud walls over a full basement. The basement will be poured concrete with exterior insulation. It is a one floor above basement plan. The inner main floor wall will be over the concrete while the outer will be over insulation. The simplest way to support the outer wall is to 'cantilever' the floor framing over the concrete. Yes this creates a wood "thermal bridge" at each floor framing member but the heat loss is modest and tolerable.

We are using 2" of exterior polyiso foam with air-barrier established at the Zip sheathing. Our first choice in regards to the basement rim joist was to use closed-cell spray foam. Now I understand that we should avoid this "foam sandwich" but open-cell is an option due to its vapor permeability properties. Then I read more about foam and am a bit afraid of spray foam in general.

We recently had soy foam insulation applied to our dining rom and living room wall and a garage wall. We had situation where the original siding of the house on the garage level was not properly secured to the framing and there was air coming from outside the house getting trapped between the wall directly above it (dining room/living room) causing the sheetrock or dry wall to smell. We removed the sheet rock and insulation. There was no mold or any rodent infestation but the wood was old and smelled.