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How I Achieved a 21% Increase in Airtightness


I’ve got a record of 14 blower door tests on my condo. Many of them were during home energy rater classes, as we’d bring them here for the confirmed rating they needed to complete. The early ones were horrible! But I had a good reason. Our laundry room ceiling was half gone because of a water leak. (Thanks, upstairs neighbors!) After that we had a bunch that were still bad. Now we’ve had another big jump in airtightness. Wanna see the numbers?

Evolution of a leaky condo

Stage 1. In 2011, our laundry room had only half a ceiling because of said water leak. That open ceiling was connected to the stairwell and the fireplace chase, which had a lot of connection to the attic of our building. I’m embarrassed to show you the numbers, but here they are:

6100 cfm50 ==> 29.6 ACH50

I told you it was embarrassing.

Stage 2. After replacing the laundry room ceiling, we were significantly more airtight. We did 8 blower door tests over a three or four year period during this stage. Still bad. Still embarrassing. Here are the averages from those 8 tests:

4300 cfm50 ==> 20.8 ACH50

 I really shouldn’t be putting those in bold. Why am I drawing so much attention to it?

Stage 3. You know about the work I’ve done in our master bath. I described the air leakage pathways I found in the exterior wall. And there was a lot more, too, because of all the plumbing penetrations and connections to interstitial spaces. But at the same time I was fixing the bathroom, our owners association had spray foam installed beneath our floor. Most of the increase in airtightness is due to that improvement. Here are the latest numbers, measured twice on two different days:

3418 cfm50 ==> 16.5 ACH50

Still embarrassingly high, but better. Now we’re within 10 ACH50 of meeting the Georgia energy code, which requires new homes to test at less than 7 ACH50. So my goal is to get this place that tight before we sell. That means changing the water heater because…gasp…we still have a natural draft model. Talk about embarrassing!

Blower door testing the bathroom

As you can see in the photo at the top of this article, I did a blower door test on our newly remodeled master bathroom. The frame was too wide for the 24″ door, but I squeezed it in between the frame and the wall and tried to seal the gap with blue painters tape. I think there was still a fair amount of bypass. Here’s the result I got:

208 cfm50 ==> 28.4 ACH50

Not great in terms of ACH50, but that 208 cfm50 was the total leakage of the bathroom. I didn’t do a pressure test to check for leakage only to the outside. Still, 208 out 3418 is only 6% of our total leakage, and the actual number for the bathroom is probably significantly lower.

What the bathroom looks like now

We’re almost done with the bathroom remodel. We just bought a light fixture this weekend, being pointed to by my wife Elaine in the photo below. We still need a mirror, shower doors, and new plantation shutters for the window.

Elaine showing off the new bathroom light fixture
Elaine shows off the new light fixture in our remodeled primary bathroom

I love the shower! We installed a temporary shower curtain while we wait for the shower doors so it’s in use already. You can’t see it in the photo below, but we installed a linear drain, which I learned of in a Bob Borson article he wrote 5 years ago.


That’s the latest on our bathroom remodel and condo airtightness. I’ll let you know when I get down below 10 ACH50.


Related Articles

Air Flow Pathways in a Leaky Bathroom Wall

7 Reasons to Gut Your Bathroom When You Remodel

How to Fix a Leaky, Underinsulated Exterior Wall



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This Post Has 3 Comments

  1. Love the bathroom redo, and
    Love the bathroom redo, and the linear drain. The most beautiful part is what you did inside the walls.

    I’d tape 6 mil poly to the inside of the bathroom walls and insert a duct blaster fan. You might find you have much better numbers for the bathroom. Otherwise, where are you getting 208 cfm?

    Have you pressurized the whole condo to 50 Pa. then followed smoke to determine where most of the air is going? Or performed zonal diagnostics?

    Thanks for sharing your B.S. adventures.

  2. Allison, did you choose the
    Allison, did you choose the light fixture because it looked like 3 rolls of duct mask? Just kidding.

  3. Nice work on the bathroom!
    Nice work on the bathroom! About the light fixture, is it upside-down? I have a similar type, and the openings face downward. Better illumination for make-up (my wife) and much easier to replace bulbs (me). Also, I put LED bulbs in it, to reduce energy and heat.

    Great article, thank you.

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