Tuesday, December 14, 2010

Understanding Common Area Drains and Vent Pipes

By: Jim Digre

Hidden behind the walls of every condo owner's unit is a myriad of plumbing pipes. They consist of supply, drain and vent pipes. The supply pipes are the source of hot and cold water to each unit, the drains obviously take away the waste water and the vent pipes serve, in combination with fixture traps, to allow sewer gasses to be vented outside (vents) and keep the gasses from entering the units (traps).

Today I want to talk about common area drains and vents. These pipes typically run vertically and serve the needs of multiple units. They are common area systems and fall under the responsibility of the Association to repair. Keep in mind however, that if the problem is in a pipe branching off of the common pipe and serving only your unit, the repairs are your responsibility.

Since these pipes serve multiple units in any given tier of a building, when there is a problem with either a common vent or drain, it will most likely cause symptoms in more than one unit in the tier. So, if you and your neighbor(s) are both or all experiencing the same problem (slow drains, backups, sewer gas smells, unusual sounds coming from drains), you can be relatively sure that it is a common area pipe or vent that is causing the problem. If this is the case you should contact your board or management company to explain the problem and seek help in getting it fixed.

A clogged common drain will usually cause sink, shower or toilet backups in the units nearest to and above the point of the clog when water is used on the floors above them. If a main drain is clogged below the first floor, the first floor units can sustain serious backup problems when water is in use by multiple units above them. Common area blockages can be caused by many things but are usually the result of non-soluble particulates being put in the drainage system. Rags, construction materials (paint, plaster, etc.), children's toys and anything else you can imagine are the type of things that can cause these clogs. Be aware that although these common pipes are the responsibility of the Association and a shared repair expense for all unit owners, if it is determined that you caused the problem through your own negligence, you may get stuck with a very costly repair bill. Never letting little children play around the toilet nor allowing construction materials to be put into any drain can save you and your neighbors plumbing problems that can be expensive and complicated to repair.

A blocked vent is a relatively common problem caused by anything from leaves, to dead squirrels and birds, to ice dams in very cold weather. Symptoms range from bubbles in the toilet bowl when it is flushed, to slow drainage, and all the way to siphoned (empty) traps and sewer gases entering the building. This happens because vents also serve to balance air pressure in the drain system. A bad vent blockage can cause a vacuum to develop in the drain and some or all of the water in your sink traps and or toilet to be sucked out when someone uses the toilet or fixtures above you. Should you notice fluctuating water levels in your toilet or smell sewer gas in your unit, you should suspect the possibility of a vent problem in the building.

I hope this post has given you a little better understanding of what's going on in the pipes behind your walls.

Dowling Properties has been serving the needs of condo residents for over 25 years. When thinking about a management company consider our experience and expertise and let us guide your association smoothly to a successful future. Call 708-771-0880 or visit our website at: http://www.dowlingproperties.com/


  1. I read an article once on how to clean common area drains using baking soda and vinegar but can't seem to find it again. Can you offer any help?

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  5. My Board keeps talking about "risers" when discussing the common drain system. Can anyone enlighten me as to what part of the common drain system risers are? Thanks

    1. Risers is the piping that runs straight to the top of the building that makes up the vent. It's open at top.

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