How to Build a Retaining Wall

Are you sitting at home, gazing out your window at that unruly slope in your backyard, wondering how you can transform your outdoor space?

The answer could be a retaining wall, and in this article, we’ll look at all the ins and outs of how to build one. Whether you decide to take the DIY route or opt for the help of a professional landscaper, creating one of these backyard favourites could be the perfect way to revolutionise your outdoor space.

But only if you approach it the right way.

Retaining Wall Regulations in Australia: What You Need to Know

In NSW, the construction of retaining walls is governed by strict regulations to ensure they’re safe, durable, and visually pleasing. Any retaining wall climbing over one metre (100cm) needs a building permit, and a qualified structural engineer must be present to draw the structural designs.

These rules are enforced to guarantee that the retaining wall can withstand the earth load and hydrostatic pressure it is likely to encounter. 

It’s also important to communicate with your local council about the specific rules and regulations in your area, as one suburb can differ from another.

Likewise, retaining walls exceeding 4 feet (approximately 1.22 metres) in height should be designed and supervised by a professional landscaper in Sydney, not just for legal reasons but also to affirm their sturdiness and longevity. Bear in mind that the higher the retaining wall, the more crucial the structural considerations become.

This is where hiring an engineer comes into play; they will ensure that your retaining wall is fit-for-purpose, not only functionally but also aesthetically. 

At Trinity Landscape & Sports, we’ll make sure all of these intricate rules and details are taken care of from the beginning, so you don’t have to worry about whether you’re approaching your project the right way.

Choosing the Right Materials for Your Retaining Wall in Australia

Successfully building a retaining wall is largely dependent on what kind of materials you use. Thankfully, there are quite a few options available in Australia, each with varying degrees of aesthetics, durability, and budget considerations.

The most commonly used materials include:

• timber
• blocks or crushed stone (or crushed rock)
• brick
• concrete,
• and even recycled materials.

If you’re tossing up on which to choose, timber is a popular choice, especially for a raised garden bed or walls less than one metre in height. Although it offers a natural aesthetic appeal, timber lacks the durability of sturdier materials. It’s best to use pressure-treated timber or wood specifically designed for ground contact to enhance longevity. 

Meanwhile, stone and brick walls are highly coveted for their visual appeal and durability. They offer a wide range of design and colour options; however, they require professional expertise, especially for walls over three feet. 

Concrete walls, while less visually appealing than stone or brick, are also popular for their strength and versatile applications. They also offer a more affordable alternative that’s just as simple to install, especially with modular concrete blocks. 

For those looking to build a sustainable retaining wall, recycled materials can also be used, especially because they have the added bonus of looking just as good as they are for the environment.

Things to Consider When Building a Retaining Wall

There’s a lot to think about when you’re considering how to build a retaining wall. These factors include:

• Aesthetics
• Practicality
• Structural aspects
• Long-term stability
• Durability
• Financial constraints.

So, how do you get started when there’s so much to look into? Here are our top first steps to take before really diving into your retaining wall project:

1. Identify the type of ground your retaining wall will be built on. This will significantly influence your choice of materials and installation method, especially when preparing the foundation. You need to assess whether the soil is sandy, clay-rich, loamy, or consists of other types. Each type responds differently to pressure and moisture and requires suitable preparation and handling techniques.
   
2. Engage a professional engineer or landscaper in the design process when the wall is taller than 4 feet. Their expertise will ensure a reliable, safe, and visually appealing retaining wall structure that is capable of dealing with substantial loads and withstanding all the pressure.
   
3. Consider the intended height of your wall. Retaining walls typically fall into three categories: small retainer walls, walls up to three feet high, and walls taller than three feet. Depending on the height, different types of retaining wall blocks might be required. For instance, walls taller than three feet typically require an engineered wall block.
   

Tools and Equipment Needed for DIY Retaining Walls

While you’ll need to think carefully about the materials you use, gathering the right tools and equipment for the job is equally important.

Here are the must-have tools you’ll need to build a retaining wall:

• Shovel: Essential for digging the trench that forms the foundation of the retaining wall. A sturdy, competent shovel is crucial for breaking into tough ground, removing rocks or concrete chunks, and efficiently excavating earth.
• String line and Pegs: These are used to mark the area where the wall will be erected and ensure that it is straight.
• Level and Tape Measure: These precision tools are necessary to ensure the wall’s horizontal and vertical accuracy. They will ensure that your wall is level and maintains the correct dimensions, even if you’re doing tiered walls.
• Wheelbarrow: Helpful for transport of materials, particularly heavy items like stones or gravel.
• Compactor: A plate compactor can compress the soil and base material for block placement, preventing settling and movement over time.
• Trowel: A hand tool that spreads or shapes items like cement and mortar for perfect block alignment.
• Masonry Saw or Brick Chisel: This is particularly useful when working with interlocking landscaping blocks. A masonry saw can make a clean, precise cut, while a chisel and a hammer can also be used for less precise cuts.

How to Build a Retaining Wall: Step-by Step

It all starts with building the first layer. This step may seem straightforward enough, but the trick is in the small details that can dictate just how long your wall lasts and what you can do with it.

Here’s a step-by-step guide to follow when you’re embarking on the first phase of your DIY retaining wall:

• Step 1: Start by digging a trench. This trench will form the base of your wall. The dimensions of the trench will depend on the size of your wall and the type of soil in your area. Remember that the trench width should be slightly wider than the retaining wall blocks.
• Step 2: Once the trench is ready, create a base using gravel. Add the gravel base in two layers, making sure to pack down thoroughly after each layer. This creates a steady base for the first row of blocks.
• Step 3: Now, start installing the first row of blocks. Using a torpedo level, ensure that they are level side to side and front to back. This will ensure that the blocks sit correctly and provide a solid foundation for the proposed wall.
• Step 4: It’s now time to add a layer of rough gravel behind the first row of blocks. This gravel layer, usually about 3–4 inches, helps facilitate effective drainage, which is crucial for the wall’s stability and durability.
• Step 5: Add more layers by adding one block at a time, ensuring the seams are staggered. This creates a robust and aesthetically pleasing structure. Make sure each layer is level as you go.
• Step 6: Apply construction adhesive to firmly secure the top row of blocks. This creates a professional finish and strengthens the overall structure, making it durable and ready to withstand both time and harsh weather elements.
• Step 7: Use a level to help you along the way, and ensure you check vertically and horizontally for any unevenness. 
• Step 8: Add a layer of gravel behind the retaining wall blocks. This layer of gravel should ideally be around 15 cm deep. This gravel acts as a barrier between the soil and the retainer wall, allowing water to drain away. In addition, it provides support and weight to hold the blocks securely.
• Step 9: Place the drainpipe. This pipe should be positioned at the lowest point of the straight wall, laid so that the water drains away from it to avoid damaging it.
• Step 10: Use landscape fabric to line the gravel and soil. This lining prevents the soil from clogging up the gravel and drainpipe, ensuring your drainage system will continue working efficiently in the long run.

Finishing Your Retaining Wall: Sealing and Backfilling

The final step is to seal your retaining wall off and ensure it’s adequately backfilled where needed.

‘Sealing’ refers to protecting the exterior surface of the retaining wall. It is especially crucial for retaining walls constructed with concrete, which are susceptible to water damage. By applying a suitable sealant, you provide an extra layer of defence against the elements, think wind, rain, and erosion, ultimately prolonging the life of your wall. 

Once you’ve applied the sealant and thoroughly dried, it’s time to move on to ‘backfilling’. Backfilling means filling in the empty space behind your newly constructed wall. You can use materials like soil or sand to act as the backfill. This not only strengthens the wall but also allows for further landscaping design in the future, such as popping in plants. 

Start by introducing soil or sand in thin layers behind the wall, and then compact it, either manually with a hand tamper or, for larger retaining walls, using a mechanical compactor. Repeat this process until you’ve filled the entire space behind the wall. Ensure the final layer of backfill leaves enough room for a layer of topsoil if you plan to landscape the area with grass or plants. 

Not Sure How to Build a Retaining Wall Yourself? 

If you’re looking to build a retaining wall, consider the services of Trinity Landscape & Sports instead. Our team of professionals has extensive knowledge and expertise in building retaining walls from start to finish, offering an end-to-end solution that’s cost-effective, sustainable, and designed to last.

Contact us now for a quote or for reliable guidance you can trust.

Key Takeaways

• Building a retaining wall on your property means you have to consider legislative regulations in Australia.
• You need to select the right materials from the beginning.
• The design of a retaining wall includes considering location, soil type, and landscape needs.
• Appropriate tools and equipment are essential for a successful construction process.
• The foundation’s correct placement and construction determine the overall strength and structural integrity of the wall.
• Building the first layer requires careful attention, as it is the foundation for subsequent layers.
• Constructing layers relies on knowledge of certain construction techniques for the best results.
• Checking and ensuring that the wall is level throughout the construction process is a pivotal responsibility.
• Installing drainage is a critical factor in Australia, particularly given the local weather conditions.
• Sealing and backfilling the wall correctly means you can enhance its durability and appearance.