Basement Flooding

Updated 01/05/2011

That mature tree in your front or backyard may be the cause of your basement flooding. Roots from trees located near the sewer line often grow through small cracks in the mortar around the tile joint. Once inside the tile, the roots continue to grow and form large masses which create an obstruction in the pipe.

As long as the sewer line is used regularly, the roots usually stop growing at a point which will still permit ordinary usage. Trouble occurs when a large object is flushed down the sewer and lodges against the roots or when there is an exceptionally heavy amount of rainfall and the roots prevent the water from flowing through the sewer as quickly as needed in order to prevent a backup.

This problem may be corrected by the following solutions:

Sewer Cleaning
In many cases, periodic rodding is all that is needed to control root growth and reduce the likelihood of sewer backup. Rodding may be needed as often as every six months or as infrequently as every few years, depending upon how fast the tree roots grow.

Copper Sulfate Treatment
Many homeowners have had good results by flushing a small quantity of copper sulfate crystals down the sewer at regular intervals. The copper sulfate reduces the rate of growth without harming the tree. Although this treatment may not eliminate root growth, it often increases the interval between roddings.

Sewer Pipe Replacement
The most effective (and most expensive) method of eliminating tree roots is to dig up old sewer pipe where the obstruction is located and replace it with new pipe. The good news is the sewer pipe has joints with an extremely tight seal which virtually eliminates the possibility of tree roots growing into the sewer line in the future.

Tile Replacement
In a small number of cases, improper installation of sewer pipe or the settling of soil under the pipe may cause the tiles to break or separate. In cases where broken or separated tiles are the cause of basement flooding, the only choice is to dig up the affected section of pipe and make the necessary repairs.

When a heavy rainfall causes the quantity of storm water to exceed the capacity of the village's sewer system, pressure builds up in the system and water can back up into unprotected basements. If your basement is affected by backups caused by surcharging in the system, there are several courses of action available to you.

Install a Floor Drain Standpipe
A standpipe installed in the floor drain will raise the overflow level. The standpipe is designed to hold back the water only if it would have flooded several inches deep. If the pressure builds to a higher point, it is better to let some of the water flow onto the floor in order to equalize the pressure, rather than take a chance on having the sewer and floor break. The standpipe may be left in place at all times if the floor drain is not needed.

It is not a good idea to plug the floor drain when the sewer surcharges and the flow begins to back up through the drain. If the drain is plugged, pressure in the piping under the floor may build up sufficiently to break the tiles and heave the basement floor.

Install a Backwater Valve
A mechanical valve or a check valve will help prevent basement flooding. A check valve that closes automatically when flow through the sewer line reverses may be installed either outside the house or inside the basement, depending on your specific situation. A mechanical valve is normally located outside the basement and must be opened or closed manually.

A Word of Caution

Check valves installed in sewer lines sometimes become clogged with debris and fail to close completely. When this happens, the valve will slow down the flow of sewage but will not stop it completely. For this reason, a valve should not be depended upon completely, and the valve should always remain accessible for service and repair. Remember that when a valve is installed in a house sewer, the house plumbing cannot be used during a storm when the valve is closed to prevent basement flooding.

Install an Overhead Sewer System
An overhead sewer is a system in which all sewage from above-ground level flows by gravity to the village sewer, but all sewage and storm water collected below grade in the basement must be pumped up to the house sewer at a connection near the basement ceiling. There are no direct connections between the main sewer system and the basement, so there is no way for the sewage to backup into the basement area.

Although an overhead system is very effective in eliminating basement backups, the plumbing changes required make it a costly solution. However, it is still a good choice for homeowners who have a substantial investment in finished basements or who have valuable equipment or storage items housed in the basement.

One disadvantage of an overhead system is that the pumps used to force the water up from the basement level will not operate during a power outage, so overflow could occur if the power is out for an extended time. Even so, the overhead system in most cases is the most effective way to prevent basement flooding.

When excessive ground water is allowed to accumulate around the foundation of the house, water may seep into the basement through the basement floor and walls. There are three common problems which may cause water to build up around the foundation.

Footing Drains
Most basements have a footing drain around the outside wall which is designed to collect ground water in the soil and keep it from seeping through cracks in the basement floor and walls. In older homes, the footing drain is connected directly to the house sanitary sewer. When a basement develops leaks in the floor or walls, it is often due to blockage or breakage of the footing drains. When the footing drains are not functioning properly, the ground water collects around the foundation of the house instead of draining into the sewer system.

If your basement is flooding due to problems with the footing drains, there are three possible solutions:
  1. Disconnect the footing drains from the sanitary sewer and install a sump pump
  2. Eliminate deep roots
  3. Clean the footing drains
Exterior Grading
Basement floor and wall leaks can also be caused by excessive amounts of ground water collecting around the basement walls due to improper grading. It is extremely important that the ground around the foundation be sloped away from the house for several feet in order to prevent excessive amounts of water from accumulating in the soil next to the house. Grade changes require approval from the Engineering Department.

Downspout Drainage
If the downspouts connect with the house drain or sewer, basement flooding can occur when the underground connections become broken, causing the water to seep through the foundation in the vicinity of the break. Or if the downspout is emptying into a sewer which is clogged by tree roots or other obstruction, the sewer may back up into the basement.

Downspouts connected to the sewer system are illegal and must be disconnected. It is advisable to disconnect the downspouts and let the rain be absorbed into the ground instead of entering the house sewer. If rainwater from downspouts is being discharged onto the ground, be sure to use splash blocks or other means to direct the flow of water well away from the house foundation.