Lawn and Garden

Installing a French Drain

Lawn + Garden Projects

Installing a French Drain

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BLACK+DECKER B+D Contributor 120 Projects

A French drain is a very simple, but very effective solution for poorly draining lawn areas. It involves digging a trench for gravel-covered length of pipe that filters runoff from the lawn, leading it to a low-lying area such as a gutter or wooded section of the property. Never direct a French drain or any other drainage improvement to a neighbor’s property.

The most important part of the French drain is the slope. Maintaining a reasonable slope ensures that the runoff will follow the drain. The drain tube itself is covered with permeable landscape fabric. The idea is to allow for water to flow through, while blocking fine soil that could clog up the holes in the drainpipe. Do not use rubber or standard plastic sheeting or pond liners. These will not allow for the free flow of water. You should use clear gravel to surround the pipe for the same reason. Don’t use gravel with fines that could clog or block the holes in the drainpipe.

Your tile should underlie the lowest part of the problem area and slope slightly toward an above-grade exit point. Use a 2 x 4 with a level on top to ensure the trench floor carries a gentle downward slope. The trench needs to be at least 1 inch deep where gravel covers it in the problem area. The tile will exit into the gently sloped swale that will carry the water away.

How to Install a French Drain

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    Use stakes, mason’s string, and a string level to determine a drain path with an above-grade exit point below the level. Use a power edger or spade to cut the turf at the outside edges of the drain trench—usually 8" to 14" wide.

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    Use a handheld turf cutter or spade to dig up the sod along the trench line. Store the cut sod in a cool, shaded place and moisten regularly while you dig the trench.

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    Dig out a squared trench over the length of the drain. Place the dirt on a tarp next to the trench site. Use a 2 x 4 with a level on top to ensure the trench slopes slightly to outlet.

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    Line the bottom of the trench from start to end with permeable landscape fabric wide enough to run 1 ft. up each side. Add about 1" of washed gravel to the bottom of the trench.

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    Lay perforated pipe (called drain tile) all the way along the trench. Gravel is not needed toward the exit of the tile where the trench becomes shallow.

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    Add 3" to 4" of gravel on top of the pipe and then fold the edges of the landscape fabric over the top of the gravel and pipe, essentially making an outer sheath of fabric. 

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    Fill the trench with soil, and tamp down, leaving about 1" for the sod. Scratch the top of the soil lightly with a garden rake.

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    Replace the sod you removed. Roll the sod to ensure firm contact with the soil and water well along the length of the trench. Cover the outlet of the tile with a PVC grate and/or large rocks.