Up on the Roof Top: What is a Plumbing Vent?

plumbing vent

As per the standards, Ed Lawton of B to B Home Inspections is only required to inspect roofing from ground level or the eaves.  However, Ed will more often than not, get up on the roof to inspect more than the shingles on the roof.  Ed will inspect all the vents.  There are several vents located on roof tops and for the purpose of this article, we will discuss the plumbing vent.

What is a Plumbing Vent?

As you are aware, when you use the toilet, sink, laundry, etc, piping carries the wastewater away into a septic tank or a sewer.  But, were you aware that all this piping also requires venting?

If there is no vent, a number of problems may occur:

  • The fixture without an adequate vent may drain slowly
  • The drain will likely make gurgling noises
  • The water in the trap could siphon out, resulting in a potent sewer smell
  • The smell emitted from an unsealed trap (Methane Gas) poses a health risk

An ABS Vent is a plumbing vent for the release of sewer gases. In a nutshell, when you flush the toilet, the stink goes down and the gases travel up and out through a vent in the roof.

Venting and Flashing

Whenever something is vented through the roof, it needs proper flashing around it to prevent leakage. When Ed is performing an inspection of the roof, he is inspecting the vents and surrounding flashing too.

Recent Finding

plumbing vent - roof boot In a recent inspection, Ed inspected the ABS plumbing vent on the roof.  The bottom edge of the ABS plumbing vent was lifted from the roof. The nails that secured the vent pipe were rusted through, which could have been the cause of the vent flange/flashing to lift from the roof.

Ed recommended the installation of a new roof boot to prevent potential leakage into the home. He advised the buyer to secure a qualified person to evaluate further and repair.

The problem with a flange lift is that during a rain storm, the wind can drive water under the flange and enter the hole where the pipe comes out the roof.  The result? A roof leak!


Solutions are dependent upon the specific problem.  In the finding above, Ed recommended a new roof boot.  However, only install a new roof boot if needed.

Many times, an issue like this may be repaired with Black Jack. Black Jack is black roof cement in a caulk tube.

If new flashing is required, Ed recommends a long lasting galvanized flashing.

To wrap up, the plumbing vent on the top of the roof is to release the stinky fumes of the waste heading to the septic or sewer.  A plumbing vent, like any other vent, is a penetration in the roof.  When there is a penetration in the roof, it must have adequate flashing in place to prevent roof leaks.