Retaining Wall Approvals in NSW: Exempt, CDC or DA?

Retaining walls are among the most misunderstood structures in residential construction. Because landscapers build them and garden centres sell the blocks, people assume they are landscaping. Legally and structurally, they are engineering: a retaining wall permanently resists earth pressure and water pressure, transfers load to its foundations, and – when it fails – fails onto whatever is below it, which on Sydney’s subdivided hillsides is usually a neighbour’s yard, a driveway or a house.

NSW regulates them accordingly, with a three-tier approval system: exempt development (no approval needed) for small walls meeting strict criteria, complying development (CDC) for walls associated with other approved works within prescribed limits, and development application (DA) for everything else. This guide explains where the lines sit, what drainage obligations apply at every tier, and when an engineer stops being optional.

Tier 1: Exempt development – the small-wall allowance

The State Environmental Planning Policy (Exempt and Complying Development Codes) 2008 allows genuinely minor retaining walls to be built without any approval – but only if every criterion is met. The commonly applicable limits include:

• Height no more than 600mm above or below existing ground level;
• Setback from lot boundaries – the exempt provisions require separation from boundaries (commonly at least 1 metre), which surprises people, because the boundary is exactly where most owners want the wall;
• Separation from other retaining walls – walls cannot be stacked into a terraced system to dodge the height limit; minimum separation between walls applies;
• No redirection of water – the wall must not redirect surface water or groundwater onto adjoining land, and drainage must be managed;
• General exempt-development preconditions – the land itself must be eligible (heritage, environmentally sensitive and certain other categories are excluded).

Miss any criterion – a 700mm wall, a wall hard on the boundary, terraced walls a metre apart – and the wall is not exempt, full stop. The criteria are prescriptive; check the current provisions of the Codes SEPP (or have a professional do it) rather than relying on the folklore version, which usually remembers the 600mm and forgets the rest.

Tier 2: Complying development – walls within a bigger project

Retaining walls are frequently needed as part of a new home, duplex or pool being approved as complying development. The Codes SEPP deals with this through its earthworks and retaining wall provisions within the relevant codes (the Housing Code, Low Rise Housing Diversity Code and others): retaining walls and structural support associated with the complying development are permitted within prescribed height and location limits, with a critical engineering trigger built in – support for excavation or fill beyond the prescribed depth must be a retaining wall or structural support certified as structurally adequate by a professional engineer.

Practical implications for CDC projects:

• The walls must be shown on the CDC documentation – location, height, materials and the engineer’s design where required. A certifier cannot approve what is not documented, and walls added on site during construction are non-compliances;
• Height limits under the codes are tied to the cut and fill limits of the code itself; substantial site re-grading can push the whole project out of the CDC pathway, not just the wall;
• Drainage behind and around the walls forms part of the stormwater documentation – see below.

Tier 3: Development application – everything else

A wall that is neither exempt nor part of compliant complying development needs consent via a DA: tall walls, boundary walls outside exempt limits, terraced systems on steep sites, walls on heritage or environmentally constrained land, and standalone walls not associated with other approved development. The DA is assessed on merit – visual impact, amenity, drainage effects on neighbours, structural adequacy – and approval will be conditioned on engineering design and certification. On steep sites, the retaining strategy can be the central issue in the assessment, and early geotechnical input pays for itself.

When do you need an engineer?

Short answer: earlier and more often than the height thresholds suggest. The regulatory trigger under the Codes SEPP framework is that support for earthworks beyond the modest prescribed depth must be certified by a professional engineer, and councils and certifiers apply equivalent expectations through DA conditions and the Construction Certificate process – commonly requiring engineered design for walls above roughly knee height, and always where a wall supports a surcharge. But the regulatory floor is not the engineering reality. Get a structural design regardless of approval tier when the wall:

• supports a surcharge – a driveway, pool, building footing or vehicle load above the wall multiplies the pressure on it;
• retains towards a neighbour – failure consequences (and liability) land next door;
• is in reactive clay, fill or wet ground – Sydney’s shale-derived clays and old uncontrolled fill are notorious wall-killers;
• is part of a terraced system – walls interact; the lower wall carries more than its own soil;
• replaces a failed wall – the failure is information: something (usually water) was not designed for the first time.

Drainage: the reason retaining walls fail

Ask any engineer what kills retaining walls and the answer is water, in two distinct ways – and both carry compliance obligations at every approval tier:

Hydrostatic pressure behind the wall

Saturated backfill roughly doubles the load a wall carries compared with drained soil. The standard defence is built into any competent design: free-draining granular backfill, a subsoil (agricultural) drain at the base of the wall connected to a lawful stormwater outlet, weep holes where appropriate, and drainage geotextile or membrane detailing. A wall built without a functioning subsoil drain – or with a drain that connects to nothing – is a wall on a countdown.

Redirected surface water onto neighbours

Cutting and filling changes how a site sheds water. Every approval tier prohibits redirecting surface or groundwater onto adjoining land: it is an explicit exempt-development criterion, a design requirement under complying development, a standard DA condition – and independently of all of them, causing a nuisance to a neighbour’s land is a civil liability. The wall design must show where intercepted water goes: collected at the top of cuts, drained at the base of walls, and carried to the site’s lawful discharge point, not concentrated over the boundary.

Boundary walls: the extra layer of complexity

Walls on or near boundaries add non-planning issues worth resolving before construction: whose land the wall (and its footings) actually stands on – a surveyor’s set-out is cheap insurance; who benefits from and who should pay for a wall retaining fill on one side and cut on the other; interaction with the Dividing Fences Act 1991 (which covers fences, not retaining walls – a common misconception; the wall is generally the responsibility of the party whose works made it necessary); and access to the neighbour’s land to construct, which needs their agreement or, failing that, an access order. Combined fence-on-retaining-wall structures also affect the fence height assessments in exempt provisions. Document the arrangement with the neighbour in writing – the wall will outlast both current owners.

A practical decision path

• Under 600mm, clear of boundaries, no water redirection, eligible land? Likely exempt – verify every criterion against the current Codes SEPP, keep drainage lawful, and build it properly anyway.
• Part of a home, duplex or pool going through CDC? Include the walls in the documentation with engineering design where triggered; check the project’s cut and fill stays within the code.
• Taller, on the boundary, terraced, or standalone on constrained land? DA, with structural (and often geotechnical) design from the outset.
• In all cases: subsoil drainage to a lawful outlet, no water onto neighbours, and an engineer whenever surcharge, neighbours or bad ground are involved.

Frequently asked questions

Do I need council approval for a retaining wall under 600mm?

Not if it meets all the exempt development criteria in the Codes SEPP – which include boundary setbacks, separation from other walls, drainage requirements and land eligibility, not just the height. A 500mm wall hard against the boundary, or one of a terraced pair, generally is not exempt. Check the current criteria for your land before building.

Can I build a series of 600mm walls instead of one high wall?

No – the exempt provisions require minimum separation between retaining walls precisely to prevent terraced systems bypassing the height limit, and closely spaced walls act structurally as one high wall anyway. Terraced retaining on a steep site is an engineered design and normally a DA matter.

Who is responsible for a retaining wall on the boundary?

Generally the owner whose earthworks made the wall necessary – if your excavation or fill created the level change, the support obligation is yours, and the Dividing Fences Act’s cost-sharing regime applies to fences, not retaining walls. Historic walls of unknown origin are murkier; get legal advice, and a structural inspection if the wall is distressed.

My existing retaining wall is leaning – what should I do?

Treat it as a live structural issue: keep loads (vehicles, storage, new fill) away from the top, and get an engineer’s inspection promptly. Leaning usually signals saturated backfill or failed drainage, and walls tend to fail progressively then suddenly. Replacement walls need approval under the same three-tier framework – and this time, working subsoil drainage.

Contrive Consultants provides civil and drainage design for retaining walls across Greater Sydney – from exempt-tier drainage advice to engineered terraced systems on steep duplex sites – with structural and geotechnical partners as required. See our services, call +61 497 848 111, email info@contriveconsultants.com.au or contact us before your wall becomes a case study.