How to Make a French Drain

Overview

Although French drains are by and large associated with diverting roof water from home foundations, these simple structures can play a useful part in garden design as well, lessening the need for hand-watering, opening new areas of your yard to recreational or leisure use, and improving drainage in problem areas. Consider building French drains to improve water use and balance in all parts of your yard.

Building a Simple French Drain

Step 1

Dig a trench at least 12 inches deep and 6 inches wide the length of your problem area. This may be from a downspout area where water consistently pools to the edge of your property, near the base of a slope that produces pools of water or at the highest edge of a garden bed to slow runoff that damages plants. French drains can also be laid along the edge of a patio or walkway to speed drainage.

Step 2

Dig the trench so that the bottom slopes gradually down from the waterlogged area. Experts suggest that as little as a 1% grade will move water away from problem areas. Dig the trench long enough that it ends, if possible, 10 feet from the problem area, so that water is genuinely diverted from the area where it accumulates.

Step 3

Line the dug trench with permeable landscape fabric and add gravel to within 2-3 inches of the top. Fabric will keep surrounding soil from silting into the gravel and eventually clogging the drain.

Step 4

Cover the gravel with landscape fabric and either replace turf or add topsoil and reseed. In areas of severe problems, builders may add a layer of sand over the gravel and fabric, then replace grass.

Building a Piped French Drain

Step 1

Purchase perforated drain pipe to lay in the trench for even more rapid water removal. You may wish to mark out a straight drain path with string and stakes before digging, to be certain that this inflexible pipe will fit. Increasing the depth and width of your trench, along with its downward pitch, will also speed water flow.

Step 2

Layer fabric, part of the gravel, pipe, more gravel and a final layer of fabric to complete your drain.

Step 3

Add several inches of sand on top of fabric, then a thin layer of topsoil and grass seed or turf for maximum absorbency.