Causes of Basement Flooding

Flooding of basements can occur at any time, anywhere. Even basements that have never flooded before are susceptible.

There are a number of causes of basement flooding including:

  • Foundation leakage;
  • Overland flooding; and
  • Sewer backup.

1. Foundation Leakage

Foundation leakage occurs when groundwater enters a home. Groundwater is water that is naturally located below the ground's surface. The groundwater level can be, at times, above the level of the basement floor. The City of Windsor has some areas of naturally occurring high groundwater levels.

If you find water around the walls of the basement, you may be experiencing leakage through the foundation.

In general, homes usually have some form of drainage system built around them. Foundation drainage systems generally include weeping tiles around the outside of the home, which drain to the sewer system or to a sump pump. These systems are designed to keep the groundwater level around the foundation lower than the basement floor. Some homes (mostly newer homes) also have a waterproofing membrane included on the outside foundation walls.

Failure of foundation drainage system can cause water to enter the basement in three ways:

Seepage (Infiltration)

  • If the water table rises, water can enter the basement through cracks, holes and other unintended flow paths. This is generally considered to be part of the aging process of the home and the materials used to build it. Regardless of the condition of the drainage materials and pipe work around the foundation, if water can enter the foundation floor or walls via cracks and holes it will likely do so in heavy rains, ground thaw, or snow melt periods when there is a lot of water in the ground. Settlement of the lot grading around the building and downspouts discharging water too close to the home can increase the quantity of water around the foundation and increase the risk of water entering through cracks and holes.
  • Solutions to seepage can include regrading of property to ensure that water moves away from foundation walls and sealing of cracks and holes to remove the pathway for the movement of the water.

Sump Pump Failure

  • If your basement is equipped with a sump pump(s), it can mean that the foundation drainage system of your home requires some assistance to keep up with the groundwater around it, or it simply cannot drain adequately by gravity to surrounding ground or sewer. New homes are required to have a sump pump in these situations. Sump pumps, when working properly and adequately maintained, can safely pump excess water above the foundation and away from it. Ideally, the water should be routed to the lawn or storm sewer. If the pumps cannot keep up, or it fails to operate (perhaps due to a power failure or malfunction), the groundwater level around the foundation can rise to the point that it flows up and out of the sump onto the basement floor. The City of Windsor recommends that sump pumps be installed with an overflow to the lawn, so in the event that the storm sewer is full, the water has another place to go.
  • If you have problems with high groundwater levels around your home, you may qualify for the City of Windsor's Basement Flooding Subsidy Program, which includes incentives for the installation of a sump pump for homeowners that currently do not have one.
  • The "Climate Resilient Home" has been upgraded to include a sump pump with overflow.

Weeping Tile Failure

  • Over time, the foundation drainage system can deteriorate. This may be due to a partially or fully collapsed pipe, or due to sediments plugging the pipes. If this happens, the drainage of water around the foundation is either impeded or completely blocked. As a result, the groundwater level around the foundation gets too high and it may spill into the basement via the sump if one exists or via cracks in the foundation.

2. Overland Flooding

During periods of heavy rain or rapid snowmelt, surface water may pool around the house, or accumulate in hard surface depressions such as driveways or roads adjacent to a home. Close proximity to a natural stream or roadside ditch can also present a risk. During extreme weather events, this water can flow into the home through low lying windows, doors, below-grade entrances, etc. Generally, proper grading on the property will reduce the risk of surface water getting into your home.

3. Sewer Backup

Most homes in the City of Windsor only have one connection to the sewer system, and that is the sanitary sewer lateral. However, newer homes built in the last 25 years or so, as well as some older neighbourhoods, have storm sewer laterals as a component of the foundation drainage system described above.

These laterals form either one or two intentional connections to the municipal sanitary and/or storm collection systems. The City's sewer systems are maintained through a variety of municipal maintenance programs. However, when a blockage occurs, or when the systems are overloaded during heavy rains, a sewage backup can occur. Here are a few reasons why sewers backup:

Sewers are Full

  • When the sewers are full, this is called "surcharged." It means the pipe system is full, and the water level in the sewer manholes may rise well above the top of the pipe and in some instances overflow out of the manhole cover. If the sewage level in the system exceeds that of your basement, flows can be blocked, or worse, sewage can flow towards your home. When this occurs, wastewater may enter your basement by way of the lowest fixture, which is usually a floor drain, shower drain, sink, washbasin or toilet.
  • The underlying cause of this is more water in the system than the system was designed to handle. The recent large storms that hit Windsor (e.g. September 2016 and August 2017) saw more rain fall on the city than the design standard for the system. This contributed to sewer backups experienced in the city.
  • The Sewer Master Plan currently underway is looking at various short-term and long-term actions to help minimize these impacts.
  • The "Climate Resilient Home" has been retrofitted with a backwater valve to reduce the risk of sewer backup.

Blocked or Failed Sanitary Laterals

  • The sanitary sewer lateral, just like the shingles on your roof, or your driveway, is a feature that will degrade over time possibly leading to a collapse of the lateral blocking sewage from flowing to the City's sanitary system. Another reason for blockage of a sanitary sewer lateral is simply due to what is being flushed down the toilet. Toilets are for human waste and toilet paper only. To learn more about what not to flush check out our wastewater video. Under these scenarios, the sewage created from within the home will not drain to the City sewer and can lead to a backup of your own sewage.
  • Sanitary laterals can be inspected by a camera to determine the condition of the lateral. Blockages can often be cleared by eeling the laterals. However, in some cases the lateral will need to be replaced. The City of Windsor has a program in place to support residents that require a sewer lateral replacement (private drain connection).
  • For more information on why basements flood, visit the Institute for Catastrophic Loss Reduction (ICLR). ICLR has also created a series of videos, including one called Why Basements Flood (ICLR)

For more information on environmental initiatives:

  • Phone: For general information, call 311. For detailed inquiries, call 519-255-6100 ext. 6127.
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