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January 21st, 2013 · No Comments


It is a well known scientific fact that water always flows downhill by the easiest possible route!   The basic concept of a French drain is a slightly sloped trench filled with round gravel and perforated pipe to divert underground water away from your house.  This is a common drainage system primarily used to prevent ground water from penetrating or damaging building foundations by providing an easy channel allowing water to flow.

A French drain is in no way connected with anything French!   Henry French, an American Judge and Farmer from Concord, Massachusetts, designed and promoted the French drain in his book in 1859 promoting farm drainage.  French´s drains were made with clay tiles, but modern drains use 4-inch diameter plastic pipes.     The solution to a persistently wet basement or a soggy lawn could be a French drain, particularly if you live on a slope.

Surface and sub-surface water runs through the spaces between the round gravel and perforated pipe at the bottom of the trench, which should be sloped.   Emptying a safe distance from the house, the water has travelled freely through the pipe.

  If you have a driveway that is continually water-logged or a soggy lawn for example creating problems with surface water, then a shallow French drain or curtain drain is useful.   This type of drain need only be sufficiently deep to divert water.

If the shallow drain doesn´t keep water out of your basement, you may need a deep French drain.  This is also called a footing drain and runs round the perimeter of the house at footing level.  This is difficult and expensive should it be necessary to add later but can easily be installed during the house construction.

A French drain is dependent on gravity.  

A sump pump may be required to lift collected water piped to a basement basin and send it to the storm drain system if the property is built on flat ground.

Interception of water into your basement if it continually enters, can be remedied by building a French drain at the point of entry.   Install a perforated pipe all the way round the perimeter of the basement floor after cutting a channel and chipping out the concrete. A collection tank sunk into the floor receives the water via a solid pipe and a pump sends it out to the yard or storm drain.

If you are building a retaining wall on a hillside, incorporate a French drain behind the first course of stones or blocks.   Otherwise the wall could be undermined or even tipped by water moving down the hill or building up behind the wall.  To avoid clogging with silt, drape landscape cloth across the base or footings and up the slope before adding the pipe and adding the pipe and drain gravel.  Nearing the top of the wall, fold the cloth over the top of the gravel and cover with several inches of soil.

French drains in Spain are a common occurrance due to the dry, hard ground and flash flooding makes them a necessity.

One French drain specialist in Spain is M3BT who are an establised construction company working with the major insurance companies throughout Spain.

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