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What Causes Basement Moisture?

Alison Faria
Alison Faria

Basement moisture is caused by a number of structural problems, such as inadequate grading, missing or defective downspouts or gutters and structural cracks. There are several signs that indicate the presence of basement moisture. These signs can include damp spots on the floors or walls, peeling paint, mildew or mold, musty odors, and warped paneling. If not fixed, these problems can become health hazards and can also lower the value of the home.

Inadequate grading can cause basement moisture when the ground around a house slopes inward, toward its base. Water then can flow into the basement, especially after rain or snow storms. Devices such as sump pumps can remove the water, but moisture can still be present from water that has settled in the sloped soil outside of the basement. This problem sometimes can be fixed by placing up to six inches (15.2 cm) of soil around the house so the ground slopes away from the home's base.

A man installing a basement floor.
A man installing a basement floor.

Gutters and downspouts are usually meant to direct water that falls on the roof away from the house. When either one of these things are missing or damaged, water can flow to the immediate areas surrounding the basement, which can result in basement moisture. A possible remedy is to place one downspout for every 50 feet (15.24 meters) of roof eaves. The downspouts should extend about four feet (1.22 meters) away from the house.

A sump pump can help eliminate basement moisture.
A sump pump can help eliminate basement moisture.

Window wells, or drains placed right next to a basement's wall, can sometimes be built incorrectly. When this happens, water can flow toward, rather than away, from a house's foundation. This can be fixed by filling the window well from the footing to the actual window sill with coarse aggregate. Also, there should usually be another drain extension that goes from the footing to the window well's base.

House foundations made of concrete can develop cracks as they age. If floor joists are not connected to the foundation's wall, which is usually also the basement wall, then that can cause the wall to start cracking and moving. Water can then seep into the cracks when it rains or snows and evaporate during warm weather, causing basement moisture. One way to fix this is to use anchor bolts to secure the foundation and joists. The cracks might need to be drained and cleaned of any mold or mildew before that can be safely filled.

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    • A man installing a basement floor.
      By: Lilyana Vynogradova
      A man installing a basement floor.
    • A sump pump can help eliminate basement moisture.
      By: Tim Glass
      A sump pump can help eliminate basement moisture.