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Flashing Windows in a Foam-Sheathed Wall

PatriciaCranberry | Posted in Green Building Techniques on

CZ3. My WRB went on top of the sheathing. The WRB in the window openings (“the excess”) was laid back on to the sill, jamb and head of opening and stapled in place. Then 1″ of rigid foam was added. The vertical and horizontal seams of the rigid foam were taped above and below each window. 1×4 furring was “picture framed” on the flat around each opening. 1×4 vertical furring was installed to create a rainscreen. I think the sill and side of windows can simply flash to the foam. It acts as WRB along with the 3/4inch air space. But what about the head?

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  1. GBA Editor
    Martin Holladay | | #1

    Remember, you are flashing the window rough opening, not the window. For more information, see Installing Windows In a Foam-Sheathed Wall.

    How to flash the head depends on the type of head trim that you plan to install. On a traditionally trimmed window with exterior casing, you will install Z-flashing above the head casing. The siding should lap over the vertical leg of the Z-flashing.

    If the rough opening is properly flashed, you don't really need to flash the window for watertightness. You just need to detail the window for airtightness.

  2. PatriciaCranberry | | #2

    Kind like this? Except in my case, the rigid cap flashing or just z flashing will tape directly to the rigid foam.

  3. Expert Member

    Unlike that illustration, it's a good practice to bent the ends of the head flashing up, not down, to create an end dam.

  4. PatriciaCranberry | | #4

    Up...not down.....feeling better. thanks!

  5. Smipau29 | | #5


    what would the detail look like for Innie Windows with rigid foam as the WRB? I know the article in regard to innies and outies where it references WRB plain for innie windows would most likely not be at the rigid foam.

    Currently Tyvek is the air barrier and foil faced rigid foam as the WRB then rain screen. Attempting to finalize details for an innie window since the structure will have zero OH ( yes I have read your stance on No overhangs but wasn’t able to convince my client otherwise). A PVC “picture frame” , on the edges, will extend out 2” from the cladding giving coverage of roughly 2.5” for the window. Both PVC Horizontals will be sloped.

    I assume the detail will roughly be similar to BSC Deep energy retrofit builder guide Wall 1a assembly prehung door. However, I’m concerned about attaching the pvc trim and of it should be flashed in. Also concerned about how to attach the PVC trim piece with out having to remove insulation in order to install a 2x nailer. I would like to fasten similar to the second attachment.

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