Air Leaks in Your Basement? How to Spot and Seal Them

Seal air leaks in your basement to stop the loss of your home heating energy.

A typical family spends about a third of its annual heating and cooling budget — roughly $300 — on air that leaks into or out of the house through unintended gaps and cracks. With the money you waste in just one year, you can plug many of those leaks yourself.

Don’t overlook your basement as a source of air leaks. Cold air can enter your basement through air leaks that are both above and below ground. Air infiltrating your basement can be sucked into your upstairs rooms, causing your furnace to work harder than it should. The remedy is to look for air leaks in your basement and seal them.

Plug Large Gaps in Basement Walls

Low-expansion polyurethane foam in a can ($10) is ideal for plugging openings 1/4-inch to 2 inches wide, such as those around plumbing pipes and vents that pass through basement walls to the outside. 

A standard 12-ounce can ($5) is good for 250 feet of bead about half an inch thick. After application, the foam slowly expands to about twice its size, making it a good choice for large cracks. After it dries, cut off excess foam with a utility knife or putty knife.

The plastic straw applicator seals shut within two hours of the first use, so to get the most mileage out of a can, squirt a lubricant such as WD-40 onto a pipe cleaner and stuff that into the applicator tube between uses.

Related: Plumbing Leaks: 8 Smart Tips to Stop Them

Plug Small Gaps in Basement Walls

Caulk makes the best gap-filler for openings less than 1/4-inch wide, such as those cut around electrical boxes. Silicone costs the most (about $8 a tube) and works well when sealing nonporous materials, such as metal flashing. Acrylic latex caulk ($2 to $4 a tube) is less messy to work with and cleans up with water. Use high-temperature caulk around vent pipes that get hot, such as those for the furnace or water heater.

Seal Air Leaks Where Foundation Meets the Wall

In most older houses with basements, air seeps in where the house framing sits on the foundation. Spread a bead of caulk between the foundation and the sill plate (the wood immediately above the foundation), and along the top and bottom edges of the rim joist—the outermost piece of framing material that runs along the top of the sill plate.

Related: How Much Does It Cost to Fix Foundation Problems?

Jeanne Huber

Jeanne Huber is the author of 10 books about home improvement. She writes a weekly column about home care for the Washington Post.