Perforated pipes and french drains are both used for drainage. French drains combine several elements to compose a drainage system; perforated pipes are manufactured plastic devices. French drains are typically used as part of a storm-water infiltration strategy with perforated pipes frequently included as a component of the french drain. French drain systems are only used for exterior surface and subsurface drainage. Perforated pipes are often associated with structures such as foundations.
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French Drain System
French drains are installed as a storm-water management technique for slowing and reducing runoff from a site. They're also used in agricultural installations for field drainage. Though french drains don't necessarily include perforated pipes the addition of pipes has become a common feature of french drains. The pipes can be connected to an above ground discharge pipe or collect groundwater moisture through the perforations. The components of the french drain, fabric and gravel, work together to keep debris from entering the pipe.
Perforated pipe is a plastic pipe pierced with small, multiple openings evenly distributed. The pipe can be smooth or corrugated. It's used widely for drainage in foundations, retaining walls, road bases and septic systems. When buried underground, the perforations can get clogged with sediment, reducing its efficiency and eventually making it ineffective. The pipes shouldn't be installed where heavy loads, such as traffic, will be traveling over it. They can become crushed by compacted ground.
French drains are shallow trenches lined with landscape fabric or geotextile cloth to filter sediment, then filled with gravel. Perforated pipe is buried in the gravel. The trench is placed to capture runoff and allow it to infiltrate the ground, thus reducing the amount of storm-water that leaves the property. French drains should be installed professionally; excavation has a significant impact on foundations and drainage. The location of pipes and the discharge point are also serious considerations.
French Drains and Perforated Pipe
The gravel for the trench should be screened -- uniform 3/4- to 1 1/2-inch with no silts or fines -- and the pipe should rest on an inch or so of the gravel. Cleanouts can be installed to access the pipe with a snake or water jet to clear it of debris or sediment. Turf can be planted on top of the trench with the addition of about 4 inches of coarse sand for the base.