Leaking Vent Pipe Collars

 In this article we will cover some of the more common roofing leaks caused by plumbing vent pipe collars.  Many other types of roof leaks exist with quite a few topics covered in our other articles on Leak Diagnosis.  We will begin this article with plumbing vent pipe collars.  These are the collars around the plumbing pipes that protrude through your roofs surface. Plumbing vent pipe collars consist of a metal base which is usually made out of aluminum and a rubber boot that is integrated into the top of the collar. This rubber boot on the collar is available in different sizes according to the size of the pipe being flashed. 

        When collars go bad the majority of the time is due to failure of this rubber boot on the collar.  Failure of collar boots usually take the form of either splits in the rubber or deterioration of that same rubber over time.  If you have water entering your home from a broken or worn out collar often you can temporally stop the leak by having your roofing professional caulk the open area of the collar.  Once weather allows you can then have the collar replaced properly. 

        Not all collar leaks are due to bad rubber boots.  Some times leaks are caused by the plumbing pipe itself not being properly cleaned before the new collar is installed.  This can be especially prevalent on older cast iron pipes that have pits or years of old roofing cement attached to them.  Another leak that may mimic a bad collar is when the plumbing pipe itself is the cause of the problem.  When the plumbing was installed in your home the plumber routed the plumbing vent pipes through the walls and ceilings up through the top of the roof.  Over the years we have seen some of these pipes leak at the elbow joints.  Let me explain what I am referring to. 

        The top of the plumbing vent pipes protrudes through the roof and is open to the sky.  Even though this pipe is for venting air at times during a rain storm the pipe can have water enter and flow through it.  This is normally not a problem since any water that enters a plumbing vent pipe will eventually find it’s way to the homes sewer line.  The problem arises when one of the elbows or joints in the pipe experiences some type of failure.  Usually you can diagnosis this type of leak by having your roofing professional go up into the attic during a rain storm and feel the outside of the pipe right below where it goes through the roof.  If the outside of the pipe is dry but you see water somewhere below the plumbing vent pipe itself you may have a leak at one of the joints in you pipe.  Conversely if you feel water on the outside of the pipe it is very likely a bad boot on the collar.

        A few other indications of a leaking or broken collar are water stains on first floors of two story houses.  If you see a water stain on the first floor ceiling of your two story house first eliminate the most obvious cause which would be leaky plumbing in a bathroom or water closet on the floor above. Once that has been checked if you are still experiencing a water leak have your professional roofer go up on the roof and check your plumbing vent collars.  A broken collar can allow water to travel around the outside of the plumbing pipe where it will usually follow until the pipe turns or hits a elbow in the pipe.  Sometimes the first elbow or turn in the pipe is your kitchen ceiling where the vent pipe was heading to connect up with your kitchen plumbing. 

        One final note on plumbing vent pipe collars.  Even though the majority of leakage by these collars occurs at the rubber boot you should also have your professional roofer check the hard flange that the boot is attached to.  They will want to to a through inspection to make sure this part of the collar is seated and sealed properly.  Maryland Shingle Roofing and Siding Contractors offers a complete line of roofing and siding services.  Please feel free to contact us if we can be of any assistance.


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