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How do I insulate brick wall from the heated side of house?

dghall | Posted in GBA Pro Help on

I am working on a 1978 built, brick house in Juneau, Alaska. Was seeing moisture on drywall and some mold. After removing drywall found 2X2 nailers, 2 feet on center nailed at the grout line. Between the nailers was 1.5 inches of white bead board. Found a few places where the air was leaking in and believe that they have been taken care of.

Other info:
wall is above grade
appears to be single, standard size, red brick constructed wall

I am not sure how to continue…how much insulation can I add for the climate and not damage the brick?

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  1. Expert Member
    Dana Dorsett | | #1

    The EPS board was tight to the masonry? If yes, that's potentially a large part of the problem.

    In rainy Juneau the direct wetting of the brick from the exterior doesn't allow a huge amount of drying toward the exterior. Even in warmer-drier places than Juneau brick veneer siding needs an air gap between the brick & the next layer as a capillary break to prevent moisture from wicking in toward the interior, and to provide additional drying capacity for the brick.

    If you replace the EPS with 1" thick foil face polyiso a half-inch off the brick it will have roughly the same R-value as the 1.5" EPS, giving it a bit of drying cavity, and an additional capillary break (the foil facer.) That isn't sufficient R-value for dew point control for R13 batts a the fiber/foam boundary in most of US climate zone 7, and there is the potential for wintertime moisture accumulation from interior moisture drives. But for the more modest mid winter average temps of teh panhandle it's pretty close to working. A WUFI simulation would tell you for sure, but short of that using a sheet of 2-mil nylon (Certianteed MemBrain as the interior side vapor retarder should nudge it over the line.

    The mid-winter average temperatures in Juneau are about +25F, comparable to many US zone 5 locations, the primary difference being that it's an 11-12 month heating season rather than 8-9 months for US zone 5. In those comparable zone 5 an exterior R5 would be sufficient dew point control for use of Class-III vapor retarders (like standard latex interior paint.)


    e peak coolth is about the same, but considerably longer in duration in Juneau.

  2. GBA Editor
    Martin Holladay | | #2

    I don't understand the construction of the wall you are describing.

    If the brick wall is only one-wythe thick -- in other words, if it's brick veneer -- you still need wall framing (at least 2x4 studs, not 2x2 nailers).

    So is there any chance that this is a multi-wythe brick wall -- that is, a structural wall?

  3. Expert Member
    Dana Dorsett | | #3

    I was presuming there was already a 2x4/R11 or R13 structural studwall on the interior side of the nailers & foam.

    If this house has ONLY the 1.5" EPS between 2x2 nailers it's woefully under-insulated for the climate, and it would be useful to know the method of joist attachment to the structural brick to come up with the most-reasonable approach to insulating it adequately.

  4. dghall | | #4

    Martin and Dana...thanks for your responses.

    I have been crawling around in the crawl space and taking some measurements to clarify things.

    The house is single story
    The brick wall is built, at grade, on a concrete block wall
    The wall in question is on the gable end
    The joists run parallel to the gable end wall...there appears to be a space between where the brick wall begins and the rim joist, with that joist sitting on a wood plate on the concrete block wall
    The only framing on the inside are the 2X2s...a 2X6 is on edge at the ceiling and floor with the 2X2s running vertically between other framing

    As near as I can figure out the wall is a single brick wall...I measured from the inside corner of the wall in question to the edge of the glass in the nearest window and it is 46"...went outside and measured from same corner to edge of glass and got 51". That is only a 5" difference which is about the thickness of the brick plus the nailers.

    In the crawl space...
    question about joist is dealt with above
    at a vent, I can see the edge of the brick and it looks to be only one brick thick. Difficult to tell much else in the crawl space because the ground is covered with the plastic running up and sealed on the concrete block wall, the joist bays insulated, with rigid foam and foam sealant along the joist sitting on the concrete block.

    And yes, it appears to be "woefully" under insulated for our area. This is my concern but when I started to learn about brick walls I became concerned and a little confused. Am not familiar with brick, (have a fair amount of experience with wood construction) and after doing some reading, was concerned about just adding more insulation without understanding how brick "works" in this climate.

    Hopefully I have filled in some blanks for you both and look forward to your reply and anyone else who may have something to offer. The wall has been uncovered for over a week now and the owners are wanting to get things buttoned up...there is some colder weather in the forecast.


  5. Expert Member
    Dana Dorsett | | #5

    So, what are your performance goals here? To get to an IRC 2015 code levels, or something less than that, but still solves the condensation & mold issues? Are you intending to get around to other walls at some point, not just the gable end that exhibited the problem?

    IRC 2015 code max U-factor for walls is U0.045, which is a "whole-wall-R" of R22.2, after factoring in all thermal bridging, and the R values of everything else, not just the insulation, such as R-values of the brick veneer, the interior & exterior air films, the wallboard, etc. One solution that makes it would be a continuous 3" of foil faced rigid polyisocyanurate board cap-nailed to the 2x2s , leaving the channels between the 2x2s open as a capillary break and drying channel. There are others.

    If the joists aren't being supported by the gable end, this would be sufficeint. More care has to be taken when insulating around the joist supporting structures, but it sounds like that's going to be a separate project for a later date(?)

  6. GBA Editor
    Martin Holladay | | #6

    Dana is right that you can install a continuous layer of rigid foam, at least three inches thick, in an airtight manner, and be OK from the R-value perspective.

    But if I were you, I would call in an engineer to determine if the house is structurally safe. Even though a gable wall doesn't bear any roof loads, the wall you describe is very unusual. I wonder about wind loads, for example.

  7. Expert Member
    Dana Dorsett | | #7

    It's good to think about seismic resilience too, given the geographic location.

  8. dghall | | #8

    Dana and Martin...thanks again for your response.

    The initial and primary goal was to find the reason for, and a solution to the damp and moldy walls. I believe I have that covered.

    Opening the wall up revealed the lack of insulation. So now am just trying to find a way to safely increase the r value. There is talk of doing something with the other walls but not at this time. The possibility of insulating the exterior has been discussed as well.

    A question about the 3" hang the drywall would you use screws long enough to go through the foam to the 2X2s? Also there are two outlets on the wall that will need to be considered. Could the channel for drying be less if the decision is to remove the 2X2s and reduce the space to say 3/4" or 1"?

    As far as the structure goes...the house was purchased last spring and and engineers report went with it with no mention of structural problems. The house is 30 years old and has survived several earthquakes. I have looked at all the exterior walls and find no cracks. The construction does seem unusual...there may be some rebar or other "tie-together" reinforcing that is not visible.

    Only other problem is that neither of the two building supply stores in town carry 3" polyiso...only 1", 1.5", and 2". Would have to make two layers.


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