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Musings of an Energy Nerd

Deep-Set Brickmold Trim for ‘Innie’ Windows

A Canadian manufacturer has developed waterproof exterior jamb extensions for vinyl windows

Installed as an "innie," this vinyl window is trimmed on the exterior with deep-set vinyl brickmold. The trim integrates exterior jamb extensions and a deep sill with vinyl casing. Note that the corners of the trim are factory-welded. [Photo credit: Chris Isaak, Northerm Windows]

If you install flanged windows on the exterior side of a sheathed 2×4 or 2×6 wall, and you then install exterior rigid foam, you end up with an “innie” window. Innie windows work well. Before you can install furring strips and siding over the exterior rigid foam, though, you need to come up with exterior trim details (sometimes called “exterior jamb extensions”).

Anyone installing innie windows needs to install weather-resistant (and waterproof) details to trim the exterior jambs, the exterior head, and the wide exterior sill. This isn’t impossible, but it’s fussy work that is rarely detailed well. Some builders use solid PVC trim (cellular PVC like Azek); some builders use copper flashing. Almost all builders who come up with site-built details like this end up using peel-and-stick flashing for the tricky spots, covered with some type of durable material to hide the peel-and-stick.

A new approach for exterior jamb extensions

During a recent visit to the Cold Climate Housing Research Center (CCHRC) in Fairbanks, Alaska, I saw a wall mockup that displayed an intriguing new way to trim innie windows. Ryan Tinsley, a research scientist at the CCHRC, explained that the trim system was developed (and is now sold) by Northerm Windows of Whitehorse, Yukon. (Capital Glass in Anchorage, Alaska, is a U.S. distributor of Northerm Windows.)

One architect who specifies the detail is John Berg of Stantec, an architectural firm in Whitehorse, Yukon. I called Berg on the phone and asked about the use of deep-set brickmold.  “We struggled for at least twenty years with these window details, as more and more insulation was installed on the exterior of the structure and our walls got thicker,” Berg told me.

This window mockup at the Cold Climate Housing Research Center shows cutaway versions of vinyl components sold by…

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  1. charlie_sullivan | | #1

    This is a huge step forward. On the surface, it's a faster, likely cheaper way to get a reliable, durable installation. But beyond that, it will save headaches for clients who can't find a builder who knows how to put a window in a thick wall, or who find one who thinks he knows how, but actually doesn't. And it will save headaches for contractors who know exactly how to do it right, but want to avoid the hassle of making sure everyone on the crew is getting all the details right.

    As much as I like the concept of "keep craft alive", there are a lot of building details that are better done in a factory, rather than being re-invented and made piece by piece on the job site.

  2. Expert Member

    I agree with Charlie. This might well be what determines the location of windows in deep walls for builders who didn't want the time consuming and potentially problematic task of detailing innie windows.

    Two very small points:

    The text says you can order then in the NWT, but their plant is in the neighbouring territory of Yukon.

    The section supplied by Stantech used J trim above the window where there should be a drip flashing.

    1. GBA Editor
      Martin Holladay | | #5

      Thanks. I've made the correction concerning Yukon. I appreciate your help.

      (And I agree with you about the J-trim. J-trim isn't head flashing.)

      1. Expert Member
        MALCOLM TAYLOR | | #6

        Thanks for the blog. It's great to hear about innovations like this. Hopefully other manufacturers follow suit.

        I bet a go0d half of Canadians (myself included) couldn't label the three territories correctly on an blank map.

  3. coldclimatehousing | | #3

    A big thank you for the informative article and for the enthusiastic visit to CCHRC in our remote corner of the country here in Fairbanks, Alaska.

    One of the focuses of the Cold Climate Housing Research Center is developing and designing solutions to bring high efficiency, high-performance homes to the affordable housing market. As important as "keeping the craft alive" is when it comes to affordability, there is very little luxury for craftsmanship. The solutions to accomplish this on a budget rely on meticulous detailing that is durable and practical.

    Here is a case where those who can afford to choose by voting with their pocketbook can make a difference. Selecting a window product like the one described will help support the market and encourage competition which will make high-efficiency building solutions more affordable for all. If individuals with means made choice like this with there homes as they have with organic foods a similar transformation could be made in the residential housing industry.

  4. AntonioO | | #4


    Not exactly the same idea, but here's something offered by Canadian fiberglass window manufacturer, Duxton.

    1. stephen_murdoch | | #9

      Antonio beat me to it - Duxton is the only window company I've found doing something similar - but there's some serious sticker shock involved.

      1. GBA Editor
        Martin Holladay | | #10

        Antonio and Stephen,
        Thanks for the information on Duxton. Every manufacturer uses different terminology. It looks like the relevant Duxton feature is found in the so-called "Perimeter options" -- specifically, the "New Wide perimeter option" or the "350 Panning perimeter option." Antonio's link brings you to the right page; see the image below.

  5. AndyKosick | | #7

    I don't think spending hours detailing peel-and-stick membranes is what most people mean by "keep craft alive." There are still plenty of places to bring craftsmanship to a build. This kind of detail is probably the number 1 gripe I hear from builders when proposing increased exterior insulation. This could be a solution that tips the scales for a project. Hope it makes it to the lower 48 soon.

  6. PAUL KUENN | | #8

    I'll still need Azek and Trex for all the old 2x4 walls that I add 4-6" of insulation to but at least we have a great solution and it's actually being sold. Yah Hey Canada! Guess I should have stayed in AK. Love the CCHRC.

  7. ianmci | | #11

    So much vinyl.... I won't knowingly use it in my projects because I find it so horrifying from an environmental and public health viewpoint. I know GBA feels that the vinyl industry has made improvements in the raw material production and recycling, but I would love to see details that...don't rely on vinyl.

    1. GBA Editor
      Martin Holladay | | #12

      Here are links to two articles with photos and details on trimming innie windows without using vinyl brickmold:

      "Innie Windows or Outie Windows?"

      "Windows in Thick Walls"

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