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Community and Q&A

Suggestions for retrofit rainscreen window flashing?

mchelnov | Posted in GBA Pro Help on

Because of moisture entrapment, I need to rebuild the outer portion of a wall. Originally a stucco on durock on WRB, on plywood sheathing, It is being replaced with Hardie plank on furring on Roxul rigid IS on WRB on plywood. This means the windows will end up being inset…and flashing will have to be installed at the sill, jamb and head. I’m concerned about the sill specially… how to handle the ends of it where it butts up to the jamb. I would appreciate creative ideas about how to handle this intersection specially…Also I’m open to any ideas for the head and jamb . here is a link to details I have come up with..

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  1. white_pine_vista | | #1

    We're building new and going for outie windows so this might not apply to your situation, but many of our other details are similar: fiber cement siding over 1X4 strapping over 2" rigid rock wool over house wrap as air and water barrier over plywood (then staggered stud 9.25" wall w cellulose). I attached some photos of our window flashing details. We used rigid foam 'frames' around the 2" extended plywood window boxes to nail the window flanges into and tape the peel and stick to. The foam is caulked to the house wrap and the flashing and trim details are visible in the photos. I will do a blog post about the window flashing details but here is our initial window post

  2. GBA Editor
    Martin Holladay | | #2

    How far you go with your window flashing details on a retrofit job is a judgment call. The best way to proceed is to remove each window and to flash the rough opening before re-installing the window.

    That's a lot of work, so many people are tempted to come up with a way to avoid the chore.

    Only you know whether you can get away with leaving the windows in place. Among the factors: how much rain do you get? How wide is your roof overhang? Is the roof overhang two stories above the windows or one story above the windows?

    It sounds like your retrofit job is being performed because of "moisture entrapment" problems. That's not a good sign. It might be wise to remove your windows and flash the rough openings correctly.

  3. mchelnov | | #3

    Martin and Patrick,

    thanks for your input! I'm willing to flash things properly ...slipping under existing Air /water quandary is how to do that with a recessed window ...Were you able to look at my details on the link above?...I'm using what I think is a pretty good detail for the sill and the head flashing...the jambs are another matter.and specially at the bottom of the jamb where the sill flashing intersects with the jamb....Do you have a knowledge source for inset window flashing? I know Passive house prefers inset (recessed) windows, so there must be some details that have been developed....

  4. GBA Editor
    Martin Holladay | | #4

    This type of flashing is usually made on site by a sheet-metal worker equipped with a brake.

    As you pointed out, the critical locations are the bottom corners of the windows. You need to come up with a way to prevent water that runs down the window jambs or the rough jambs from being trapped in the wall.

    Links to GBA's details for "innie" windows can be found on this page:
    Building Plans for a Deep-Energy Retrofit

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