Tuesday, 1 January 2008


I have a problem with water building up behind a new retaining wall in the garden. How can I drain it without disturbing the foundations? Thanks T.W. By e-mail

You could put in a French Drain. A French drain is a drain with no pipe. The water collects in a gravel or stone filled channel that starts from the surface of just below it. The advantage of a French drain is that is easy to construct and with the use of modern ground fabrics very efficient.

Stage One
First you need to dig a trench behind the wall, away from the foundations, about 15cm wide and as deep as required with a fall off 1 in 100 so that the water flows. Next the trench should be lined with ground sheeting which is available at most builders’ merchants. This sheeting allows water to pass through, but not the soil particles such as silt and clay that often block drains after a number of years.

Stage Two

Fill the trench inside the sheeting with a clean stone, 20mm is ideal or clean broken bricks. The trench can be filled to the surface or filled to about 10cm below the surface and the sheeting wrapped around it. Then backfilled with topsoil over the top.

Stage Three
The drain will need to end in a soak away. This is a large cube shaped hole lined with porous ground sheeting and filled with clean gravel or clean rubble. The idea is that when the drain is working the water runs into the soakaway and over a few hours soaks (away) into the surrounding ground soil. For this reason it is best to pick an area of land that drains freely!


Steve A said...
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Steve A said...

check out this informative blog at www.frenchdrain.blogspot.com

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