Plumbing Vent Problems in Your House | Sewer and Drain

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House Plumbing Vent, Sewer and Drain

The purpose of a plumbing vent in your house is to remove sewer gases from the drainage system and equalize its atmospheric pressure. Without the plumbing vent, our toilets and all other home plumbing fixtures might not be draining properly, can cause unusual noises (like gurgling or belching as and after they discharge), and could be responsible for an unpleasant sewer gas smell inside the house.

A house plumbing vent is one of those features that may easily become compromised.


Some of the most common reasons for the plumbing vent to lose its performance is our lack of knowledge during remodeling, the house age, and / or miscellaneous stuff (including bad luck).
Plumbing vent too short above the roof surface - 10 inch required for cold climates to prevent clogging with snow and icePlumbing vents too short above the flat roof, min 10 inches required for cold climate Lets go outside and look at your house’s roof; you should be able to see a plumbing vent stack – a piece of pipe penetrating the roof surface (if your plumbing fixtures have been located far away from each other, there could be more that one plumbing vent visible above the roof, but at least one should be 3” or 4” in diameter).

It’s usually the same material as the rest of your plumbing drain system, but in older homes, there might be 2, 3, or even more types of pipes connected together (cast iron, galvanized, copper ABS, PVC). If you have a flat roof, you will most likely have to get up there to check your plumbing vents – be extremely careful, or have a professional do it for you!).
Corroded and displaced plumbing vent pipe requires replacementBroken, leaking plumbing vent pipe connection in attic areaPlumbing vent pipe left open in attic area. It should continue through the roof and discharge sewer gases to exterior

If you can see the roof surface and you can’t see the plumbing vent pipe … you’re not alone.

The most common reasons for this scenario are:

  • The main plumbing vent stack starts at the lowest part of your house structure. Decades ago, in older homes, the most common type of the plumbing vent pipe was cast iron – it could settle, shift under its own weight and along the entire length
  • Plumbing vent pipe could have corroded and separated sliding under the roof surface
  • Another possibility is that your old roof has several layers of roofing material, and the plumbing vent is still there but its top edge level is the same as the roof surface.
  • Sometimes plumbing vent disappearance may also be blamed on the roofer – if it was too short, he could just go over it with new roofing material; or the plumber just stopped it in the attic or forgot to install it at all


Plumbing vent flashing must be properly installed and vent stack pipe should extend at least 6” above the roof surface. For cold climates, it should be 6” above the highest expected snow line (10” above the roof), unless otherwise specified by your local building code.

So if it’s not above the roof, and you do have plumbing in your house, something is wrong and the best place to start searching for the plumbing vent is in the attic.

Look for a pipe that penetrates the floor – the area usually corresponds to the toilets locations, kitchens, and other plumbing fixtures in your house. Sometimes plumbing vent pipe might be hidden under the insulation or simply laying on the attic floor. You should consider yourself lucky if you can locate it in the attic because sometimes it’s just a mystery, and could be an expensive one.

Plumbing vent pipes separated in attic areaBroken plumbing vent pipe in attic areaCracked - separated plumbing vent pipe in attic areaIf your plumbing vent pipe is where it suppose to be, check the attic periodically anyway. You might be able to spot the problem early, and save yourself  a costly repair. Some of the problems that might be visible from the attic:

  • Cracked plumbing vent pipe
  • Plumbing vent pipe separated at connections
  • Leakage stains, roof decking damage around the roof surface penetration caused by improperly installed plumbing vent flashing, sometimes damaged or even missing
  • Missing plumbing vent on the ejector pump wellBesides all the common plumbing fixtures, you may also have an ejector pump installed in your house. It might look just like a regular sump pump, but it serves your plumbing fixtures located below the main drain line.

    The ejector pump well, its cover, and all penetration points should be sealed to prevent sewer gases from escaping into the living space. Sewer gases should be discharged to the exterior through the plumbing vent pipe attached to the well cover.

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This article was written by Dariusz Rudnicki

I'm a retired Illinois home inspector, founder and editor of checkthishouse.com, a blog which attracts around 2 thousand readers daily and is dedicated to answering the many questions of home owners and home buyers. Connect with me on Google+ Find me on Google+ Local

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