Basement air sealing

Basement and crawl space gaps, cracks and holes are often in close relationship with other openings in the upper parts of the house, and are a major cause of energy loss, in cold climates.

Basements and crawl spaces are also areas with dangerous pollutants – mold spores, radon and other gas and chemicals from insecticide treatment, and sealing possible leakage paths is the easiest way of preventing pollutants from entering the living areas.

Basement air sealing is critical for...
» lower energy bills.
» better indoor air quality
» solving moisture problems

Energy loss through the basement

In leaky homes, basements and crawlspaces are subject to positive and negative pressures alway, pushing air in and out of the home, in close relationship with attic and other air leaks in the upper parts of the house.

Hot air leaking into the attic and out of the house (in the winter) creates depressurization and suction points in the basement, which induces outside cold air to enter through gaps and openings in the basement…

And this is reversed in hot weather: hot air will leak into the house through gaps and cracks in the attic and the upper parts of the house, making cooler air to sink and to leave the building through openings in the basement.

Obviously, if there isn't any air leaks in the upper parts of the house, basement leaks will not have the same importance. But they still may interact with the living area, and be a cause of discomfort and problems - unless there is an effective and continuous air barrier between the living rooms and the basement.

Air sealing & Water sealing & Moisture

Any sealing job in your basement should be carried out in conjunction with other basement improvements, namely insulation and groundwater management and sealing; that’s important to also solve moisture problems.

Basement Air sealing materials

Basement air sealing materials
Foams and caulks
Polyethylene sheets
Rigid foam polystyrene

Besides the foams (or caulks) used to seal other parts of the house, consider also rigid foam polystyrene and polyethylene sheeting (and new products such as Tuff-poly and Tu-tuf…).

Polyethylene sheets are a strong air and water sealing material; they are commonly used to control ground basement moisture.

Rigid foam boards of extruded and expanded polystyrene are mostly used to insulate and air-seal the basement walls and the floors. Concrete slabs should be insulated with these materials. They are excellent to reduce heat loss in cold climates. Polystyrene provides both insulation and air-leakage control.

Basement Air leakage areas

Many basements have service penetrations (for telephone, electricity, TV, fuel, etc.) that should be carefully sealed, from the inside, the outside, or both…  Do not forget below-grade penetrations. They too should be sealed.

Areas to inspect and to seal
Service penetrations, sills and band joists, deck floors.

Consider also sealing the sills and band joists, and the floor deck between the basement and the first floor. Many floors have service penetrations, that should also be sealed, even when it is hard to access them. That’s very important to create an effective and continuous air barrier between the basement and the upper floors.




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