A French drain or weeping tile (also trench drain, filter drain, blind drain, rubble drain, rock drain, drain tile, perimeter drain, land drain, French ditch, sub-surface drain, sub-soil drain or agricultural drain) is a trench filled with gravel or rock or containing a perforated pipe that redirects surface water and groundwater away from an area. A French drain can have perforated hollow pipes along the bottom (see images) to quickly vent water that seeps down through the upper gravel or rock.
French drains are primarily used to prevent ground and surface water from penetrating or damaging building foundations and as an alternative to open ditches or storm sewers for streets and highways. Alternatively, French drains may be used to distribute water, such as a septic drain field at the outlet of a typical septic tank sewage treatment system. French drains are also used behind retaining walls to relieve ground water pressure.
All types of French drains depend on gravity to drain water away. If you have a French drain on flat land, you’ll probably need to connect a pipe to it to carry away the water it collects. Usually homeowners using a French drain on flat land will run pipe from the drain to a collection basin, where it’s then pumped into a storm drain system. As of July 2011, having a standard French or curtain drain installed cost about $10 to $16 per linear foot.
A curtain drain is a trench filled with gravel and perforated pipe to channel water away from the house. Lining the ditch with filter fabric will help the system last longer. I avoid generic landscape weed-blocking fabrics, opting instead for a high-quality product such as Typar landscape fabric. Line the ditch sides with fabric, then fold the fabric over the gravel a few inches below the surface. Fine aggregate, such as silt, will be prevented from sifting down deep into the curtain drain where it would eventually clog the pipe.
As long as you’re digging up the yard, you might as well incorporate gutter drains into the same ditch, just don’t connect gutter drains to perforated pipe. Instead, run gutter pipe alongside the curtain drain. And for safety’s sake, don’t forget to call 811 before you dig so you know you won’t be running into buried electric or gas lines.
It’s like a gutter for the foundation
When installed correctly, a curtain drain can intercept surface runoff and groundwater before it gets to the foundation. The water flows into a ditch that should be 18 in. to 24 in. deep and sloped downhill. Terminate the drain in an area where flowing water won’t create problems. Lining the ditch with filter fabric helps to keep the pipe clean so that the drain works maintenance-free for a long time.
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