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Community and Q&A

Coping Metal on Parapet Wall

monchgreen | Posted in General Questions on

Hi! As described in an earlier post regarding low slope membrane roof – coping metal on parapet wall not angled properly, rain falling on coping runs over siding instead of to membrane. Suggested fix by installer is to attach an right-angled piece of same color metal to outside edge of coping as shown in attached. Any thoughts? Much appreciated.

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  1. seabornman | | #1

    It could work, but might pool water on top of the coping. Are there splice plates or is coping overlapped? Does the membrane carry through underneath without penetrations? How will they attach angle?

  2. monchgreen | | #2

    Hi Joel - yes if could be assumed that water would pool on top of coping which is overlapped but caulked. The membrane is screwed to outside of parapet wall as shown below in first picture - not screwed on membrane side which is preferred. The angle would be attached with some sort of double-sided tape. BTW general contractor has offered to pay for replacement coping metal that would be taller than existing metal by a couple of inches in front and angled to direct water toward membrane with half-inch drip edge as well (as in second picture) but original installer suggests would not make any difference to replace and is pushing this 90 angled-metal idea. Thank again!

    1. Expert Member
      MALCOLM TAYLOR | | #3

      What argument can your installer make that the replacement flashing will not make a difference? That's just silly. Make sure the new flashing has hemmed-edge extending out at least an inch.

      If the angled metal will cause water to pool on the flashing, it will significantly shorten its life. That option has a real DIY feel to it. Not something that should be considered for what is essentially a new build.

      All that being said, both solutions only address the very small amount of water that falls directly onto the cap-flashing and drains to the exterior. You are still going to get all the rain that hits the exterior wall unimpeded by any overhangs, so I'm not sure how much of the problem either option really solves.

  3. monchgreen | | #4

    Thanks, Malcolm - much appreciated! Current flat coping has 4 inch front. New coping as current would only be screwed on siding side. How does this look? Thanks again.

  4. Expert Member
    Akos | | #5

    Your sketch is good, it is really what should have been installed in the first place. You don't need much slope, even 1/2" drop over the 11" is more then enough for proper drainage.

    If you really want to protect your siding, I would extend the coping and create a bit of an overhang. Even 6" would make a big difference in keeping water off the siding. It would change the look of the house slightly but would still maintain the modern aesthetics.

    It would also be a good spot for accent lighting.

  5. monchgreen | | #6

    Thanks, Akos - much appreciated!

  6. monchgreen | | #7

    Thanks again for advice from GBA. Builder and roofer have agreed to replace metal coping on parapet wall with attached design. Again, metal will be attached on outside only over the flat parapet wall with membrane underneath and pieces overlapped with caulk. Question - any problem with inside drip edge at 1" - too much? Any other comments truly welcome.

  7. seabornman | | #8

    The SMACNA Design Manual says 1/2" - 3/4" so 1" is probably fine. The Manual also shows a continuous cleat on the front side and exposed fasteners on the back side. This is the way I have specified for many years. It provides a straighter exterior flashing plus no exposed fasteners on the good side. See

  8. monchgreen | | #9

    Thanks, Joel! I will keep 1" on both sides. Likewise thanks for the link - a good design - cleaner than what I have for sure...

  9. walta100 | | #10

    I like the drawing. Now let’s see the plan for a water tight corner assuming you have a few.


    1. Expert Member
      MALCOLM TAYLOR | | #11


      Like all metal cap flashing, you can either lap or create a standing seam. I would expect any contractor to adhere to the guidance of their governing professional association. For example, here is the one for us here in BC:

  10. Deleted | | #12


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