Why basements leak after heavy rain in Louisville

Where the water comes from

Louisville sits on heavy clay over limestone. After a big storm the clay stays saturated for days and groundwater keeps moving toward the lowest point it can find. Near the river, the creeks and in the lower parts of town, the water table is high after wet weather. That water presses against the basement walls and under the floor.

Where it gets in

• The floor edge. Most Louisville basements leak at the joint between the floor slab and the wall, pushed in by the water table rising in the clay.
• Through the wall. Block walls let water move through them. White powder on the block (efflorescence) is minerals left behind by that water.
• Cracks. Poured walls crack as they cure and settle. Under pressure, the crack becomes a pipe.
• Window wells and low spots where water pools against the house.

What makes it worse

Roof water dumped next to the foundation is a common cause of a wet basement. A downspout that ends at the wall puts the whole roof's runoff into the soil right where the basement is. A sump discharge that ends a foot or two from the house sends the same water back down along the foundation.

How it gets fixed

• Start outside. When roof water is the cause, buried downspout extensions are often the first, cheapest step.
• Interior drainage. When water comes in at the floor, an interior system opens a channel around the perimeter, sets drain tile in gravel at the footing and runs it to a sealed sump. The walls get a liner so water coming through the block runs down behind it into the drain. That is basement waterproofing.
• Exterior waterproofing. When the wall itself is failing, the outside of the wall is dug out, sealed and drained. See exterior foundation waterproofing.
• Crack repair. A single crack that weeps can often be sealed on its own.

Why paint does not hold

Waterproof paint holds back water until the pressure behind it is greater than the bond, then it peels. It treats the symptom. Drainage relieves the pressure, which treats the cause.

If the basement is wet right now

The flooded basement guide covers the first 24 hours: safety, getting the water out and drying the space before mold starts.