Shed/garage insulation question
I have a shared/garage that I’m trying to make into a workshop. The construction puts it somewhere between a pole barn and a standard framed structure so I wanted to get some advice on how best to proceed. I read the pole barn articles and several others on this site, but since this structure falls somewhere between the two I still have some questions.
To start, my goal is to “take the edge off” the current temperature extremes (Zone 4a with interior temps ranging from as high as 100 degrees in the summer down to freezing in the winter), to make it into a reasonably habitable 80-50 degree range with a small ac unit or heater.
The building is an old (1930’s) 16’ x 16’ garage with ~2×4 wall framing and 2×6 rafters. The roof is a traditional asphalt shingled roof with a recently installed ridge vent. The walls however are simply corrugated sheet metal nailed to the framing.
I’d like to avoid removing all the sheet metal, so my thought is to install 2” rigid foam centered between the wall studs and use spray foam around the edges to ensure an airtight seal. After installing the insulation I’d cover the interior walls with plywood or OSB leaving an air gap between the insulation and plywood (as well as the insulation and metal siding). For the roof, I was going to add 4” of rigid foam between the rafters and again use spray foam seal around the rafters, leaving a 2” gap between the roof and the insulation for air to flow from the soffits to the ridge vent.
I was considering a product like silver board with foil facing on one or both sides to help create an air barrier as well as a radiant barrier. Would a foil faced rigid insulation with spray foamed edges work well enough in this scenario? Is there an advantage to using insulation with foil facing on both sides? Any recommendations on foam type if this plan would work?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part