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Cutting vent-stack hole in metal roof

Eric_Yettru's picture

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Hello - I need to cut a "perfect" vent-stack hole in some metal roofing. Are there any suggestions as to the best method? Should I use a bi-metal hole saw? Electric metal shears? The roofing is a bi-ribbed design which leads to my next challenge - how to flash around the vent stack. I've seen rubber gaskets used and I wonder how they hold up compared to comparable vent-stack flashing used for 3-tab asphalt roofing. Any ideas/suggestions/comments would be greatly appreciated. Thanks,Eric.

(post #171195, reply #5 of 6)

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Hello - I need to cut a "perfect" vent-stack hole in some metal roofing. Are there any suggestions as to the best method? Should I use a bi-metal hole saw? Electric metal shears? The roofing is a bi-ribbed design which leads to my next challenge - how to flash around the vent stack. I've seen rubber gaskets used and I wonder how they hold up compared to comparable vent-stack flashing used for 3-tab asphalt roofing. Any ideas/suggestions/comments would be greatly appreciated. Thanks,Eric.

(post #171195, reply #1 of 6)

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Hi Eric,

I cut vent holes with a sabre or jig saw after drilling a starter hole. There is a round rubber vent flashing with a bendable metal base that will conform to the metal ribs. Use a butyl tape or caulk under the base. I think they're widely available.

jiml

(post #171195, reply #2 of 6)

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Instead of drilling a hole, our plumber shoots a gun up through the ceiling from the inside and out the roof -- gets a perfect line every time!

(post #171195, reply #3 of 6)

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I use Ice Shield, or similar products over the decking and under the roof. It clings to the side of the Vent Stack, and makes a nice backup in case the flashing fails. I like the metal flashing better, and I think it holds up to heat and sun better.

(post #171195, reply #4 of 6)

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Eric: You can cut your hole several ways. It does not matter. Use a method you are familiar with or good at. Snips, hole saw, saber saw you still get a hole. We use drill & snips or chisel & snips. The only flashing to use is dektite or equal. They are flexible, will move with the roof and they last. We have used them for years and have had no failures when installed correctly. If no one in your area carries them call Dynamic Fastener @ 800 821 5448. They are available in 9 or 10 sizes. If you discuss your situation with the sales person they will help you select the correct fastener & sealant.
Ron.

(post #171195, reply #6 of 6)

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Eric, It may be unnecessary to mention this, but mark your hole plumb from the stack not square to the roof. Your finish cut will be more oval than round.

If nothing else is available, a standard plumbing vent jack will work. Run the sides and bottom over the roofing and the up-slope side under the metal. I use plenty of butyl caulk under and at the top edges. Rain is usually less of a problem than snow. Walk good. david