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Community and Q&A

Exterior Insulation on Brick House

nipperkin | Posted in General Questions on


We are currently in the process of doing a full renovation + 2nd story addition to our 1940s double brick bungalow. We are located in zone 6 (Toronto, ON) and looking to insulate and air seal as best we can given the existing structure we have to work with. We’ve already opted for an upgraded HVAC system including an HRV system and air filtration.

We we originally planned to add 2″ of rigid insulation on the exterior (existing brick and new 2×6 framing), but due to increased costs of materials, labour, etc. we are debating reducing this to 1″ or possibly none. We have the option of spray foaming the entire house on the interior, but we also have slotted joists on the main floor which I’ve read can be susceptible to freeze/thaw issues. I’ve also read there may not be much insulation gain by adding only 1″ on the exterior and this would be more of an air/vapour barrier then actual valuable insulation value.

The house is only about 650 sq/ft per floor so it’s not overly large. Is adding the 1″ exterior insulation + spray foam a recommended application in this scenario? Also, is it advised to add any additional air barrier, etc. over top the existing brick wall construction either with or without additional exterior insulation.

Any advice would be greatly appreciated.

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  1. Deleted | | #1


  2. Expert Member
    Akos | | #2

    Unless your brick is in bad shape or very ugly, it is a shame to cover it up. In most cases you can do interior insulation with SPF only. You should not need interior 2x6 framing though, you can go with 2x4 or 2x3. Try to offset the framing from the brick so the you can get a layer of foam behind the studs. This significantly increases the assembly R value for zero cost.

    Insulating brick from the interior is never without risk, but it seems that SPF works in most older Toronto homes.

    Double row of brick with air gap between is also good for R3, which you can use to reduce the amount of insulation. You only need to go with 3" of cc SPF in your walls.

    If you do want to cover the brick and insulate on the exterior, you can skip the SPF on the inside and go for batts for the inside. Just make sure you fix the window flashing details and install a WRB over the brick before the foam goes on. For a 2x4 interior stud wall with R14 batts, you would need about R7 exterior rigid insulation.

    For the new construction, with the current cost of lumber, I find going with a 2x4 stud walls with 2" of exterior rigid polyiso much cheaper than 2x6+r5. In the end it depends on what your contractor is comfortable with.

  3. nipperkin | | #3

    Hi Akos

    Thank you very much for the detailed response.

    I should have also mentioned we are renovating the existing main floor, which includes a front addition and changing some existing windows. Although the brick seems to be in good shape, with all these changes, leaving the brick exposed doesn’t really make sense given all the other work being done. Our plan was to use hardie board on the exterior and while we were at it throw on some additional rigid exterior insulation all the way down. Most of this was planned / designed prior to material costs sky rocketing.

    So, if we decide to use SPF on the interior only and completely forego rigid on the exterior (ie just use a siding), is there a risk in freeze thaw issues? In particular if we spray foam the existing main floor headers where the joists are slotted into the brick (not exposed to the exterior though)?


  4. Expert Member
    Akos | | #4

    SInce you won't be keeping the brick, I would insulate form the outside.

    To hang siding on brick, you'll have to strap it out, adding rigid under the strapping is minimal extra labor cost. This saves you having to worry about floor joists and also increases the interior floor area.

    SPF is something I prefer to design out of a build. It is really best to use it for sealing up difficult details just as rim joist, intersection between the brick and the new 2nd story addition and any other complicated air barrier transitions.

    P.S. As to your question about moisture. Insulating brick from the inside is never black and white proposition. Any insulation there always increases the risk of moisture damage, whether this becomes is hard to predict.

    1. nipperkin | | #5

      Thanks again Akos!

      Your suggestion is inline with the way I had originally hoped to do the wall construction and insulation. We only have enough room to put on 1" of rigid exterior insulation. Unfortunately, mixing and matching spray foam and traditional insulation will end up costing more then doing all 3 floors in spray foam (basement, main, addition). Our rationale for entertaining no exterior insulation was that using SPF throughout the interior + exterior insulation might be overkill for the small footprint of the house.

      Since we can only add 1" on the exterior, we are going have to insulate on the interior (which is currently brick covered with plaster) to get a reasonable R value. In this case does it make sense to use SPF on the entire house?

      Another concern of mine is the use of vapour and/or air barriers across the wall construction. Since we are insulating from inside, which have a vapour barrier (as per code), would adding WRB over top of the brick and between the rigid insulation pose any issues? When I mentioned adding WRB over the brick our contractor suggested this wasn't commonly done.

      Thanks so much!

      1. Expert Member
        Akos | | #7

        I would not put the brick between two layers of impermeable insulation. If you want to do both SPF+ rigid, make sure the rigid you use is permeable (unfaced EPS, permeable polyiso or rigid mineral wool). With closed cell foam you don't need an interior vapor barrier as the foam itself acts as one.

        What is the reason for the 1" limit? Installing 1" of foam is about the same work as installing 3" but allows you to skip interior insulation. Along with more interior space, it saves you the cost of spray foam.

        WRB is vapor open, it won't effect moisture movement. When you are installing any siding over masonry, there should always be a wrb. This can be over the foam or under the foam, but should be there. Your windows should be flashed to this layer. This can't be skipped. Bulk water leaks into the brick will eventually saturate it and it will rot your pocked floor joists.

  5. GBA Editor
    Kiley Jacques | | #6

    Bear in mind something Martin talks about in this article (one I highly recommend for you): Insulating Old Brick Buildings . . . “if you insulate the wall on the interior, you’ll make the bricks colder during the winter . . . and cold bricks are always wetter than warm bricks. . . . and that [moisture] can make the wall vulnerable to freeze/thaw damage.” A few key takeaways: 1. The colder the climate, the greater the risk of freeze/thaw damage. 2. The thicker the insulation, the greater the risk of freeze/thaw damage. 3. Some bricks are more vulnerable to freeze/thaw damage than others; there are tests to determine whether your building has good bricks or bad bricks. His advice? Insulate the exterior and hire a consultant to assess the brick.

  6. nipperkin | | #8

    Thanks Akos & Kiley. This has been very informative and validations some of my assumptions on the matter.

    Akos - To answer your question about why we can only add 1" on the exterior, it's because we are working with limited space between property lines along with zoning concerns.

    1. hesmasi | | #9

      Hi what did you end up doing? We are in a similar situation in Toronto, would love to hear how it went.

      1. nipperkin | | #10

        We ended up going with spray foam on the interior and 1" of GPS rigid insulation on the exterior. The house isnot 100% completed, but seems to have worked out well so far. Even with the very cold temperatures we've had and only radiant floors in the basement + a 5000w heater upstairs the house is surprisingly warm and comfortable. Time will tell, but this seemed like the best balanced approach for us given our constraints.

        1. hesmasi | | #11

          Great thanks for sharing.

          Did you do siding over it? Let me know what company you used in Toronto. Doing the exact same project, if you're comfortable sharing that would be great.

          1. Jonny_Toronto | | #12


            I am also in Toronto and looking at the same type of brick retrofit. Do you have any companies that you would recommend for this? Thanks! email is [email protected], if that is easier

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