Today I received a request to test 4 units for a small apartment building. He says the building is 32x52 which is 1560 SF. There is 4 apartments which are 1 bedroom and living room plus bath and small kitchen. If I test each unit, I suspect they are approx 400 SF. These units will have to be very tight. He wants me to open all the doors and test from one end of the hall. I have never done this is 10 years so not sure this is kosher.
Most of the work I do is retrofit of older buildings. Marriage wall leakage is often significant, although typically more through duct leakage between units than through the wall itself.
The way we'd normally do this is to mount one blower door in the hallway, then a duct tester blower door in the individual unit. You'd first test the total leakage of the unit with adjacent apt windows open which will give you the total leakage of the apt. Then you turn on the hallway blower door so the hallway pressure equaled the apt pressure the reduction you see if the wall to the hall. Then open one apt door and close the window and the change is the shared wall, repeat for apt on the other side and you see the reduction as the shared wall with that apt. Now you've got leakage to outdoors which has the leakage between floors included but that should be small.
Alternatively, one blower door in the hallway could be used to measure the total leaks of all four.
What's important is to understand what they/he want to measure. Once clear on that, we can come up with a way to measure it.
Thank You, Colin! Those are very good points and processes to do some Zone Pressure Diagnostics techniques applied to multi family buildings.