How to Install French Drains

Divert groundwater from the basement or foundation with the help of gravel and fabric.
BPF_original_french-drain-step-7c_h

BPF_original_french-drain-step-7c_h

Good drainage is important to ensure that a home stays dry and free of mold. If groundwater collects in the basement, it is not only an inconvenient eyesore for the homeowner, it can also lead to wood rot and mold.

The most reliable way to eliminate undesirable, free-standing water is to install French drains with slotted pipes, filter fabric and gravel. The old way of installing French drains is to do it without the gravel and the fabric. Without the gravel and the fabric, however, the drain can clog up with sand and soil over time.

The best practice for installing French drains is to use perforated drainage pipes, which allow water to enter or exit through small openings along the pipe. The perforations can be circles or slots. But slotted pipes are better than pipes with small round holes because they tend to reduce the amount of fine soil particles that get into the pipe.

Here's how to do it:

  • Dig a trench along the outside of your footing. The trench should be at least 2 feet wide, and can be as deep as 6 feet for a basement or as shallow as two feet for a slab-on-grade home.
  • Lay the pipe on the virgin soil. It is very important that the pipe always be sloped from a higher starting point to an ending point of lower elevation, so gravity can force the water out. The grade should always slope away from the home to ensure that the water is directed away from the walls of the home.
  • Cover the pipe with at least 12 inches of washed gravel.
  • Lay filter fabric over the gravel to prevent any soil from clogging the pipe.
  • Back-fill the foundation with top soil back to its original grade height.

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