The cold bedroom over the garage
A room above a garage is cold for a simple reason: its floor is the garage ceiling, and the garage is nearly outside. Batts stuffed between the joists sag away from the subfloor over time, leaving a gap where cold air moves under the floor. The thermostat in the hallway never sees it, so the furnace does not respond.
Foam sprayed to the underside of the subfloor, between the joists, stays in contact with the floor and seals the rim where the joists meet the outside wall. The ceiling drywall comes down, the foam goes in, and the drywall goes back. The floor upstairs stops being the coldest surface in the house.
Framed walls and metal walls take different foam
A stick-framed garage or shop gets treated like a house: open-cell foam fills the stud bays, or closed-cell where the wall is thin or likely to see water, and the top plates and penetrations get sealed on the way. If the walls are already drywalled, we talk about whether opening them is worth it or whether the attic and the shared wall do most of the job.
A metal shop is a different animal. The walls are a single sheet of steel on purlins, with nothing to fill, so closed-cell foam is sprayed straight onto the inside of the panels. It bonds to the steel, seals every lap and fastener hole, and keeps the panel warm enough that indoor moisture stops condensing on it, which is why metal shops drip in October.
Ceiling or roof deck
Where a garage has a flat ceiling with an attic above, the attic floor is usually the place to insulate, the same as the house. Where the shop is open to the rafters or the metal roof panels, the foam goes up on the roof from inside, which brings the whole volume inside the insulated shell and matters if you heat the shop or run a mini-split.
If the shop will never be heated or cooled, say so. Foam on the roof panels still earns its keep by stopping the drip and the summer radiant heat, but the thickness and the areas we recommend change when comfort is not the goal. The estimate is written for how you use the building.
The overhead door and the slab
No amount of foam on the walls fixes a door that leaks around all four edges. An insulated door with a good bottom seal and side weatherstripping is a door company’s job, not ours, and it is worth doing alongside the insulation. The man door and any windows get the same attention.
The slab stays uninsulated in nearly every garage and shop, and that is fine; the floor is a small part of the heat loss. What we do see at the slab is settling: a garage floor that has dropped at the overhead door or cracked across the middle, which is a lifting job we can look at on the same visit.
- Insulated overhead door with bottom and side seals
- Weatherstripped man door and sealed windows
- Sealed openings around pipes, wiring and the flue
- A floor that has settled at the door, which is a lift
Covering the foam and what to send us
Spray foam inside an attached garage normally has to be covered, by drywall or by a coating applied over the foam, and the same can apply in a shop depending on its use. The estimate names which one your building needs. Foam left exposed in a finished garage is not something we leave behind.
Before the visit, send photos of the shared wall, the ceiling, the overhead door and a corner where wall meets roof, plus the approximate dimensions and whether it is framed or steel. Say what the space is for: parking, a heated shop, a gym, storage. That decides the foam, the thickness and the covering.
In short
- The wall and ceiling an attached garage shares with the house come first; they leak garage air indoors.
- A cold room over the garage is fixed from below, with foam held tight to the subfloor between the joists.
- Framed walls take foam in the stud bays; metal walls take closed-cell sprayed onto the panels.
- Insulate the attic floor over a flat garage ceiling, or the roof from inside a shop open to the rafters.
- The overhead door is a door company’s job, a settled floor is a lift, and garage foam usually gets covered.