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Ask-The-Experts > Installation

New installation over existing square vent
I'm a fairly competent DIYer and have decided to tackle a re-roof of my home using metal roof over existing asphalt shingles. I understand all the basics, including the need for an appropriate barrier between the existing roof and the new roof and all the roof/ridge/rake trims, etc. The one thing that has me stumped is how to handle the exhaust vent for my oven. The original builder vented through the roof (don't ask me why -- I don't know). It's got a big (I'm guessing 8") pipe coming up into a square covered vent opening. I've found no one that offers anything to accommodate this when using metal roofing. How do you seal this up properly? (Note, moving the vent to the soffit would probably be very difficult and to the outside wall even more so (brick).

I'm looking at a 26-gauge classic rub sheet roof. The roof pitch is 5/12. We don't get a lot of water here (it's rained here about 2-3 times in 2011), but when it comes it usually pours (several inches at a time). We DO get high temps (regularly 110+ in the summer) and high winds (20-30mph is normal, plus we are reasonably close to the gulf and have an occasional hurricane). Not sure if any of that's important, but figure it can't hurt for you to know all the facts.

Hope y'all can help!
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Thanks for the question.
Pipe vents are certainly a challenge, but very doable.
It is beneficial if the pipe is small enough to land completely in the 'flat' of the panel.
Regardless, if the pipe vent can be installed such that water is directed around the vent and not trapped, a rubber pipe boot can be used.
If the pipe is too large or located such that water would be trapped, then a panel endlap at the pipe is needed. The down slope panel should be installed first, then the pipe vent and finally the upslope panel.
This follows the roofing fundamental that materials are layered so that up slope material is on top of down slope material.
David Stermer
I have a similar question regarding exhaust vents and tubular skylights. I reroofed a home with standing seam paneling after tearing off the old composition roof but "saving" the built-in flashing around an existing tubular skylight. However I was unable to reposition it favorably to just the flat pan of the panel and thus had to cut a rib section out to accommodate the flashing.

I did not cover the flashing (which is kind of thick) by layering it as mentioned in the comments above, but just made a round hole in the metal, carefully caulking the cracks and then caulking the outer (existing) flashing right flat to the metal pan and screwing in with neoprene washered screws. Also made sure the exposed standing ribs which were severed were filled with sealant so no water could enter that way.

I did the same with a new metal bathroom exhaust vent with the metal flange, in one case caulking and screwing it flat to the metal pan without having the upper section of the panel covering the upper section of the built-in flashing. It is a fairly low pitch roof and it seemed counterproductive to have a slice in the panel above although preferred I assume.

My question is, is it always forbidden to attach a metal flanged roof vent the way I described? Or should I rip it up and try to cover the upper section with a few inches of metal panel. And could one splice a section of standing seam paneling over the upper section of the vent to accomplish the same thing?

I'll attach some pictures.
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