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Interlink unlocks exquisite retaining

Bring out the best in your client’s property by building a beautiful retaining wall using reclaimed railway sleepers

Building a timber retaining wall can be an excellent way to enhance both the functionality and aesthetics of an outdoor space. Whether it’s to create level areas on a sloping section or to provide an attractive cover for an earth bank, a well-constructed retaining wall can serve multiple purposes. In this guide, Interlink walks through the process of building a simple post and rail wall using railway sleepers that are suitable for most environments.


It’s important to note that even low retaining walls must adhere to certain engineering standards to ensure stability, regardless of whether they require a building consent or not. Currently in New Zealand, a retaining wall less than 1.5m and non-load bearing does not require building consent. However, all building work must comply with the Building Code, even if no building consent is needed; meaning, for example, drainage is required, as indicated in Step 10 below.

The 12-step process

  1. Plan and measure the length and height of the wall, ensuring compliance with the building code.

  2. When using railway sleepers, ensure they are thick and solid sleepers. Use either treated railway sleepers (using the appropriate PPE gear), or a hardwood sleepers with ‘mulseal’ or similar protective coating (a tar-like water proofing substance) applied over the embedded sections of the posts and the side of the rails going into the bank. 

  3. Level the ground behind the wall to facilitate proper drainage.

  4. Dig 500mm diameter holes, ensuring a depth equivalent to 70% of the wall’s height.

  5. Set the end sleeper posts in concrete first, starting with 100mm of concrete in the holes and placing the posts on top.

  6. Lean the posts slightly back into the hill for stability. Applying timber bracing to pegs on the ground and up to the posts top will assist to keep the posts in position while the concrete sets.

  7. Install string lines at the top and bottom between the two end posts, then install intermediate posts using the string line to line them up. Tip: place a 20mm spacer at each end post under the string line to allow the line to be 20mm offset along the wall; to avoid inadvertently moving the string line. Concrete all your intermediate posts in place as per step 5.

  8. Allow the concrete to set properly, typically over a couple of days.

  9. Fasten horizontal rails to the back of the posts, starting from the bottom and working upward.

  10. Install a drainage system for the wall, including clean drainage metal and drain coil covered with a filter sock or geotextile fabric to reduce silting.

  11. Continue filling with drainage metal, ensuring a minimum of 300mm against the bottom of the wall. Keeping backfill and drainage metal separate with a sheet of geotextile fabric.

  12. Top up with topsoil to assist plant growth, if desired.


Building a timber retaining wall requires careful planning and execution to ensure stability and longevity. By following these 12 steps, you can create a functional and visually appealing structure that enhances your client’s outdoor space. Remember to adhere to local building codes and regulations, as outlined elsewhere in this publication, and consult with professionals if your wall exceeds certain height or load-bearing thresholds.  


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