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Theoretical question on air leaks

shrews01 | Posted in General Questions on

Assume a older house has 100 air leaks all of equal size and 50 are inaccessible. Would air sealing the 50 accessible leaks make a difference? I assume it would, but maybe there is something I’m missing

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Replies

  1. Expert Member
    Akos | | #1

    Since stack pressure is constant, assuming all holes are the same size, sealing half of them reduces your air leaks by half. Depending on how leaky the original building is, reducing the air leakage rate by this much would be a big difference in energy use.

    Since air leaks are usually not evenly distributed through the house, it also matters which air leaks you seal first. Since stack pressure is the greatest there, any leaks near the basement or in the attic will have the biggest effect. Sealing holes near the neutral pressure plane (about 1/2 building height) of the house will have little effect except on windy days.

  2. Charlie Sullivan | | #2

    Good explanation!

    Just to clarify, when Akos says stack pressure stays constant, that means it would be the same regardless of how many leaks you seal. It varies over time, as a result of temperature variation indoors and out.

  3. Jon R | | #3

    Straube suggests that typical wind causes about 5 pascals. This is more than typical average stack effect pressure, so probably best to put more effort into the prevailing windward and leeward sides.

    https://www.buildingscience.com/file/5864/download?token=QnV0HMXG

    1. Expert Member
      Malcolm Taylor | | #7

      Jon,

      Good point, although at least wind doesn't occur constantly the way the stack-effect does.

      I think the main reason we typically concentrate on air-sealing the bottom and top of buildings is that that's where it's usually the poorest, and in the case of ceilings/roofs, where the effects of air-leakage can cause the most damage.

  4. Andy S | | #4

    Theoretically, Aerobarrier would be able to seal all 100 holes.

    1. Expert Member
      Malcolm Taylor | | #5

      Andy,

      I'm surprised you don't hear more about AeroBarrier and existing homes. It seems like a better application for the technology than new builds.

      1. Andrew C | | #8

        Only somewhat facetiously, I suspect a lot of people don't want to use Aerobarrier because it would require that they first clean up their house and clear all their junk off of all the horizontal surfaces in preparation.

        I agree, Aerobarrier seems like a great application for existing builds where you can no longer access a lot of areas.

  5. JWolfe1 | | #6

    Thanks for asking this question and thanks for the responses.

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