What kind of experience have folks had using blower doors in multifamily buildings?

I hear conflicting info on when and how BDs can be used and useful here.  What are your experiences?  Photos?

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I did a couple of duplex/triplex units last week and was told to test one unit at a time and disregard adjacent units. I wonder if the numbers might be slightly lower if the units were all depressurized at the same time, and I may get a chance to find out.

 

More on this topic: http://www.greenbuildingadvisor.com/blogs/dept/green-communities/bl...

Blower door testing multifamily buildings is just as useful as testing single family homes. The energy savings is usually correspondingly less, since there's typically less exterior exposure. The big difference, of course, is in learning how to deal with leakage to adjacent units. In a row, or townhouse complex, this can be a very minor consideration. Adjacent units would tend, on average, to be pressurized similarly with respect to the outdoors. For accurate testing, we would want to have access to the neighbors units, either to install a blower door in them, and equalize the pressure across any shared walls, or at the very least to open a window/door to treat neighboring units as the outdoors.

 

In larger, multi-floor, buildings, the leakage within the building begins to have a significant impact. If we restrict ourselves to energy savings, and ignore the equally significant indoor air quality concerns, air leakage to the outdoors is no longer the only concern. Depending on a units location within the building, top floor vs. bottom floor etc.., the air leakage due to the stack effect (movement of warm air up the building column) can have major energy savings implications. In a cold climate, it's entirely possible to see units at the top of a tall multifamily building with their windows open. This is typically because the movement of warm air from the lower floors is so significant that the top units are feeling too hot. The net effect of opening windows, naturally, is to draw yet more warm air up, further cooling lower units, causing them to want even more heat. You can see where this is going...

 

The solution, when it comes to air sealing, is to not only isolate leakage to the outdoors, which can be done by neutralizing leakage to adjacent units and floors, but also to learn to isolate leakage to each adjacent unit, hallway, and floor. Not easy once a building becomes occupied.

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