Q: The wall and blown-in attic insulation in my fairly new house are at recommended levels, but my utility bills are still too high. What other areas should I check for inefficiency?
A: You are correct that the walls and ceiling are the areas of the greatest heat loss from a house—proper insulation in those areas is of utmost importance. But it’s also possible that many other areas in the exterior “thermal envelope” of your house have insulation voids or air leakage which can contribute to unnecessarily high utility bills.
First, check your walls and attic. As your house is “fairly new,” you can probably rest easy that the walls are adequately insulated, most likely with faced batts that fit tightly between wall studs. “Facing” refers to a material that acts as a vapor barrier.
Attic insulation – Since you have blown-in attic insulation, check its depth. Depending on how it was blown in, it may have settled and no longer reaches the required depth and R-value for your climate. Also, using a rake, make sure it’s level across the attic floor. Wind coming in the attic vents can blow it around, creating high and low spots.
Wall Outlets – Where there’s a break in the thermal envelope of your home, there’s potential for energy loss. One common spot is electrical wall outlets and switches on outside walls. Often, they are completely uninsulated and the vapor/air barrier is not taped tightly to them.
Switch off the circuit breaker to these outlets and switches. Remove the faceplate. If you can get the tube from the urethane foam spray can into the wall around the conduit box, shoot some expanding foam in there. This should fill insulation voids and seal it.
Even if you were able to shoot in insulation, and definitely if you could not, install foam draft sealers behind the faceplates. They add only a slight amount of insulation, but they will improve the overall seal to reduce air infiltration.
Recessed ceiling lights are another typical area of energy loss. These are particularly bad because they get hot, which creates a natural upward draft. The most efficient option is to replace your old canister recessed lights with new, efficient sealed models.
Don’t just pour or pack insulation against recessed lights in the attic. This can cause older styles, which were not designed to be insulated, to overheat. You can caulk around the hole in the attic floor and the canister, but some room air will still leak out through the canister itself.
Ceiling paddle fans are another place to check. If you installed them yourself after the house was built and added support blocking, the insulation level will be less there. There may also be air leakage where you cut the hole to run the wiring. Push the insulation away and caulk the attic floor hole around the wire, then cover it with additional insulation.
Door and window frames – Next time you are painting the trim around doors and windows, pry off the decorative molding. You may find quite a large uninsulated gap between the rough opening and the door or window frame. Apply low-expansion foam in the gap—but use it sparingly because it can deform the frame as it expands.
Sill plates and rim joists – The sill plate is the piece of lumber that rests on the top of the foundation. The rim joist rests on top of the sill plate, and your house walls rest on the rim joist. The rim joist, often 2 x 10 feet or larger lumber, typically is not insulated.
Buy kraft paper-faced fiberglass batt insulation and cut it into short lengths to fit against the rim joist between the floor joist. Standard wall insulation batts are effective. With their short length and the floor joists, they should stay in place without stapling.
Foundation wall interface – While you are looking at the rim joist and sill plate, you will probably see a gap between the top of the foundation and the sill plate in spots. The top of a concrete foundation wall is seldom perfectly level and smooth. Apply urethane foam insulation from a can all along the sill plate/foundation wall interface. This will block outdoor air leakage and add some insulation value to that area.
If you have a question for Jim, please email firstname.lastname@example.org, or mail to James Dulley, Michigan Country Lines, 2859 W. Jolly Rd., Okemos, MI 48864. Be sure to let us know which electric co-op you receive service from. Visit dulley.com for more home improvement and do-it-yourself tips.