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Just had our on-demand water heater replaced. A few days later, I noticed rain leaking around the vent pipe in the attic. The vent pipe has flashing installed on the metal roof, similar to the pic below. It looks like there's a small tear where it seals to the pipe and in general just looks like it's deteriorated a bit. I'd like to replace it with a similar flashing but I'm not sure how to handle all of the screws that were installed around the existing flashing. If I back those out, what must I do to ensure no leaking around them when they are removed? How do I make sure I don't reuse a hole by accident or insert a new screw too close to an existing hole and cause a tear in the metal roof?

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  • Why not plan on reusing all the holes in the metal roof instead of making a whole new set of them?
    – FreeMan
    Commented Nov 13, 2023 at 19:43
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    I'm not sure I could screw through the new flashing and hit every existing screw hole.
    – gnomer
    Commented Nov 13, 2023 at 20:06
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    Maybe include a pic of the existing install. Someone might see a better way of fixing it that won't involve new holes...
    – FreeMan
    Commented Nov 13, 2023 at 21:03

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Hopefully the last guy used #10 roofing screws. Use #12 roofing screws for your installation. Butyl tape makes a nice gasket material instead of (or in addition to) sealant. Leave an unsealed couple inches at the low point so that any water that infiltrates can drain.

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You need screws with neoprene washers.

Metal rood screws with neoprene washers

If you need to make new holes, put one of these screws in the old holes too, to seal them up. Additionally, I'd consider some Henry's, which does come in white too, but maybe under a different name. Replace the flashing and parts as needed, fill all old holes with a screw and washer, then put a generous coat of Henry's on the whole area.

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  • Ok, that makes sense. So new screws in the existing holes, sealant over them, then replace the flashing.
    – gnomer
    Commented Nov 13, 2023 at 20:08
  • @gnomer No, replace flashing first. 1) Get all the new parts into place, 2) screw them down, 3) apply sealant.
    – user177013
    Commented Nov 13, 2023 at 20:14
  • I'm not a big fan of the "generous coat of goo" approach. It looks like poo and can obscure actual problems. Seal the old holes. Install. Seal the new holes.
    – isherwood
    Commented Nov 13, 2023 at 22:03
  • @isherwood Except the OP says it is leaking... I turn to the goo when it's leaking. I've wasted too many hours on roofs with a leak, moving this, shifting that, when these days I just slap some goo around the flashing. Yeah, you see it, but really only when you're looking for it. You'll forget it's there and probably never see it again. Unless it really stands out, which can be the case on occasion.
    – user177013
    Commented Nov 13, 2023 at 22:18

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