Troubleshooting Existing Design-Related Whole Building Performance Issues
Zonal/Zone Pressure Mapping
Zonal pressure testing is a critical part of locating the source of air leakage. While the house is under blower door pressure, we can see how much pressure relief happens in any room (or ‘zone’) when it’s closed or opened to the house. This tells us if the zone we are measuring is more inside or outside.
Every room of your home (including the attic, garage, and crawlspace) should be either 100% inside or 100% outside the enclosure based on its Zonal Pressure Proportion (ZPP). Anything in between shows an opportunity for improvement through pinpointed air sealing. If the attic shows a 60% ZPP before a much-needed air sealing of the attic floor plane, then the ZPP should be much closer to 100% after the improvement. If you air sealed and insulated between the attic and outdoors, it should have moved in the opposite direction- closer to 0% when completed.
Air leakage in buildings represents from 5% to 40% of the space-conditioning costs. Controlling air leakage is one of the most important functions of weatherization, and often the most difficult.
An air barrier is a building component designed to stop air leakage. The air barrier combined with the insulation defines the thermal boundary.
The main goals of air leakage control are to:
Protect insulation’s thermal integrity.
Reduce direct cooling or heating of people and building components by outdoor air.
Avoid moisture migration into building cavities.
Air sealing may provide these additional benefits:
Reduce vermin’s access to indoors.
Reduce flow of air pollution from external sources.
Reduce rainwater leakage.
Enhance fire safety.
Traditional thought was that existing buildings were relatively airtight, except for seams where building materials joined, especially around windows and doors. In the past, engineers tried to estimate air leakage based on the length and width of cracks between building materials. Estimating crack size was not accurate because it neglected major air leaks in hidden locations.
From 1975 to 1985, scientists and technicians developed and implemented instruments to assess air leakage, including blower doors, infra- red scanners, and tracer-gas analysis. With these developments, we now know that the building’s hidden air leaks are usually more important than seams between building materials. As a result, technicians have found new ways of finding and sealing these hidden air leakage pathways.
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