The main advantage of installing a French drain in the basement is security from basement flooding. Basement flooding can be a serious and expensive problem. Many basements that suffer from flooding or poor drainage use sump pumps to remove excess water. A French drain works with a sump and sump pump to offer very good protection against basement flooding by allowing water to drain away through special pipes that run below the basement floor. This removes water before it can flood a basement, and it also reduces hydrostatic pressure against basement walls, which can be a problem with other basement waterproofing systems.
French drains consist of pipes that have small holes drilled in them and are placed securely in a bed of gravel. These drains were originally used to help outdoor drainage. They are still often used outside of a basement, to make sure that ground water drains away from a home quickly, before it can seep into the basement. Exterior French drains can become clogged, however, and they require periodic maintenance.
If outdoor drainage cannot keep a basement dry, a French drain can be installed inside as well. When installing a French drain in the basement, a contractor will cut a trench through the concrete floor of the basement, just inside the basement walls. This trench will be lined with gravel. A pipe with drain holes will be placed in the trench and connected to one or more sumps.
When the system is installed, water that would have leaked through the cove joint at the base of the basement wall will flow into the trench beneath the floor. The water will then flow into the sump, where a sump pump will pump it safely away. Outdoor French drains sometimes work without a pump and rely on gravity, but a French drain in the basement generally requires a sump pump. A French drain system that uses a sump pump with a battery backup can handle a great deal of water and will keep working even if the power is disconnected during a major storm.
This type of drain in the basement can be especially useful in areas that have a very high water table. These areas can experience slow but steady basement seepage, which a French drain system can prevent, allowing basements to be finished and preventing mold from growing. Houses built near rivers or in areas that regularly experience heavy rains that lead to basement leakage are excellent candidates for the installation of a French drain in the basement.