Use this 3 part SimpleSpecs™ master covering Subdrainage to specify perimeter and underfloor subsurface drainage systems, sometimes referred to as “French drains”.
Filter fabric is required to prevent silt from entering the drain lines which can eventually cause blockages. Pipe with filter fabric wrap is a good idea, but the drainage fill also needs to be surrounded by filter fabric.
Subsurface drains are sometimes installed without slope but at least some slope is required to minimize silt buildup.
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 groundwater pressure.
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