What to know before you start
Check with your local council to see they if they have any restrictions on retaining walls. Generally if they are over 900mm high or close to a building, they will need to be designed or certified by an engineer. You may also have to go through the building approvals process as well.
Using timber sleepers is the cheapest and most DIY friendly material to work with. You can leave them to weather naturally, paint them or use a stain to add colour without hiding the timber grain. The simplest way to use sleepers is to lay them flat on the ground and then stack them up to achieve your desired height. Make sure the first sleeper goes down level and that you stagger the joins to the row below.
Thinner retaining walls can be built by placing the sleepers on their edge, using posts to support the load. Place the posts to suit the length of your sleepers plus one in the middle of each. Use thicker sleepers for your posts and aim for a post-hole depth about 1.5 times the height of the wall. Concrete your end posts in first, then stretch a stringline between them to line up the other posts. Push the sleepers against the posts and use heavy-duty batten screws to join them together. For something a little different, you could even place the timber sleepers vertically (see image above).
DIY masonry blocks
For a solid look of a low masonry wall without the tradie price tag, check out the range of interlocking block retaining wall products. They’re specifically designed for the DIYer so you don’t need to construct complicated footings or mix up mortar to build your wall. Start with a level, compacted bed of road base and lay your first row on it. The next row just sits on top, interlocking with the one below. Continue up to your wall height. To finish it off, capping pieces are glued to your top row.
There’s a wide range of colours, surface textures and styles to suit all types of designs and you can coordinate the colour of your wall with other elements of the garden such as the pavers for a unified look.
Bricks or concrete blocks
If you’re after a rendered or bagged finish on your retaining wall, use bricks or concrete blocks. They’ll need a solid footing to sit on and you’ll need to mix up mortar to join the blocks together. Concrete blocks in structural applications will need to be filled with concrete to create a solid wall.
Don't forget drainage
Drainage is an important part of retaining wall construction. Install an agricultural drain (often referred to as an ag drain) at the bottom of the wall and backfill behind it with a free draining material such as blue metal.
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