Brick Foundations: Moisture and Insulation
Last Post 03 Sep 2015 04:10 PM by Dana1. 3 Replies.
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andy383User is Offline
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02 Sep 2015 04:05 PM
Hello All, I work for a developer and we have an existing property with a brick foundation set on field stone "footing". In the past (before I started working for the company) they would have stabilized the foundation, then used closed cell foam on the inside of the foundation wall. The space in the basement becomes living space so a wall is framed in front of the spray foam. I imagine there is some opinion regarding the building science of this method. Namely, does the brick then become saturated because we've taken away its ability to dry? The wall extends above grade about 4'+ so in theory, it can dry there but the boss usually paints the wall. The architect suggested a drainage plane on the inside of the wall. Just below that will be stone, perf pipe that will drain to a drywell outside. From the drainage plane we have a space, then thick poly, studs, gyp, etc. In this scenario, do we solve the brick moisture but create another problem inside the living space with trapped moisture? Any thoughts would be greatly appreciated. Thanks Andy
jonrUser is Offline
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02 Sep 2015 09:14 PM
I have a similar situation with below grade block, uncovered on the interior. That's ultra breathable and with dehumidification, it will normally (but not always) not puddle. An interior drainage plane leading down to a drain is a sure thing for harmlessly removing water. Hoping that there will be enough interior drying to keep up with entering water is a gamble (and the odds go down as you restrict drying). And of course exterior drains that prevent the water from getting that far are even better.
Dana1User is Offline
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03 Sep 2015 04:08 PM
The brick generally is not adversely affected by moisture except for freeze/thaw spalling in unusually wet conditions in cold/very-cold climates. It doesn't need to dry toward the interior. What climate zone is this?

Field stone does not readily wick moisture up from the ground beneath the footings (unlike CMU or poured concrete). The primary moisture issue is bulk water wetting at the above grade section, and surface drainage. Exterior waterproofing of the below-grade brick is useful, as it an interior side drain.

Painted brick can still dry toward the exterior if you use a latex paint. If you use a vapor tight paint on the exterior and it's too vapor-tight on the interior (HOW much cc foam are you planning for?), the paint would fail long before you'd see freeze/thaw spalling.

If you're concerned about moisture wicking up into a wooden foundation sill, jack the house up 1/8-1/4" a section at a time, and slip in some EPDM sheeting, copper flashing, or vapor-impermeable peel'n'stick membrane as a capillary break prior to installing the closed cell foam. (It's not as big a deal as it might sound.)

If you're NOT putting additional insulation in the studs, there's no point to the poly sheeting, and it could create a potential moisture trap. And if you ARE putting fiber insulation in the studwall, a vapor-permeable or semi-permeable air barrier on the exterior side would be needed. (Houswrap works.) For the interior finish on the wallboard nothing more vapor tight than standard latex paint should be used.

At 2" (R12-R14) most closed cell foam is in the 0.4-0.5 perm range, which is reasonable as long as there is exterior waterproofing below grade. But if you're planning on more than that it could be an issue, and more details about the climate & assembly construction would be necessary.
Dana1User is Offline
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03 Sep 2015 04:10 PM
BTW: Empty cavities often need fire-blocking about half-way up and at the top to meet code, and this would include the gap between the closed cell foam and the studwall.
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