As shown in basement plumbing, the sanitary sewer line drains toilet waste, laundry tubs, and (sometimes) the basement floor drain to the sanitary sewer main in the street. Clean stormwater and groundwater is handled by downspouts, footing drains, and sump pumps.
Often basement flooding is caused by these two sewer systems being interconnected. Some houses have the downspouts, footing drain, and/or the sump pump connected to the sanitary sewer service. During a heavy rain, stormwater enters the sanitary sewers, causing backups into one house and overloading the main lines, contributing to backups in other houses.
Don’t cause your own flood! Keep your sewer lines clear!
- Keep roots from trees and shrubs out with root killer.
- Make sure your yard clean-out vent will keep debris out.
- Don’t pour dangerous liquids down the drain (motor oil, paint, pesticides, poisons, epoxies, etc.).
- Don’t pour grease, fat or cooking oil down the drain (they solidify later).
- Don’t flush large solids, such as diapers, down the toilet.
Sewer backups can also be caused by events not related to storms or flooding. Individual service lines can be plugged by grease, waste, tree roots, breaks in the pipe, or saturated ground. Proper maintenance, like pouring tree root killer down the toilet or floor drain can prevent most of these problems.
The sewer mains can also be plugged by the same causes, or by vandalism or illegal dumping in manholes. These problems can be fixed by the owner or the Village, depending on where the stoppage occurs.
There are four ways to stop sewer backup that occurs when the sewer main is overloaded and backs up through the sanitary service line into the house: floor drain plug, floor drain standpipe, overhead sewer, and backup valve. Each of these measures work for buildings with basements or below-grade floors.
Floor Drain Plug
The simplest way to stop sewer backup is to plug the opening where it first occurs (see the basement plumbing graphic). This is at the floor drain, the sanitary sewer system’s lowest opening in the house. Two inexpensive measures can be used: a plug or a standpipe. Both can be purchased at local hardware stores and are easy for the handyperson to install.
Floor drain float plug
The flood drain plug stops water from flowing in either direction. Therefore, if the laundry tub overflows or other spillage occurs, it will stay in the basement unless the plug is removed. Because of this, it may be best to leave the plug out under normal circumstances and put it in place only during heavy rains.
One variation is a plug with a float. It allows water to drain out of the basement (see illustration, left side). When the sewer backs up, the float rises and plugs the drain (see illustration, right side). A float plug permanently installed will not interfere with the floor drain’s normal operation.
Precautions: A plug left in the floor drain may contribute to a wet basement if water from a laundry tub spill or a leaky pipe cannot drain out. Float plugs are known to have been jammed open by a small amount of debris. A plug does not tell you if there is a problem in your sewer service line. If the plug is not tight enough, pressure can eject it. Therefore, a plug is not recommended for flood depths greater than one foot.
A standpipe is an inexpensive alternative to a floor drain plug. When the sewer backs up, the water moves up the pipe. If properly installed, water pressure cannot build up to blow a standpipe out of the floor drain. The system works unless the backup is so deep that it goes over the top of the pipe.
Precautions: Neither the plug or standpipe stops backup from coming out of the next lower opening, like a laundry tub or basement toilet. Sealing the base of the toilet to the floor will protect you until the water backs up higher than the top of the bowl.
Because water pressure depends on the height of water in the pipes, a standpipe does not reduce the pressure in the pipes (or under the floor, if the pipes leak). Because the pressure under the floor is the same with a standpipe or a plug, standpipes and plugs are only recommended for flood depths of one foot or less and for buildings with cast iron sewer lines underneath the floor.
Overhead sewer arrangement
An overhead sewer is generally viewed as the most effective sewer backup protection measure. It acts like a standpipe but without the shortcomings. A sump is installed under the basement floor to intercept sewage flowing from basement fixtures and the basement floor drain. An ejector pump in the sump pushes sewage up above the flood level. From there it can drain by gravity into the sewer service line. Plumbing fixtures on the first floor continue to drain by gravity to the service line.
Unless the house is subject to overbank flooding, it is unlikely that the sewers will back up above ground level. If water does go higher, a check valve in the pipe from the ejector pump keeps it in the pipes. Backed up sewage is enclosed in the sewer pipes and doesn’t overflow laundry tubs or basement toilets.
Although more dependable than a standpipe, an overhead sewer is more expensive. A plumbing contractor must reconstruct the pipes in the basement and install the ejector pump. It can cost $3,000 to $7,000.
Precautions: The ejector pump requires electricity to work, so battery backups are recommended. The basement is disrupted during construction and the ejector pump needs periodic maintenance. This work requires a licensed plumber and a permit from the Planning and Development Department.
Sewer Backup Valve
A backup valve stops the water in the sewer pipes. While not as foolproof as an overhead sewer, installation is less disruptive to the basement.
Older versions of this approach were located in the basement floor and relied on gravity to close the valve. If debris got caught in the flapper, the valve did not close tight. Because of its unreliability, valves were discouraged and even prohibited in some communities. Today’s systems are more secure. They include installing two valves in line, using better, more watertight materials, or counterweights that keep the valve open all the time so debris won’t catch and clog it.
Larger valve systems are usually installed in a manhole in the yard, well away from the basement wall, so there is less disruption during construction and no concerns over breaking the pipes under the basement floor. The cost of this type of backup valve is comparable to the cost of an overhead sewer, in the $4,000 to $6,000 range.
Precautions: The ejector pump and the valve require maintenance. This work requires a licensed plumber and a permit from the Planning and Development Department.