DEAR CORBETT: Multifamily Blower Door Testing Nuances

Good day Corbett,

I wanted to let you know, that I really enjoy your approach to the whole building science and your building performance workshop website. I am relatively new as a Resnet Rater and the county where I live is Collier County in Florida.

They recently adopted the new code standard set by the state. My question relates to multifamily condo units. I have a client that did renovations to a 2,500 sq. ft. penthouse condo and the front door to the unit is I a common area. The county wants them to perform a blower door test in order to obtain their certificate of occupancy.

I realize this would be a compartmentalize test, since I can only have access to the unit they renovated for their client. Knowing that I will encounter not only leakage to outside but also internal leakage between units. I was wondering what the best approach would be to ensure a successful test. Collier County requires between 3 ach and 7 ach for a test to pass code.

Any information would be appreciated. Thanking you in advance.

Best Regards,
Norm Giguere
www.blowerdoorenergyexperts.com

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Dear Norm-

Thanks for your question, it's a good one! First off, you should be fine if they did a good job with the renovations- 7 ACH50 is not terribly hard to achieve.

When you set up your blower door at the front door of the condo, you'll blow air out into the common hallway, so you want to make sure all possible windows/doors in that hallway are open to the outdoors. Use the emergency exits if necessary (make sure maintenance knows what you're up to).

You'll be testing the condo's leakage to everything outside of it, including the downstairs unit, but that's intended. They really will have air leaking between the two condos, if there are leakage pathways, and you want to be testing for that and including it in your blower door test result.

Ask your code official if they want the result to pass the residential code or commercial code, because you have to test at 75 Pa in commercial. I always advise doing a multipoint test (get the flows on at least two pressures, like 25 Pa and 50 Pa) so you can extrapolate the 75 Pa if anyone ever wants it in the future. Saves you a trip.

AS AN ADDED BONUS, consider doing a Zonal Pressure Test on the unit downstairs, to see how much the blower door is affecting it. Always nice to have more data than you need.

Happy Testing,
Corbett

How to Master the Multi-family Blower Door Test

Hello Corbett,
A need to run a Blower Door test at a 3 house complex here in Greece. The houses are in the row, this means that normally I should have three Blower door devices, in order to measure the house in the middle. But I have only one Blower Door!
Additionally, I will need to hand over a written document (report), in order to certify the construction to the Passive House Institute. Do you have any suggestions?
Best and thanks in advance,
Stefanos

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Hey Stefanos-
Great question! You do not, in fact, need multiple blower doors, because you actually want to include the unit-to-unit air leakage.  The measurement of all uncontrolled air leakage to outdoors and to other townhouses is a valuable one, and it should be the goal especially when building to Passive House (or PassivHaus) standards.  Watch this video for a visual explanation:

Motivational Metrics: How Zonal Pressure Testing Works

In this home performance testing video, Corbett demonstrates advanced air leakage testing using zonal pressure diagnostics and a pressure pan. Learn how to get more out of your blower door with no extra investment in test equipment, how to interpret the data, and what to do about it during home improvement or new construction optimization. In the second video, Corbett clarifies his use of percentage-based interpretations of zonal pressure diagnostics, after several respected home performance pros had technical challenges for the method used.