Drainage is an important part of retaining wall installation.

The purpose of drainage is to move water away from the surface of the wall.

This stops the water from building up and exerting force on the wall with the result it may collapse. It also reduces moisture on the wall surface which can cause building materials such as timber and masonry to deteriorate. Our waterproofing section has additional information on protecting retaining walls.

The most basic components of drainage behind a DIY retaining wall are gravel and slotted drainage pipe. The retaining wall is backfilled with gravel to 100mm (or level required) and then the pipe is laid before topping with more gravel.

The gravel acts as a pathway with gravity moving the water downwards. Being a large particle size it also acts as a filter to minimise silt build up in the pipe. The pipe then carries the water away from the wall.

Agricultural or Ag Pipe is a flexible and durable PVC subsurface drainage pipe with slots. It is available either with or without a knitted filtration sock which is used to prevent clogging.

Materials In The Raw stocks both blue metal and recycled aggregate to use as drainage gravel. We also have both unsocked and socked 65mm and 100mm agriculture (slotted) pipe.