Monday, June 22, 2015

Foam v. Fiberglass: Basement Box Sills

Basement box sills can be significant areas for energy loss in any home. Located where the basement ceiling joists (those that support the first floor of the house) meet the exterior foundation walls of the home, leaky box sills can be a significant source of energy inefficiency in a structure, allowing for outside air infiltration.

Traditionally, these areas have been insulated with fiberglass batts. This practice creates a poor thermal barrier from outside temperatures and does nothing to prevent cold air infiltration. Using closed cell spray foam provides both insulation and air sealing and has become the new standard for modern, efficient homes.

The photos to the right provide a thermal image of the underlying result of using just fiberglass batting in the box sill – air leakage around flows right through the batting and continues to impact basement temperatures. This is also known as "replacement air" because warm air leaking up and out the top floor is typically replaced from this area. Energy auditing tools, like an infrared camera or blower door test, discovered this problem years ago and are used more and more to identify leaky box sills in homes today.  

Contact us to learn about this and other places your home will benefit from by having an energy audit done. 



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