New vent flashing on existing mineral rolled roof

moto goosey

I am doing some renovation and need to add a plumbing vent. I was planning to use an aluminum/ rubber vent flashing from Home Depot (Oatey "all flash no calk roof flashing") but a friend told me that I should use mesh tape and roofing cement on this type of roof material.

I had a Solatube installed recently and it looked liked they did a good job installing the flashing that came with that. (Image attached) My plan was to copy them by: Making a 3" hole through the roof, make a horizontal slit in the roofing at the sides of the hole as wide as the flashing, cut a small radius in the roofing to clear the bulge in the flashing, slide the top half of the flashing under the uphill flap of roofing using Henry 209 sealant under the bottom half and along all the edges and securing the flashing with galvanized roofing nails on the sides and bottom.

Does this sound right to you guys? Any advise is appreciated!

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Slyfox

The sun tube was flashed, ok, but I would not call it good.
The bottom of the flange can be left exposed on a low sloped application,
but the sides should have been flashed all the way down each side.
(Not an immediate problem, but probably will be an issue later on.)

I would pop the pipe through, wrap it in roof cement & rag, then stick a pipe flashing on it and flash it into the membrane like they did the sun tube except make sure it slides far enough up under to where both sides are properly protected.
You would only need one face nail at the bottom of the pipe flashing and that would be covered with a metal caulking.

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moto goosey

Thanks for the reply, Slyfox.

How should I get the metal flashing under the roofing if I put the pipe through first? It seems like I could only lay it on top of the roof and then it would leave a joint along the top and sides that overlapped the wrong way.

Thanks,
Dan

Slyfox

Sorry, I was thinking as a roofer in my reply instead of a DIY'r.
I would have a piece of field membrane to cut around the pipe and use a square nose trowel & torch to heat the nearest lap above and open it up to allow the new membrane under.
The new membrane would go over the existing.

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