Garage wall insulation
T1Speer
| Posted in General Questions on
I am insulating my detached garage. The garage wall studs are 2×6’s construction. I am using batt insulation and did not plan or need a full R19 in the walls. If I use a R15, 3 1/2 inch thick with a vapor barrier. Is acceptable and would I leave the air space since this insulation product will not fill the depth of the cavity on hot or cold side of the stud cavity? I live in the mid atlantic region of the US and plan only a low temp maintenance heating of the garage space.
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If you are using commodity fiberglass batts, the cost upgrade is so little that I'd suggest you consider upgrading to 5.5" thick R-19, since you are paying for heating the garage, presumably for decades. It might be an additional $100 in materials and negligible extra labor. Well-installed insulation in well-built walls lasts many decades, and may cut your wall's heat losses by about a third. Typically energy costs increase over longer time periods.
Typically commodity fiberglass batts are rated R-19 for 5.5 and R-11 for 3.5", unless they are different materials (e.g., Roxul ComfortBatt R-15 3.5" mineral wool), or unless you saw an "all wall" R-15 for 3.5" commodity fiberglass, but insulation-only R-19 for 5.5" batts.
I guess you plan to leave the airspace, next to the sheathing. There are issues with air current convection within the empty stud spaces next to sheathing that can increase heat losses. Putting the insulation deeper into the cavity to eliminate that air space is more work.
Are you covering the interior with drywall?