How to Install Exterior Gravity Drains

Gravity drains are based on the principle that water flows downhill. They're installed on a sloped channel that allows gravity to carry water away to a safe discharge point. Plastic pipe is typically used for the drain and buried in the channel to terminate in a swale, ditch or open area where the water flows into a municipal system or disperses. Pipes may be perforated or solid, depending on the application -- solid pipes are best for fast water removal while perforated pipes allow water to infiltrate slowly into the ground and gradually reduce the amount of runoff.

Fluorescent spray paint
Shovel
Rigid, 4- to 6-inch perforated PVC pipe
Couplers
45-degree elbow (Optional)
1/2-inch to 1-inch washed gravel
Geotextile cloth
Coarse sand

Instructions

- 1
  Choose the route for the drain, from the high point to the low point, where the runoff can discharge. Mark the route with a line of spray paint along the center.
- 2
  Excavate a channel along the marked route by starting at the low point. Dig the channel 5 to 6 inches wide and 8 to 12 inches deep. Slope the channel to a minimum 1 percent grade or 1 foot of drop for every 100 feet in length.
- 3
  Spread washed gravel along the base of the channel to a depth of 2 inches. Lay geotextile cloth on top of the gravel that is wide enough to wrap around the pipe when it's laid. Overlap any joints in the material by 12 inches.
- 4
  Place the perforated PVC pipe onto the geotextile cloth. Lay perforations down for a French drain and up for a foundation drainage. Ensure the slope is maintained by shifting the gravel under the pipe, as necessary, to build or reduce the grade.
- 5
  Use 45-degree elbows on the pipe, as necessary, if there are turns in the routing of the channel. Connect pipe lengths together with couplers manufactured for the type of pipe and make sure the connections are watertight.
- 6
  Pack washed gravel to a 2-inch depth around the pipe. Leave the outlet end of the pipe exposed, or daylighted. Place 3 to 4 inches of coarse sand on top of the gravel, then add topsoil. Seed or sod the channel as desired.

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