# Cutting Vent Hole in Roof How To Wanted



## wildbilly (Feb 16, 2009)

Does anyone have a good procedure for installing a roof vent through a asphalt shingle roof? I'm going to a 2" vent with a metal/rubber vent flashing. It's cutting the hole that I'm concerned about getting it in the right spot relative to the shingles.

I would think the best way would be to drill a small hole from the underside that just goes through the wood only; tricky I know. Then poke something in the hole to push up the shingles. Then you can see where that hole is and adjust so that a 2" hole would just under the edge of a row of shingles. Now where to cut from for the two++ inch hole??? Try and remove some shingles and get down to the felt and cut it from the top?? It will top out here in MN at 48 today so the shingles won't be that soft and only colder and rainy/sleety(so I must get it right the first time) for the near future.


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## Mazz (Mar 23, 2009)

wildbilly said:


> Does anyone have a good procedure for installing a roof vent through a asphalt shingle roof? I'm going to a 2" vent with a metal/rubber vent flashing. It's cutting the hole that I'm concerned about getting it in the right spot relative to the shingles.
> 
> I would think the best way would be to drill a small hole from the underside that just goes through the wood only; tricky I know. Then poke something in the hole to push up the shingles. Then you can see where that hole is and adjust so that a 2" hole would just under the edge of a row of shingles. Now where to cut from for the two++ inch hole??? Try and remove some shingles and get down to the felt and cut it from the top?? It will top out here in MN at 48 today so the shingles won't be that soft and only colder and rainy/sleety(so I must get it right the first time) for the near future.


Can't help there, but I would run the pipe to a soffit vent if possible and avoid any roof penetrations. Especially if it's only a 2".


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## 47_47 (Sep 11, 2007)

Why does the pipe have to be relative to the shingles? Drill a pilot hole from the inside through the shingles to locate the vent pipe. Remove the shingles in this area, cut your hole, install your vent pipe and flashing, re-fit the shingles. 

BTW, your hole will be oval and not round (roof slope).

Do not run the vent pipe into a soffit vent. Do you want sewer gases in your attic?


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## wildbilly (Feb 16, 2009)

The flashing is meant to slide under the shingles upslope thus the hole should be near the edge of the shingles so you can slide it up under them.


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## Scuba_Dave (Jan 16, 2009)

What kind of vent - purpose?

You specify roof vent = to vent heat from the attic?

Do you have to do it now?
Cold weather is a bad time to be messing with shingles


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## DUDE! (May 3, 2008)

just a thought, but I would figure the route of the pipe would determin where you penentrate the roof. If you try to get to careful with where on the roof, you'll end up with a leak. As already said, cut your hole, remove shingles in the area of the hole and go from there. One step at a time, install pipe, fix new hole in the roof. good luck.


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## wildbilly (Feb 16, 2009)

It's a 2" drain vent. I want to get it done now so I can move on. It's a drain for washing machine and a 1 1/2" kitchen sink vent will connect to it. I could just try and get it in the heat vent that is there for now. I can move the vent within reason plus plastic is flexible. It's now going to stay dry tomorrow but only hit 40.


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## kennzz05 (Nov 11, 2008)

Dont know if code allows but any other nearby vents you could tee into or y into


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## zosoplumber (Nov 21, 2008)

just use a 2 " hole saw bit from inside the attic, it will make a nice clean cut through the wood and shingles, the roof boot you install will make it water proof, and to find out where the hole needs to be drilled, use a plumb bob, by holding the string end up to the wood and lining the plumb bob up center with the 90 or tee you have below.


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## brokenknee (Dec 13, 2008)

zosoplumber said:


> just use a 2 " hole saw bit from inside the attic, it will make a nice clean cut through the wood and shingles, the roof boot you install will make it water proof, and to find out where the hole needs to be drilled, use a plumb bob, by holding the string end up to the wood and lining the plumb bob up center with the 90 or tee you have below.



Yep, just cut/drill the hole were it needs to go, then put the flashing under the singles. It is rare that the singles work out to were they just fit over the flashing with out having to trim a little around the top.


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## II Weeks (Jan 6, 2009)

a 2" hole will not fit a 2" pipe. if the roof is lets say, 9/12, you'll need a 3 1/2" hole saw. Do what the others suggested. drill a pilot hole. get up on the roof, if you can. peel back the shingles even with and above the drill bit. either use a sawzall or circular saw and cut in a rough opening of 3-4" inches round or square, doesnt really matter. Install the boot, pipe and with tar under the top and two sides, not the bottom. cut the shingles to fit around the boot. its usally a fast and esy job


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## johnnydanger (Dec 21, 2008)

Could you use a mini-vent in this application, instead of going through the roof?


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## al's sewer (Apr 7, 2009)

to mark the hole i usually use a plumb bob. hold it up against the roof from the inside and center it with your pipe. If you don't have a plumb bob just use a heavy nut or washer tied to a string. use a sawzall or hole drill to make the hole.


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## stubborn1 (Oct 24, 2008)

Is a 2" vent pipe through the roof legal in your area? In my area, we can't run anything smaller than a 3" vent through the roof due to concerns with the vent freezing up in winter.


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## kenmac (Feb 26, 2009)

al's sewer said:


> to mark the hole i usually use a plumb bob. hold it up against the roof from the inside and center it with your pipe. If you don't have a plumb bob just use a heavy nut or washer tied to a string. use a sawzall or hole drill to make the hole.


 
I use string & nail for marking location use drill for pilot hole & sawzall to cut


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## Jwhitman (Aug 25, 2009)

A question for II Weeks. In the picture attached showing the vent flashing. Is the bottom edge of the plumbing vent stack flashing attached using nails? If so should these nails be sealed with caulking, is there a chance for leaking due to the holes the nails make?
Thanks,
J


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## Jon39 (Jun 2, 2010)

From time to time I need to put a 6" range hood vent pipe up through a roof; apart from a very expensive (and deep) 6" hole saw, is there a way to project the circle onto the pitched roof, either from above or through the OSB from below, to define the oval hole to be cut out?


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## bluejeans (Apr 15, 2010)

stubborn1 said:


> Is a 2" vent pipe through the roof legal in your area? In my area, we can't run anything smaller than a 3" vent through the roof due to concerns with the vent freezing up in winter.


 Why not?


Its called hoars frost.


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