Insulating room above a garage..

4 years ago

Hi hive mind! Like so many, I have a bonus room above a garage that is difficult to manage the temperature on. We had professionals install spray foam insulation on the knee walls and add a vapor barrier, but that doesn't seem to have done the trick.

We believe cold air is getting in from the garage below, but have no idea if that's accurate and have heard mixed reviews about the success of blind blowing loose insulation, and don't have the stomach for *another* $5k+ project to tear out the garage ceiling drywall, insulate, and replace...... I've also read this can have mixed results because there is so much space between the subfloor and the ceiling of the garage (in the case of blow in).

So that got me thinking -- Also on our list *happens* to be replacing the carpet in that room, which made me wonder - is there an underlayment (above subfloor) that is insulating? So it would be subfloor (as is) + thermal insulating underlayment + carpet pad + carpet. Has anyone tried this?

I've been doing some googling, and there are rubber/polymer soundproofing solutions hotels use but haven't been thermally rated, and cork seems to be as good if not better than loose cellulose (though obviously it wouldn't be inches of the material - maybe 6mm or below). So thought I'd reach out. Anyone a solution they believe in or have ideas I should look into that will help us insulate the bedroom's floor (ceiling of garage) without having to pull up the subfloor or remove the drywall? I'm all ears! Thank you!

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Comments (5)

sktn77a
4 years ago
Yes, I think a suitable carpet underlayment would help. Do you have the option of adding another HVAC supply and/or return to the bonus room, too?
irol96
Original Author
4 years ago
Thank you! We've had a few people check out the supply/return and say what we have is adequate. We may have a culprit of needing more HVAC wrap insulation on the ducts but they think the return/supply situation is surprisingly accurate.
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mike_home
4 years ago
Like so many, I have a bonus room above a garage that is difficult to manage the temperature on.

This is a common problem when a room is isolated from the main part of the house and their is a single zone. The bonus room gets hotter in the summer and colder in the winter than the rest of the house. You can spend money on improving the insulation. Bit it is not a guarantee you will be able to manage the temperature as well as you would like.

The alternative solution is to install a separate heating and cooling system. It can simple and inexpensive as an electric space heater and a window air conditioner, or more elaborate as a mini split heat pump. You have to decide how much money you want to invest to make the room more comfortable.
PRO
G & S Floor Service
4 years ago
A good moisture barrier should help. You can apply one or two coats of poly or epoxy based moisture barriers to help reduce with vapor transfer. You can then install your underlayments over it. If, you do cork, use 3mm cork incase you want to replace your carpet with wood later on in the future.
PRO
Charles Ross Homes
4 years ago
Living areas above garages are indeed more difficult to condition because they are typically constructed over unconditioned garage bays and have sloped ceiling areas which limit insulation options.

On a retrofit basis, you can use injection foam in the joist bays without the need to tear out the drywall. I suspect your rim joist is poorly air sealed, so insulating that area would be a priority. You indicated that you have spray foam in the knee walls, but if there are other walls which have batt insulation, make sure they have an air barrier on the back side (plywood, OSB sheathing or house wrap.) Fiberglass batts don't work well unless air can be trapped in the stud or joist cavity.

You'll be more comfortable if you have either a HVAC unit dedicated to the space (mini splits tend to work well in this application) or a multi-zoned central system with the room over the garage controlled by a separate thermostat.