Not a pro but DIY and I want to put an extra plumbing vent in my roof when they reroof soon. Will use 1 1/2" pipe and was wondering about holesaw technique. My roof pitch is a simple ranch (4 in 12?) and was wondering if I drill a 2" hole with a hole saw, straight on (90 degrees) will the pipe be able to stand upright and make it through the hole ok? --thanks
Roof vent and hole saw
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wwhitney
In the Trades
A 1-1/2" Schedule 40 pipe is 1.90" outer diameter. When you project that up onto your 4:12 roof, you will get an ellipse, with the minor axis still 1.9", but the major axis equal to 1.9" * sqrt(12^2 + 4^2)/12 = 2.003".
If you drill a 2" hole perpendicular to the roof, you might think you'd just need to open it a little to get to 2.003" across the upslope-downslope dimension of the hole. But that doesn't account for the thickness of the roof. If you're just drilling 1/2" thick sheathing, then the thickness of the sheathing will interfere by 1/2" * 4 / sqrt(12^2 + 4^2) = 0.158". But just on one side of the hole, on the other side the edge of the hole will slope away from the pipe.
So if you just want to drill perpendicular to the roof, use a 2-1/4" or 2-1/2" hole saw, depending on how thick the roof layers you are drill through are.
An approach to give you an elliptical hole would be to cut a wedge with a 4:12 angle (18.4 degrees). Then if you tack that to the 4:12 roof in the obvious way, you'll have a level face you can drill through plumb to get an elliptical hole. Now you can use a 2" hole saw.
A quicker but trickier approach with a 2" hole saw would be to use an extra long pilot bit. Then drill the pilot hole plumb (start off perpendicular and start angling the bit towards plumb as the bit enters) and use that to run the hole saw plumb. This would require a good grip on the drill and some finesse; don't try it if you aren't comfortable.
Cheers, Wayne
If you drill a 2" hole perpendicular to the roof, you might think you'd just need to open it a little to get to 2.003" across the upslope-downslope dimension of the hole. But that doesn't account for the thickness of the roof. If you're just drilling 1/2" thick sheathing, then the thickness of the sheathing will interfere by 1/2" * 4 / sqrt(12^2 + 4^2) = 0.158". But just on one side of the hole, on the other side the edge of the hole will slope away from the pipe.
So if you just want to drill perpendicular to the roof, use a 2-1/4" or 2-1/2" hole saw, depending on how thick the roof layers you are drill through are.
An approach to give you an elliptical hole would be to cut a wedge with a 4:12 angle (18.4 degrees). Then if you tack that to the 4:12 roof in the obvious way, you'll have a level face you can drill through plumb to get an elliptical hole. Now you can use a 2" hole saw.
A quicker but trickier approach with a 2" hole saw would be to use an extra long pilot bit. Then drill the pilot hole plumb (start off perpendicular and start angling the bit towards plumb as the bit enters) and use that to run the hole saw plumb. This would require a good grip on the drill and some finesse; don't try it if you aren't comfortable.
Cheers, Wayne
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Wow -- thank you ! I just need to go through one layer of 7/16" OSB so, I'll use the 2 1/4". I'm assuming you need to be next to a rafter or close so you can anchor it in the attic as well. Wondering also if they make some sort of anchor that you can fit around the pipe inside the attic? -- thanks again.
See the bottom of page 3 and page 4. https://www.iccsafe.org/wp-content/uploads/20-18927_GR_2021_Plumbing_Venting_Brochure.pdf
Maybe you want two inch pipe. Or 3 inch.
https://codes.iccsafe.org/content/IPC2012/chapter-9-vents -- see section 903.2.
Also see https://www.energystar.gov/ia/partn... Temperature Reference Guide - 2015-06-24.pdf
99% Heating Temperature (°F)
starting page "30" and ending on "33" for Indiana. But that is 99% rather than 97.5%. Also, https://www.in.gov/dhs/files/53.28-09_Wagner_3101.4.pdf seems to say that Indiana deletes that section as a requirement.
Maybe you want two inch pipe. Or 3 inch.
https://codes.iccsafe.org/content/IPC2012/chapter-9-vents -- see section 903.2.
Also see https://www.energystar.gov/ia/partn... Temperature Reference Guide - 2015-06-24.pdf
99% Heating Temperature (°F)
starting page "30" and ending on "33" for Indiana. But that is 99% rather than 97.5%. Also, https://www.in.gov/dhs/files/53.28-09_Wagner_3101.4.pdf seems to say that Indiana deletes that section as a requirement.
Jeff H Young
In the Trades
I use 2 1/8" bit and hold drill at more of an angle level to the floor of house not on a 4/12 angle , whatever you do dont buy a hole saw for one hole unless your building a piano . if you only have a 2 inch make it work we are talking about wood right like plywood? it dosen need to perfect
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