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Community and Q&A

Flashing an Extended Window

user-7075008 | Posted in General Questions on

Our  windows will protrude 1″ proud  of our 1″ zip sheathing. This is not enough depth for our furring (3/8) and siding (9/16) to guarantee the siding wont extend past the window frame. Can we install 1-1/2″ wide  furring around the window opening , flash over the furring, and install the window to the 1’1/2″ flashed furring…  and then of course  flash over the window flange and then bring the  wall furring strips down . There will be no wood casing around the windows. The siding will meet the edge of the window frame.

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  1. Expert Member


    Yes, it's quite common to install windows outboard of the rain-screen battens. One advantage is it is easier to provide a drainage path at the sill for any water that might get in.

    1. user-7075008 | | #2

      Any tips on how to get your flashing membrane neatly over the furring without causing bubbles? The flashing will go over the 3/8 furring and on to the sheathing.
      Maybe it's better to use Liquid flashing. We run our flashing the entire perimeter of the windows

      1. Expert Member
        MALCOLM TAYLOR | | #3


        I'm not sure you need to extend the flashing tape back onto the sheathing if you make the furring strips around the window wide enough.

        1. user-7075008 | | #4

          Seems like water could get behind the top furring strip if it’s not flashed to the sheathing

          1. Expert Member
            MALCOLM TAYLOR | | #5

            Ah - I see the problem. Usually the top of the window is protected by a head-flashing which extends back to the sheathing. If the windows are mounted on the furring, you need an additional piece of head-flashing that extends down over the first one and back to the WRB once it has cleared the window flange.

  2. user-7075008 | | #6

    Won't the rubber flashing over the nailing flange be enough as long as I can detail the flashing over the furring and on to the sheathing? The additional drip cap will lessen the crisp design we have. The windows come with an integral drip cap .

    1. Expert Member
      MALCOLM TAYLOR | | #7

      It depends where you are. Our code specifically requires a head flashing with end dams, but as I understand it many jurisdictions don't. Probably where you are a peel & stick membrane run over the furring at the head should suffice.

      I wasn't suggesting that the additional metal flashing be visible. It would run down the sheathing, out over the furring, and lap over the vertical leg of the typical head-flashing. Only a small part of that metal head-flashing would protrude on top of the flange of the window.

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