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Community and Q&A

Thoughts on this Unconventional Window Head Flashing Detail

olandsns | Posted in Building Code Questions on

Owner builder here. I’m building a small shed workshop, permits required and pulled, and am in a bit of a dispute with the inspector over my window flashing detail.

I’ve framed the building with hardie panel over battens, and building paper. No sheathing. This is to code and good enough for a shed given the price of osb.

I’ve installed the windows over the hardie. In retrospect, I would have installed them first and put the hardie over top of the flange and head flashing.

with the hardie being considered my sheathing membrane, I have sealed the sill, jamb with liquid applied flashing, taped the sides of the flange and sealed the head flashing with liquid applied.

the inspector wants me to pull it all down and put the flashing inbound of the hardie, and building paper. He doesn’t trust the liquid applied.

frankly, I think my solution is fine. There’s going to be trim and caulking above that. That’s 3 levels of protection, keeping moisture from getting in behind the window flange.

I see people using zip tape here and calling it good, but my inspector says gravity method or nothing.

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  1. Expert Member


    Unfortunately what we think of the detail doesn't really do much to resolve your dispute with the inspector.

    Practically whether the detail will cause problems probably depends on how exposed the window head is, and what climate you are in. Here in the PNW having the flange protected by sealants or tape isn't something I'd do or expect to get away with, unless that occurred behind the cladding.

  2. walta100 | | #2

    Unless you can pull a rabbit out of your hat by finding a drawing from your windows and or siding manufacture showing exactly what you built, it seems very unlikely you can win this dispute.

    The smart move is a quick surrender and to redo it correctly.


  3. Patrick_OSullivan | | #3

    Is the WRB over the top flange of the window? It doesn't sound like it. Regardless, sealing the head of the window to the cladding means that water behind the cladding but above the window will be directed inside, which is probably not what you want.

  4. Jon_R | | #4

    If you adding siding, I'd see the similarity of what you have to Zip sheathing with fluid applied WRB. Water behind the Zip is typically not considered an issue. But then Zip is designed/tested for this water barrier role.

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