Thanks in advance. Short story is we have a small leak coming in around our bathroom vent pipe on our flat, modified bitumen roof. Just got back from the supply house where I learned that they only have the lead boots in one height, about 1.5' or so. I know that the vent up there now is at least three feet or so.

So, question is, can I just cut down the existing vent? Will it do any harm? I suppose I can just go at it with my reciprocating saw. But I want to make sure I am not violating any codes or rules. This was a roofing supply house, so I was surprised they only had them in one size. Is that common?

Thanks!

Do not cut the vent pipe back. You need a flashing that slides down over the pipe, (see image) check them out at; Roof vent pipe flashings from FAMOUS PLUMBING SUPPLY Good luck, Tom

Speedball, thanks for the response and for the link and photo. I am a little confused. Most roofers I have spoken with suggest the lead boot. I am not suggesting getting rid of the vent, the lead boot slides right over. Rather, for the boot to work I need to shorten the vent stack by about 1 or 2 feet. It would end up extending up from the roof about 1.5 ft. Is that to short?

The link is great, I was unable to find a rubber boot that worked on a flat roof, but given the age of the stack, I am afraid it won't get the type of sel it would with a pvc stack.

It's going to depend upon where you live. Here in the Tampa Bay Area the vents are 6 to 8 " over the roof line. Up North the vents are higher. What's the average height in your area? Regards, Tom

Ok, excellent, thanks! What part of the code covers this? Is it building or plumbing? Maybe I can find the code answer myself.

I assume that the concern is not plumbing but water intrusion, right?

This is the only lead boot they sell and they are the major roofing company here, so that must say something, right?

Is it OK to use the type of boot you suggested in your first post or just for sloped roofs? If I use it, would you suggest I replace the cast iron with pvc, or can I just sand it a bit to clean it up? The type of boot sound a lot easier to work with.

What do you think?

Thanks for everything!

Local variations of the plumbing portion of the building code.

Both: The boot seals against the pipe to prevent water intrusion. The height of the stack is so that roof air currents don't PUSH sewer gas into the home. It's going to have to higher than the any edge walls.

Yep, roofers generally replace the worn boots.

This link confirms a lot of what I said. Vent Stack Out Wall Versus Roof? [Archive] - DoItYourself.com Community Forums

It suggests roofing cement and paintable caulk on the edges. I'd go with caulk designed for roofs. You'll find that in the roofing department of the big box stores.

Cast Iron or galvanized pipe? Most everybody paints the vents except the PVC ones.

Speedball has to get the CI part of this question.



Thanks for everything!

Wow, thanks for the very thorough response. I would love to use a boot as described by Speedball, but they all appear to be for sloped, composite roofs. I cannot find ones made for flat roofs. The issue is, they all have a slope built into the boot itself. Any suggestions?

If you perfer the lead flashing and if you can find some sheet lead, probably from a roofing company. You would need one piece about 12 inchs X 14 inches, this is to fit against the roof. Now you need another piece as long as the vent is tall plus about three inches, and it needs to be wide enough to wrap around the vent. As you wrap it around the vent leave it a little loose, cutting it maybe a 1/4 inch larger. Now as it is laying on a work bench or something use a soldering iron to run a bead down the seam where the two edges meet. No cut the bottom off this sleeve to match the pitch of your roof. After you have done this stand the sleeve on the 12 X14 piece as near center as you can get it. Now using the iron again run a bead around where the sleeve meets the flat piece. Now punch a hole in the middle of where the sleeve sits on the flat and then ream the hole out with a sharp knife.

Put the flange on the vent and slip the edges in under your shingles, making sure it will be water tight at the roof area. Now at the top cut the excess lead off leaving enough that you can turn it down into the vent pipe.

Well, at least the flat flashing exists somewhere on this planet:

Flat Roof-Mounted Plumbing Vent Pipe Flanges/Flashings

Looks like you can buy online. Galvanized and copper materials. For frost areas and non-frost areas.

Letmetell u- Wow, sounds like a plan, but I just don't trust my soldering skills.

KISS- Beautiful. Those look excellent, but present the same problem as my lead boot which is that my vent pipe is easily 2-3' tall and these look to be about 1.5', same as my lead boot. I am happy to cut the vent pipe, as your site's installation page directs, but others here have suggested that could be a bad idea.

For the plumbers, does the code dictate how far up from the roof it must extend, or how far above any walls? Do parapet walls count?

No! You don't understand! Your lead flashing must roll back over the top of the vent, The Flat Roof Flashings KISS put up slip over the vent and seal it with a neoprene gasket. Good luck, Tom

Check out the installation page for the flashings KISS posted. They looked like they seal the way you describe, but they don't. Even the directions call for cutting the vent pipe.

That said, I think I have found ones that do. Can I use them on and old, pitted cast iron stack or do I need to replace at least the part that comes from the roof with PVC, or do I sand or somehow prepare the pipe. I can see how this would work perfectly with PVC, but I am afraid of a lack of a perfect seal on the cast iron.

You pull out the telescoping part of the flasing to the desired height and then cut the vent back. You would use the #1 Flashing that has a leas seal that conforms to the rough surface of cast iron and is locked in place with a ring clamp. Good luck, Tom,

I stand corrected, for sure. Tom, would you use this on your own house, assuming you had a 100 year old flat roof rowhouse? Or are there any better options out there?

I assume to install just adhere it to to roof with some roofing cement and screws and then go over it with more cement and asphalt coated fabric? Correct?

Thanks!

This is the flashing I'd use if I didn't want to cut my vent back to accept a lead flashing.
That's the way I'd install it. Good luck, Tom

Excellent! Thanks to everyone who assisted here. I will give these folks a call on Monday and order one. Thanks!

Tom- Just curious, who usually handles the roof penetration when a plumber installs a new vent, the plumber or does the homeowner have to hire a roofer?

You generally don't put screws in flasing in a flat roof. Defeats the purpose. Roofing cement + caulk around the edges.

In my area the plumber makes the hole and installs both the vent and the flashing. You could hot mop it in I guess but I prefer something a little more substantial. Plenty of roof cement and wood screws that don't penetrate would seem to be the answer.
Regards, Tom

Guys, thanks so much to both of you. This seems like the solution. I am with Tom, I am going to screw this down a bit, just for added security.

Gee... it took only 19 posts to install 1 roof-jack !:D:D:D