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Window trim flashing details on a flanged window?

BrunoF | Posted in General Questions on

I plan to have Marvin Elevate, flanged windows installed using the Marvin Method and integrated into Benjamin Obdyke hydrogap WRB.  This means that the WRB will lap on top of the upper nailing flange for positive drainage.  The windows will then need to be trimmed with 5/4 x 4 trim and usually, the siding folks apply z flashing to the top of the trim.  If they do that, should the hydrogap be cut so the z flashing goes under, or should they use tape, or some other method?

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  1. Expert Member


    You have two choices:

    - You can put the head-flashing (with end-dams) directly onto the head of the window frame and lap the WRB over it. Then the Z flashing over the trim will sit on the WRB. If you do this, hold the trim up about 1/8" above the head-flashing to allow a drainage path.

    - You can locate the head-flashing over the trim, and lap the back leg under the WRB. Note this is not the Z flashing the siders would use, and I wouldn't leave installing the head-flashing to them.

    1. BrunoF | | #2

      Option 1 seems more likely to be implemented correctly...maybe I should then tape the z-flashing to the WRB or just leave it as anything behind it will drain out at the top of the window?

      1. Expert Member
        MALCOLM TAYLOR | | #3


        I agree. If you go with option one, I would leave the Z flashing un-taped. It's basically just there to stop water getting in at that junction.

        1. Ryan_SLC | | #4

          I tend to agree with the expert Malcolm on this.

          Benjamin Obdke that you are using says no horizontal taping.

          I agree. With perfectly installed and taped Everbilt house wrap by the general contractor, the horizontal tape was holding water for days even though I couldn't see it. No visible tape fish mouths either.

          That came off and I did Obdyke FlatWrap with no horizontal taping after my experience.

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