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What stage to do a blower door test?

bobhol | Posted in General Questions on

I would like to do a test when windows and doors are in.My builder thought when the drywall is done .His concern is the attic space would not be sealed until that time .I am using exterior foam so no interior vapor barrier ….any thoughts?

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  1. GBA Editor
    Martin Holladay | | #1

    If you have a vented unconditioned attic, you need to have something to establish your ceiling air barrier -- ordinarily, that would be your drywall ceiling -- before you can do a blower-door test. Ideally, you would hang the ceiling drywall first (and give it at least one coat of tape), but leave the walls without drywall, and then do your blower door test -- but that usually isn't possible.

    The bottom line is, "it depends." The most important question is, "Where is your air barrier?" If the wall and roof sheathing are your air barrier -- as might be the case if you have an unvented conditioned attic -- then you probably want to conduct your blower-door test before any drywall is up (so that any leaks you discover are easier to seal).

  2. bobhol | | #2

    Thanks Martin...the attic will be unconditioned with a hatch for access,so maybe I will have to wait for drywall... but any leaks will not be accessible to repair. If that is the case ,the blower door test is for information only ...

  3. davidmeiland | | #3

    Modern-day drywallers should get used to a percentage of their customers wanting work done slightly out of normal sequence, to accommodate blower door testing of the shell. In your case, they can stock the job as usual, then hang and tape the ceilings so you can do your blower door test. They step aside for a few days while the insulators do their thing, then it's back to normal. If you wait until after drywall to test, and you *need* to meet a certain standard, you're taking a chance. How big the chance is depends entirely on what your builder knows about air-sealing.

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