I intend to insulate the ceiling of my "unheated" double-car garage that is attached to my new townhouse. I intend to put some bats or rolled insulation between the joists. Although the garage exterior walls are all well insulated, the metal door has minimal insulation so I don't expect to create a warm garage---just one a bit less cold. 1) How thick should the new insulation be for the effect I want? 2) Do I need any vapour barrier? 3) The soffits seem clear, so I wonder if there is any need for a roof vent?
Answer:
I wouldn't insulate the ceiling unless the garage will be heated because that can promoe more condensation followed by sagging ceiling drywall. Like any attic cavity, there should be ventilation at the top of the garage roof.
