I’m starting a project to renovate my garage and convert it into a livable room or play area.
I’m in Québec in a house built in the early 1970s, and that space is very poorly insulated so it gets very cold. It’s inside the envelope of the house, so it really hurts my heating bill and makes everything less comfortable.
Among the projects is to replace the single pane window, as well as replace the garage door with a well insulated framed wall with a window and exterior door.
But step 1 is to replace the outdoor wall. It was installed very badly. It’s got 2x3s nailed directly to the bare concrete, with sheets of white styrofoam in between. No vapor barrier. Then straight to drywall.
As you can see I’ve ripped out most of the insulation. But before ripping out the 2×3, I was wondering. Do I gain anything by keeping the lumber and putting in a solid wall of foamboard on top of it? I know I’m going to lose 1.5 inches of room size, but do I gain a significant amount of R value by having an airgap?
Obviously doubling up on insulation is good, but are they diminishing returns?