Certifying a Passive House is not a one-way process. The Passive House Institute US works with builders to make sure their plans are on track to meet Passive House requirements. One step in that process is review of our Passive House Planning Package energy modeling - the software calculation of how much energy the house will use.
We recently heard back from PHIUS, and aside from a few minor corrections they said that things were very well done. This means we are on track to achieve Passive House Certification, pending final testing and submission of supporting construction documentation.
To further ensure that we will pass all the final tests, we performed a diagnostic air tightness check before the foam and insulation were installed. Andrew Morphis with Green Hammer Construction out of Portland volunteered their blower door services to identify and locate any remaining points of air leakage in the exterior envelope while the primary air barrier (exterior sheathing) was still exposed. The blower door was ultimately cranked up to a 100 Pascal pressure differential while the interior was heated with a temporary heat source, and we toured the house with a infrared gun to spot areas where cold air was seeping in. There was very little to find aside from a door that had two corners where the weatherstripping was creased.
The standard we are tying to meet here is no more than 0.6 air changes per hour at a 50 Pascal pressure differential (0.6 ACH 50). This means that only 60% of the entire volume of air in the house will be exchanged with outside air over the course of an hour. If this seems like a lot of air movement, consider that the house is depressurized, which greatly accelerates the transfer. A typical new house is easily ten times leakier. We tried to generate an actual ACH 50 number, but Andrew did not have a small enough ring to get an accurate result. The leakage was so low that a smaller ring will have to be implemented for the final blower door test. We are confident that at least 0.6 ACH 50 will be met in the final test based on our initial testing.
Many thanks to Andrew Morphis and Green Hammer Construction for donating their time and expertise, and to builder Blake Bilyeu for helping me (hopefully) get the details straight!