Testing for airtightness

After a lot of diligent work from the framing and carpentry crews, we’ve reached the point where the house is tight enough for a preliminary blower door test. The purpose of this test is to measure how airtight the home is.  See what does a blower door air leakage number mean?.  The energy code specifies no more than 3 air changes per hour when depressurized to 50 pascals – this is about the pressure that a 20 mph wind would exert on the house. This would be about the equivalent of an 18” x 18” open window in a house this size.  The more airtight the home, the better.  A few weeks ago the crew sealed up the few unfinished openings (door to the garage, the unfinished cupola) and then our LEED and HERS rater, Mark, set up the blower door apparatus in the front door.  Craig did the honors and fired up the fan.  We were all pleasantly surprised to get a much tighter house than code, on the order of 0.75 air changes per hour (ACH50)!

We’ll do another BDT after all the mechanical systems and the interior insulation is installed, but before we put up the drywall, so we can get a last chance to fix any air leaks.  Then of course we’ll need a final test when the house is complete in order to calculate our HERS rating and apply for our LEED and other certifications.  We are definitely on track to produce a tight and well-insulated home!  Congratulations to our crew for their careful attention to every seam, gap, and penetration.