When you think of a retaining wall failure images of a crumbling structure may come to mind. Although these kinds of failures do occur, they are typically the result of major weather events like earthquakes or floods.

Most retaining wall failures happen slowly over time—things like small cracks that appear in different areas of a wall, or a wall that slides a little bit every year until the movement from its original position becomes noticeable. One thing’s for sure: Once a retaining wall begins to slide or slant it won’t stop without major repairs. It may even need to be replaced.

The failure of a retaining wall on your property, or its collapse—which is referred to as a “catastrophic” failure—could put your home, family, and others in danger.

Consider this: In December two Maryland families were forced to vacate their homes because the retaining wall behind their property failed beyond repair and needed to be replaced. As a result, the soil beneath their residences became unstable and gradually began to slide downhill.

Here are two more reasons why retaining walls fail.

Inadequate Drainage

Not only does a retaining wall do the obvious job of confining the earth, it can also add visual appeal to your landscape. Since many retaining walls are situated on hills or slopes, where the natural flow of water is downward, a properly installed wall should have a drainage plan and system that allows for the flow of water (usually rainwater) away from the base of the wall.

An insufficient drainage system can cause rainwater to collect at the base of the wall, which can result in soil saturation. Water that pools at the bottom of retaining walls is the leading cause of failure, since it can put the wall under added pressure, especially when the water freezes and expands.

Exposure to the Elements

Constant exposure to sun, rain, and wind are guaranteed conditions for retaining walls, and the materials used to construct them will be subject to expansion in hot conditions and contraction in the cold. That’s why the material composition of a retaining wall is critical to its durability—wood will rot with time and metal will rust. Also, over the lifespan of the wall, groundwater, rainwater, and wind can cause soil erosion.

It’s important to reiterate that extreme weather, like major flooding, hurricanes, tornadoes, and severe winds, can cause the sudden catastrophic failure of a retaining wall.