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Community and Q&A

Insulating a brick foundation wall

John Spencer | Posted in Energy Efficiency and Durability on

I’m in Cincinnati, working on a 1820’s building on a hillside lot. Sometime long ago a building was built adjacent to this building and they filled the 4′ space between the two building and capped it with a concrete walk. The basement extends above grade/sidewalk about 2 feet on this side.

We recently repaired the cement parging that is above this walk and sealed the brick above the parging with a siloxane based water repellent (during our extended drought this summer). We also sealed the sidewalk to the building with caulk. The problem is the brick wall has been saturated with water and after our recent rains is again, and mostly at the top above grade with some wet areas below.

Now we are insulating this building and walkout basement. Where we have stone foundations (with minor leaking) we are installing a perimeter drainage mat that continues up the wall 12″, installing EcoStud channels (recycled plastic studs) and closed cell spray insulation to 2-3″ then applying hardy bd. and our finish material. But on the Brick area we are concerned about trapping this water in the brick which has been able to dry out to the inside. The section of wall is 13′ long and includes a brick fireplace where we plan on installing a wood stove, the brick wall is 12″ thick and the basement has a 9′ ceiling. Any suggestions?

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  1. John Spencer | | #1

    plan is attached

  2. Riversong | | #2

    Can you install rain gutters, if not extant, to divert rain away from the walkway? I realize there is an adjacent building involved as well.

    But, if you're worried about blocking inward drying potential, how about insulating the brick walls with mineral wool rather than foam?

    Also, check and repoint if necessary the mortar joints on the exterior of the exposed brick wall. Siloxane won't seal open cracks.

  3. John Spencer | | #3

    neither building drains toward the walkway and both have gutters, we do need to do some repointing on that side of the building..... wouldn't the mineral wool also permit condensation to from on the cooler brick surface during the summer months?

  4. Riversong | | #4

    Perhaps, depending on how well indoor humidity is managed. But condensation is less of a problem on a high-capacity hygroscopic material like a 12" thick brick wall, which can absorb and release it as the conditions on each side change. It works like thermal mass, but moderating changes in indoor humidity rather than temperature.

    If the basement space will be air conditioned or otherwise dehumidified in summer, this should not be a problem. And, even without AC, this should not be an issue of non-vulnerable finishes are used (no paper faced drywall, for instance). It's surface moisture that contributes to mold growth.

  5. John Spencer | | #5

    The current thoughts on the finishes are tile in the bathroom areas, and clay plaster/paint in other area over hardy board or greenboard base material... We have a very humid spring and summer even before its hot out and this room opens out onto a private garden where i would like to keep the doors and windows open as much as possible (the site also gets great wind and AC is not usually needed except a few days in August). In my current place I have to keep the AC on all summer and run a dehumidifier to keep the basement walls dry, I'd like to avoid that here.

    If I continued the closed cell spray insulation over the brick, I would not be contributing moisture from the interior but the brick moisture content would swing with the soil moisture. This building has been empty for going on 50 years with minimal damage to the brick at this point from freeze thaw damage so I'm wondering it what harm it might be to seal the brick from the interior at this point.

  6. Riversong | | #6

    I would avoid greenboard or any substrate with paper facing. And I would concentrate on keeping interior air away from the brick and not worry about vapor diffusion. A thick enough layer of clay plaster is also an excellent hygric buffer (and promotes a healthy negative ion count). I would let the bricks breathe. The siloxane does not impede vapor permeance to the outside and using vapor permeable materials on the inside would similarly allow the old bricks to continue to happily breathe.

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