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Detailing flashing, waterproofing, and the various layers of exterior roof insulation and at the valleys and sidewalls

Irishjake | Posted in General Questions on

I am playing with how to integrate the different layers of thick exterior insulation, flashing and WRB at the top of the window/door trim, at the roof/sidewall, and at the valleys when using the PERSIST or ETMMS type methodologies. The window and door details are obvious when it comes to flashing right to the window or door flanges, but the other details are a bit more complex.

For instance:
Normally a “Z-flashing” is installed above window/door trim and flashed all the way back to the sheathing, behind a small rainscreen, but with two thick layers exterior NEOPOR insulation (9″ on the walls & 14″ on the roof), this detail along with the detail where the where the roof meets the sidewall of a dormer or where the top of the dormer roof meets the roof above, or where the valleys of two roof lines come together isn’t as straight forward.

Any resources where some details for this can be found. I’ve seen many section views for eave details, but not the others….

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  1. GBA Editor
    Martin Holladay | | #1

    These details depend on where you decide to install your water-resistive barrier (WRB). If you decide to install your WRB on the exterior side of the rigid foam, it's easier to integrate your WRB with your window and door flashing.

  2. Irishjake | | #2

    Martin - Yes these details would be better if that was the case, but I don't believe putting the WRB at the outside of the insulation is a durable (with the caveat that the flashing, WRB and insulation are integrated right!)

    My WRB; Prosoco MVP is a spray/rolled applied membrane that goes directly on the sheathing and behind the insulation. Prosoco MVP or CAT5 will be used on the roof under the insulation also.

  3. GBA Editor
    Martin Holladay | | #3

    So if your WRB is installed at the sheathing layer, you'll need to get out your brake and bend some deep Z-flashing.

  4. Irishjake | | #4

    Yes deep "z-flashing", but if the insulation goes to the top of the window buck, where does the z-flashing on top of the window trim and door trim go? Does the window buck end up being as high as the window trim, possibly leaving uninsulated space above the window or door, or do you just flash to the backside of the rainscreen to capture the gross water and let the other spray-on flashing at the window flange shed out to the outside?

    What about the sidewalls on the dormers? The layers of insulation are all staggered, so there isn't a direct line back to the sheathing....except at the window and door bucks.

  5. GBA Editor
    Martin Holladay | | #5

    To be sure we're all on the same page, it's time for a sketch. You can make a sketch with a pencil and paper if you want, and take a photo of the paper.

  6. Irishjake | | #6


    Here is a labeled diagram of my foundation/sill detail - which shows how my flashing, insulation, siding, etc., all work from the sheathing out. I am trying to do this in each of the scenarios I described above too, just trying to work out the details. I've included an unlabeled diagram of my window and insulation and window buck detail too.

    Joe L. states and shows in the article "Zeroing In" that the window and door flashing can be flashed to the backside of the rainscreen strapping when using rigid foam on the exterior. So I may do that at the head of my trim on my windows and doors.

    Still working out the sidewalls.

  7. GBA Editor
    Martin Holladay | | #7

    Your WRB is back so far from the siding that you don't have to flash the window head all the way back to the WRB.

    If I were you, I would extend my window head flashing from the outer surface of the outer layer of Neopor to the window head or to the top of the exterior head casing.

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