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Community and Q&A

Insulating a northern brick house

Morgan Jones | Posted in Energy Efficiency and Durability on

I am in Winnipeg, MB and have a Eaton’s catalog house (1917) with a wall detail of an outside course of brick/small airgap/brick. As a character house I don’t want to lose the exterior brick work. To get some kind of insulation i was going to frame in. I had figured 1inch EPS foam, then studs against that layer then fill the studs with XPS and seal the foam as a vapour barrier. I will be having to redo windows trim anyway so not a big concern on wall thickness. Would this be the right approach? i figured with the air gap between brick courses i wouldnt have to worry about the brick not being able to expel water from any potential condensation.

Not easy to figure out what to do this north in terms of insulation without a massive exterior layer of insulation that would kill any exterior character brick work.

any thoughts?

Morgan

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    Filling the studs with XPS is a waste of good foam, since the studs are 4-5x as thermally conductive. A 2x4 wall with 3.5" of XPS in the cavities comes in at about R11-R12 "whole wall" after factoring in the thermal bridging of the framing, the R-valvue of the brick & gyprock, the air films, etc.

    For less money you can 2" of foam strapped to the wall with 2x2 or 2x3 furring through-screwed to the brick with 4.5" masonry screws, then install split 3.5" thick rock wool batts (split down to 1.75% nominal) between the furring. The gypsum board then gets mounted to the furring.

    XPS has hefty greenhouse gas footprint due to the HFC blowing agents use. As the HFCs leak out over a couple of decades the performance drops to about R4.2/inch, the same as EPS of similar density. EPS is blown with pentane, most of which leaves the foam rapidly and is recaptured at the factory, and it's R-value is steady over time. So from a total environmental cost/benefit point of view you're better off starting with EPS, which is usually cheaper than XPS to boot.

    With 2" of EPS and R6-ish rock wool between 2x3 furring 16" on center the whole-wall R comes in at ~R14 whole-wall after everything is factored in. If you're unconcerned about additional thickness, adding another inch of EPS (and longer screws) would bring it to the R19-R20 range.

    If the interior brick wythe is structural, with the floor an ceiling joists embedded it's worth buying a small closed cell foam spray kit and sealing really well at the brick/wood penetrations with an inch or so of spray foam.

  2. GBA Editor
    Martin Holladay | | #2

    Morgan,
    Adding insulation on the interior side of an old brick house is risky, especially in cold climates. Interior insulation makes the bricks colder and wetter, thereby increasing the chance of freeze/thaw damage to the bricks.

    For a thorough discussion of the risks and possible approaches to insulating this type of building, see this article: Insulating Old Brick Buildings.

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