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Community and Q&A

Capillary Break at Top of Foundation Wall

steeplechase | Posted in Green Building Techniques on

I’ve got a question in regards to location of where to put the capillary break.  I read a lot about it being put on top of the footing.  I can understand that, especially if planning to insulate on the exterior of foundation wall with conditioned basement space.  What about insulating on the interior with closed cell spray foam that connects to the sub slab vapor barrier (Stego) and also a capillary break at top of walls?  My general plan is along those lines with the top capillary break being a peal and stick membrane below the sill plates.  It seems to make sense to me as all of the concrete will essentially be outside of the vapor control layer.  The below grade wall heights range from 8′ to 5′ or so.  Its essentially walk out style tucked into a hillside in VT.  Other information that may be relevant is that for the two walls that go above slab height, we used full waterproofing spray with dimple mat and then will be back filling with crushed stone down to our perimeter drain.

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  1. Expert Member
    Peter Yost | | #1

    Best practice is to place a capillary break (non-porous material such as a membrane or a closed-cell foam such as sill seal) between any porous materials: the cold joint between the footer and the foundation wall, the top of the foundation wall, between any cladding and the rest of the assembly, between soil and the basement slab.


  2. JC72 | | #2


  3. steeplechase | | #3

    As I mentioned, I plan to have capillary breaks between all of the concrete and adjoining materials ( top of wall, inside of wall, sub slab), the only spot where there wont be one will be between the footer and the foundation wall.

  4. Zdesign | | #4

    On top of the footing should be included. Most of the moisture transfer is from there to the foundation wall. I used Drylock Extreme on mine.

    1. qofmiwok | | #6

      The manufacturer was adamant when I talked to them that Drylock Extreme not be used for this purpose.

  5. steeplechase | | #5

    On top of footing would be nice but short of removing already poured (and engineered) walls that is not an option. As I mentioned in my original post, my logic of isolating the footings and walls outside of the vapor barrier seems to make sense. Stego below slab connected to closed cell spray foam on interior of poured walls ( dimple mat and crushed stone on outside) which ties in with vapor impermeable ( vycor or other) on top of walls. Based on that, it seems that any moisture coming up from capillary action would dry to the outside.

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