The Room That Never
Matches The Thermostat

Because the floor is doing the job of an exterior wall and was never built like one. The Department of Energy’s Building America guidance explains it: when the floor insulation is not in contact with the subfloor, the gap lets air move, pulling heat out of the floor system and robbing the insulation of its effectiveness. Most bonus-room floors were insulated with batts that sagged into exactly that gap.

The room loses heat through five cold surfaces, the floor over the garage and the exterior walls and ceiling, faster than one or two registers at the end of the duct run can replace it. Sealing and insulating the floor cavity changes the loss; a bigger furnace just changes the bill.

Building America’s standard, which we follow: the insulation has to be fully aligned with the air barrier, in full contact with the subfloor above, with no gaps. In practice that means opening the garage ceiling, sealing every seam and hole in the subfloor, sealing the rim joists and the garage wall top plates, and installing insulation that stays pressed against the subfloor, usually dense-pack or spray foam rather than batts.

Sometimes we can dense-pack the cavity through holes drilled in the garage ceiling and patch them. When the cavity has ducts, wiring, or sagging batts that have to come out, the drywall comes down in that area and goes back up afterward. We tell you which before quoting.

A bonus room with sloped ceilings usually has short knee walls with an unconditioned attic space behind them. Those walls need an air barrier on the attic side and insulation in contact with it, plus a sealed floor between the knee wall and the eave, or cold attic air runs under the room’s floor. We treat the knee walls and the floor as one system.

A section of floor that extends past the foundation or the wall below it, common in two-story Front Range plans. The underside is exposed to outdoor air and the cavity connects to the house floor system. Without a sealed air barrier at the exposed end and insulation against the subfloor, the whole floor along that wall runs cold.

Yes. A leaky floor over the garage pulls garage air into the room above it, which can include exhaust and anything stored down there. Sealing the subfloor seams, the rim joist, and the top plates is both a comfort fix and the reason the code treats the garage-to-house boundary as an air barrier.

It usually is now, for the same reason: the floor and the knee-wall attic bake all afternoon and push heat in. The same sealing and insulation that holds heat in during January keeps it out in July.

One day for most bonus-room floors done from the garage, two when knee walls and a cantilever are part of it or the ceiling has to come down. We blower door test before and after so you can see the change.

Floor and wall insulation and air sealing qualify under Efficiency Works and Xcel programs depending on your utility. We confirm which applies to your address and file it.