Photo by Intiaz Rahim
Q: I’ve heard that energy can be lost through my home’s basement. Is that true? If so, what can I do to make my basement more efficient?
A: Yes, basements and crawl spaces can account for a large portion of your home’s energy use, and there are several ways to improve their overall efficiency.
Moisture is a common problem in basements and crawl spaces and can lead to mold, rot and lowered effectiveness of insulation. It’s a good idea to solve moisture problems before you make efficiency improvements. Look carefully for signs of water damage or moisture buildup, such as rotting wood, mold, a stain on a wall or floor or a musty smell. Search online for “test basement walls for moisture” and you’ll find a simple test you can conduct yourself. Crawl spaces can be muddy or even have standing water in them if gutters or the slope of the landscaping drains in the wrong direction. Once drainage problems are solved, the crawl space should have a ground vapor barrier.
If you have a forced-air heating system, carefully inspect the ductwork running through the basement or crawl space. Unless you’re in a newer home or the ductwork has been tested and sealed in the last decade, your system is likely leaking. Sealing these leaks helps your system distribute air more efficiently and should make your home more comfortable. The best way to seal ducts is with duct mastic. Metallic tape is the next best solution, but do not use duct tape. An energy auditor or HVAC professional can test your home’s ductwork and identify the best solutions.
You’ll find lots of air leaks in basements and crawl spaces, particularly where pipes and wires enter or exit the space. Air often enters the home around the sill plate, which sits on top of the foundation. If you can get to the sill plate, apply caulk around it. You can also increase efficiency by sealing any gaps or leaks around basement windows.
Insulation is an effective tool for reducing energy use and improving comfort, but the applications are quite different in basements and crawl spaces. In both cases, the insulation strategy and the installation must be done correctly to prevent mold or exacerbate moisture problems.
The place to begin in basements is the rim joist, which is right above the sill plate on top of the foundation wall. Rigid foam board can be carefully fitted between the joists.
Insulated basement walls make the room more comfortable. If you’re building a new home, there are advantages to insulating the outside of the foundation wall, but this isn’t practical for most existing homes. You can insulate the inside of the foundation wall if you’re sure moisture is not leaking through the wall from the outside. Experts do not recommend fiberglass insulation in contact with the foundation, which was a common practice for decades. Instead, they prefer sprayed-on foam or rigid foam board applied directly to the foundation wall. A wood-framed wall can be butted up against the rigid foam and insulated with fiberglass or mineral wool batts. The bottom plate of the wall, which sits on the concrete floor, should be pressure-treated wood.
There are two ways to insulate crawl spaces. The most common approach is to insulate under the floor with fiberglass batts. This allows the crawl space to be vented to the outside, which alleviates any moisture buildup. If all the right moisture control and drainage steps have been taken, the crawl space can be unventilated, and the insulation can be applied to the foundation walls instead of underneath the floor. That said, there are pros and cons to this strategy, so consult with a local expert.
Send questions to Energy Q&A, South Carolina Living, 808 Knox Abbott Drive, Cayce, SC 29033, or email energyqa@scliving.coop.