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Community and Q&A

Increase size of Z-flashing if I need to add a slope between SmartSide panels?

etting | Posted in General Questions on

SmartSide 4×8 panels require the z-flashing on horizontal seams to be sloped slightly toward the outside, but I gather that z-flashing is made with right angles so that the seat would be flat, not sloped.  For SmartSide that’s 3/8″ thick, should I buy 7/16″ or 1/2″ Z-flashing so that I can bend the seat into a slight slope (which would slightly reduce how far outward the seat reaches)?  Or am I missing something, as it seems strange that this common use of Z-flashing would require it to be bent by the user?

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  1. Expert Member
    Akos | | #1


    The flashing is there to keep water getting into the top edge of the panel, no slope is needed (doesn't hurt, but not required). Just use as is. I would want the Z flashing to be pretty much flush with the top of the siding (just a bit more than the panel thickness) for cleanest look.

  2. etting | | #2

    Thank you, Akos. I assume that the slope is intended to keep water from pooling on the z-flashing seat where, if it were deep enough, it could start soaking the bottom of the upper panel. If I were to use the flashing as-is, would your recommendation for "just a bit more than the panel thickness" be 7/16" or 1/2", or do they make the 3/8" a little bigger than 3/8" to allow a slight margin on 3/8" panels?

  3. Expert Member
    Akos | | #3


    My experience is with the 5/16" thick Hardie panel. The min bend for my flashing shop is 3/8 so that set the size. The vertical gap was 1/4" , not much water would get stuck there.

    I would get a piece made up and see how it looks.

  4. Expert Member


    Are you buying pre-formed flashing, or getting the pieces bent by a fabricator? If the latter, you can get any slope y0u want on the horizontal portion.

  5. etting | | #5

    I agree, Akos, that the gap reduces the likelihood of water soaking into the upper panel. Perhaps there's also a concern that water would seep through the junctions of two pieces of flashing, but that doesn't seem likely to amount to much.

    Thank you, Malcolm. I was planning to buy it off the shelf, where it's around $5 for 10 feet. I expect having it fabricated would be much more expensive. What size of pre-formed flashing would you recommend for 3/8" SmartSide if a) I intend to bend it and b) if I dont? Would you bother to bend it?

    1. Expert Member
      MALCOLM TAYLOR | | #6

      I don't think you would have much luck getting a useful or consistent bend unless you had your own break. I'd rely on a small capillary gap between the flashing and panel above and not worry about it.

  6. etting | | #7

    Thank you, Malcolm. I was wondering how I'd bend it decently. I surmise that the slope they recommend may be ideal, but it's more than most would take the time and expense to implement.

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