How to Build a Retaining Wall in Australia (Step-by-Step Guide)

Building a retaining wall is one of the most common landscaping projects in Australia, but getting it right requires careful planning, proper materials, and an understanding of local regulations. Whether you are considering a DIY garden wall or engaging professionals for a major structural project, this step-by-step guide walks you through the entire process.

Before you start, be aware of South Australian regulations — walls over 1 metre high require engineering certification and council approval. For full regulatory details, see our SA retaining wall regulations guide.

Step 1: Planning and Design

Every successful retaining wall starts with thorough planning:

Assess Your Site

• Measure the height: How much soil needs to be retained? This determines your wall height and whether engineering is required
• Measure the length: Total wall length affects material quantities and cost
• Check the soil: Adelaide's clay soils require specific drainage measures. Sandy soils in coastal suburbs need different footing designs
• Locate services: Call Dial Before You Dig (1100) to locate underground services before any excavation
• Check access: Can machinery reach the site? Restricted access increases costs significantly

Choose Your Material

The most common materials for Adelaide retaining walls are:

• Concrete sleepers: Best all-round choice for walls 600mm–2m. $350–$500/lm at 1m high
• Timber sleepers: Most affordable for walls under 600mm. $200–$350/lm at 1m high
• Concrete blocks: Best for curved walls. $400–$550/lm at 1m high
• Gabion: Best drainage performance. $450–$600/lm at 1m high
• Natural stone: Premium appearance. $500–$800/lm at 1m high

Use our retaining wall calculator to estimate costs for your specific dimensions and material choice.

Step 2: Permits and Approvals

In South Australia, the rules are clear:

• Walls under 1 metre: Generally exempt from council approval, but must still comply with the Building Code and not affect neighbouring properties
• Walls 1 metre to 2 metres: Require engineering design and council development approval
• Walls over 2 metres: Require full engineering, council approval, and building certification
• Walls on boundaries: May require notification to or consent from your neighbour
• Walls near buildings: Must not undermine or surcharge existing building foundations

Your local council (e.g., City of Adelaide, City of Mitcham, City of Onkaparinga) can confirm specific requirements for your area.

Step 3: Excavation and Site Preparation

With plans approved and materials ordered, construction begins with excavation:

1. Mark the wall line: Use string lines and stakes to mark the exact position and height of the wall
2. Excavate the footing trench: Typically 400–600mm deep and 300–400mm wide, depending on wall height
3. Level the trench base: The footing must be level and on solid, undisturbed ground
4. Compact the base: Use a plate compactor or hand tamper to compact the trench base

For walls on Adelaide's clay soils, dig the footing trench during drier months if possible. Wet clay becomes extremely difficult to work with and compaction is compromised.

Step 4: Footings and Posts

For sleeper walls (timber or concrete):

1. Set post positions: Mark post locations at 2–2.4 metre centres along the wall line
2. Dig post holes: Deeper than the footing trench — typically the post should extend below the footing by at least one-third of the wall height
3. Set posts in concrete: Use N20 concrete (20 MPa), ensuring each post is plumb and at the correct height
4. Brace posts: Temporarily brace each post until the concrete cures
5. Allow curing time: Wait at least 24–48 hours before loading sleepers

For block walls:

1. Pour a concrete strip footing: Typically 200–300mm deep and twice the block width
2. Level the footing precisely: Block walls require an extremely level base — any error is magnified as courses are added
3. Allow full curing: 3–7 days for the strip footing before laying blocks

Step 5: Wall Construction

Sleeper Walls

1. Slide sleepers into the post channels from the bottom up
2. Check level and alignment as each course is added
3. For timber sleepers, nail or screw each sleeper to the posts
4. For concrete sleepers, the post channels hold the sleepers in place

Block Walls

1. Lay the first course on a bed of mortar, checking level constantly
2. Build up courses, staggering joints for strength
3. Install geogrid reinforcement at specified courses for taller walls
4. Fill block cores with concrete and reinforcement as specified by the engineer

Step 6: Drainage Installation

This step is critical for Adelaide conditions. See our detailed retaining wall drainage guide for comprehensive information. The essentials are:

1. Lay ag-pipe: Place 100mm ag-pipe along the base of the wall, wrapped in geotextile fabric
2. Ensure fall: The pipe must fall at least 1:100 toward the outlet point
3. Add drainage gravel: Backfill 200–300mm of 20mm crushed rock behind the wall, full height
4. Install geotextile: Place geotextile fabric between the drainage gravel and the retained soil
5. Connect to stormwater: Direct the ag-pipe outlet to a stormwater connection or soak-away pit

Step 7: Backfilling

1. Backfill behind the drainage gravel with suitable fill material
2. Compact in layers of 200–300mm to prevent future settlement
3. Do not use heavy machinery directly behind the wall during backfilling
4. Grade the finished surface to direct surface water away from the wall

Step 8: Finishing

• Install coping: A capping on top of the wall protects the top course and provides a neat finish
• Grade and landscape: Shape the soil above and below the wall for drainage and plant garden beds
• Install fencing: If a fence is required on top of the wall, this is the time

Tools and Equipment Needed

A retaining wall project requires specific tools and equipment, depending on the scale:

For Small Walls (Under 600mm DIY)

• Shovel, mattock, and wheelbarrow for excavation
• Spirit level (1200mm minimum) and string line
• Tape measure and marking stakes
• Hand tamper or plate compactor (hire)
• Drill driver for timber fixings
• Safety gear: gloves, safety glasses, steel-capped boots

For Larger Professional Projects

• Mini excavator (1.5–3 tonne) for excavation and material handling
• Plate compactor for base and backfill compaction
• Concrete mixer or premixed concrete delivery
• Laser level for precise levelling over long distances
• Lifting equipment for heavy concrete sleepers (60–80kg each)

Most of these items can be hired from Adelaide equipment hire companies if you are tackling a smaller wall yourself. For larger projects, professional landscapers bring all necessary equipment as part of their service.

Safety Considerations

Retaining wall construction involves significant physical risks that must be managed:

• Underground services: Always call Dial Before You Dig (1100) before any excavation. Adelaide has extensive underground networks of gas, water, electricity, and telecommunications that can be dangerous if struck
• Trench safety: Excavations deeper than 1.5 metres require shoring or battering to prevent collapse. Even shallower trenches can be dangerous in unstable soils
• Heavy lifting: Concrete sleepers weigh 60–80kg each. Use proper lifting techniques and mechanical assistance where available. Back injuries are common in manual retaining wall construction
• Working on slopes: Sloping sites present trip and fall hazards. Secure footing and proper scaffolding or access equipment are essential
• Concrete handling: Wet concrete is caustic and can cause chemical burns. Wear gloves and protective clothing when mixing and pouring footings

Should You DIY or Hire a Professional?

For walls under 600mm on level ground with good access, a handy homeowner can achieve good results. For anything taller, steeper, or structurally important, professional construction is strongly recommended.

Qualified landscapers bring experience with Adelaide's specific soil conditions, knowledge of SA regulations, access to machinery, and the skills to ensure proper drainage. The cost difference between DIY and professional installation narrows significantly when you factor in tool hire, material wastage, and the risk of costly mistakes.

Visit our retaining walls page to explore your options, then read our retaining wall cost guide for detailed pricing. When you are ready, connect with qualified Adelaide retaining wall builders for free quotes and professional advice.