Locating Air Leaks 10 - Sealing Basement Leaks Locating Air Leaks 10 - Sealing Basement Leaks

Stopping the Chimney Effect

Outside air drawn in through basement leaks is exacerbated by the chimney effect created by leaks in the attic. As hot air generated by the furnace rises up through the house and into the attic through leaks, cold outside air gets drawn in through basement leaks to replace the displaced air. This makes a home feel drafty and contributes to higher energy bills. After sealing attic air leaks, complete the job by sealing basement leaks, and stop the chimney effect.

Locating Basment Air Leaks

A common area of air leakage in the basement is along the top of the basement wall where the cement or block comes in contact with the wood frame. These leaks can easily be fixed in portions of the basement that are unfinished. Since the top of the wall is above ground, outside air can be drawn in through cracks and gaps where the house framing sits on top of the foundation. This perimeter framing is called the rim (or band) joist. In the basement, the above floor joists end at the rim joist creating multiple cavities along the length of the wall, and many opportunities for leakage.

Materials Checklist for Basement Sealing

  • Silicone or acrylic latex caulk and caulk gun
  • Expanding spray foam

Seal All Seams in the Rim Joist Area

Though you may not be able to see cracks in the rim joist cavities, it is best to seal up the top and bottom of the inside of the cavity. Also, rim joist air sealing is especially important at "bump out" areas such as bay windows that hang off the foundation. These areas provide greater opportunities for air leakage and heat loss. Caulk is best for sealing gaps or cracks that are 1/4 inch or less. Use spray foam to fill gaps from 1/4 inch to about 3 inches. We also recommend you seal penetrations that go through the basement ceiling to the floor above. Generally these are plumbing vent stacks and furnace pipes.

Areas to Foam or Caulk

  • Along the gap between the sill plate and the foundation.
  • At the bottom and top of the long rim joist on each end of the house.
  • The top and bottom of the rim joist in each cavity.
  • All electrical, water or gas penetrations and any venting ducts that pass to the outside.

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