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Green Building Blog

Part 2 of GBA’s Video Series on a Passive House Project

“Airtight Mudsills” is the second episode in a series of videos on the construction of a Passive House in ­Falmouth, Massachusetts

At the Passive House job site in Falmouth, Massachusetts, the architect specified Tremco acoustical sealant, a layer of polyethylene, and an EPDM gasket. The complicated sandwich is a belt-and-suspenders approach to air sealing the gap between the top of the foundation wall and the mudsill.
Image Credit: Fine Homebuilding

At the Passive House job site in Falmouth, Massachusetts, architect Steve Baczek specified a mudsill gasket.

But to make sure that the gap between the top of the foundation and the sill plate didn’t leak, Baczek took a belt-and-suspenders approach by also specifying the use of Tremco acoustical sealant. Sold in tubes at specialty retailers and online, the black sealant installs easily with a caulk gun. It’s exceedingly sticky and highly elastic, and unlike construction adhesive, it never cures.

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GBA Pro members have access to all of the videos in the Passive House video series.

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Here is the link to the “Airtight Mudsills” video.

To see Episode One of the series, click here: “Passive House Design.” (The first episode is available to all GBA readers, including non-members.)


  1. user-4989474 | | #1

    Hi Steve:

    I ended up building cape in Chatham, and used the same approach as in the video you presented. I did end up with 8-12" of poly underneath the sill on the exterior of house. Is this something that should simply be trimmed off or did you incorporate some type of a finish with this extra poly on the outside?

  2. GBA Editor
    Martin Holladay | | #2

    Steve Kreisher,
    I'm not sure whether Steve Baczek will answer. In the meantime, here's my advice: Trim away the protruding polyethylene with a utility knife.

  3. qofmiwok | | #3 Is this the Tremco acoustical sealant everyone uses? Acoustical Curtainwall?

    1. Expert Member
      Michael Maines | | #4

      It is, but it stinks and is full of nasty ingredients. This is an almost-zero VOC product that performs similarly:

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