Wet Basement Floor Causes

What are Wet Basement Floor causes?

This is a simple question to answer. Wet basement floor causes have three distinct factors:

  1. A high water table.
  2. The basement floor is made of porous concrete.
  3. The basement floor is located below the frost line.

A High Water Table

Most people know that the water table has something to do with ground water. The word table provides an image of a flat surface, like the surface of a tabletop. It may be visualized as the ‘surface’ of the subsurface materials (sediment, gravel and clay) that are saturated with groundwater in a given geographical area. There is also a general understanding that in times of drought, water table levels may drop.

water table

The water table lies underground and is the level at which the soil and gravel are completely saturated with water. There is often some seasonal change in the water table, due to rain or drought. A high water table is especially common in areas where the soil is not well drained due to high levels of clay.

The level of the water table varies greatly due to amount of rainfall, time of the year and type of soil that surface water drains through. The water table is generally higher in areas with high density soil related to clay content. The denser the soil is, the slower the movement of the water (percolation) of the water through the soil occurs. The rate at which the high water table descends is related to the percolation rate, which is related to soil density.

Water tables can become elevated when they receive more water than they drain off. This can be from unusually high amounts of rain, or excess water from higher elevations. High water tables are often above the level of basement floors or crawlspaces. This almost always causes flooding in these areas.

Concrete is Porous


Most homes have a basement floor that is made of concrete. Concrete is a composite construction material composed primarily of aggregate, cement, and water. Concrete is porous. Water is a primary ingredient of concrete from the beginning. As the concrete cures the evaporable water, water that can evaporate away, does so and is lost. As the water evaporates it leaves the pores in the concrete that were saturated with water empty. These empty pores make the concrete porous.

The Basement Floor is Below the Frost Line

Snow melts, rain falls. Much of this moisture is pulled deeper into the frost line by gravity. The frost line is the depth in the ground in which the water NEVER freezes. This is important in a building’s construction because if a footing and foundation wall are built above the frost line, the chances of that basement heaving will occur go up. Heaving occurs when the soil expands and contracts due to freezing and thawing. When the soil expands and contracts it can cause damage to a building’s foundation. This is why a footing for a basement is placed below the frost line.

Because this seepage is constantly moving beneath the frost line, you should expect water related problems year round. Times of extreme seepage occur usually in early spring and late fall. Of course a catastrophic event like a Nor’easter or a Hurricane can happen at any time.


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