Q–I just had blown-in insulation put in my attic. My question is that I have a one-car attached garage and the installers didn’t insulate above that garage. There is no partition in the attic separating the living area of the house from the garage. In other words, they just stopped when they came to the garage.
Would it not be better to insulate the whole attic?
Sandy Szidik, via email
A–You’re fine as long as you’re not spending energy dollars to heat or cool the garage (more about that later), according to Paul Torcellini, a staff engineer with the National Renewable Energy Lab, which is run by the U.S. Department of Energy.
“There’s really no reason to insulate the crawlspace or attic space above a garage,” says Torcellini.
Attic insulation serves two purposes. The first is to prevent warm air in a heated space from rising up and escaping out through cracks in the ceiling. The second is to prevent cold air from infiltrating into the room when winter winds blow (attic insulation also helps keep an air-conditioned room cool).
Since there is no heat that you’re trying to contain in the garage, there’s no reason for insulation above. In other words, insulation over the garage is not going to help your living space inside the house stay and feel warmer.
However, it’s important that the insulation that was placed in your attic extend slightly over the garage space to make sure it’s protecting the room adjacent to the garage, says Torcellini.
And there are still steps you can take to make your living space more energy-efficient.
For example, if the wall between the garage and the adjacent room is hollow, you might consider filling that cavity with insulation to prevent heat loss and infiltration, just as you would with an outside wall.
Also, make sure that the door to the garage is a solid-core door and has a good door sweep on the bottom to keep the cold air out. You should consider it an exterior door not only from an energy-efficiency standpoint but also a safety standpoint.
Now, if you are heating and/or cooling your garage, you might want to consider insulating the attic space above. That will lessen heat loss. But the bigger issue there is the tremendous waste of energy in heating or cooling a garage. Insulating is not going to help much with recouping those large energy costs.
“Every time you open you garage door, you lose a tremendous amount of heating and energy dollars,” says Torcellini.
An option here is to stop heating and cooling the garage. If there is a register in your garage that is blowing heated air into it, the simple solution is to close it.
You might also want to consider insulating the attic above the garage if your furnace or boiler and water heater are located in the garage. But a more efficient step would be to build a closet around those appliances and insulate that to prevent the cold air from reaching those appliances, causing them to work harder.
