Why Do Basements Leak?

…So why do basements leak?

The first step in building a new home is digging a huge hole into the ground. The soil that is eventually exposed after the hole is dug, is clay. Clay is expansive, which means that it expands when it is wet and shrinks when it is dry, similar to a dense sponge. After the hole is dug, the foundation footings and foundation (usually poured concrete) are poured over the clay soil and the foundation walls (usually concrete block or poured concrete) are then constructed. Since the soil that the foundation is resting on is clay, this causes what is also known as the “clay bowl effect”. Again, clay is expansive, it retains water and drains it slowly, meaning that the soil is subject to change causing eventual changes in the foundation. Hence the foundation for problematic basements is laid out.

When the hole is first dug, the hole is bigger than the actual size of the home to allow workers access to the perimeter of the foundation/foundation walls, this area is called the “over dig area”. When the foundation walls are finished, the “over dig” is then back filled with soil. Hence the second most common reason for a wet basement. When the “over dig” is back filled, the soil used needs to settle. Why does the soil in the back fill needs to settle? Consider that the soil will eventually settle and become more compact, leaving a slope around the perimeter of the home. Gravity will then pull the flow of water directly toward the foundation walls.

Water building along the foundation walls causes hydrostatic pressure. Hydrostatic pressure increases in proportion to depth measured from the surface because of the increasing weight of fluid exerting downward force from above. In other words, more water equals more pressure. The pressure is looking for release so it will push against the foundation/walls until it is relieved. Sooner or later, water will find its way into the basement, causing water damage, jeopardizing the integrity of the foundation and a slew of other potential problems.