From the City of Lakewood Ohio‘s City of Lakewood Sewer System Planning Project FAQ Sheet 1a:

Sources of Basement Flooding – Basement flooding can result from one or more of the following conditions:

1. Water can seep into basements through cracked walls, floors and windows. This is caused by structural problems with the house itself such as exterior grading that directs the water toward the house or non-working building drains such as blocked downspout or foundation pipes and laterals. Downspouts incorrectly connected to the foundation drains can also cause seepage.
2. Sewage can enter basements through the floor drains during rain storms when there is more water trying to enter the sewers than the sewers can hold. This type of flooding is related to limited capacity in the public sewer. The sewers work properly but can not keep up with the additional flow generated by heavy rain storms.
3. Sewage can enter basements through the floor drains during rain storms when there is a blockage in the public sewer system. Blockages and pipe failures can develop during heavy rains when improper foreign materials flushed down toilets or washed into catch basins from the street become lodged in the sewer.
4. Sewage can enter basements through the floor drains during rain storms when the lateral between the house and the street is clogged. A large amount of water comes down the downspouts and driveway drains during heavy rains. If the storm lateral is clogged, this water will back up and flow into the sanitary lateral underneath through loose joints and broken pipe. If the sanitary lateral is even partially blocked by roots or improper foreign materials flushed down the toilet, the excess storm water will back up into the basement.

What have Property Owners done to reduce basement flooding in Lakewood?

Residential back flow prevention devices – No one can ever guarantee that basement flooding will never happen again, even after public system improvements and private property corrections have been made. Or, property owners may not wish to wait for the overall system to be upgraded and restored. One solution some owners have used is to install a residential “back flow preventer“. This is an automatic valve device that can be installed on the sanitary lateral (sewer) below the floor where it exits the basement (downstream of the floor drains) which allows water to flow out of the building, but closes when water tries to flow backwards.

There can be problems:

• The unit must be cleaned frequently to ensure that the valve closes tightly when needed.
• If the sanitary lateral outside the building is old, loose or cracked, the back flow preventer will cause flood water to flow out of the lateral, through the ground and into the basement through cracks in the floor or walls or even the floor drains.
• Buildings with downspouts connected to the sanitary lateral under the basement floor will still flood.
• Residents can not use toilets, sinks, laundry or showers while the backflow preventer is in operation.

The City of Regina, Canada has toubleshooting pages on causes and solutions to basement flooding: Diagnosing and Solving Flood Problems

Toronto is offering to disconnect downspouts from city sewer connections for free: Toronto Downspout disconnection program

Other resources:

City of Winnipeg: Protect your Home from Basement Flooding