How to Build a Durable Retaining Wall Step-by-Step

Have you ever looked at a sloping garden and wondered if there was a way to both make it more functional and attractive? Are you dreaming of a practical DIY project that can give you level areas for entertaining, planting, or simply relaxing? Building a durable garden retaining wall might be the perfect solution. In the following guide, we’ll break down everything you need to know, from planning to finishing touches, so you can create a retaining wall that stands the test of time.

Building a retaining wall is easier than you might expect, but it does require careful preparation. You’ll need to explore which materials suit your environment, check local council guidelines in Australia, and gather the right tools. Plus, we’ll explain each step in a straightforward, friendly way, so you can take on this project with confidence.

Planning and Preparation

Whether you’re brand-new to DIY or already have some building experience, planning and preparation will be key to a successful retaining project. Retaining walls often support heavy loads, so ensuring everything is calculated correctly prevents future collapse or unnecessary costs. Below, we’ll examine what to consider before you pick up any tools.

Understanding Local Council Requirements in Australia 

In Australia, most councils have regulations that specify where you can build, how tall your wall can be, and what building permits are required. It might seem like a chore at first, but following these rules keeps everyone safe and avoids issues down the track. Some councils allow walls up to a certain height without approval, while others have strict guidelines regarding drainage and structural engineering. If you’re unsure, make sure that you reach out to your council or consult a licensed professional.

Choosing the Right Type

Once you have an idea of what’s allowed, it’s time to pick a material that fits your style, budget, and environment. A sleeper retaining wall (commonly built with treated pine or hardwood sleepers) is often affordable and offers a rustic look. A block retaining wall, on the other hand, uses concrete masonry units that are resilient, easy to stack, and come in many designs. And if you want a classic, timeless feel, a retaining wall with bricks or a sandstone block retaining wall might be the perfect choice. By comparison, bricks can blend nicely with existing structures, whereas sandstone blocks bring natural beauty to any outdoor space.

Sourcing Materials

When sourcing materials, you’ll want to consider both cost and availability. Retaining wall sleepers from Bunnings are a popular option, especially if you’re looking for a convenient, local supplier of timber. Likewise, many landscaping supply yards across Australia stock a range of masonry blocks and sandstone blocks. Some suppliers even custom-cut sandstone blocks to precise dimensions, so you can save time on site. Comparing costs, delivery options, and quality ensures you make the most of your budget before the first shovel hits the dirt.

Site Assessment and Soil Considerations 

Not all soil is created equal. Clay-based soil holds moisture and expands, while sandy soil drains quickly. Understanding how your chosen site behaves when wet or dry helps you plan for suffcient drainage. It’s also wise to check for any underground utilities such as water pipes, gas lines, or electrical cables.

Calculating Height, Load, and Drainage Needs 

Next comes the vital part: dimensions. How high do you want your retaining wall to be? The height influences both material size and how you construct the footings. You’ll also need to anticipate the load behind the wall. If you’re holding back a steep slope, you might need deeper footings or reinforced sections. Drainage is equally important. Water buildup behind a wall is a leading cause of failure, so planning for weep holes, gravel backfill, and drainage pipes is absolutely key.

Step-by-Step: How to Build a Retaining Wall

Now, we get to the heart of it: constructing your retaining wall. This section will walk you through each phase of the build, so you can tackle the project one clear step at a time. Whether you’re building a sandstone block retaining wall, a block retaining wall, or a sleeper retaining wall, the basic principles remain consistent.

Marking Out the Wall Location 

This step prevents confusion when you start excavation. Aim for a neat, straight line if you want a more formal look, or use a gentle curve to blend the wall naturally into the landscape.

Excavating the Footings and Levelling the Base 

Once marked, it’s time to dig. Footings must be wide and deep enough to bear the weight of the wall without shifting. For a standard garden retaining walls of moderate height (say up to a metre), a trench about 600mm wide might be sufficient, but always consider local guidelines and engineering advice. Compact it thoroughly using a plate compactor or tamper. Proper compaction now prevents settling later. If your design calls for a concrete footing, pour it and allow it to set as per the manufacturer’s instructions.

Installing Drainage and Moisture Barriers 

To combat this, install a strip of agricultural (ag) pipe at the base of your excavation, ensuring it has somewhere to drain to—preferably an existing stormwater system or a lower section of your garden. Cover the pipe with coarse gravel. If you’re using timber sleepers, consider adding a moisture barrier behind the sleepers to protect them from prolonged dampness. For a block retaining wall or brick setup, damp-proof membranes can also prolong the structure’s life.

Positioning the First Course

Your first row, also known as the first course, sets the tone for the entire wall. Place your sleepers, blocks, or bricks on the prepared footing, using a spirit level to make sure each piece is plumb and lined up accurately. If you’re using bricks or blocks that require mortar, mix the mortar to the recommended consistency and lay them evenly, leaving appropriate gaps or mortar joints. For timber sleepers, secure them with galvanised posts or brackets, checking alignment as you go.

Building Subsequent Layers and Ensuring Structural Stability 

Continue stacking each layer. For blocks or bricks, stagger the joints so they don’t line up vertically—this adds strength. Timber sleepers often require galvanised steel posts to hold them upright, especially if the wall is more than one sleeper high. Keep verifying each level with your spirit level. When it comes to higher walls, you might need to add lateral supports or geogrid reinforcements to handle extra soil load. Because every property is different, follow engineering or council guidelines for walls above certain heights.

Backfilling and Compacting

After placing each course or a set of courses, backfill the space between the wall and the soil with free-draining material such as gravel or crushed stone. This step helps water move freely to your drainage pipe. Avoid simply dumping soil in one go. Instead, fill in layers, compacting each layer to minimise air pockets. By layering and compacting gradually, you decrease the chance of your new retaining wall shifting over time.

Final Checks and Finishing Touches 

When you’re satisfied that everything is straight, secure, and well-drained, give your retaining wall a final inspection. Look for any gaps in mortar joints, loose gravel along the backfill, or areas where water might pool. Make minor adjustments as needed, because it’s easier to address small issues now rather than face major repairs later. If desired, add decorative caps to block or brick walls, or treat timber walls with a protective stain for extra durability. Stand back, admire your work, and get ready to enjoy a more functional and stylish outdoor space.

Conclusion

By taking the time to select the right materials, follow local council guidelines, and meticulously install drainage, you can create a garden retaining wall that looks fantastic and serves you for many years. Whether you went for a traditional sleeper retaining wall, a diesel-tough block retaining wall, a timeless sandstone block retaining wall, or a classic retaining wall with bricks, the method is basically the same: solid foundations, proper water control, and consistent upkeep.

Ultimately, how to build a retaining wall is all about understanding the site’s needs and following each step with care. If you take on this project with patience, you’ll discover just how rewarding it can be. Seeing your once-sloped patch of land become a functional, levelled space is worth every bit of planning and effort.