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building a retaining wall

How to Build a Sleeper Retaining Wall with Steel Posts in 8 Steps

Do you have DIY aspirations on building a sleeper retaining wall? Well, the good news is, you probably won’t need council approval or an engineering certificate if your retaining wall is under 1m in height.

A retaining wall can instantly transform your landscape and add a unique aesthetic to your garden. Sleeper retaining walls restrain soil erosion, and provide new functional space for raised flower beds, terraces, fire pits and much more. Simply put, it’s a great asset to your property that can increase its value!

How Much Does A Retainer Wall Cost? Read this to find out!

In this step by step guide, we’ll  show you how to build a sleeper retaining wall with steel posts. If you’re ready to create a gorgeous outdoor space that you can be proud of, then let’s get started.

STEP 1: Check Local Regulations

We briefly mentioned council approval in our intro, but let’s elaborate.

Australia states and territories have varying regulations when it comes to building retaining walls on your property. Depending on your wall’s height, material, location and design, you may need a building permit. As such, you’ll want to contact your local council and double-check the regulations in your area.

As we said, any sleeper retaining wall over 1 metre in height will  likely require a building permit. You’ll also need to hire a structural engineer to approve the wall’s design and its stability.

Lastly, if your retaining wall is being built on a property line, both you and your neighbour will have to share the costs in its construction. Just ensure to inform them as early as possible to sort any disputes.

Step Two   – Inspect Your Area

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Before you commence digging, you’ll need to thoroughly inspect your retaining wall area. Pay special attention to the slope of your garden, and remove any plants or rocks that might interfere with your wall’s construction.

Next, you’ll need to measure your area to ensure your built wall isn’t too big or small. You should know where your wall will start and end.

You should also know the size and length of your steel posts, calculating how deep they need to be installed. Generally speaking, steel post depth should equal the wall’s height plus 100mm for cover on steel. So if your wall is 3.0 metres high, then your steel posts should be 3.1 metres deep. 

Now, you’re ready to start digging!

Step Three – Time to Dig

Post holes will be dug with a 450mm diameter, at a depth equal to your retaining wall’s height. Your holes should be equally spaced, as this will keep your sleeper retaining wall level and structurally sound. If holes are not spaced equally, your wall may have a noticeable tilt.

Always remember that hole diameter and size depends on the size of your steel posts.

Step Four – Cut Your Sleepers

Your sleepers are the building blocks for your retaining wall. To ensure a flush finish, you’ll need to accurately measure and cut your sleepers at the same length and height.

Remember: Measure twice and cut once! You don’t want to have some sleepers longer than others.

Step Five – Place Your Steel Posts and Attach Sleepers

Once your holes are dug, insert your steel posts into the ground, making sure they’re level and straight. Mix your concrete and pour it to the bottom of your hole. You’ll want to take extra care not to overfill your holes, as you’ll be left with a large build up of concrete on the ground.

You should now then have adequate space between posts to set up your sleepers. Not sure if you need an H Beam or an I Beam? Read this!

Step Six – Installing Your Sleepers

concrete retaining walls

After waiting overnight for your posts to set and dry, you’ll be able to place your sleepers between them. Generally speaking, there should be an allowance of 7mm-10mm between the sleeper and post. To find out, place a sleeper between posts, and measure.

Planning on installing a fence on your wall? Here’s How to Weld a Colorbond Fence on Top of a Concrete Sleeper Retaining Wall

Step Seven – Soil Plug

A soil plug is to fill your wall at the top, stopping eroding soil from getting inside. If you have open-ended pipes, you’ll need to install a soil plug and backfill your wall.

Step Eight – Drainage and Backfilling

Many retaining walls don’t just stop lateral soil pressure, but also water pressure. If you have a water source nearby, you may experience hydrostatic pressure that could eventually cause your wall to collapse.

Place a drainage pipe behind your retaining wall with at least 1 in 100 fall away (1 cm drop over 1m length of wall). It should also be on a bed of 10-20mm clean drainage material.

Backfilling your wall should be the last step in building your retaining wall. You’ll need to fill areas where previous materials were removed.

Install a minimum of 12 inches of granular backfill directly behind your retaining wall for proper drainage. The rest of the area can be filled with native soil.

Remember that the primary purpose of a retaining wall is to stop soil pressure. So without backfilling, you may as well install a freestanding wall!

How Many Sleepers Do I Need for My Retaining Wall?

The number of sleepers primarily depends on your wall’s height and length. To quickly find out, multiple the distance between posts by the number of posts. You could then add an extra 10% of sleepers to your calculations just to be safe.

Sleeper length depends on your sleeper retaining wall’s height. If your wall is over a metre long and requires council approval, we recommend corresponding with a qualified, structural engineer before hiring a builder.

High Quality Concrete Sleepers and Steel Posts with RWS

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Now that you have the basics on building your sleeper retaining wall with steel posts, it’s time to get started. If you know how large your wall is, we can provide you with high quality steel posts and sleepers at discounted prices. We provide a range of retaining wall concrete sleepers in Melbourne that are reinforced with steel, perfect for your retaining wall! Our services are also available in BrisbaneGold Coast, and Sunshine Coast.

Browse our site or contact us for more information on our range of sleepers, steel posts and retaining wall services!

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