Top Tips And Choices For Low Retaining Walls by Nicki Jackson

A sloping site tends to be the main reason we encounter for requiring retaining walls, but the need for them does crop up quite often so we thought it might be worth looking at them briefly just in case you’re thinking of having one built!

In a nutshell a retaining wall is a vertical structure that holds or retains the soil behind it so it doesn’t erode or slide away.

Some things to know before you start:

  • If a retaining wall is to be built along a boundary, ownership of the boundary needs to be clarified before any work commences – you must have the right to build a wall; in some cases, be aware that party wall agreements may be required.
  • For any retaining walls 1m or higher a structural engineer should sign off/develop plans with you/your designer.
  • Planning will be required for a retaining wall if it is to be built alongside a public highway, footpath or pavement and it is 1m high or more; or is on or adjoins a listed property; or is 2m high or more.

A retaining wall:

  • Should never be built on topsoil; regardless of the materials it is made of it will always require footings which will be at subsoil level, but the width, type, length and depth of those footings will vary with the materials and height of the structure being built.
  • Will often require a lot of earth being moved and having to be dealt with, which is where much of the cost is incurred in installing them.
  • Needs to be constructed of material that will endure the force of the load it is retaining.
  • Requires a damp proof membrane and drainage solutions (land drains) to be installed behind it – appropriate to the materials – since the outside will be mainly dry and the inside mainly wet because of the material it is retaining.
  • May look different over time as water and wind may affect its’ facing material.

Some top material choices for garden retaining walls include:

Brick – aesthetically uniform and tidy, different bricks will be used for the main body of the wall and those for the foundation. There are various bonds (laying patterns) available to choose from, the most common and familiar being stretcher bond with ‘bucket handle’ (i.e. concave) pointing. Interestingly regions often have specific bonds and pointing methods synonymous to the area, but if you want something different from the norm be sure to specify your chosen building method. Whilst stretcher bond may be an efficient use of bricks it may not be aesthetically what you were hoping for. Bricks aren’t very expensive but the skill to design and build with them will be costly.

Sleepers – often imbuing a garden design with a contemporary feel, sleepers are fairly inexpensive and are easily available. Softwood is usually cheaper than hardwood and whilst hardwoods are stronger, more expensive and will last a long time, softwood sleepers should last a good 10 years if sourced and used correctly. Sleepers can be laid in a number of ways – horizontal, vertical, flat, on the side – offering a variety of aesthetics but for a more industrial look sleepers can also be used with a steel support system such as an I beam with the sleepers slotted in.

Gabions – incredibly versatile and aesthetically flexible these are essentially a wire basket or cage (different wire patterns available) filled with an aggregate of choice, the fill should obviously be larger than the mesh aperture. They come in various sizes – usually in 500mm increments – and thicknesses of wire and if it is galvanized the basket should last a good 50 years or so. A geotextile will be needed behind the wall and over the footings to stop any soil/fines making its way into and through the other side of the gabion itself.

Finishes:

Render – the stalwart of contemporary garden design, this is a method of covering a wall constructed with concrete blocks (or an old wall you want to improve). The render isn’t hugely expensive but the skill to apply and obtain a good finish is. The top and corners of rendered walls are vulnerable. Coping stones on top of the wall will protect the top as well as help avoid discoloration of the render if they have drip grooves cut into the underside of them. This reduces rain running down the face, which in turn reduces algae buildup.

Bonding – this is a process where a thin tile is bonded to a wall. It is often a cost-effective solution, it does require skill to get the aesthetic right, but when done well can be a fantastic feature in any garden.

© Nicki Jackson, Blue Daisy Gardens 2021