Air Leaks in Your Basement? How to Find and Seal Them
Polyurethane foam in a can is ideal for plugging openings 1/4-inch to 2 inches wide, check for them around pipes and vents that pass through basement walls to the outside.
A standard 12-ounce can sprayed in place will slowly expand 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.
Plug small gaps in basement walls
Caulk is generally best for the smaller gaps, such as those cut around electrical boxes. Silicone costs the most and works well when sealing nonporous materials, such as metal flashing. Acrylic 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 its 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.