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downstream from the blower door

BCinVT | Posted in General Questions on

The blower door has become a measure of how tightly a house has been assembled as far as air infiltration. It seems as if it may actually be getting more credit than it deserves as an indicator of overall quality, but if kept in perspective it does provide one easy way to predict how well a building may perform. But it seems that the blower door is not being used to confirm how well the initial performance holds up over time. This would be useful to better understand where weaknesses may lie in the accepted materials and techniques being used to achieve the initial ratings. Are there any longitudinal studies of buildings using blower doors?

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  1. ERIC WHETZEL | | #1

    On the Passipedia website...

    ...there is a pdf describing the history of the original multifamily Passive House project in Darmstadt, Germany:

    Around p. 25 they talk about the resiliency of the air barrier.

    Overall, it appears the air barrier is still holding up well.

  2. Expert Member
    NICK KEENAN | | #2

    I had a similar conversation with a friend who is a mechanical engineer. He's a good friend but I consider him a mediocre ME. I was railing against over-sizing of HVAC units, and he said, "but what about ten years from now when the house isn't tight any more?"

    I didn't have an answer.

    1. Expert Member
      MALCOLM TAYLOR | | #3


      That's an interesting point, and especially pertinent to assemblies that rely on very good air-sealing to be viable and not fail.

      One of Ben Biogie's rules in his recent blog was that houses shouldn't rely on the vapour performance of it's parts. I'd suggest a similar injunction that assemblies shouldn't rely on maintaining their air-seals.

      I wonder what level of air-seal degradation we should assume and plan for? I expect it varies depending on what strategy was used.

      1. ERIC WHETZEL | | #4

        To your point, Malcolm, this is why we decided to use a continuous insulation approach on our house --- 2x6, Zip sheathing, 4" of Rockwool --- to try and bury much of the air barrier towards the middle of the wall assembly in hopes that it experiences less stress from potential water intrusion or temperature and humidity swings. Time will tell I guess.

        Using a double stud wall assembly worried me since the air barrier is directly behind the cladding.

        Someone deciding between various wall assembly approaches might find this interesting:

        1. Expert Member
          MALCOLM TAYLOR | | #6


          I'm not worried about your place. You are an obsessive air-sealing machine. It's the rest of us that might be problematic.

          Seriously though, burying a robust air-barrier well into the wall makes a lot of sense.

          A couple of the double-wall projects featured here on GBA (like Stephen Sheehy's) have done that too, usually with the air-barrier on the outside of the interior wall.

      2. Expert Member
        NICK KEENAN | | #5

        In my experience, most of the air-seal degradation comes at the hands of guys with screwguns and sawzalls in their hands.

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