Retaining walls: the 500 mm rule, AS 4678 and when an engineer is mandatory
WA applies the tightest retaining wall threshold in Australia. Below a certain retained height you are generally exempt; above it you need a building permit; above that you need certified structural engineering. Get this wrong and the council can order it removed.
A retaining wall is the one landscape element that can hurt somebody. That is why Western Australia regulates it harder than any other state, and why the threshold is lower than people expect: 500 millimetres of retained ground. Two courses of limestone block. A single sleeper on edge.
Most Perth blocks landscaped once already have a wall at or near that line, often built without a permit by a previous owner. Renovating means you inherit it — and a council can direct you to remove it. This lesson is the paperwork, not the build; construction sits in retaining walls in Phase 8.
What a professional does at this stage
A landscaper who has been burnt once does three things before drawing anything. They measure retained height accurately and write it on the plan, because every later decision keys off that number. They assume a permit is required and try to disprove it. And they get the answer in writing — an email to council building services with a sketch, a height and a boundary distance, and the reply kept on file. A phone call is worth nothing eighteen months later when a neighbour complains.
The reason is commercial. A wall that turns out to need a permit after it is built costs you demolition, engineering, the permit, a doubled Building Services Levy and the rebuild — and if you never fix it, it surfaces at settlement when the buyer’s conveyancer asks for the paperwork.
Measuring retained height
Retained height is not the height of the wall face you can see. It is the vertical distance from finished ground level on the low side, at the toe, to the top of the material retained on the high side — measured at every point along the wall, because your ground is not flat. Three traps:
- Tiered walls. Two 400 mm walls stepped one behind the other are not two exempt walls. Wanneroo assesses tiered walls on total height: if the upper wall sits inside the failure wedge of the lower one, the two behave as one taller wall.
- Adding to an existing wall. One more course is building work in its own right, and several councils treat any addition as triggering a permit regardless of the extra height.
- Cut versus fill. Excavating 300 mm on the low side of an existing 400 mm wall gives you a 700 mm wall you did not build and did not get approved.
Work from the datum you set in levels, falls and datum and record top-of-wall and bottom-of-wall at each change in ground level — exactly the notation councils ask for.
The exemption, in full
Everyone quotes the 500 mm. Almost nobody quotes the rest of it. Schedule 4 clause 2, item 6 of the Building Regulations 2012 exempts a retaining wall that:
- retains ground no more than 0.5 m in height; and
- is not associated with other building work, or with the protection of land adjoining the land the wall is on; and
- is not work of a kind to which sections 76, 77, 78 or 79 of the Building Act 2011 relates.
All three. Fail any one and you need a permit at any height.
Condition 2 catches renovators. A 400 mm wall built as part of a job that also includes a permitted patio or pool is “associated with other building work”. A 300 mm wall whose real job is holding up the neighbour’s soil is “protection of land adjoining” — height is then irrelevant.
Condition 3 is the boundary condition. Sections 76 to 79 cover encroaching beyond your boundary (footings and backing blocks count), adversely affecting the neighbour’s land, and affecting a boundary retaining wall that protects their land. “Adversely affect” is broad: reducing stability or bearing capacity, damaging a structure, or changing natural site drainage. Each carries a $25,000 penalty and each needs the adjoining owner’s written consent on a BA20 before the permit issues. They have 28 days to respond.
And check the exact wording your council uses. Wanneroo says a permit is required where a wall exceeds 500 mm; Greater Geraldton says 500 mm or greater. On a wall designed to exactly 500 mm, those two sentences give opposite answers.
Surcharge: the word that changes the design
A wall designed to hold soil only is non-surcharged, and the maximum heights published for block systems at Perth landscape yards are almost always non-surcharged figures. Add any of these and the load case changes:
| Surcharge | Typical source |
|---|---|
| Fence load | Colorbond on top of the wall, catching wind |
| Vehicle load | Driveway, crossover or parking within roughly 3 m |
| Structure load | Shed, patio post, pool, spa, footing near the top |
| Water load | Pool or soakwell discharging behind the wall |
Two rules from published council guidance: a fence must not be used to retain soil unless it was designed to, and a boundary wall must sit entirely within one property — it may not straddle the boundary. A dividing fence fixed to your wall needs an engineer to design the fixing. Cost-sharing with the neighbour is a civil matter, not a council one, and sits in dividing fences.
Planning approval is a separate question
The building permit asks “is it structurally safe?”. Development approval asks “is it allowed here?”. Different departments, different applications, planning usually first.
The R-Codes deemed-to-comply rule is easy to remember: behind the street setback, set the wall back from the boundary by at least its own height — 0 m for 0.5 m or less, 1 m for a 1 m wall, 3 m for a 3 m wall, measured from natural ground level at the boundary. Forward of the street setback line you are capped at 0.5 m above or below natural ground level. Exceed either and you are applying on design principles. See R-Codes and your council.
When an engineer is mandatory
In practice, at 500 mm. Wanneroo requires engineer’s details for every retaining wall application; Greater Geraldton requires design and certification at 500 mm or greater. Your building surveyor cannot sign a certificate of design compliance without one. The compliance path is NCC 2022 clause H1D3(2), satisfied by designing to AS 4678 — which covers walls from 800 mm to 15 m. Below 800 mm your engineer still has to demonstrate compliance, just not via that route.
Recent change worth knowing. WA is phasing in compulsory registration of building engineers under the Building Services (Registration) Act 2011. Structural registration opened 1 July 2024, and the current government guidance (updated 9 July 2026) says the transition runs to 1 July 2027, after which unregistered building engineering work is an offence carrying a fine of up to $25,000. The scheme expressly covers incidental structures — which is what your wall is. Ask your engineer today whether they are registered with the Building Services Board.
Note too that a retaining wall is an incidental structure, not a Class 10a building, so the concession that lifted the registered building contractor threshold to $50,000 for Class 10a work on 1 July 2026 does not cover it. Work valued at $20,000 or more still needs a registered building contractor or owner-builder approval.
The dangerous parts
- Excavation collapse. Perth sand has almost no cohesion. A vertical face cut in dry sand fails without warning, and a cubic metre weighs roughly 1.6 tonnes. Batter, bench or shore it, and never stand in an unsupported excavation deeper than your waist.
- Silica dust. Cutting limestone, concrete block or pavers dry generates respirable crystalline silica. Wet-cut or use on-tool extraction, and wear a fitted P2.
- Walls already moving. Do not excavate at the toe of a wall that is leaning, bulging or cracked. Engineer first.
- Services and assets. Check Water Corporation proximities — 2 m from a gravity sewer, 4 m from a water main under 300 mm — and apply under section 90 if you are inside them. See locating services.
Money and time
Budget 0.32% of the estimated value for an uncertified permit application or 0.19% for a certified one, minimum $121, plus the Building Services Levy (minimum $61.65 up to $45,000). Add the engineer’s fee — get it in writing — and any council bond; Wanneroo charges $130 non-refundable for its street and verge bond plus a $2,000 refundable bond once works exceed $20,000. Other councils differ. Allow 10 business days for a certified decision, 25 for an uncertified one, with development approval on top.
Found an existing unapproved wall? The retrospective route is a building approval certificate (form BA13), and the levy doubles to 0.274%.
What this changes downstream
Three lines into your workbook: the retained height of every proposed and existing wall, the council’s written answer on permit and development approval for each, and the surcharges each wall must carry. Those drive the engineering brief, the boundary consent, and a real number in building the quote.
The next lesson does the same job for everything else you might build — patios, pergolas, decks, sheds and screens — where the thresholds are different again and changed on 1 July 2026.
Checklist
- Measure the retained height of every wall you are considering
- Confirm the current thresholds with YOUR council, in writing
- Check boundary proximity and surcharge conditions, which tighten the rules
- Budget for engineering certification where required
Watch
Link Block Walls - Drainage & Finishing - Part 3
Four minutes on the part of a retaining wall you cannot inspect once it is finished, and the part the engineer's detail is mostly about: drainage aggregate behind the wall, agricultural drain at the base, and geotextile separating the drainage zone from the backfill. Watch it so that when a drawing lands on your desk with a hatched zone and an ag line on it, you know what those two lines are doing and why leaving them out is the most common cause of a wall failing.
A Queensland supplier demonstrating its own block system. The drainage principle is universal; the block product, the soils and the permit thresholds are not. In Perth the backfill is usually free-draining sand, which makes the geotextile more important rather than less, because sand migrates into open aggregate.
Where to go deeper
Every link below was fetched and checked before it shipped. Nothing here is a guess.
- Freegovernment20 min for the relevant clausePerth / WA
Building Regulations 2012 (WA) — current consolidation
Parliamentary Counsel's Office, Government of Western Australia
Why this oneThis is the actual law, not somebody's summary of it. Download the current HTML or PDF version from this page and go to Schedule 4 clause 2, item 6 — the exemption for retaining walls is three lines long and every word in it does work. The version in force when this lesson was written is dated 23 July 2026; the page always serves the current one, so check the version date at the top before you rely on it.
Change this for PerthThe consolidated regulations are a large document and the site serves it as one file. Use your browser's find function for "retaining wall" rather than scrolling.
Link checked 2 Aug 2026
- Freegovernment30 minPerth / WA
Building Act 2011 (WA) — current consolidation
Parliamentary Counsel's Office, Government of Western Australia
Why this oneThree parts of this Act decide what happens to a retaining wall. Section 3 defines a retaining wall as an "incidental structure", which is why it is caught by the permit system at all. Part 6 (sections 75 to 80) is the work-affecting-other-land regime that governs boundary walls. Sections 110 to 112 are the building order powers that let a council direct you to demolish or remove something built in contravention. Version in force at time of writing: 28 May 2026.
Link checked 2 Aug 2026
- Freegovernment15 minPerth / WA
Work affecting other land
Building and Energy, Department of Energy, Mines, Industry Regulation and Safety
Why this oneThe regulator's plain-English version of Building Act Part 6, and the page that tells you which form to use. It sets out the two situations where the neighbour's consent must be obtained before the permit is issued (encroachment, and adversely affecting the land), the four situations handled outside the permit process, and the difference between form BA20 and form BA20A. It also states the 28-day period the adjoining owner has to respond.
Link checked 2 Aug 2026
- Freegovernment15 minPerth / WA
Retaining walls and site works
City of Joondalup
Why this oneThe clearest council page in Perth on the topic, because it handles the planning question and the building question on one page instead of pretending they are the same thing. It states the building permit exemption (a wall not exceeding 0.5 m), reproduces the R-Codes height-to-setback table, and shows how the street setback limit changes with the R-code applying to your lot. Read it even if you are not in Joondalup — it is the best worked example of how the two systems interact.
Change this for PerthThe R-code numbers on this page are Joondalup's local application. Your own council's local planning policy may set different figures for the street setback area.
Link checked 2 Aug 2026
- Freegovernment10 minPerth / WA
Retaining Wall Information Sheet
City of Wanneroo
Why this oneA second council, stating the same threshold in different words — which is exactly why you must check your own. It confirms a permit is required where a wall exceeds 500 mm, where you are adding to an existing wall, and where tiered walls exceed 500 mm in total; that structural engineer's details are always required for a retaining wall application; and that a dividing fence fixed to a retaining wall needs an engineer to design the fixing. It also prices the street and verge bond ($130 non-refundable administration fee, plus a $2,000 refundable bond once works exceed $20,000). Marked correct as at July 2025.
Link checked 2 Aug 2026
- Freegovernment10 minPerth / WA
BS12 Retaining Wall Information and Checklist
City of Greater Geraldton
Why this oneThe best published explanation of surcharge anywhere on a WA council site, and the reason it is here despite not being a Perth council. It defines a "non-surcharged" wall, warns that a fence should not be used to retain soil unless designed to, states that a boundary wall must sit entirely within one property and may not straddle the boundary, and requires the site plan to show any driveway or crossover within 3 m of the wall. Note the wording of its threshold — 500 mm or greater — which is subtly different from Wanneroo's exceeds 500 mm.
Change this for PerthGreater Geraldton, not Perth. The surcharge and boundary principles are general WA practice; the fees, the development approval trigger and the submission checklist are that council's own. Use it to understand the concepts, then confirm the numbers with your council.
Link checked 2 Aug 2026
- Freegovernment20 min for clause 5.3.7Perth / WA
Residential Design Codes Volume 1
Western Australian Planning Commission / Department of Planning, Lands and Heritage
Why this oneThe planning half of the answer, and it is a separate question from the building permit. Clause 5.3.7 Site works carries the deemed-to-comply rules: Table 4 sets the minimum setback from a lot boundary at the same figure as the wall height (0.5 m or less needs 0 m, a 2 m wall needs 2 m), measured from natural ground level at the boundary. Clause C7.1 caps fill and excavation between the street boundary and the street setback at 0.5 m above or below natural ground level. The version current at time of writing is dated 10 April 2026.
Change this for PerthThe standalone clause 5.3.8 Retaining walls was deleted by amendment dated 2 July 2021 — retaining walls are now assessed under Site works. Local governments can also modify clause 5.3.7 through a local development plan, so your local planning policy may override these figures.
Link checked 2 Aug 2026
- Freegovernment10 minPerth / WA
Building engineering registration
Building Services Board / Building and Energy
Why this oneWA is part-way through making engineer registration compulsory and this is the page that tells you where in that process we are. Registration of structural building engineers opened on 1 July 2024, a transition period runs until 1 July 2027, and the scheme explicitly covers design work for an "incidental structure" — which is what your retaining wall is. Read it so you know what to ask the engineer you are about to pay. Last updated 9 July 2026.
Change this for PerthAn older Building and Energy page still states 1 July 2026 as the mandatory date for structural engineers. This page, updated more recently, states 1 July 2027 for all four areas. Either way the direction of travel is the same — ask your engineer whether they are already registered with the Building Services Board.
Link checked 2 Aug 2026
- Freestandard10 minAustralian
NCC 2022 Volume Two, Part H1 Structure
Australian Building Codes Board
Why this oneThe free way to see the actual compliance path your building surveyor is assessing against. Clause H1D3(2) says Performance Requirement H1P1 is satisfied for an earth-retaining structure if it is designed and constructed in accordance with AS 4678. The explanatory note is the useful part: AS 4678 covers structures between 800 mm and 15 m in height, and does not apply to landslip sites, sustained cyclic loading or water-retaining structures.
Change this for PerthThe NCC is a national code adopted by each state. Read it alongside the WA appendix, and remember it answers "is this design compliant" — not "do I need a permit", which is answered by the WA regulations.
Link checked 2 Aug 2026
- Paid · $308.30 incl. GST for a single-user PDFstandardAustralian
AS 4678-2002 Earth-retaining structures
Standards Australia (distributed by Intertek Inform)
Why this oneThe document AS 4678 the NCC points to — 117 pages, published 26 February 2002, still listed as current. It is the design basis your engineer will work from, covering earth pressure, drainage, durability and the classification of walls by consequence of failure. Buy it only if you intend to read design calculations; for everyone else the free NCC page above tells you what it is for and the engineer you hire already owns it.
Change this for PerthThis is a reseller listing, which is where the price was verified. Standards Australia's own store also carries it. Some public libraries and TAFE WA campuses provide reading access to Australian Standards at no cost — ask before you buy.
Link checked 2 Aug 2026
- Freegovernment15 minPerth / WA
Approval for works near Water Corporation assets
Water Corporation
Why this oneThe step almost every homeowner misses. Under section 90 of the Water Services Act 2012 you must request Water Corporation approval before working within prescribed proximities of their assets — 2 m of a gravity sewer or main drain, 4 m of a water main under 300 mm, 6 m for larger and pressure mains, with wider limits for buildings and structures. Retaining wall applications are lodged through BuilderNet rather than the standard form. Their guidelines were updated on 9 November 2025 and offsets are now measured from the edge of the pipe, not the centreline.
Link checked 2 Aug 2026
- Freegovernment45 minPerth / WA
Code of Practice: Excavation
WorkSafe WA
Why this oneAn approved code of practice under WA's work health and safety laws, which means it is the benchmark a regulator or a court would measure your excavation against. It applies to all WA workplaces where excavation occurs and covers ground collapse, battering, benching, shoring and the assessment of soil conditions. Read it before you cut a face into Perth sand behind a wall, because sand has effectively no cohesion and gives no warning before it goes.
Link checked 2 Aug 2026
- Freegovernment10 minPerth / WA
Building approvals — forms, fees and the Building Services Levy
Building and Energy, Department of Energy, Mines, Industry Regulation and Safety
Why this oneWhere the forms and the money live. It names every form you will touch — BA1 certified application, BA2 uncertified, BA3 certificate of design compliance, BA13 building approval certificate for work already built, BA20 and BA20A for adjoining owner consent — and publishes the current fees: 0.32% of the estimated value for an uncertified application and 0.19% for a certified Class 1 or Class 10 application, each with a $121 minimum, plus the Building Services Levy. Page last updated 23 July 2026.
Link checked 2 Aug 2026
The rules, with sources
WA regulation changes. Each point below names its primary source and the date it was last checked — always confirm with your own council before you build.
A building permit is not required for a retaining wall only if all three conditions are met: it retains ground no more than 0.5 m in height; it is not associated with other building work or with the protection of land adjoining the land it is on; and it is not work of a kind to which Building Act 2011 sections 76, 77, 78 or 79 relates.
Building Regulations 2012 (WA), Schedule 4 clause 2, item 6 ↗ · checked 2 Aug 2026
A retaining wall is an "incidental structure" under the Building Act 2011 section 3, which is what brings it inside the building permit system. It is not a Class 10a building, so the Class 10a concession that removed the registered building contractor requirement for work under $50,000 from 1 July 2026 does not apply to retaining walls.
Building Act 2011 (WA) section 3; Building and Energy ↗ · checked 2 Aug 2026
Doing building work without a building permit is an offence under Building Act 2011 section 9, carrying a fine of $50,000 for a first offence, $75,000 for a second, and $100,000 plus 12 months imprisonment for a third or subsequent offence.
Building Act 2011 (WA) section 9 ↗ · checked 2 Aug 2026
A permit authority may make a building order under Building Act 2011 section 110, and under section 112(2)(b) that order may require a person to demolish, dismantle or remove a building or incidental structure that has been built in suspected contravention of the Act.
Building Act 2011 (WA) sections 110 and 112 ↗ · checked 2 Aug 2026
Written consent from each affected adjoining owner is required before a permit is granted where work will encroach beyond the boundary (section 76) or adversely affect other land (section 77), and separately where work affects the structural, waterproofing or noise insulation capacity of a boundary retaining wall that protects adjoining land (section 79). Each carries a penalty of $25,000. "Adversely affect land" includes reducing the stability or bearing capacity of the land, damaging or reducing the structural adequacy of a structure on it, or changing natural site drainage. Consent is sought using form BA20 or BA20A, and the adjoining owner has 28 days to respond.
Building Act 2011 (WA) Part 6; Building and Energy, Work affecting other land ↗ · checked 2 Aug 2026
Under the R-Codes Volume 1 clause 5.3.7 deemed-to-comply requirements, retaining walls, fill and excavation behind the street setback must be set back from the lot boundary by at least the height of the works — 0 m for 0.5 m or less, 1 m for a 1 m wall, up to 3 m for a 3 m wall — measured from natural ground level at the lot boundary. Between the street boundary and the street setback, walls, fill and excavation are limited to 0.5 m above or below natural ground level.
Residential Design Codes Volume 1 (version dated 10 April 2026), clause 5.3.7, Table 4 ↗ · checked 2 Aug 2026
Under NCC 2022 Volume Two clause H1D3(2), Performance Requirement H1P1 is satisfied for an earth-retaining structure if it is designed and constructed in accordance with AS 4678. AS 4678 covers earth-retaining structures between 800 mm and 15 m in height.
Australian Building Codes Board, NCC 2022 Volume Two, Part H1 Structure ↗ · checked 2 Aug 2026
WA's building engineer registration scheme commenced 1 July 2024 under the Building Services (Registration) Act 2011. Registration of structural building engineers opened 1 July 2024 and a transition period applies until 1 July 2027, when registration becomes mandatory for all four prescribed areas. Performing building engineering work after that date without the required registration is an offence carrying a fine of up to $25,000. The scheme covers design work for a building or incidental structure.
Building Services Board / Building and Energy, Building engineering registration (page last updated 9 July 2026) ↗ · checked 2 Aug 2026
A permit authority must decide a certified building permit application within 10 business days and an uncertified application within 25 business days, excluding time spent awaiting determination of a related development application. If it does not decide in time the application is taken to be refused and the fee must be refunded.
Building Act 2011 (WA) section 23; Building Regulations 2012 (WA) regulation 20 ↗ · checked 2 Aug 2026
Current building permit fees are 0.32% of the estimated value of the work for an uncertified application and 0.19% for a certified Class 1 or Class 10 application, each with a minimum of $121. The Building Services Levy is 0.137% of the value of work over $45,000, with a minimum of $61.65 for work valued at $45,000 or less. For unauthorised work the levy doubles to 0.274%, minimum $123.30.
Building and Energy, Building approvals (page last updated 23 July 2026) ↗ · checked 2 Aug 2026
Under section 90 of the Water Services Act 2012, Water Corporation approval must be requested before carrying out works in, over, under or within prescribed proximities of their assets — including 2 m of a gravity sewer or main drain and 4 m of a water supply pipeline under 300 mm. Retaining wall applications are lodged through BuilderNet. Since 9 November 2025 offsets are measured from the edge of the pipe rather than the centreline.
Water Corporation ↗ · checked 2 Aug 2026