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Preinsulation blower door test expectations

BuildingAHome | Posted in Energy Efficiency and Durability on


I am having my builder do a blower door test after mechanicals have been put in but before insulation is done to do some blower door directed air sealing and make sure we are on track. My end goal is 1.0 ACH50. What sort of numbers should I expect at this stage? The end goal? Or close to it?

The construction methods are zip sheathing, liquid flashing between the foundation and sheathing joints, OSB flange over the top plates to connect the exterior sheathing to the interior ceiling drywall (which will be in place for this test), and the windows taped on the inside with Tescon Profil. I am trying to stay away from spray foam, so the wall cavities and attic will have blown fiberglass when we go to insulate.

Should I expect the insulation and drywall steps to reduce my ACH noticeably or should I try to get the ACH to <=1.0 at this stage?


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  1. nynick | | #1

    I'm just a homeowner who has just built a large 3 car garage with an ADU above it, and am now renovating a 150 year old house, trying to get it as tight as possible, however...

    I'm unsure why you would bother with a blower door test at this point. If you'll be introducing smoke this could be a good idea for air infiltration sealing but the real test comes after insulation and sheetrock.

    Your ACH goal is ambitious. I hope you are installing an ERV/HRV and considering a dehumidifier within your system as well. Good luck!

    1. Expert Member
      MALCOLM TAYLOR | | #3


      "I'm unsure why you would bother with a blower door test at this point"

      A blower door test once everything is complete just tells you how you did with no way to improve it - and at that point all the decisions that rely on air-sealing (mechanical system sizing, etc) have already been made.

      Blower door testing is best done once the primary air-barrier is in place but still accessible for further sealing.

      1. nynick | | #7

        Ok. thx Malcolm.

  2. walta100 | | #2

    The idea of a pre drywall blower door test is better as a daydream than in real life. Yes, I had that daydream also.

    In the real world this test requires the drywall ceiling to be in place and mudded but the drywall not yet be installed on the walls. This puts lots of steps out of sequence. It is hard enough to get drywallers to show up and work. Now you want them to do 33% of the job and come back in a few weeks to do the rest. If you somehow make this happen you will not have made any friends.


    1. crawfordesquire | | #4

      your response is accurate only if the wallboard ceiling is your air barrier. plus, the OP said he'll have the wallboard ceiling up if i read correctly.

      for me, i almost don't want to know a blower door score if it can't be improved. which means pre-wallboard.

      1. Expert Member
        MALCOLM TAYLOR | | #5


        Yeah, the problem presupposes you are using the drywall as your primary air-barrier on the ceiling, and something else on the walls - which may or may not be the case.

        1. BuildingAHome | | #6

          Yes, sorry I didn't make it clear. I am using the drywall on the ceiling as my air barrier. All of what is intended as an air barrier will be complete prior to this test. I would consider the ACH getting lowered after the rest of the insulation and drywall as "luck". But I have never done this before so maybe it's normal to expect those things to reduce the ACH by 0.5 or something so all I reasonably need to shoot for in the first test is 1.5 or something. Just hoping someone with experience here could help me out.

          1. Expert Member
            MALCOLM TAYLOR | | #8


            No need to apologize, your question seemed very clear to me.

            I have nothing to go on but intuition, but I suspect that if the drywall is installed with no additional measures to make it an effective secondary air-barrier (gaskets, etc.) you should probably anticipate the drop in ACH it gives to be pretty small. Looking at any gains as a lucky bonus seems like a good idea to me.

  3. Expert Member
    DCcontrarian | | #9

    I would not expect insulation to improve air infiltration at all. Final drywall would. But on the other hand, a lot of holes get cut into the walls of the house in the final stages of construction when fittings and fixtures get put in. Unless you're constantly looking over everyone's shoulders it's hard to make sure those holes get sealed.

    So I would go for the end number at this stage.

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