How to Build a Small Retaining Wall

Introducing a small retaining wall into your property is something every homeowner can achieve, not just those seasoned DIY enthusiasts or professional landscapers.

In this guide, our experts at Trinity Landscape & Sports have provided detailed steps on building a small retaining wall, addressing challenges such as soil erosion, creating tiered levels on a slope with a retaining wall step, or boosting your property’s visual appeal with a brick wall that offers both aesthetic appeal and structural integrity.

Designing Small Retaining Walls

Installing a retaining wall takes time, financial investment, and effort, so to save on hassle, you must prioritise strategic design when planning your next project.

Start by identifying specific requirements on your property that you will need to tailor the retaining wall design to meet, such as controlling soil erosion or building raised garden beds. Common considerations revolve around the topography of your property.

For example, walls on steep inclines are more crucial than flat surfaces.

Selecting the Location 

Establish the exact position of your retaining wall before making any material purchases to determine the necessary height of your wall. Surveying and marking where you plan to build can help you understand the most effective retaining wall type for your specific site conditions.

Strategic Placement for Garden Beds

For walls designed to support raised garden beds, placing the structure at the top of a slope can help control erosion and reduce the need for extensive excavation. Strategic positioning optimises the area for gardening activities.

Determining Block Retaining Wall Height for Stability

The required height of your retaining wall block after block will vary based on your specific goals. For instance, a two-foot wall may be sufficient for a small terrace, while more significant slopes or deeper digs may demand taller constructions. You may need to consult a specialist landscaper or engineer to ensure the wall’s height is adequate for stability and safety.

Assessing Soil Volume and Material Needs

A frequent mistake in DIY retaining walls is underestimating the soil volume the block wall needs to retain. A simple miscalculation can impact the structure’s durability due to intense soil pressure. Early evaluation of the site and the necessary materials can facilitate better decision-making as the project progresses.

Securing Necessary Permits

It’s also essential to secure the appropriate permits from local authorities before you begin construction to ensure compliance with local building codes. If you fail to do this, you could face penalties and see your hard work undone.

Sourcing Suitable Materials

Your choice of materials is pivotal in constructing a resilient and aesthetically pleasing retaining wall.

Concrete blocks are a cost-effective and straightforward option for constructing DIY retaining walls. They can be easily stacked to create a secure structure and are more affordable compared to other materials like poured concrete or stone.

Poured concrete is also highlighted as the most economical material option compared to alternatives like pressure-treated pine and stone.

Concrete Sleepers

Concrete sleepers are widely preferred for their strength, minimal maintenance, and variety in size, colour, and texture. Their interlocking features ease installation and contribute to the wall’s structural stability. Choosing those with a textured finish is advisable to enhance the grip and safety of a straight wall in wet conditions, thereby improving your retaining wall’s overall stability and longevity.

Natural Stone

Natural stone is cherished for its traditional appearance and ability to integrate naturally into garden landscapes, providing a sturdy and appealing look. However, the non-uniform sizes of these stones require careful handling and placement, potentially prolonging the construction period.

Wood or Timber

Wood or timber provides a classic, welcoming aesthetic ideal for garden environments but demands regular maintenance to avoid degradation from moisture, such as warping or rotting.

Steel Posts

Selecting the correct type of steel posts—standard 100PFC or more robust options like the 150 PFC, 150UC37, or 200UC46—is essential for the wall’s foundational support.

Steps to Build a Small Retaining Wall

Excavating and Preparing the Gravel Base

The foundation is the backbone of your retaining wall, ensuring stability and preventing soil erosion. A solid foundation consists of a compact gravel base or even a concrete base (depending on the circumstances) and reliable backfill to avert any shifting or tilting of the structure.

Begin the construction by excavating a trench to lay a deep, stable gravel base:

• Call 1100 Before Digging: Always call Before You Dig Australia on 1100  to identify and avoid underground utility lines, preventing dangerous situations like explosions or electrocution.
• Mark and Excavate Trench: After marking out your trench, excavate to the required depth, ensuring the trench is twice as wide as the sleepers you plan to use.
• Lay the Gravel Base: Lay a gravel base to evenly distribute the weight of the wall and enhance erosion control. Fill the trench with a 15cm layer of 2cm road gravel for the base, compacting it vigorously with a heavy-duty compactor at 5cm intervals. This method ensures a level and firm foundation for placing the sleepers.

Think of this as constructing a layered cake—each layer must be firm and level before adding the next, as uneven layers could destabilise the wall, jeopardising its structural integrity.

While incorporating geotextile fabric above the gravel may prevent soil from blending into the base, it’s only required if the existing soil has organic matter that could impede drainage. Before adding this layer, assess the local environmental conditions and the likelihood of debris build-up, which could block the drainage system.

As the foundation of a building is to its overall stability, so is the base of a retaining wall to its longevity and effectiveness.

Now, you’re ready to start building the retaining wall.

Building the Small Retaining Wall

Once you’ve established a firm gravel base, it’s time to begin constructing the retaining wall.

Step 1: Prepare the Base

Start by laying a gravel or concrete base where your concrete retaining wall will be built. The base should be stable and level, as it will support all subsequent layers of sleepers. Landscapers (like us) will prioritise stabilising the initial layer before moving onto others.

Step 2: Place the First Layer of Sleepers

Position the first layer of sleepers directly on the gravel base. Use a level to ensure each sleeper is perfectly horizontal for the wall’s overall stability and aesthetic, especially in designs with curved corners or on sloped terrain.

Step 3: Check and Add Subsequent Layers

Continue adding layers of sleepers on top of the first. Before placing each new layer, use a level to check the alignment of the sleepers. For added stability and aesthetics, consider using two courses of concrete retaining wall blocks. This ensures that the wall remains even and structurally sound as it builds upward.

Step 4: Choose the Type of Sleeper

Decide between interlocking and standard sleepers for your diy retaining wall.

• Interlocking sleepers provide extra stability but may limit adjustment possibilities after placement.
• Standard sleepers offer more flexibility for adjustments but might need to be more stable.

Consider the demands of your specific project when making this choice.

For accurate placement, consider using a straight edge like a long wooden or metal bar to guide the placement of sleepers. This tool helps keep alignment consistent from one sleeper to the next, ensuring a straight and visually appealing wall.

It’s essential to frequently check the alignment of the wall with a level as you add layers. Any deviation from a true horizontal could lead to structural issues in the future.

While some builders prefer to use mortar to enhance the bond between sleepers, remember this can increase the project’s complexity and alter the wall’s natural appearance. The choice to use mortar should be based on your design preferences and environmental considerations.

Step 5: Purchase Sufficient Materials

Ensure you have enough sleepers for your wall. We recommend buying an extra 10% more than your initial calculation to accommodate any potential mistakes or adjustments needed during the building process.

Step 6: Backfill the Wall

After the sleepers are securely in place, backfilling should commence. For those looking to build the cheapest retaining wall, using cost-effective materials and methods such as poured concrete or salvaged materials can significantly reduce costs. This involves methodically placing and compacting soil behind the wall to reinforce it against the pressures of gravity and moisture, ensuring the wall’s long-term stability and effectiveness.

Backfilling is crucial for the wall’s stability and drainage. Begin backfilling immediately behind the sleepers, compacting each layer as you go to ensure even distribution and adequate compaction. Each layer should be tightly packed to support the layers above it.

Step 7: Final Checks and Adjustments

After the wall is constructed and backfilled, do a final check for any misalignments or instability issues. Make adjustments as necessary to ensure the wall is stable and meets your aesthetic and functional standards.

Securing Effective Drainage for Your Retaining Wall

Effective drainage is crucial to constructing a retaining wall, as it ensures its stability and durability. Inadequate drainage can lead to water accumulation behind the wall, which increases soil pressure and risks structural failure.

Here’s how to set up an effective drainage system:

Step 1. Install a Perforated Drainage Pipe

Place a perforated drainage pipe at the base level behind the retaining wall. These pipes, often made from flexible plastic, feature small holes that collect and divert water away from the wall.

Ensure the holes face downward to maximise water intake.

Step 2. Use Filter Fabric

Line the trench for the drainage pipe with filter landscape fabric to prevent soil particles from clogging the pipe. Overlap seams by at least 2.5cm and secure the fabric with landscape staples.

Wrap the fabric around the pipe and secure it carefully so you don’t damage the pipe. This will maintain a clear water passage.

Step 3. Choose the Right Backfill

Avoid using whatever soil is at hand. Opt for high-quality, well-draining materials to backfill behind the retaining wall. This prevents water from being retained in the soil, reducing pressure on the wall.

Step 4. Prepare the Soil and Base

The type of soil beneath and behind the wall impacts its stability. To provide a strong foundation, build the wall on well-drained soil.

Place a layer of gravel under and around the drainage pipe to facilitate water flow and support the pipe system.

Step 5. Backfill Correctly

After installing the drainage pipe and securing it with filter fabric, backfill the area with 2cm minus road gravel, compacting it every two inches to create a solid yet permeable layer. This step is essential to ensure the drainage system functions properly and supports the stability of the low retaining wall.

Step 6. Maintain the Drainage System

Check and maintain the drainage system regularly to ensure it remains unblocked and functional. This proactive approach helps extend the life of your retaining wall and prevent future complications.

As you continue your project, these tips for ensuring adequate drainage will help protect your investment, enhance your property’s value, and improve its aesthetic. Building a retaining wall is a considerable effort, but with careful planning and execution, it will serve as a lasting and valuable addition to your landscape.

Key Takeaways

• A well-designed retaining wall starts with detailed planning and a careful choice of location.
• The height of your retaining wall will determine the amount of materials and the time you’ll need to invest.
• Choose materials that are built to last, such as stone or concrete. Consider your budget, the aesthetic compatibility with your property, and the indigenous conditions.
• A robust foundation is critical to your retaining wall’s long-term stability and integrity. Ensure it’s level, firm, and composed of suitable material like crushed rock or concrete.
• The preparation of your gravel base is paramount. It must be adequately compact and levelled.
• The building process involves stacking your selected materials in deliberate, well-measured layers, ensuring they bond entirely to each other and the foundation.
• If using timber sleepers, consider using galvanised screws for a stronger hold. Always apply the rule of overlapping the joints between rows.
• Proper drainage is essential to prevent water build-up behind the retaining wall, which can lead to pressure and instability.
• For efficient drainage, use a perforated pipe and filter fabric system, covering the pipe with gravel to protect it from soil and debris.

Need Help with Your Next Retaining Wall Project?

If constructing a retaining wall seems daunting, turn to Trinity Landscape & Sports.

Our skilled professionals possess comprehensive experience crafting retaining walls from the ground up. We provide a full-range service that’s both affordable and sustainable, ensuring a durable and well-built structure.

Reach out today for a consultation or a quote to get started.