Call the Roofing Professionals for a Leaking Roof Vent Stack

Call the Roofing Professionals for a Leaking Roof Vent Stack

Written by American Building Roofing on . Posted in Blog


Degraded vent-stack waterproofing is a common cause of roof leaks on shingled house tops. Vent stacks are pipes that carry stinky gas up and away from your plumbing or gas lines. Usually, they extend above your roof, although some vents are designed to be flush with the roof for better curb appeal.

Wherever there’s a roof stack, there’s a hole made in the roof decking to accommodate the pipe. In order to prevent water and pest penetration around the pipe, several layers of waterproofing are used under and over the shingles and around the stack. If you notice leaks under the location of vent stacks, you must have the roof inspected and any holes around stacks repaired.

How Pros Examine the Roof Vent Components

It’s best to let professionals inspect and repair your roof’s leaking vent stacks. They know how to spot the signs of water penetration. They go over your roof thoroughly, looking for damage on the vent stack cover, the pipe itself, and the protective layers where it meets the roof. They gently lift adjacent shingles to determine the locations and causes of leaks and other damage.

Vent stack waterproofing consists of a wide collar, called flashing, which is placed under the shingles and around the opening for the pipe. A gasket and pipe covering are then usually added to the vent stack. The flashing and vent coverings are unique for each vent, in order to accommodate the roof pitch, shingle size, and vent-stack type. A roofing professional examines all of the components and makes recommendations for improvements.


Flashing is destroyed by rust, rodents, UV damage, and storms. A tiny open spot allows rain and melting snow to leak into the attic and possibly into your bathroom below. If the flashing has developed leaks, your roofing expert will replace or repair it so it repels water again.

Flashing is made of a variety of materials and should be chosen based on your pipe type, your budget, and the roof environment. Your roofing pro will normally want to replace damaged roof-vent parts with similar styles of products. If these products are failing to protect your home, ask your roofing pro or roofing supply company about newer designs of vent stack materials that will work better in your situation.

In most areas, metal flashing is required for cast iron pipes, while rubber flashing is acceptable for plastic pipes. Galvanized steel flashing is easy to solder if needed, and it’s less likely to rust. Aluminum flashing can’t be soldered, but is a budget-friendly choice. Thermoplastic flashing is subject to crumbling under intense climate conditions, but doesn’t require as much caulking as other flashing types.


Rubber gaskets are often fitted over the pipe to add more sealing power around the metal or plastic flashing. These are basically large, contoured washers that fit snugly around the place where the pipe and flashing meet. A layer of roofing caulk is normally used under the gasket to seal it to the pipe and flashing. Some gaskets are crimped under an additional metal flashing layer.

Gaskets fail because they develop small rips, allowing water to trickle past the flashing next to the vent pipe and into your home. When replacing the gasket, your roofing professional should sand off any sharp edges on the very top of the pipe before slipping the gasket over it. Snags or sharp edges on the pipe may rip the gasket otherwise.

The roofer will measure the pipe’s diameter carefully to select the precise size. A gasket that’s too small will develop tears under pressure; a too-large gasket will allow water leakage around the vent stack. Some metal vent-stacks don’t require gaskets, as the various waterproofing components are soldered together or made of a one-piece design.

Vent-Stack Covers

There are a variety of vent stack covers used to protect vent pipes from becoming clogged with debris, birds’ nests, and squirrel droppings. Some vent stacks are topped with mesh, some are fitted with rodent-proof caps, and others are finished with exhaust fans to pull out bad air.

It’s wise to protect your vent stack tops from water, storm debris and leaves. Ask your roofing pro to add a top that birds and rodents can’t sit on or climb, and you now have a vent stack that’s less likely to fail.

How the Shingles Are Handled

When your roofing pro must replace a large section of leaky flashing under a vent stack, he or she will delicately remove the surrounding shingles and replace them after the repair is made. Newer shingles endure this activity much better than older shingles, which may be prone to crumbling.

Some shingles may need to be replaced if they’ve been damaged along with the vent-stack waterproofing. When you order materials to have your vent stacks repaired, it’s wise to pick up a bundle of shingles that closely match your home’s roofing. Your roofing pro will have them close at hand if replacement shingles are necessary.

You’ll find products, services, and advice for rooftop repairs—including caulk and waterproofing materials—from American Building & Roofing, Inc., located throughout beautiful Washington. Call us today to find solutions to all of your leaking roof issues.

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