Checklist Can Help Ensure Plumbing Vent Installations Are Resilient and Code Compliant

For those who walk roofs, you know the smell — the sewer stink emanating from the plumbing vents when the water in the trap evaporates. The plumbing vent serves a necessary function to vent out sewer gas and provide air to allow the flushing below to occur. Many of the current vents are much too low to properly function and can easily be covered with leaf debris and/or snow. (See Photo 1.)

Photo 1: Short plumbing vents are not code compliant and can result in sewer gas down-drafting into the building. IMAGES: HUTCHINSON DESIGN GROUP LTD.

In snow country (I would suggest ASHRAE Zone 4 and above), vents are required to be 12 inches above the roof surface. Now, we know this doesn’t always occur. Some vents barely make it above the roof. Vents along walls and tall parapets should be even taller so as not to be covered by drifting snow.

New insulation thermal values are substantial. Even before tapered insulation is added and when replacing old roofs, the new insulation thickness can bury the vent.


Raising the plumbing vent is one of the most exciting design opportunities roof system designers will face, and it should be given its proper consideration.

Some consultants and architects when designing a new roof give them no consideration and basically give it an RFO status. (RFO stands for “Roofer Figure Out.”)

Others show details that are not correct and violate the code. You cannot just insert a pipe into the vent. (You cannot do that with drains either, but that subject is for another time.) The details shown in Figures 1 and 2 are some examples from the Chicago market of how NOT to do it. The details are drawn in a manner that is not possible to execute, and both reduce the venting and violate the code. Can anyone tell me how the roofing is to be installed?

Figure 1: This design violates the code and would be impossible to execute. Look at the extension — it would be pretty challenging to place the extension on a lathe and trim off half the pipe, especially cast iron.
Figure 2: Another incorrect detail. This plumbing vent with an extension is similar to that in Figure 1, but no method of attaching the extension is shown. The joint is not watertight and the pre-molded boot is not correctly detailed at the vent. Note the gap between the insulation and vent.

Some call for their raising by specification, most without an understanding of how it can be accomplished. The spec section paragraph below is a good example:


A. Extend existing plumbing vents as necessary to provide height of eight (8) to twelve (12) inches above new roof surface. Extensions shall initiate under roof deck wherever possible.

Let’s talk a little about the goals of the vent extension design:

1. The finished vent should be a minimum of 12 inches above the roof.

2. The connection of the extension should be:

  • Secure.
  • Stout.
  • Per code.
  • Below the roof surface.
  • Able to be accomplished above the roof deck in concert with the new roofing.
Photo 2: The existing cast iron vent pipes were snapped off above the roof deck, raised with a heavy-duty, no-hub coupling and have been tied into the vapor retarder.

Over the years, we have concluded that all the above goals are accomplished by using a quadruple-strapped, heavy-duty, no-hub coupling. (See Photo 2, bottom.) The existing vent, either PVC or cast iron, should be cut off just above the roof deck, the no-hub installed, and an extension pipe added. (See Photo 2 and the detail in Figure 3.)

With the plumbing vent raised, the rest of the roof system can be designed to it. Key considerations include:

• Firestop: Fire safing should be placed at the roof deck level.

• Vapor retarder: If there is a vapor retarder, it should be flashed on to the pipe. (See Photo 2.) This seems simple enough, but you would be surprised how often this junction is not designed. How the vapor retarder is flashed into the vent pipe must be designed. Depending on the interior conditions, this transition can be critical.

Figure 3: The plumbing vent pipe extension, correctly detailed. Specific detailing is required — just like other elements penetrating the roof.

• Insulation: Roofing crews usually do not have circular-hole drill bits on the roof, and the cutout of the insulation can be very rough, leaving gaps, which are not desired. (See Photo 3.) I suggest that you call out that these voids be filled full with spray foam insulation. (See Photo 4.)

Photo 3: The new insulation has been cut to fit over the new vent extension. The resulting void should be filled with spray foam insulation.

• Membrane: Like the insulation, the membrane is typically off cut, and often the pre-molded boot flange barely covers the cut. I suggest that you design a target patch to be placed over the vent. A hole smaller than the pipe’s diameter should be cut so that when the target patch is set over the vent pipe and onto the membrane, it has a slight return up the pipe. (See Photo 5.)

• Pre-molded pipe boot: The target patch can now be cleaned, and a pre-molded pipe boot installed. Be sure to specifically call out that water cutoff mastic be placed between the boot and the vent pipe. A stainless-steel clamping ring should be installed. Specify that polyurethane sealant be placed atop the boot, and call out the color. (You would be amazed as the variety of colors I see.)

• Edges of the target patch: To ensure long-term resiliency, we strip in the edges on the target patch in EPDM membranes. (See Photo 6.)

Getting What You Designed

As you can see form the above, there are numerous steps for the contractor to undertake, and many will be new for them.

Photo 4: Similar to a vent pipe, the void around this steel tube column has been sealed with spray foam.

To help ensure that everything is designed and installed correctly. We developed a Quality Assurance Compliance list for plumbing vent extensions. New staff use this document to understand the complex interrelationship of components and ensure compliance to the contract documents. We have also found that contractors like to provide this list to their foreman to show what we will be looking for.

Plumbing Vent Extension Quality Assurance Compliance

1.         Has the vapor retarder been sealed to the existing vent pipe?

□          Yes      □          No

a.         Openings (voids) at deck sealed with fire safing?

□          Yes      □          No

Photo 5: The target patch has been nicely installed with a return up the vent extension and with rounded corners.

2.         Has the vent pipe been snapped off +/-2” above the roof deck and extended with cast iron pipe utilizing a heavy-duty, no-hub coupling with four draw bands?

□          Yes      □          No

3.         Has the void between the substrate board and existing pipe been filled with spray foam insulation?

□          Yes      □          No

4.         Is the base layer and tapered insulation cut to fit around the vent pipe and all gaps filled with spray foam insulation?

□          Yes      □          No

5.         Has the field membrane been installed tight to the pipe penetration?

□          Yes      □          No

Photo 6: The pre-molded boot, water cutoff and stainless steel draw band have been installed. The edges of the target patch have been cover stripped. Quiz question: Are there any punch list item(s) for this installation? Answer at the end of the article.

6.         Is the 24” x 24” EPDM target patch installed with turned up flanges onto the pipe penetration, then sealed with lap sealant?

□          Yes      □          No

7.         Have the 6” self-adhering cover strips been installed over the target patch edges?

□          Yes      □          No

8.         Has the pipe boot been installed appropriately onto cleaned and primed membrane?

□          Yes      □          No

9.         Is there water cut-off mastic between the pre-molded boot and pipe? 

□          Yes      □          No

10.       Is the stainless steel clamping ring installed and tightened?

□          Yes      □          No

11.       Has polyurethane sealant been installed along the top edge of the boot?

□          Yes      □          No


The plumbing vent is often viewed as an insignificant element impinging on a roof system. In today’s positively pressured buildings, air leakage into roof systems — no matter the material — is a concern and can lead to long-term consequences. So, let’s all work together to rise above the stink.

About the author: Thomas W. Hutchinson, AIA, CSI, Fellow-IIBEC, RRC, is a principal of Hutchinson Design Group Ltd. in Barrington, Illinois. For more information about the company, visit

Answer to the Quiz Question in Photo 6: There is no polyurethane sealant over the top of the pre-molded boot.

About the Author

Thomas W. Hutchinson, AIA, CSI, Fellow-IIBEC, RRC
Thomas W. Hutchinson, AIA, CSI, Fellow-IIBEC, RRC, is principal of Hutchinson Design Group Ltd., Barrington, Ill., and a member of Roofing’s editorial advisory board.

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