How to build a French drain

A French drain is basically a trench in the ground containing a perforated pipe on a bed of gravel. It effectively directs water away from a foundation or redirects groundwater from flooded areas. The concept is as simple as the construction. The components of a French drain are a 4-inch diameter perforated pipe, washed drainage gravel and landscape fabric. Here’s how to build a french drain.

Flexible drain pipe is an acceptable and more economical choice, but rigid pipe – which is a bit more expensive and requires glued fittings – is crush-proof and can be cleared with a power snake if necessary.

How to build a French drain

First call the local utilities providers and have any underground utilities marked before you start to build a french drain.

Now determine where the French drain should go to do the most good. Ideally a French drain should be located on a slope that allows the water to flow away from the problem area. The area should also be located where you can dig easily. If there is no slope, you’ll need to create one in the trench you dig for the drain. To be effective, you need a grade of 1 percent, which is a drop of 1 foot for every 100 feet in length.

Use spray paint to indicate where you plan to dig the drain.

Digging is the most difficult part. You need a trench 8 to 12 inches wide and 18 to 24 inches deep. Larger trenches provide better drainage and are less likely to become clogged.

Line the trench with water-permeable landscape fabric. The fabric will help keep dirt out of the trench, allowing the gravel to accept and divert more water. Cut the fabric so you have about 1 foot of fabric extending up and over each side of the trench. Add 2 to 4 inches of gravel to the bottom of the trench.

Lay the pipe on top of the gravel with the drain holes facing down. Cover the drain pipe with gravel to a level of about 3 to 4 inches below grade. Fold the landscape fabric over the top of the gravel.

Fill the trench with topsoil and reseed or replant the area.

Tools and materials needed to build a french drain

• Shovel
• Striping spray paint
• Top soil
• Sand
• 4-inch drain pipe
• Landscape fabric
• Gravel