A French drain is highly effective and you will find it in a variety of uses. Generally speaking it is a drain, normally along a footing, constructed of tile laid in a bed of gravel and designed to collect water and carry it away from a footing or unwanted location. Consequently the term French drain is often synoptic with the terms drain tile or perimeter drain.
In Vancouver you may find your neighbor’s land is at a higher elevation than yours and you may have problems with excessive moisture on your property. Water from your neighbor’s property may be running down the slope on to your property. One remedy here is to install a French drain.
Historically the French drain was as simple ditch with a pitch that was ample enough to run water away from the protected area. Today French drains are made with perforated pipe known as weeping tile. French Drains are commonly dug down 36-48 inches. Then 1 1/4” rock is placed at the bottom of the trench and a corrugated pipe is placed over this rock. Once in place, the trench is filled with more rock to approximately 4-6” below grade. The last 4-6” are then topped with soil and/or sod.
Landscaping textiles are used to prevent migration of the drainage material and to prevent dirt and roots from entering into and clogging the drainage pipes. The primary reason for the perforation in the pipe is to allow the water to drain along the full length of the pipe and to discharge any surplus water at the pipes end .
If land is flat a catch basin and discharge pump (sump pump) may be necessary to contain water
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