What is a Retaining Wall? Applications, Types & More

A retaining wall is a structure designed to hold back soil and control changes in ground elevation. These walls are essential for stabilising sloped land, preventing erosion, and creating level, usable areas in construction and landscaping.

In this guide, you’ll learn when retaining walls are required, how to choose between different types and materials, what to consider in the design process, and what’s involved in council approval and installation. Keep reading to make informed decisions for your next project.

Introduction to Retaining Walls

Retaining walls are permanent soil retention systems used in engineering, architecture, and landscaping. These walls are designed to retain backfill or earth in areas with varying terrain elevations. Whether it's a suburban backyard in Sydney or a highway embankment, retaining walls provide soil stability and aesthetic shaping to the landscape.

When is a Retaining Wall Required in Construction?

A retaining wall is required when a construction site involves significant changes in elevation, soil instability, or water runoff risk. Retaining walls ensure structural integrity by stabilising soil, redistributing loads, and creating safe, level surfaces for buildings, landscaping, and roads.

Common scenarios requiring retaining walls include:

• Sloped land with a gradient steeper than 1:6: To prevent landslides and soil erosion.

• Excavation next to structures: To hold back earth near basements, foundations, or garages.

• Cut-and-fill developments: Where land is reshaped for multi-level building pads or driveways.

• Stormwater control: Where water flow needs to be redirected to avoid pooling or soil washout.

• Tiered landscaping: To create usable outdoor zones, garden beds, or pedestrian paths on hilly terrain.

Applications of Retaining Walls in Construction

Retaining walls are used across residential, commercial, and civil infrastructure projects.

• Residential: Garden beds, pool areas, retaining driveways, sloped backyards

• Commercial: Shopping centre parking platforms, warehouse loading zones

• Infrastructure: Rail lines, roadways, tunnels, culverts

Importance of Retaining Walls

Retaining walls are critical for managing slopes and soil stability on construction sites. They allow builders to:

• Prevent foundation failure on sloped plots

• Manage stormwater runoff to avoid flooding

• Expand usable space in difficult terrains

• Comply with slope-related building codes in Sydney

Slope Management and Soil Retention

A retaining wall reduces slope angles, redistributes soil weight, and prevents soil movement. In areas with 1:4 or steeper slope gradients, retaining walls control gravitational pull and keep soil in place during rain, excavation, or vibrations. This is especially important in clay-heavy soils like those in many Sydney suburbs.

Types of Retaining Walls

There are 6 major types of retaining walls used in construction. Each has distinct engineering mechanics.

Gravity Walls

Gravity walls resist earth pressure through their own weight. Constructed from stone, concrete blocks, or bricks, they are best for walls under 1 metre and are often used in residential settings.

Cantilevered Walls

Cantilever walls use reinforced concrete in an “L” or “T” shape to convert lateral soil pressure into downward force. They are ideal for retaining walls between 1.5 to 6 metres.

Anchored Walls

Anchored walls use cables or rods drilled into the ground and anchored with concrete or plates. This design suits deep excavations and areas with unstable soils.

Sheet Pile Walls

Sheet pile walls use steel, vinyl, or timber planks driven vertically into soft soils. They are commonly used along waterfronts or in tight urban areas.

MSE Walls

Mechanically Stabilised Earth (MSE) walls use layers of geogrid within compacted backfill, combined with concrete or modular facing units. They are common in large infrastructure like highways.

Gabion and Crib Walls

Gabion walls consist of wire cages filled with rock, ideal for natural aesthetics and erosion-prone zones. Crib walls use interlocking concrete units and are effective for gravity retention in landscaping.

Types of Materials Used in Retaining Walls

The materials used in retaining walls impact strength, durability, appearance, and cost.

Concrete and Precast Systems

Concrete blocks and precast panels are strong, versatile, and quick to install. Precast is often used in commercial or civil projects.

Timber and Brick

Timber sleepers are cost-effective but less durable, suited for small garden walls. Brick offers classic aesthetics but limited structural capacity for high-load sites.

Natural Stone and Gabion

Natural stone delivers premium visuals with high durability. Gabion systems offer flexibility, permeability, and resistance to freeze-thaw cycles.

Engineering Principles Behind Retaining Wall Construction

Every retaining wall must be engineered to safely withstand soil pressure, environmental conditions, and external loads. Design decisions are based on geotechnical data, site topography, structural requirements, and long-term durability.

Soil and Drainage

Soil type and drainage design directly affect a wall’s stability and lifespan. Clay-rich soils expand and contract with moisture, increasing lateral stress. To relieve water pressure behind the wall, drainage systems, such as weep holes, geotextile membranes, and gravel backfill must be integrated into the structure.

Load and Height

Structural loads determine the wall’s footing depth, reinforcement needs, and material selection. Walls over 600mm in height require engineering certification under NSW regulations. Live loads from vehicles, buildings, and pedestrian use, along with surcharge loads from adjacent features, must be factored into the structural design.

Design and Aesthetics

A well-designed retaining wall must meet both structural and visual requirements. Wall alignment, step-backs, and finishing materials should enhance surrounding architecture while maintaining strength and compliance. Aesthetic considerations include surface texture, colour, and how the wall integrates with vegetation or landscaping elements.

Compliance & Council Approvals

Across Australia, retaining wall construction must comply with local council regulations and the national building code. Walls exceeding 600mm in height, those supporting structures, or those positioned near property boundaries generally require formal approval and engineering certification.

Common compliance requirements include:

• Development Application (DA) for walls impacting site drainage, neighbouring properties, or safety

• Structural certification from a licensed engineer in accordance with the Building Code of Australia (BCA)

• Adherence to Australian Standard AS 4678 for Earth-Retaining Structures

• Drainage planning to ensure proper stormwater management

• Neighbour notification or consent if the wall is close to shared boundaries

Site-specific factors, such as heritage zoning, flood risk, and bushfire overlays may add extra requirements. Councils in different states may vary, but engineering input is essential for compliant design and approval.

How Long Do Retaining Walls Last and How to Maintain Them

The durability of a retaining wall depends on its material, site conditions, construction quality, and maintenance. Well-built walls can last decades, but all walls require routine care to remain safe and effective.

Signs of Wear or Structural Stress

• Cracks in concrete or mortar joints

• Bulging or leaning sections of the wall

• Water stains or pooling behind the wall

• Blocked weep holes or slow drainage

• Loose or displaced blocks, sleepers, or stones

Lifespan by Material Type

Concrete and precast systems: 50–100 years with proper drainage and footing

• Natural stone: 75–100 years, especially with dry-stacked, mortared systems

• Gabion: 30–50 years depending on wire quality and drainage

• Timber sleepers: 15–25 years, shorter in moist or termite-prone areas

• Brick: 40–60 years with regular pointing and waterproofing

Environmental exposure and soil movement can shorten service life if not addressed.

Should You Build a Retaining Wall Yourself or Hire a Professional?

Building a retaining wall may seem like a manageable DIY project, but its complexity increases with wall height, soil type, load conditions, and legal compliance. While smaller landscaping walls can be tackled by confident homeowners, structural or council-regulated walls require professional expertise.

When DIY May Be Suitable?

DIY installation may be practical if:

• The wall is under 600mm high

• It does not support any structure or driveway

• The soil is stable and drainage needs are minimal

• The site is flat and easily accessible

Homeowners should still research drainage, footing depth, and safety measures to avoid costly repairs or safety issues later.

When to Hire a Professional?

Professional Retaining wall installation is essential if:

• The wall exceeds 600mm in height

• It requires excavation, structural reinforcement, or engineered footing

• It’s located near boundaries or supports a building

• Council approval, structural certification, or stormwater planning is required

Licensed contractors understand load distribution, drainage integration, and local council codes, and they build to Australian Standards.

Murs Projects specialises in professional retaining wall systems built for long-term performance and regulatory compliance. Our experienced team handles design, approvals, and construction to deliver walls that are structurally sound and visually integrated with your site.

Contact us to discuss your project and get expert support from concept to completion.

Frequently Asked Questions

What is the purpose of a retaining wall?

The purpose of a retaining wall is to stabilise soil on sloped or uneven ground and prevent erosion. It allows land to be reshaped into level, usable areas for construction, landscaping, or access. Retaining walls also protect buildings, roads, and outdoor spaces from soil movement and water damage.

What is the difference between a retaining wall and a normal wall?

A retaining wall holds back earth and resists lateral pressure from soil, while a normal wall simply divides spaces or supports structures. Retaining walls require specific engineering to handle loads, drainage, and ground forces.

In contrast, regular walls, such as those used in homes are designed for vertical support or enclosure only.

How Much Does It Cost?

Retaining walls in Sydney range from $250 to $900 per square metre, depending on height, material, access, and engineering.

Do I Need a Permit?

Yes. Any wall over 600mm or close to a boundary must meet planning rules and be certified by an engineer.

What’s the Best Material for My Property?

You can use:

• Concrete for long-term strength

• Stone for premium aesthetics

• Timber for affordable short-term projects

• Gabion for drainage-critical, rural or creek-side properties