ENVELOPE LEAKAGE TESTING
In the mid 2000‘s, when the California Energy Commission (CEC) did their own study of homes constructed to the strict national standards for energy efficiency (Energy Star), they unfortunately found that these homes were not performing as advertised. The lack of performance was linked to the unexpected and uncontrolled movement of air, from inside to out, robbing the home of its tempered comfortable air, causing more energy to be consumed in order to keep it comfortable. As a result, the CEC now requires Energy Efficient Designs to be field tested to determine the magnitude of leaks, confirming the performance assumptions made by the architect about the expected energy consumption of the building as evaluated through computer modeling.
The leakage rate of air is measured in cubic feet of air per minute (CFM) at air pressures similar to a 20 mile per hour wind speed, or as discussed in applied building science terms, 50 pascals. In addition to tempered air loss caused by wind, the internal stratification of air (low cold air and high hot air) caused air to exhaust out of a home. This is known as the stack effect. We have known of the discomforts caused by unwanted air leakage in homes through the urban legend of the “drafty victorian house”. Trying to make a drafty house comfortable takes much more energy, something Energy Efficient Design avoids.
The applied building science instrument used to measure envelope leakage is called a Blower Door, which depressurizes a house to 50 pascal and records the leakage rate. The Blower Door is used by Architects and HERS Raters to test newly constructed and existing homes. Home performance contractors use the Blower Door to test the home they are about to work on, and to monitor the quality of their construction.