Do I need to insulate exposed foundation in my garage?

Question

I have a 2 story split-foyer ranch. The bedrooms upstairs are above the garage and noticeably colder than the rest of the house (I live in Connecticut so winters get pretty cold).

There's no climate control in the garage, and the garage is partially underground on one side and entirely underground on the other (house is built into a hill). The foundation is exposed on both sides, bare concrete probably 4 feet high and sticking into the garage about 1-2 feet.

The garage doors are insulated and weather sealed, and I have two windows on the side of the garage that's partially above ground. The ceiling is finished so I can't see what kind of insulation we have between the garage and the floors above. I do know that sound doesn't carry very well, except for things hitting the surface (or vibrating like the garage door opener).

Obviously it'll be colder in the garage than in the house, but I'm looking for ways to keep it a little warmer than it is now. I'm wondering if it would be worthwhile to put insulation on the exposed foundation. I suspect not, since the cement floor of the garage will also be pulling heat out.

Any other suggestions for quick things to check for heat loss from a garage?

Answer 1

Rooms above garages are often done improperly. It's amazing, because it really isn't all that difficult, but a lot of people seem to mess it up.

Unfortunately, there's no "easy" way: You're going to have to remove some drywall to inspect and see how the insulation in the ceiling is done. There may or may not be a gap in the space, depending on how the ceiling was done. Even just taking the temperature above the insulation in that space will tell you a lot (above the insulation, it should be close to room temperature).

Drafts in that space are absolutely killer, it means there is a direct source of outside air. Black on the insulation is a good sign of airflow, indicating drafts.

Basically, if the ceiling space isn't totally sealed, the only thing you can do is turn the garage into a conditioned space (very expensive, in terms of both construction costs and ongoing energy costs), and even then, if the problem is between the insulation and sub-floor, it won't help.

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What should be there at a minimum is a continuous vapour barrier, with a layer of insulation on top. The vapour barrier should be sealed to the subfloor or the vapour barrier from the walls above. The insulation should go all the way around the edge (in the headers), so the insulation is continuous from the floors up to the subfloor. There should absolutely be no drafts, exposed concrete, or anything directly connected to the outside that is uninsulated.

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The best way (in my opinion) to seal this space is to use closed-cell spray foam, and form a continuous seal across the bottom of the entire subfloor. This gives you great insulation, no drafts, and acts as a vapour barrier as well (vapour barrier is not needed in this case -- though some building inspectors still don't understand this, so check your local codes). It also is better at ensuring fumes from vehicles in the garage can't get into your living space (in theory, vapour barrier prevents this as well, but 6mil vapour barrier is easier to puncture than a couple inches of hardened foam).

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Though you may be able to find something obvious and fix it, be prepared that there's a possibility that the only "fix" is going to be to completely tear down the ceiling of the garage and re-do it properly.

If you're going to spend money and time on this, do it right.

Answer 2

Installing foam is expensive and its success relies on the skill of the installer. If the day or the surface that will accept the foam is too cold, the foam will not stick. Google foam problems or similar to see the horror stories. A cheaper, better DIY result, a job that you can start, stop and come back to, as you wish, is to install sheet polystyrene. A one inch layer of polystyrene can be cut with a knife as a tight push fit between the joists, this will save about 90% of the heat lost through your floor. If you a really keen and want the best insulation, fill the spaces between the joists with sheet polystyrene, then fix another layer 3 inches thick below the joists to stop your heat leaking downwards through the wood of the joists. Cover this with two layers of drywall, this will give you a 60 minute fire wall.