It’s hard to believe that a blower door test could feel…if not routine, than not like a really big deal on just our third Passive project. I mean, that 0.6ACH50 target we learned about in Certified Passive House Consultant sounded so difficult– more than ten times tighter than code-required!!–but, it turns out, with a builder like Evolutionary Home Builders and a sound airtightness strategy, it requires rigor but is predictably achievable. So for this blower door test, our rater, Jason LaFleur of EcoAchievers, suggested we put the call out to our Passive House Alliance (Chicago chapter) and USGBC-IL to see who would like to come witness it. And we had a great turnout!
So, what does that reading of 129cfm mean? Fundamentally, when Lindsey started the fan, she depressurized the house–sucking air out out it–so the leakage rate is telling us, when we get the pressure to the 50 Pascals baseline, that the sum of all leaks we have in the building envelope–all the windows, doors, plumbing and electrical penetrations, etc.–only allow 129 cfm to flow through them.
We calculate Air Changes per hour (that’s the ACH) by multiplying our cfm reading by 60 to get cubic feet per hour, then dividing that by the house volume (18,991 cu. ft.) to get 0.41ACH50. Comfortably below the “old” 0.6ACH50 requirement. But with PHIUS+ we have a new way of expressing leakage, which is cfm of leakage per square foot of thermal envelope area. Simpler calculation: 129cfm/5664s.f. = 0.023. The PHIUS+ requirement is 0.05, so we’re less than half of that–a very good result. Bravo Evolutionary Home Builders, and thanks to EcoAchievers for the testing!