How to make a French drain

A French drain is typically 40cm wide and 50cm deep. Slope the channel sufficiently (minimum gradient of 1 in 40) to direct the water in a straight line or gentle curve to where you want it.

When the soil has been removed, lay strong plastic sheeting at least 1,5m wide in the drain. Then fill it to a depth of 30cm with non-compacting rubble, stones or broken bricks to provide a soak-away for the excess water. Fold the excess plastic over the top in such a way that soil will not enter the drain. Alternatively, buried piping connected to the downpipe can be used.

A French drain could also be used without the plastic liner to allow water to percolate into the soil along its entire length. Once filled, cover the surface of the drain with a grid. The grid could be concealed with containers, pebbles or even lawn. If the French drain is to be placed under lawn, make sure you choose a fine grid that will allow water to pass through but not soil. Place the grid 20cm below the ground surface and place lawn over the top. Alternatively use a pipe with holes along its base (for example, Kaytech Geopipe).