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Old 06-30-2019, 07:29 PM   #1
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Cutting a hole in a low pitch roof


I need to cut 2 holes into a low pitch roof (essentially flat). Im venting a kitchen range hood and a dryer duct.

The plan is to:

  • drill a pilot hole in the roof b/w two joists. Leave the drill bit in the hole, climb up to the roof and find the bit.
  • From the roof I'm going to trace the vent pipe onto the roof
  • Cut the hole with a jig saw
  • Apply roof mastic to the underside of the roof vent's flanges and secure into the hole.
  • Drill a few screws around the outer edges of the roof vent's flange to secure
  • Roof mastic the screw heads
  • attach the ducting from the inside the building
Is this a good plan? What would you guys do differently?


Here's a pic of the roof vent.
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Old 06-30-2019, 07:40 PM   #2
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Re: Cutting a hole in a low pitch roof


Nope, not a good idea at any cost. Almost flat and slight angled roofs are not meant for venting and will absolutely leak. Have you looked into the possibility of soffit venting?
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Old 06-30-2019, 07:49 PM   #3
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Re: Cutting a hole in a low pitch roof


What type of low pitch roof system is it?
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Old 06-30-2019, 07:52 PM   #4
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Re: Cutting a hole in a low pitch roof


What kind of roof is it? Metal, asphalt, rubber?
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Old 06-30-2019, 07:55 PM   #5
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Re: Cutting a hole in a low pitch roof


Quote:
Originally Posted by chandler48;
Nope, not a good idea at any cost. Almost flat and slight angled roofs are not meant for venting and will absolutely leak. Have you looked into the possibility of soffit venting?
Thanks Chandler!

IT's a very old 3 family building (100 years old) and it doesn't have a soffit. I'll take pics tomorrow.

What if i build a pitch box on the flat roof?

Roof pitch box video:

I have a few current roof penetrations. Two plumbing vents, skylight, louvered air vent, roof ladder.

Both plumbing vents and the louvered air vent have leaked recently. Fortunately the top floor is being renovated and I can spot and repair the leaks when it's raining. Nothing serious, but I get your point.
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Old 06-30-2019, 07:57 PM   #6
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Re: Cutting a hole in a low pitch roof


Quote:
Originally Posted by Yodaman;
What kind of roof is it? Metal, asphalt, rubber?
Asphalt.

I'll take some pics tomorrow. I'll also take some pics of the neighbor's newly renovated roof highlighting his roof penetrations.
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Old 06-30-2019, 08:11 PM   #7
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Re: Cutting a hole in a low pitch roof


It can be done although through a side wall is preferable. How you tie it back depends entirely on the system that the roof is based on.
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Old 06-30-2019, 08:14 PM   #8
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Re: Cutting a hole in a low pitch roof


Quote:
Originally Posted by Windows on Wash;
It can be done although through a side wall is preferable. How you tie it back depends entirely on the system that the roof is based on.
Pics tomorrow morning. thx
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Old 07-01-2019, 07:25 AM   #9
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Re: Cutting a hole in a low pitch roof


Ok here are some pics. All labeled.
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Cutting a hole in a low pitch roof-img_5409.jpg   Cutting a hole in a low pitch roof-img_5410.jpg   Cutting a hole in a low pitch roof-img_5416.jpg   Cutting a hole in a low pitch roof-img_5417.jpg  
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Old 07-01-2019, 08:38 AM   #10
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Re: Cutting a hole in a low pitch roof


That looks like rolled asphalt roofing. Yes?
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Old 07-01-2019, 09:06 AM   #11
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Re: Cutting a hole in a low pitch roof


Quote:
Originally Posted by huesmann;
That looks like rolled asphalt roofing. Yes?
I believe so. I dont know much about roofs.
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Old 07-01-2019, 12:37 PM   #12
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Re: Cutting a hole in a low pitch roof


I would not use that style of vent termination on a flat roof in NY, unless you like water or snow getting in or blocking the air path.

Again, I think you need to really pre-plan (I know I'm a thorn in your side about this) the entire building including all of these vents. You will have 3 vent hoods, 3 dryers, 3 or 6 bath exhaust, and don't remember about the existing furnace/boiler/wh, and 8 or nine plumbing fixtures each floor. Not to mention make-up air you might need and proper attic venting. That's a lotta holes in this roof, and if you terminate them separately, but combine the risers in vertical chases through the 3 floors it will be a little crowded when they terminate out the same point on the roof.

Code addresses minimum distances vents from intakes, from alleys/lot lines/adj walls, height, etc. You should be thinking either curbed risers, extended goosenecks, or capped pipes like the neighbor.

I know you're trying to do this under the radar, and don't want to call attention by renting a bucket to put holes up high in the exterior walls, but there are many issues that keep arising from this project that having pros onboard could have thought about it first.
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Old 07-02-2019, 08:54 AM   #13
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Re: Cutting a hole in a low pitch roof


Quote:
Originally Posted by 3onthetree
I would not use that style of vent termination on a flat roof in NY, unless you like water or snow getting in or blocking the air path.

Again, I think you need to really pre-plan (I know I'm a thorn in your side about this) the entire building including all of these vents. You will have 3 vent hoods, 3 dryers, 3 or 6 bath exhaust, and don't remember about the existing furnace/boiler/wh, and 8 or nine plumbing fixtures each floor. Not to mention make-up air you might need and proper attic venting. That's a lotta holes in this roof, and if you terminate them separately, but combine the risers in vertical chases through the 3 floors it will be a little crowded when they terminate out the same point on the roof.

Code addresses minimum distances vents from intakes, from alleys/lot lines/adj walls, height, etc. You should be thinking either curbed risers, extended goosenecks, or capped pipes like the neighbor.

I know you're trying to do this under the radar, and don't want to call attention by renting a bucket to put holes up high in the exterior walls, but there are many issues that keep arising from this project that having pros onboard could have thought about it first.

@3onthetree - You're not a thorn in my side. You ask great questions and really make me think things out further. It's appreciated.

My plan for ventilation on the 3rd (top floor) is to vent out of the roof. Range, dryer, and 2 bathrooms.

On the 1st and 2nd floors, I will ventilate out of the back of the building through the wall.

As you mentioned its an access issue. Without setting up scaffolding I cannot get access to the back of the 3rd floor.

Vent termination: I am planning on raising the vent off the ground 3' to prevent it from getting buried in snow. Good point on using a capped rain pipe or gooseneck.

The attic is ventilated through a ridge vent on the skylight and that louvered metal box.
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Old 07-02-2019, 10:38 AM   #14
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Re: Cutting a hole in a low pitch roof


If i use a pitch pan, with vent pipe protruding through:

1. What type of foam should I fill the pitch pan with?
2. What goes on top of the pitch pan to cover it?
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Old 07-02-2019, 12:31 PM   #15
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Re: Cutting a hole in a low pitch roof


I see a roof in my area using pitch pan boxes for their penetrations.





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