Pumbing vent damaged by sliding snow (C) Daniel Friedman Rooftop Plumbing Vent Repair
How to fix a snow or ice damaged or broken plumbing vent from the rooftop

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Rooftop plumbing vent stack repair: this article describes detailed procedures for repairing a broken-off plumbing vent stack from the roof top. This plumbing vent repair procedure avoids having to cut open a cathedral ceiling or remove the roof covering outside and results in a leak-proof and sound repair to the plumbing vent system.

The article describes repairs to plumbing vent damage caused by snow and ice sliding down a roof where snow guards should have been installed.

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Plumbing Vent Repair Procedures: on-roof

Plumbing vent made out of soda bottles (C) Daniel FriedmanPlumbing vent damage from missing snow guards

At SNOW GUARD FAILURES we used this broken plumbing vent to illustrate how Sliding snow v bent over this large ABS plumbing bent and broke it right off inside the roof cavity.

[Click to enlarge any image]

Our photo at left and explained below shows an emergency repair at this broken plumbing vent.

Notice the arrow pointing to that yellowish color at the broken end of the vent? That's foam insulation.

This roof is installed over a cathedral ceiling with foamed insulation. That's not a design that tolerates water in the roof structure very well. Looks like a leak point.

Why you should care about a broken off plumbing vent: leaks into the roof cavity

At below left you'll see that even with the plumbing vent stack broken and bent over nearly touching the roof surface, the rubber boot installed in the photos above managed to avoid a flood of melting snow into the roof cavity.

Rubber boot keeps most water out of the roof cavity even with a broken roof vent stack pipe (C) Daniel Friedman Roof damage at plumbing vent means needed snow guards (C) Daniel Friedman

The next photo at above right shows the broken off ABS stub inside the roof cavity. The foam insulation was found to be a bit wet around the vent and was left to dry. Had this defect gone long un-noticed rainwater leaking into the roof structure would have eventually risked a costly mold catastrophe.

In addition to rain water that could soak the roof cavity through the open plumbing vent boot flashing, moisture carried upwards by the building plumbing vent system could condense under the metal roof deck, soaking the foam insulation and ultimately leading to a costly rot or mold contamination issue.

Plumbing vent original installation (C) Daniel Friedman Eric Galo Galow Homes The plumbing vent stack above-roof portion, a 3-inch vertical segment of heavy ABS pipe, had been glued into an ABS elbow inside the roof cavity. The sliding snow and ice snapped off the ABS just above the outer lip of that elbow, leaving an inch of plastic pipe still glued in place inside the fitting.

Our photo at left shows this same plumbing vent at the time of original construction. You can see that the vent was extended up through a standing seam metal roof - a durable installation but one that makes future access to repair a broken-off above-roof plumbing vent mast ... well, difficult to put it politely.

The question was, how are we going to make a proper repair with the least disruption to the building roof or finished interior?

Watch out: especially where the plumbing vent pipe is installed through a cathedral ceiling and metal roof surface there is no easy access into the roof cavity. In an attic you'd just cut off the elbow whose female end contained the remains of the ABS pipe, glued on a short extension and new elbow in the attic, and glued a new plumbing vent rooftop riser into the new elbow.

That's not so easy if you're working inside a cathedral ceiling. We didn't want to cut out the ceiling inside - a process that would involve more than just drywall repairs: you'll also lose the spray-foamed insulation around the plumbing. Insulation, new drywall, new ceiling paint are involved in an inside-repair.

From the rooftop, cutting open the metal roof to obtain sufficient working space to hack off broken pipes, re-insulate, and glue in new vent piping would be worse!

Emergency temporary plumbing vent repairs

Plumbing vent made out of soda bottles (C) Daniel Friedman

We jury-rigged a temporary plumbing vent out of soda bottles, mouth down, to direct any rainfall into the vent interior (below left), giving time to cut and prep and repair the broken plumbing vent.

For details about plumbing vent systems see PLUMBING VENT PIPING.

By making sure that the cap-end of the plastic soda bottle was inserted mouth-down and a couple of inches inside the remaining plumbing vent pipe inside the ceiling cavity, we've basically made a sort of funnel that will assure that any heavy rains falling inside the makeshift plumbing vent will go where the water should go - back down the drain line, not into the ceiling cavity.

By pressing the quart-sized soda bottle snugly into the plumbing vent opening below the roof we also assure that moisture venting upwards through the vent system exits above the roof top, not into the roof cavity.

I'm not claiming this is an IAPMO-approved design, it's a stopgap measure to keep water out of the structure. But as rainy weather was expected this gave us some breathing time to come up with a permanent repair to the broken vent stack.

Fabricating an Adapter to Repair the Broken Plumbing Vent Stack

Quite possibly we could have also found an internal splice part (a double-male insert) for 3-inch ABS piping at a plumbing supplier. For this installation Eric Galow (Galow Homes, Poughkeepsie, NY) fabricated a smaller-diameter insert that would fit roughly inside the 3-inch I.D. of the original section of vertical 3-inch ABS above-roof vent stack piping.

At below left you'll see that by cutting apart a 6-inch length of 3" ABS Galow fabricated an insert (red arrow) that was glued to the interior of the 3" ABS roof vent stack pipe (green arrow), leaving about 3" exposed for insertion into the interior diameter of the existing ABS vent elbow inside the roof cavity.

Watch out: there was more to do in preparing this assembly for a successful repair. Since neither of us has hands small enough nor fingers long enough to reach up inside of the concentric ABS piping to apply our ABS adhesive reliably, we fabricated an adhesive swab using a stick and a mini paint roller (photo below right).

Plumbing vent stack repair completed (C) Daniel Friedman Eric Galow Plumbing vent stack repair completed (C) Daniel Friedman Eric Galow

When our inserted home-made inside-adapter for ABS piping (red arrow in the photo at above left) had been glued and dried inside the 3" pipe (green arrow in the photo at above left), had been glued in place we then needed to test fit the protruding "female' end of the repair pipe section into a test section of 3" ABS pipe.


At below left I've built-up the out-of-round sides of the home made adapter-insert (below left) using ABS plastic pipe cement. At below right I'm test-fitting the male end into a scrap section of 3" I.D. ABS pipe - that's the same diameter into which our rooftop repair vent stack would have to insert.

Rounding off the male end of our home-made adapter for plumbing vent stack repair (C) Daniel Friedman Eric Galow Test fitting the male end of our home-made adapter for plumbing vent stack repair (C) Daniel Friedman Eric Galow

Watch out: we're still not finished. It was easy enough to glue the home-made adapter into the interior of the new plumbing vent stack pipe. But it was critical that the male end (above left) that was going to insert into the elbow down inside the roof cavity was round enough that it would be perfectly sealed both inside the receiving elbow and inside the vertical vent stack pipe riser.

The seal at both ends of this adapter is more important than you may think. You might figure that if the upper end of the male adapter is glued nicely into the vertical vent pipe then any rain falling down into the pipe will indeed be directed properly to the interior of the receiving elbow and remaining vent piping in the building. That's correct.

Interior view of leak points in a "repaired" plumbing vent stack assembly (C) Daniel FriedmanBut we also do not want rising steam and moist air to escape out of the receiving elbow into the roof cavity. In other words, our glue joint has to be perfectly sealed in both directions. Otherwise we'll be sending moisture into the cathedral ceiling cavity.

The solution to this problem was to hold the test fit pipes (photo above right) up to a light source. At below left the orange arrows point to daylight seen between the male adapter and the interior of the female or receiving test section of vent stack pipe.

If my ABS pipe cement was not sufficient to completely fill these irregular spaces then those orange arrows would mark precisely where moist air rising inside the building vent piping would escape into the roof cavity.

In sum, I needed to build-out the home made adapter with ABS cement until it was so close to perfectly round that I was confident that it would be glued in place with a complete seal.

We added ABS cement on the outside of the male adapter and let it dry, then test fitted it again until there was no daylight. A light sanding then prepared the male adapter end of the vent stack for insertion into the elbow up inside the roof cavity. We used the following ABS cement product for this repair:

Solving the ABS Vent Pipe Final Gluing Problems Up on the Roof

Plumbing stack pipe glued and temporarily taped in place on the rooftop (C) Daniel Friedman Eric Galow On the roof there was another problem: how the hell do you blob ABS cement around the interior of the receiving elbow in the roof cavity, the protruding male end of our vent stack assembly, and insert the assembly down through the rubber vent flashing boot that is designed to fit tightly around the exterior of the ABS vent stack pipe without having the rubber boot squeegee all of the ABS cement right back off of the pipe?

The solution was to roll back the upper edges of the rubber boot and tape them to the lower boot so that we had a larger diameter opening through which to first apply ABS cement to the interior of the receiving elbow and second to insert the ABS-cement-coated male end of the vent stack down into the elbow.

That worked. The repair assembly slid into place nicely.

I finished buy un-taping the rolled-back rubber boot, rolling it up against the exterior of the vent stack and temporarily taping it in place to hold the vent pipe in perfectly vertical position while the plastic pipe cement set and dried.

Watch out: that black tape in my photo above is just a temporary hold to keep the pipe in place without moving while the ABS plastic pipe cement dries hard. Later that tape can be carefully peeled away. If you're in doubt about the quality of the seal of the rubber boot around the outer surface of the vent pipe, use a compatible adhesive sealant in that location.

Don't rely on duct tape or similar products that will eventually break down with sun exposure.

The Completed ABS Plumbing Vent Stack Rooftop Repair

At below left is the original plumbing vent stack as installed when the roof was new.

At below right is the completed plumbing vent stack repair, along with a portion of our snow-guard installation system that should prevent the snow and ice damage in future winters. We glued-down an extra glue-on type snow guard just up-roof from the plumbing vent stack.

Plumbing vent stack repair completed (C) Daniel Friedman Eric Galow Plumbing vent stack repair completed (C) Daniel Friedman Eric Galow

A single snow-fence or snow guard, especially one located down-slope from a plumbing vent may not be sufficient to protect the plumbing vent from damage when there is a heavy snow accumulation on the roof.

Clamp on snow guards to protect plumbing vent (C) Daniel FriedmanSteps to protect the plumbing vent from future snow damage

began with a glue-on snow guard up-roof from the vent (photo at above right) and

continued with more extensive clamp-on snow guards on the roof, shown in our photograph at left and explained

and concluded with the double-row of glue-on snow guards near the roof eaves and visible in the upper left of our photograph shown at left.

The cause of the snow-damaged plumbing vent is discussed at SNOW GUARD FAILURES.

Original installation details for this plumbing vent as photos and text are at the bottom of our article on PLUMBING VENT DEFECTS & NOISES.


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