Hi,

I’m renovating a small office building that was never heated in the winter into a small home. The current wall has Vinyl siding, then 1/2 green zip sheet, then 2×6 cavity wall with R19 pink insulation, then 1/2 drywall. It’s in great shape, 10 years old.

I’d like to replace the vinyl siding with board and batten and also add insulation on the outside to prevent condensation inside the wall when we heat the building, and to provide a thermal break.

I realize that for my climate zone 5A (cool humid), I need 2 inches of insulation on my 2×6 wall according to this article:

Can I get away with only 1 inch of insulation? I like to keep the wall as thin as possible because the building only has a 12 to 10 inch overhang.

Most of the year, the inside surface of the OSB ZIP panel will be above du-point. When it does get slightly wet, it should be able to dry to the inside correct? There is no vapor barrier installed.

What type of foam would be best to use in my situation? I’m leaning towards using Roxul Comfortboard. That also allows the wall to dry to the outside incase there is moisture in the wall.

I’m also adding a rain screen material between the siding and foam/Comfortboard.

Thanks in advance for any suggestions / ideas / feedback.

Sander