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Community and Q&A

How is head flashing done with parge coating around basement windows?

ERIC WHETZEL | Posted in Green Building Techniques on

We’re using 5″ of Roxul Comfortboard on the exterior of our foundation, so our basement windows will have plywood window bucks. We’re going to use HardieBacker board to cover and protect the Roxul, mainly around the perimeter of the foundation at grade and just below, but also around the basement windows. We will then use a product called Tuff II (readily available here locally at big box stores) for the parge coat.

I’m assuming the basement windows should have both sill flashing (which we think we have figured out), but also head flashing. For the rest of the foundation, if water finds its way between the top of the foundation and the Roxul, it can make its way down to the footings and then out, but what if it makes its way to the top of our window bucks?

I searched online for this detail, but I didn’t come up with very much. Attached are two photos that show this detail, but even though there’s head flashing present in both, it doesn’t look like there’s any gap between the flashing and the parge coat. Doesn’t this defeat the purpose of having the flashing? Should we maintain a 1/4″ gap between the HardieBacker/parge and the head flashing? Should we put insect screen in this gap? And unlike the windows in the photos, ours will be “innies”.

Does anyone know of any diagrams, photos, or videos that I could look up that show this detail? Does anyone have experience making this detail work? Any alternatives that might work?


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  1. ERIC WHETZEL | | #1

    Second photo didn't upload. Here it is again. Hopefully it works this time.

  2. GBA Editor
    Martin Holladay | | #2

    I think you are overthinking this -- but perhaps I am misunderstanding your question. Even if a little water gets past the flashing, it won't do any harm below grade.

    In any case, you may with to read this GBA thread: Installing outie windows with 2-inch exterior Roxul board.

    You may also want to study this Roxul manual: Insulating Sheathing for Residential Construction.

  3. ERIC WHETZEL | | #3

    I just want to make sure I understand ---

    Go ahead and do the head flashing, just don't worry about maintaining 1/4" gap? Or forego the head flashing altogether?

    I'm just concerned about what happens if water from above (e.g. roof or wall leak) makes its way to the top of the plywood buck in a basement window.

    We will have flashing from the Zip sheathing out over the top of the foundation and past the 5" of Roxul and the HardieBacker. Is this more than sufficient, so don't worry about the top of the window bucks for the basement windows? I just want to make sure I don't mess up this detail (I'm paranoid about water infiltration generally).

    The documents supplied by Roxul and their technical support staff are all excellent, but I can't seem to find info regarding how builders detail the parge coat with basement windows anywhere (especially with insulation on the exterior of the foundation). Maybe I've just missed it.

  4. GBA Editor
    Martin Holladay | | #4

    It sounds like you have flashed the tops of your window bucks -- is that correct? -- but you are worried that there is no path for liquid water to dribble outward at this location. Is that a fair statement of your worry?

    If that's the worry, I think you're overthinking things.

    (a) There shouldn't be much, if any, liquid water at this location.

    (b) If there ever is any liquid water at this location, it can travel sideways and down (through the mineral wool).

  5. ERIC WHETZEL | | #5


    Yes, that's my worry.

    Thank you for clarifying --- I appreciate the help!

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