Why Bonus Rooms Over Garages Are Always Hot (and How Spray Foam Fixes Them)
Quick answer
Bonus rooms over garages are hot (and cold) because the garage ceiling below them is usually under-insulated and leaky. The fix is to air-seal and insulate the garage ceiling as a thermal break with closed-cell foam, isolating the room from the garage and the attic.
It's the classic Chattanooga complaint — one room over the garage never matches the rest of the house. Here is why and how to fix it.
Why that room is always wrong
A bonus room over a garage sits between two unconditioned spaces — the garage below and the attic knee-walls above. Standard batt insulation and leaky top plates let garage heat and attic heat pour in all summer.
How spray foam fixes it
Closed-cell foam on the garage ceiling underside and the knee walls air-seals and insulates that boundary as a real thermal break, isolating the bonus room from the garage and the attic.
- ✓Closed-cell foam on the garage ceiling underside
- ✓Knee-wall and roofline foam around the room
- ✓Top-plate and penetration air sealing
- ✓The room matches the rest of the house within a season
Frequently asked questions
- Will it also help in winter?
- Yes — the same thermal break that keeps garage heat out in summer keeps the cold garage air out in winter.
- Do I need to remove the existing batt?
- Usually yes, so the foam bonds to the framing and we don't trap moisture; we evaluate on site.