It's a reasonable cost effective solution. The closed cell foam will air seal well and the additional fiberglass insulation will be much cheaper and work better.

I agree I wouldn't do this in a cold weather climate as the dew point may well be in the wall and thus condensation would be a concern. However in Virginia it will likely be fine.

Depends on how much money you save on doing this. If it's just a few thousand, I'd probably just spray foam the whole thing. If it's going to save 10 grand, then in that climate it sounds like it's probably worth it.

One thing will be quality of the spray job - if you're just spaying a thin layer then it has to be done precisely and without gaps for sure.

Yes you definitely want unfazed batts. Might also consider throwing in mineral wool batts instead of fiberglass

In theory, this should be fine. In practice, it may be difficult for the applicator to ensure a minimum one-Inch coverage to ensure the inner side of the sheathing stays below the dew point. I would increase the "flash" to 2".

This will meet Code for R values in Zone 4, though it will be less than Building Science Corp.'s Joe Lstiburek's recommended wall R-40 for any place north of the Mason Dixon Line.

If you are going to spray closed cell foam on the back of the exterior sheathing you should omit the kraft paper facing on the insulation so the wall can dry to the inside. You might ask your contractor why he would want to put a vapor retarder on each side of the wall.

I agree that the foam should be 2 inches because the spraying gets more efficient and cost effective as the temperature rises with a thicker layer.

If you are going to spray closed cell foam on the back of the exterior sheathing you should omit the kraft paper facing on the insulation so the wall can dry to the inside. You might ask your contractor why he would want to put a vapor retarder on each side of the wall.

I agree that the foam should be 2 inches because the spraying gets more efficient and cost effective as the temperature rises with a thicker layer.

Since the wall will be very air tight and will not dry to the exterior, the Tyvek will not be doing much except providing a place for water to collect if there are any penetrations in it. It might be an opportunity to seal the exterior face of the sheathing with a liquid applied or self-adhering membrane.

I should add that many closed cell foams are not considered a vapor retarder until they reach a thickness of 1.5" but you should get confirmation of the actuarial permanence for 1". It might also be difficult to maintain that thickness. Perhaps a better option for a wall is open cell foam or dense pack cellulose.

This post was edited by Renovator8 on Sat, Nov 29, 14 at 7:56