Garage Insulation Calculator

Only the surfaces between the garage and heated space will — the wall shared with the house and the ceiling under living space. Those two are part of your building thermal envelope and code requires them to be insulated. The garage's own exterior walls, its door, and its slab are outside the envelope, so insulating them makes the garage more comfortable without changing your heating bill.

Not unless you heat it. A detached garage shares no envelope with the house, so insulating one you only park in will not produce a measurable saving. If you are turning it into a workshop or a gym, then it becomes worth doing — start with the ceiling, then seal the door.

On the common wall and on a ceiling below living space, yes. IRC Table R302.6 requires at least ½ inch gypsum board on the garage side of the shared wall, and ⅝ inch Type X where there are habitable rooms above. Insulating means removing that and re-installing it, so it is part of the job rather than an optional finish. A garage ceiling below an attic that connects to the house attic also needs ½ inch gypsum — a step commonly missed.

No. Kraft facing left visible fails the flame-spread limit in IRC R302.10.1, which explicitly includes facings. Foam plastic — rigid board or spray foam — needs a thermal barrier under R316.4. The relaxed ignition-barrier rule that applies in attics and crawl spaces does not reach a garage, because a garage is not a space entered only for repairs. Use unfaced batts and cover them.

For comfort and noise in a garage you heat, yes. As an energy investment, barely — published figures put the saving at a few dollars a year. Most of the loss around a garage door is air leaking past the perimeter and the section joints, not heat passing through the panels. Fit a bottom seal, side weatherstrip, and a threshold first; those cost $30 to $150 and do more than a panel kit will.

Partly. Manufacturers compute R-values at the center of a panel, and DASMA — the industry association that publishes the method — is explicit that this ignores joints, stiles, and weatherseals. One door advertised at R-12.76 measured R-7.83, with a certified U-factor implying about R-4.17. Expect roughly 30 to 60% of the published figure in practice, and prefer a tested U-factor where one is given.

Only with the right heater and a carbon monoxide alarm. Air sealing removes the leakage that was diluting exhaust fumes, so a tighter garage is more dangerous with a vehicle running, not less. Never use an unvented propane or kerosene heater in an enclosed garage — the CPSC attributes most LP-gas heating deaths to exactly that. A mini-split heat pump or a vented unit heater is the safe choice. If there is already a gas water heater or furnace in the garage, have its combustion air verified before you seal anything.