A French drain or (sub-surface drain, or sub-soil drain) is a trench of varying dimensions (1’ to 3’ wide, and 2’ to 5’ deep) that is filled with clean gravel or rock (usually ¾” class A), and contains a perforated drainage pipe (4’, or 6”, or 8”) that directs groundwater away from a problem area.
For areas of heavy clay concentration, a sump-pump station is often required for removal of water. Additionally, if the drainage area can’t naturally gravity flow the water away, then a sump-pump station will also be required to lift and pump the water away from the saturated puddled area or where the water has pooled. A sump pump is a pump used to remove water that has accumulated in a water collecting sump basin or problem area.
To prevent damage to foundations, the use of a French drain is to prevent ground water or surface water from penetrating or accumulating near the foundation causing damage to foundations. French drains are also built to distribute water behind a retaining wall that needs relief of hydrostatic water pressure. Ditches are dug by hand or sometimes a trencher is used to assist on the larger and deeper trenches when a bigger French Drain is necessary and more water needs to be re directed.
In most cases when a home is built, an external French drain is installed around the foundation walls before the foundation soil is filled back in after trenching. A pipe is placed on the bottom of the trenched area, and a layer of rock is laid on top of the pipe. Next a thick filter fabric is laid on top of the rock to keep fine sediments and particles from clogging the pipe. Once the drainage system is installed, the area is backfilled, gutter downspouts are hooked up, and the pipe(s) are routed to the sump-pump station, if one was required for installation.
The installation of a French Drain even though this may seem like a big ordeal it is nothing compared to the problems that can result from a damaged foundation where water has saturated the ground and found its way beneath the foundation of the house resulting in most cases major water damage.
Some companies might give you a list of reasons explaining why their pressure relief system is better than installing a French drain. In all actuality these two types of drainage are almost identical and serve the same purpose.
A French Drain is just another term for pressure relief. However you choose to describe it. It's job or purpose is to relieve water that has caused a soggy or saturated area on the ground or even worse has begun to collect and puddle or pool in a low lying area. Sometimes even close to the foundation of the home. This is ultimately where if not addressed proactively the damages extend and increase to significantly more than just the immediate issue at hand.
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