Expert: Daniel G. Blum - 1/4/2008

Question
Good afternoon!
My wife and I recently purchased (like last week) a 1970 colonial style home which has an integral 2 car garage below the dining room and living room areas. The garage walls are block with the exception of the one wall that separates the garage from the 'finished' portion of the basement, which appears to be framed and insulated. The ceiling in the garage is open to joists and completely uninsulated.

Oddly, the garage is conditioned with 2 ducts, and heat flows quite well from them. (I assume because the gas furnace is only 10ft away on the other side of the wall in the basement).

Would there be any reason not to add insulation in between the joists in the ceiling? I'm thinking it would help to condition both garage and above finished areas more efficiently. Secondly- because there is finished space above, is it recommended to drywall the garage ceiling for safety issues? Drywall would be a tough adventure especially given the number of water and gas pipes that are attached to the joists (not tucked in).

Also- would there be any real benefit to frame up and insulate the garage walls, or would I be bumping up against diminishing returns? I'm going to eventually set up an area in the garage for a little workshop, but I figure a good set of insulated doors,draft remediation and insulation above will give me all the comfort I'll need.

Thanks.

Answer
Dear Tom,

Thanks for your question.

First, the garage should not be heated. Since yours is, I suggest you add a fire damper in the heating duct near where it passes into the garage. Fire dampers are extremely common in commercial and multifamily housing, but almost unheard of in single family homes. But any decent commercial mechanical contractor can put one in for you.

The garage should be totally separated from the living spaces above and on the adjoining sides with 5/8 inch thick drywall. The condition you describe is not considered fire safe or safe from carbon monoxide penetration, particularly if the garage is ever used for automobiles or other fuel burning devices. If it is just used as a work shop, there is little risk. You should install at least two carbon monoxide detectors, one for the garage and one for the adjacent living area. And there must NEVER be a return air duct from the garage back to the furnace.

If the garage is normally heated like any living space, there is no need or benefit to insulate the ceiling, other than sound insulation. That's because there is no heat flow between two rooms of the same temperature. It is not usual to drywall the walls facing the exterior, as long as you don't mind looking at the insulation. If the garage is heated, the exterior walls need to be insulated. Garage doors can be relatively airtight compared to models from years ago. You can technically insulate the overhead door sections with fiberglass board, but I have never seen it done.

The opposite approach is to insulate and drywall all areas between the garage and living spaces, then allow the garage to go cold when it is not in use by closing off the heating duct shutter, provided there are not pipes that could freeze. Then when you want to use the garage, open the vent an hour or two before you need to work in there. This approach makes the most sense if you only use the garage a few hours a week.

I hope that covers the range of your options.

-Daniel