Why Do I Need Plumbing Vents?

I have seen a lot of activity on the forums and discussion groups of late about plumbing ventilation or “waste stacks” and although I have written on it before it seems that maybe a better explanation is needed to help people understand the need for vents. To start with let me begin by answering the basic question that I answered for a reader on Saturday morning, yes if you install a new sink it must have a vent. Can it be connected to an existing vent stack? Maybe but that really depends on how close the existing stack is to the new sink and how much you are already venting with the existing system.
Now let’s back up and briefly discuss what a vent does. Vents really are necessary for two reasons. The first reason is to vent captured methane or sewer gas up, out and away from the house. Every fixture has a “P” trap or device to keep sewer gas from coming back up through the sink or toilet but that doesn’t allow for the gas to escape from your pipes. The vent stacks are attached in line with all of your drain lines and run vertically up and out of the house to a prescribed height above your roof line. This height varies by code from each venue, but usually is at least 18” or higher from the roof line. These vent stacks are normally clearly visible protruding from your roof usually directly above plumbing fixture locations in your home. This allows the sewer gas to escape up and away from the area of windows and doors in the house and up into air circulation. The second purpose for vents is to allow for better drainage. The best way to demonstrate the need for this is to take a bottle of water and turn it upside down. You will notice that the water does not pour out evenly but instead gurgles out or may become trapped completely if the liquid is thicker than water. Likewise water or sewage that is draining from your house gets air pockets trapped in the drain line and without vents these air pockets keep the fluids from escaping easily and will cause drains to operate slowly or will cause them to loudly gurgle when trying to drain. Many new home owners will experience this when moving into a newly built home and discover that the plumber, in order to cut some corners, may have shorted the number of vents needed. This is especially true in rural areas where building codes are not enforced with inspections before the walls are closed up. To increase vents and have them hidden in walls can be a very awkward and messy retro fit requiring walls to be removed and new punctures to be made up through ceilings, plates and the roof. The potential for future leaks and other problems is high. Vents can be run on the outside of a house and in fact in older homes, that were retro fitted with plumbing when indoor bathrooms became the vogue, vent pipes many times could be seen running up the outside walls of the house and sticking up above the roof. Obviously the process of adding vents must be a prime consideration any time you decide to add a plumbing fixture of any kind to an existing system or plan to expand your home. This decision will become just as important as how will the plumbing drain and where will the water source come from.
Finally the gurgling I discussed earlier when water is draining can be caused by something other that a lack of original vents. If you have been living in your home for a while and the drains start gurgling then there can be other problems. The vents themselves can become clogged. This usually occurs with an accumulation of leaves and trash in the vents from where they stick out of the roof and small animals and birds have been known to used these vent pipes as ideal nesting locations. A plumbers snake or auger inserted from the roof down will usually unclog the vent and force the debris down and out through your drain lines. Gurgling can also occur when your drain lines themselves begin to clog and the water can not escape fast enough. As addressed in other blogs of mine, this too can be cleared with the use of a snake.
More and more it seems that a 25' plumbers auger begins to become one of those necessary additions to your DIY tool box or if not the phone number for your local plumber should be tattooed on a convenient apendage.