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Chapter 1
Introduction
The next most important location of leaks is in the lowest part of the building. The bottom of the building is
subject to the largest negative pressures, which induces cold air infiltration. Importantly, if spillage prone natural
draft combustion appliances are present, do not seal lower level building leaks unless you have first addressed
leaks in the attic or top part of the building. Sealing only lower level leakage areas while leaving large high level
leaks could create large enough negative pressures to cause combustion appliance backdrafting.
Figure 3: Common Air Leakage Sites
In addition to these common leakage sites, there can also be large leakage paths associated with hidden
construction details such as attached porches, cantilevered floors and overhangs. Figures 4 - 6 show a number
of potentially important leakage paths which are often overlooked by crews using traditional weatherization
techniques. Use of densely blown cellulose insulation or other barrier-type air sealing techniques at these key
junctures often result in dramatic air leakage reductions.
Figure 4: Hidden Construction Details
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