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Community and Q&A

Capillary break

Behardy | Posted in General Questions on

I am getting ready to insulate my basement in preparation for future finishing into living space. My home is located in NE Pennsylvania and was built in 1859 and sits on a field stone foundation. The foundation overall is in very good condition. It is is need of re pointing in some areas but over all in good condition. The basement is damp on two of the walls and during periods of heavy rain weeps water slowly. I have already installed a french drain to daylight around the two walls that periodically weep and are damp on the lower half for much of the year. The other walls are never damp or show any signs of moisture at any point during the year. I grew up in this house and purchased it from my father about 6 years ago so I have an extensive knowledge of the water problems that it has had. The french drain along with new gutters on the entire house, and grading to prevent runoff from getting near the foundation has significantly decreased any heavy water infiltration. The sills are in very good condition and show no signs of rot due mainly to the fact that the foundation is at minimum 18 to 20 inches above grade.

My question is in reference to an article I read on the Building Science website about damp proofing and insulating rubble stone foundations. In this article self sealing roofing membrane was used to seal the foundation on the inside and closed cell foam insulation sprayed over the membrane. The article discussed the need to jack the house up enough to slip the membrane under the sills in order to provide a capillary break to keep moisture from wicking into the sills. Some of the sills in the article had to be replaced due to root from being at grade level and severe water intrusion. My question is because my sills are so far above the existing grade and the fact that my walls are never damp more that halfway up (7 feet high walls) do i need to install the break? If I don’t will I risk rotting out my sill plates when I seal the walls? My plan for the walls that are always dry is to parge them and spray closed cell foam directly on them. Is this good practice as well?

Thanks you all for your time and knowledge I appreciate any feedback. Below is the link to the above referenced article.



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  1. GBA Editor
    Martin Holladay | | #1

    This is a judgment call. If the sill is now sound, and the wooden components of the building are well above grade, and there is good sun and air exposure on the exterior -- no bushes near the foundation -- the risk is relatively low to proceed without the capillary break at the top of the foundation wall.

  2. Expert Member
    Dana Dorsett | | #2

    Field stone foundations don't wick anywhere NEAR as much as poured concrete or CMU. Most of the fieldstone in NE PA is dense volcanic stuff like granite or basalt, which doesn't have a lot of capillary draw compared to sandstone or limestone. If the sills are in good shape now and you have more than a foot of exterior exposure of the fieldstone (with no moss growing on it- lichens are OK) don't sweat it too much.

    If there is copious moss growth on any section you probably have more remediation to do, and a capillary break for that section may be mandatory.

  3. Behardy | | #3

    Thanks for the information I appreciate it. All sides have good exposure and air circulation.

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