Creating Smooth Curves and Radius Walls with Allan Block Retaining Walls Systems: A Step-by-Step Guide

19 November 2025

Curved retaining walls don’t just hold back soil, they shape landscapes. Whether you’re designing a garden feature, terracing a slope, or defining an outdoor living space, Allan Block Retaining Wall Systems make it easy to create smooth, natural curves that complement the environment. 

This guide walks you through how to design and construct both inside and outside curves for Allan Block walls, ensuring your project looks as good as it performs. 

1. Start with Smart Planning

Before construction begins, lay out your wall design on-site. Measure the radius of each curve and refer to the Radius Chart (below) to confirm that your chosen block type can achieve the desired shape. 
If needed, adjust your design so the curve aligns with the block system’s minimum radius requirements. 

Tip: Gentle, sweeping curves generally create the most visually balanced and appealing walls. 

2. Maintain Proper Offset Between Courses 

For both structural integrity and a clean appearance, offset the vertical seams of each course by at least ¼ of the block length. 
This applies to both inside and outside curves. 

If you need to fine-tune the offset, use half-length blocks (AB Junior) or cut full blocks in half. 

3. Building Inside Curves

Inside curves create a smooth inward sweep that follows the shape of the land. To achieve this: 

• Keep the front faces of the blocks tight together. 

• Fan out the blocks evenly, maintaining a consistent spacing between the back of the blocks. 
   

4. Building Outside Curves

Outside curves extend outward and require a slightly different approach: 

• Trim the “wings” from the back of the blocks to tighten the radius of the curve. 

• To remove the wings, simply strike the back edges with a hammer for a clean break. 

This adjustment allows the blocks to sit closer together, creating a tighter, smoother radius.  

5. Determining the Radius 

Curved walls naturally require a greater setback, creating what’s known as a coning effect - the radius tightens as the wall rises. 
To maintain stability: 

• Start with a larger radius at the base course. 

• Refer to the Radius Chart to find the minimum recommended radius based on your wall height. 

This ensures that the finished wall maintains proper alignment and structural balance from bottom to top.  

6. Laying Out the Curve

To accurately mark your curve on-site: 

1. Identify your starting point. 

1. Measure straight back from that point the distance specified in the Radius Chart. 

1. Place a stake in the ground - this marks the centre of the curve. 

1. Tie a string to the stake, using a length equal to your desired radius. 

1. Swing the string in an arc to mark the line for your base course. 

Align the front faces of the base course blocks with this arc to establish a smooth, even foundation. 

7. Transitioning Between Curves and Straight Sections

When moving from a curve into a straight section or another curve: 

• Lay out the curve and the first few blocks of the next section together. 

• Slightly adjust one or two of these blocks to achieve a natural, seamless transition. 

This small step makes a big difference in the visual flow of the finished wall. 

8. Building Tighter Curves

For tighter radii, use the AB Junior block whenever possible. 
If you’re working with full-size blocks, you can remove part of the bottom notch to fit the blocks closer together and maintain the desired curve. 

Conclusion 

Designing and building curves with Allan Block Retaining Wall Systems is straightforward when you follow these best practices. By planning carefully, maintaining proper offsets, and referring to the Radius Chart for guidance, you’ll create a retaining wall that’s not only structurally sound but also beautifully integrated into its surroundings. 

Whether you prefer gentle sweeps or bold arcs, Allan Block makes it simple to bring your landscape vision to life.