Below is an exert from the book “How to Future Proof Your Home: A Guide to Building with Energy Intelligence in Cold Climates.”
Air leakage is the result of penetrations in the building not being perfectly sealed or construction assemblies not fitting perfectly together due to the nature of the materials, quality of workmanship or shifting of the assembly over time. Air leakage typically occurs around doors, windows, vents, electrical boxes and places where building materials don’t fit together properly. Often efficiency experts will demonstrate how to prevent air leakage by caulking or using spray foam around vents and windows. Doors and operational windows with leaks around the edges can usually be improved via the use of weather stripping.
Air leakage was traditionally of little concern and was even expected, as air leakage provided some ventilation to building occupants. Time and research have demonstrated, however, that air leakage can cause cold spots in wall cavities, which can lead to condensation collecting in these areas, particularly in cold climates. Over time, these areas of air leakage can become centers for mold to grow, which result in poor indoor air quality within the building and can even lead to the degradation of the wall itself. By some estimates, outside air leaking into the home, or air infiltration, is responsible for 40 percent of heating or cooling loss in the average home.
Today, rather than allowing air to leak through parts of a wall unimpeded, we take measures to prevent air leakage by means such as wrapping the wall with a membrane, or filling in voids using spray foam. In doing so, we are:
* improving the efficiency of the wall and hence improving thermal comfort;
* preventing cold spots and hence potential condensation zones; and
* saving money on energy costs.
Note that if a once leaky house is sealed to become air tight, a means of providing mechanical ventilation such as a heat recovery ventilator (HRV) should be added to ensure that air changes occur regularly within the home (to be discussed later). Regular air changes will protect the health of occupants by removing contaminants such as VOCs and mold spores while also preventing air from becoming stagnant and creating respiratory problems. Insufficient air movement within a building not only smells bad, but it can also eventually cause mold growth and will literally rot the house from the inside out. Insufficient ventilation was a problem when people first started building super-insulated houses and is likely the reason that high-efficiency envelopes didn’t catch on with more gusto.
Figure 4: Cold air will also cool the space and transfer into the interior space via small air leaks. This figure demonstrates how a slight air infiltration around the air conditioner can cool an entire area demonstrated by Spot 1 (Sp1). Spot 3 (Sp3) demonstrates the temperature of the insulated portion of the wall. This situation demonstrates how a simple cover for your air conditioner can prevent much heat loss and improve comfort.
To learn more about air leakage and how to prevent it, you can learn a lesson from Mr. Lahey of Trailer Park Boys fame: