2″ or even 4″ of foam on exterior of garage/workshop in zone 7
I am just about to put siding on my 24 x 30 garage/workshop. It is 2 x 6 construction (16 centers) with R50 blown cellulose in the ceiling and R20 batts in the wall cavities.
I’m adding 4″ foam of exterior foam vertically along the 12 ” thickened edge slab below grade (as deep as 48″ if the rock below will allow… some places it will be closer to 24″) in an effort to keep the slab from robbing all the heat.
It has three windows (tri-pane double hung vinyl)..two on the east and one on the west, the man door is on the south side and two 7 x 9 insulated garage doors are on the north side.
It occurred to me that there is little if any insulation in the headers above the overhead doors and man door. Up till now it has been unheated…. I want to heat it to about 40-45f to keep my tools rust free continuously and bump it up to about 60f when I’m working (wood work) in the dead of a Canadian winter (zone 7 Kenora Ontario).
I have a lot of extra EPS foam and could if it makes sense either…
1-add 2″-4″ (or more) of foam to the INTERIOR of the walls over the OSB (interior of garage is OSB not drywall) to deal with these substantial thermal bridges or
2- using way more material add either 2″ or even 4″ of exterior foam to the entire garage before siding it. The problem here is I would have to furr out around the windows and doors to allow for the foam,,,essentially making them innies.
The building will be occupied about 10-20% of the time.
Option #1 is cheaper and easier…will it work in a garage?
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