Blower Door Testing in Multifamily Buildings

September 01, 2011
September/October 2011
A version of this article appears in the September/October 2011 issue of Home Energy Magazine.
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The owner knew he had a problem. During the previous Wisconsin winter, ice dams had pulled a 20-foot x 5-foot section of eave and roof right off the building!

"The ice on the roof edge was 18 inches thick," he told us. "Even with the whole mess lying there on the lawn, we couldn't bust it up. We finally had to bring a crane right into the yard and lift the thing out in one big piece, so we could truck it away."

The weatherization crews working for La Casa de Esperanza (based in Waukesha, Wisconsin) knew that those ice dams meant lots of air leaks, lots of energy waste, and lots of opportunities to improve this building. They had years of experience fixing infiltration and ice dam problems. They knew what to look for, and pretty much found it all. The vented crawl space was well connected to the living space above. The windows were pretty loose, and the door weatherstripping was long gone. The attic was a mess; multiple open soffits, oversized plumbing and chimney penetrations, a huge attic hatch with no weatherstripping. Air sealing was clearly in order. Blower door testing would be imperative to ensure that the job was done well.

The problem? This weatherization project was a 50-unit apartment building.

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Any number of experienced weatherization specialists "know" there are a number of reasons why we don't test these buildings: (1) it is hard to do, (2) no one has proven that sealing apartment buildings saves energy or improves the building, and (3) it is just too costly to implement. LEED Multifamily requires blower door tests only on a sample of individual units. The Energy Star program for multifamily buildings uses the same standard. The only programs that explicitly require a whole-building blower door test for apartment buildings are the Alaska Weatherization Assistance Program and the U.S. Army Corps of Engineers.

When it comes to apartment buildings, it seems that the universal—and wrong—answer is to try to pretend that everything we know about infiltration doesn't apply.

Over the last ten years, various accomplices and I have completed close to 100 blower door tests on more than 60 apartment buildings. The buildings have ranged in size from 5,000 to 280,000 square feet, and from two to nine stories. We have used every blower door system available in the United States. Based on all this work, we have concluded that blower door testing and air sealing in multifamily buildings is not only possible, but important. The evidence is developing that, just as in single-family buildings, air sealing is the single most cost-effective measure in most apartment buildings.


In single-family homes, we know that blower door testing is the fundamental, indispensable tool for residential energy improvements. We know that in single-family homes, air sealing is frequently the single most cost-effective measure completed. We also understand that infiltration flaws cause more performance problems than any other building defect. (Although we do recognize that bad flashing jobs may be a very close second!)

And we have learned the hard way that blower door testing is crucial. I think every crew has tried, at one time or another, air sealing by inspection. But air is too slippery and buildings are too complicated—it just doesn't work. So we have learned: If you don't test, you don't get infiltration improvements or energy savings.

When it comes to apartment buildings, it seems that the universal answer is to try to pretend that everything we know about infiltration doesn't apply. We've concluded that blower door testing is difficult, it's expensive, and it's not clear that it saves energy. For most apartment buildings in the United States, none of these reasons applies anymore.

With improvements in systems, especially in software control systems, blower door tests can now be completed efficiently and accurately in almost any low- or midrise building. The most flexible systems are built around the same residential-size blower doors that are used by every energy auditor in the country. I believe it is likely that within five years every program intending to complete real and meaningful energy improvements in apartment buildings will routinely perform in-and-out blower door testing of wood-frame buildings up to 100 units.

If we intend (especially in weatherization) to provide the benefits of our skill and experience to those people who need it most, apartments buildings are a good place for us to be. In a recent DOE weatherization guidance document, WPN 11-4 notes that fully 70% of all apartment dwellers qualify for low-income weatherization. And the authors of the guidance document further conclude that 30% of all U.S. households that qualify for weatherization rent their residence.

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