What is a Retaining Wall?
A retaining wall is an essential structural element used to prevent soil from shifting due to gravity or erosion. These walls play a crucial role in stabilising sloped areas, preventing soil displacement, and creating level spaces for landscaping, buildings, and infrastructure. Retaining walls are commonly seen in construction, landscaping, and civil engineering projects, where their primary purpose is to enhance safety, extend the lifespan of structures, and provide visual appeal.
Choosing the right type of retaining wall depends on your project’s requirements, including the materials, design preferences, and intended purpose.
Types of Retaining Walls: Finding the Right One for You
When it comes to retaining walls, there’s no one-size-fits-all solution. Below is an overview of the most common types of retaining walls, along with their characteristics, advantages, and disadvantages to help you determine the best fit for your project:
Type of Retaining Wall | Characteristics | Advantages | Disadvantages |
Vertical Post Horizontal Sleeper Wall | - Uses steel or timber posts with horizontal sleepers (timber or concrete) - Simple design, quick to install - Can be natural-looking if timber is used | - Cost-effective, especially with timber - Easy to construct - Can be DIY-friendly - Flexible design for different heights | - Timber sleepers may rot over time - Steel posts can corrode if not treated - Limited lifespan for timber versions |
Core-Filled Block Wall | - Uses hollow concrete blocks filled with reinforced concrete - Strong and durable - Requires a concrete footing | - High strength and long lifespan - Can be rendered for aesthetics - Resistant to weathering and erosion | - Expensive due to materials and labour - Requires skilled construction - Needs proper drainage to prevent cracking |
Stackable Block Wall (Allan Block or Similar) | - Precast concrete blocks that interlock without mortar - Often reinforced with geogrid for stability - DIY-friendly | - Easy to install without mortar - Aesthetic appeal with various colours/textures - Can be built quickly | - Limited height unless reinforced - Requires compacted base and drainage - Can be expensive for larger walls |
Brick Wall | - Built with traditional clay bricks or concrete bricks
- Requires a reinforced concrete footing - Classic appearance | - Attractive, timeless aesthetic - Can match house brickwork - Durable if built correctly | - Expensive and labour-intensive - Requires skilled bricklayers - Susceptible to cracking if not properly reinforced |
Gabion Basket Wall | - Wire mesh baskets filled with rocks - Permeable, allowing natural drainage - Industrial or rustic look | - Strong and durable - Flexible – Can settle without cracking - Allows water drainage, reducing hydrostatic pressure - Can be DIY-friendly | - Bulky appearance - Wire mesh can rust over time if not galvanized - Requires significant rock material |
Crib Lock Wall | - Uses interlocking precast concrete or timber cribs filled with soil or rock - Open structure allows drainage - Semi-permanent | - Quick to install - Good drainage capabilities - Can be used for taller walls if reinforced | - Requires space for crib structure - Timber versions may degrade over time - Needs proper backfill compaction |
Sandstone Log Retaining Wall | - Large sandstone blocks stacked for a natural appearance - Heavy, requiring machinery for placement - Naturally durable | - Aesthetic appeal with natural stone - Strong and long-lasting - Minimal maintenance required | - Expensive, especially for large projects - Requires proper footing and machinery to place - Can be difficult to source uniform blocks |
Formed Concrete Wall | - Solid reinforced concrete wall poured on-site into formwork - Very strong and durable - Requires professional installation | - Extremely durable and strong - Can be designed for high retaining loads - Can be finished with textures or colours for aesthetics | - Expensive and labour-intensive - Requires good formwork and reinforcement - Needs proper drainage to avoid cracking |
Sheet Pile Wall | - Uses steel, vinyl, or timber sheets driven into the ground - Commonly used in waterfronts or soft soils - Thin profile but provides high strength | - Ideal for deep excavations and waterlogged areas - Space-efficient (thin wall profile) - Can be installed quickly with machinery | - Can be expensive depending on material - Requires heavy machinery for driving sheets - Not suitable for very hard soils without pre-drilling |
Mortared Stone Wall | - Natural stone bonded together with mortar - Can use random rubble stone (irregular shapes) or ashlar stone (cut blocks) - Requires a solid footing and proper drainage | - Aesthetic, natural, and traditional appearance - Strong and durable if built correctly - Works well in landscaping and heritage sites | - Labour-intensive and requires skilled masonry work - Expensive due to material and labour costs - Needs good drainage to prevent mortar failure |
What Factors Should Be Considered When Choosing a Retaining Wall?
To make an informed decision, consider the following key factors:
Height and Soil Load Requirements: Ensure the retaining wall can handle the height and soil pressure of your site. For smaller DIY walls, manufacturers often provide product information brochures to assist with design and installation. However, larger walls (typically over 600mm in height) generally require assessment by a structural engineer to ensure stability and compliance.
Additional Load Requirements: Consider external loads that may be applied to the soil at the top of the wall, such as pedestrian traffic or vehicular traffic. Attaching fence posts to a retaining wall is another common example of an external load that should be accounted for in the design.
Soil Type: Different soil compositions affect the wall’s structural stability and drainage needs.
Drainage Conditions: Proper drainage prevents water build-up, which could compromise the wall’s strength over time.
Aesthetics: Consider how the wall’s design and materials will complement your landscaping or property.
Cost and Maintenance: Balance initial costs with long-term maintenance requirements to find a practical solution.
Permits and Regulations: Consult your local certifier or council to determine the permits and regulations applicable to your retaining wall. These requirements may influence the final location, design, and specifications of the wall.
By evaluating these factors carefully, you can select a retaining wall that meets both functional and aesthetic goals.
Is a Permit Necessary to Build a Retaining Wall Yourself?
Whether you require a permit depends on your local council's regulations and the wall's size. In many areas, a permit is mandatory for walls over a certain height, walls supporting significant loads or walls within the vicinity of a boundary or existing structure. It’s always wise to consult local certifiers and councils before starting your project. Ignoring these requirements could result in fines or being forced to redo the work.
When to Engage a Structural Engineer for Your Retaining Wall Build
A structural engineer should be involved if:
The Wall is Over 600mm High: Taller walls are subject to greater forces and may require specific engineering solutions.
Complex Soil or Drainage Issues Are Present: Poor soil conditions or high water tables increase the risk of failure.
The Wall Supports Additional Loads: For walls near driveways, buildings, or other structures, expert calculations are critical to ensure safety.
You’re Unsure About Design or Compliance: Professional guidance ensures your retaining wall adheres to all codes and lasts for years to come.
Structural engineers provide the expertise needed to design a wall that’s safe, cost-effective, and durable.
Conclusion
Retaining walls are a critical component of landscaping and construction projects, providing stability, functionality, and aesthetic appeal. With so many types of retaining walls available, it’s important to evaluate your project’s needs, including soil conditions, height, and budget, before making a decision.
When in doubt, seek professional advice to ensure your retaining wall is built to last and complies with local regulations. A well-designed retaining wall can transform your outdoor space into a functional and visually stunning area for years to come.