How to Insulate a Garage

If the garage is attached, the wall and ceiling between garage and living space matter most. Insulate them to the same standard as an exterior wall (R-13 to R-21) and air seal every penetration — this also slows exhaust fumes entering the house.

A room above the garage needs R-30 to R-38 in the floor cavity, with the insulation held tight to the subfloor and the perimeter fully sealed. Cold floors above garages are almost always an air sealing failure, not an R-value failure.

An uninsulated steel door is roughly R-2 over a large area. A rigid foam kit brings a typical door to R-6 to R-9 for $80–$200 and takes an afternoon. Add new bottom weatherstripping and perimeter seals at the same time — the gaps leak more than the panels.

Unfinished stud bays take standard batts. If you plan to hang tools or sheet goods on the walls, cover with drywall or OSB rather than leaving the facing exposed — exposed kraft facing is a fire hazard and code violation in most areas.

In a detached shop, insulate the ceiling first: heat rises and the roof plane is the biggest loss surface.

Insulating alone will not make a garage warm; it just makes heating cheap. A small mini-split or a vented heater plus R-13 walls and R-30 ceiling turns most garages into usable year-round shops. Keep a floor drain or fan for melting-snow moisture.