A couple of weeks ago we had our first blower door test. A blower door test tests air leakage in a building. This test, the first of several we expect, was meant to see how tight the frame of the house is.
|The builder next to the blower door|
Since the windows and doors haven’t been installed, window and door openings were all sealed, either with house siding (i.e. they haven’t been cut out yet) or taped shut with plastic. A special blower was placed in the front door. First, the blower pulled air out from the house, depressurizing it to 50 pascals. Air pressure inside the house was less than air pressure outside causing air outside to be sucked into the house. A meter then measured how much air entered the building.
The passive house standard requires that air leakage in a building be limited to 0.6 ACH (air change per hour) at 50 pascals. This means that when the house is pressurized to 50 pascals pressure differential between inside and outside, 0.6 of the volume in the house will leak in or out each hour. For a house the size of ours we were looking for a reading of 350 (not sure what units) from the meter to meet the Passive House standard. The meter reading was 220 or less than 2/3 of the Passive House threshold.
For comparison, our builder told us he performed the blower door test on his own home, a typical leaky home, and got a meter reading of 4000. At another client’s home where they took a leaky home and did some energy efficiency work, the meter reading after the energy efficiency work was 1900. This illustrates that it’s much easier to build a house that’s air tight than it is to take a leaky house and make it air tight.
Air leakage is measured when a building is pressurized because it’s much more difficult to measure under normal conditions. The pressurized readings can then be mathematically converted to normal condition readings (by dividing by 16 or 17). The Passive House standard of 0.6 ACH at 50 pascals converts to about 0.035 ACH without a pressure differential. This means that under normal conditions only 3.5% of the air volume in a house will leak out per hour. Compare this to our builder’s leaky home where more than 50% of the volume of air will leak every hour. Much of the energy that a building loses is through air leakage. We can see here that our house will lose a small fraction of the energy that a typical leaky house loses. This is a clear example of how putting a little thought and energy into the early stages of construction can make a home much more energy efficient without a big expense.
|Fogging the seams inside the building|
After the air leakage readings were taken, the builder broke out a fog machine. This time, the blower door fan was reversed to pull air into the building and create higher pressure inside. Fog was blown against all the seams inside the building while the framing crew looked for escaping fog outside the building. The few areas where leakage was found were marked and sealed with silicon or tape.
Here's a quick video showing the fogging from outside the building:
The next blower door test will probably take place after the windows and doors have been installed.