Building retaining walls: limestone, block and sleeper

Footings, the first course, drainage behind the wall, backfill material, geofabric and the reason most failed walls failed. Plus the honest point at which you stop and call an engineer.

⏱ 3 hAdvanced🔗 11 resources (10 free)

A retaining wall is the only thing in a suburban landscape that can kill someone. It is also the element most often built wrong on Perth blocks, because deep sand gives you nothing for free. It has no cohesion of its own, it flows when it is saturated, and it will find every part of the wall you did not drain.

Almost every failed wall in this city failed for one of three reasons: the footing sat on fill, the first course was not level, or water was allowed to build up behind it. None of those are visible once the wall is finished. All of them are decided in the first two days.

This lesson is the build method. The approvals detail sits in retaining walls approval; what follows is the short version of the law plus the sequence on the ground.

The legal line, before you touch a shovel

Schedule 4 item 6 of the Building Regulations 2012 (WA) exempts a retaining wall from needing a building permit only if all three of these are true. It retains ground no more than 0.5 m in height. It is not associated with other building work or with the protection of adjoining land. And it is not work of a kind to which sections 76 to 79 of the Building Act 2011 relate — that is, it does not encroach beyond your boundary, does not adversely affect a neighbour’s land, and is not a protection structure on someone else’s property.

Those conditions are cumulative, which is why so many 400 mm walls still need a permit. A low wall holding up the fill for a new alfresco slab is “associated with other building work”. A low wall right on the boundary that takes load off next door is protection of adjoining land. Both need a permit.

Planning approval is a separate question your council answers under the R-Codes and its own local policy, and it commonly bites lower than the building permit does. The City of Joondalup publishes the rule of thumb most councils work to: the minimum setback to a property boundary equals the retained height. Half a metre can sit on the boundary; a metre needs a metre; three metres needs three. Get your own council’s version in writing.

Three more things that catch people:

The party who changed the natural ground level owns the problem. Cut or fill, it is yours. And a dividing fence is not a retaining wall — see dividing fences.
Encroaching or adversely affecting the neighbour’s land without written consent carries a fine of $25,000 per offence under the Building Act.
Nobody’s registration protects you here. Retaining walls are classed as incidental structures and are exempt from occupational licensing in WA, so unlike most building work over $20,000 you need neither a registered building contractor nor owner-builder approval — at any value. The permit and the engineering are the only real checks in the system. Use them.

What a professional does at this stage

A landscaper pricing a wall is not pricing blocks. Blocks are the cheap, predictable part.

They price the footing, the drainage and the disposal of spoil, because those three are where the money and the risk live. Then they do four things before quoting:

Lodge a Before You Dig enquiry. A wall footing is a continuous trench, usually along a boundary, which is exactly where services run. Plans are indicative — you still hand-pothole. See locating services.
Check for a sewer or easement. Water Corporation names retaining walls specifically in its clearance rules, and a wall too close to a sewer either gets piled below the zone of influence or gets moved.
Establish natural ground level with a survey, not a tape and an opinion. Every approval, every setback and every neighbour dispute is measured from it. Carry the levels from levels, falls and datum.
Decide the engineer question honestly, before the design is emotionally settled.

When you stop and call an engineer

Call one if any of these apply. Not “consider it” — call.

The wall retains more than 0.5 m. You need a permit anyway, and engineer-designed, certified drawings are the cheapest way to get one.
There is a surcharge above the wall: a driveway, a parked vehicle, a pool, a shed slab, a second wall, or ground that keeps rising behind it.
The wall is on or near a boundary, or a neighbour’s structure sits within roughly a 45-degree line up from the base of your excavation.
The ground slopes below the wall, or you are terracing — two 800 mm walls stacked close together behave as one 1.6 m wall, not two small ones.
You hit groundwater, coffee rock, or uncontrolled fill in the footing trench.

AS 4678, the standard your engineer designs to, covers earth-retaining structures from 800 mm to 15 m. Below 800 mm you are relying on the manufacturer’s system limits and good practice, and there is no standard behind you.

Choosing the system

System	What it is	Perth reality	Where it fails
Limestone block (natural or reconstituted)	Gravity wall — mass resists the soil	The Perth default. Blocks are heavy: 500 x 350 x 200 mm is 63 kg, 500 x 350 x 350 mm is 115 kg, 1000 x 350 x 350 mm is 225 kg	Uneven first course; no drainage; blocks laid on fill; walls pushed past the height the mass can hold
Core-filled concrete block	Reinforced cantilever — steel and grout on a designed footing	Strongest option, always engineered, always a permit. Slowest and dearest	Starter bars in the wrong place, cores not filled solid, footing too shallow
Concrete sleeper in galvanised posts	Sleepers dropped between H-section posts concreted into holes	Fast, tidy, popular. Post footing is everything	Post holes too shallow for loose sand, posts out of plumb, no drainage aggregate behind
Treated pine sleeper in steel posts	Same geometry, timber panels	Cheapest. Finite life in Perth’s sand and irrigation	Under-specified timber treatment, and the wall quietly rotting from the buried face outward

For any timber wall, insist on the correct in-ground treatment level and expect a shorter service life than the rest of the garden. Budget for its replacement in staging the project.

The dangerous part

Read this before you book the machine.

Trench collapse. WorkSafe WA’s excavation code of practice is explicit: nobody works in an excavation 1.5 m or more deep unless it is shored or the sides are cut back to a safe slope by a competent person, and at that depth a second person must be in the immediate vicinity. Perth sand is not forgiving here — the code gives 1.5 horizontal to 1 vertical as the safe batter for poorly graded Bassendean sand and 1 to 1 for the angular Karrakatta and Spearwood sands. Which one you have comes straight out of Perth soils. Keep spoil and machinery at least 600 mm back from the edge, two metres where you can.

Silica dust. Cutting blocks, sleepers or capping dry produces respirable crystalline silica, which causes irreversible lung disease. Concrete is under 30 per cent silica by weight, and it does not take much. Cut wet, or use on-tool extraction, and treat a P2 respirator as the last layer rather than the plan.

Manual handling. There is no legal maximum lift weight in WA — the duty is to manage the risk. A 63 kg block is a two-person lift at best, and a 225 kg block is machinery. Plan the lift before you order the size.

Heat. This work is slow, heavy and outdoors. Perth summer means starting at first light and stopping, not pushing through.

Building it, in order

1. Footing on undisturbed ground

Dig to the depth in your design detail — not to where it “feels solid”. The footing must bear on undisturbed natural ground. If you hit fill, an old service trench, a stump hole or soft spot, you dig through it and bring the level back up with compacted material, not with more blocks.

For a gravity wall, that means a levelling pad of compacted crushed limestone or lean concrete, at least 150 mm thick and extending about 150 mm past both the front and back of the bottom block. For a core-filled block wall it means a reinforced concrete strip footing with starter bars, exactly as detailed. The bottom course of any wall should be buried, so the toe cannot be undermined by surface water or by someone later excavating on the low side.

2. The first course, dead level

This is the course everything else inherits. Set a string line from a datum, lay the first block, and check level along the wall and front to back. Then check it again after the next three.

Correcting a millimetre here costs a tap with a mallet. Correcting it at course six means either a visibly out-of-level cap or a growing wedge of packing that becomes the failure plane. Do not use bedding sand to fix a bad pad — pack out the pad, then reset.

3. Drainage behind the full height

More Perth walls fail from water than from mass. Saturated sand roughly doubles the pressure on the back of a wall, and it arrives all at once during a winter downpour.

Build a continuous column of clean drainage aggregate against the back of the wall — a minimum of 300 mm deep — and take it up the full height of the wall, stopping about 150 mm below finished surface so you can cap it with soil or mulch. Not a pocket at the bottom. The full height, or water perches on the backfill above it and never reaches the drain.

At the base, lay 100 mm slotted agricultural pipe in a sock, on a bed of aggregate, to a consistent fall, running the entire length of the wall. Then answer the question most installers never do: where does it discharge? Daylight at the low end, a weep through the face, or into the stormwater system — see drainage and soakwells. An ag pipe that ends in the sand is decoration.

4. Geofabric, or the drain silts up

Perth sand migrates. Without separation it works its way into the aggregate and blocks it within a couple of summers, and you will never know until the wall bulges.

Wrap the soil side of the aggregate column in a non-woven geotextile, lap the joins by about 300 mm, and take the fabric the full height. Do not wrap the wall side — water needs to get from the wall into the aggregate.

5. Backfill compacted in layers, as you go

Backfill rises with the wall, not after it. Place it in layers of 200 mm or less and compact each one before the next.

The rule that saves walls: within about 900 mm of the wall face, use only a hand-operated or walk-behind compactor. A ride-on roller or a big remote plate that close will push the wall out of line, and once a block wall has moved forward it does not go back.

Uncompacted backfill is the reason paving behind a wall dips two years later. It is the same failure as base preparation — sand that was never compacted finding its own density with your surface on top.

6. The top

Cap the wall, and get the surface water above it moving away from the wall, not over it. Water running over the face washes out joints and stains limestone permanently. If a fence is going on top, it belongs on the higher side.

Why most failed walls failed

If you audit failed walls around Perth, the causes are boringly consistent:

No drainage aggregate, or a shallow pocket instead of a full-height column
Ag pipe present but connected to nothing
No geotextile, so the aggregate silted up and became soil
Footing on fill or on an old service trench
First course not level, so the load path stepped instead of stacking
Backfill dumped and never compacted
A surcharge added later — a driveway, a pool, a shed — that the wall was never designed for
Built over 0.5 m with no permit, no engineer and no design

None of these are exotic. All of them are cheap to prevent and expensive to fix, because the fix starts with excavating everything you put behind the wall.

What happens next

Once the walls are up, drained and backfilled, you have created the finished levels that every hard surface sits on. The next lesson takes those levels and builds the compacted base that paving, concrete and liquid limestone depend on — and the compaction discipline is exactly the same one you have just used behind the wall.

Checklist

Footing dug to design depth on undisturbed ground
First course perfectly level — everything above depends on it
Aggregate drainage and agricultural pipe behind the full height
Geofabric separating drainage aggregate from backfill sand
Backfill compacted in layers as the wall goes up

Watch

How to Build a Retaining Wall | DIY Made Easy | Adbri Masonry

Adbri Masonry12:13🇦🇺 Australian

Twelve minutes covering the whole sequence on an Australian block: setting out, excavating the trench, the levelling pad, getting the first course level, drainage aggregate and pipe, and backfilling as the courses go up. It is a manufacturer's video for its own segmental system, which means the method shown is the method the product is warranted against.

Change this for Perth

Eastern-states product and eastern-states soil. The technique transfers; the ground does not. On Perth sand you must add the geotextile separation layer between drainage aggregate and backfill, which this video treats as optional, and expect the trench sides to slump rather than stand.

Retaining Wall Heights Explained with Jason Hodges

Adbri Masonry2:51🇦🇺 Australian

Three minutes on the exact question this lesson has to answer — how high you can reasonably build yourself, when you bring in professionals, and when the reinforcement has to be engineer-designed. Useful as a sanity check on your own ambition before you order materials.

Change this for Perth

The heights quoted are the manufacturer's system limits and reflect eastern-states council practice. In WA the legal trigger is lower and unambiguous: a building permit is required once the wall retains more than 0.5 m. Use the video for the engineering reasoning, not for the threshold.

How to install a concrete sleeper retaining wall

Outback Fencing9:17🇦🇺 Australian

The clearest free walkthrough of a galvanised-post-and-concrete-sleeper wall, which is the fastest-growing system in Perth backyards. It shows post hole spacing and depth, concreting the posts, checking the line and level before the concrete goes off, and dropping sleepers in — the stage where an out-of-plumb post becomes permanent.

Change this for Perth

Filmed on the east coast promoting a specific proprietary system. The critical Perth adaptation is the post footing: in loose sand a hole that would hold in clay will not, so post depth and concrete volume are exactly what your engineer's detail should specify rather than what the video shows.

Where to go deeper

Every link below was fetched and checked before it shipped. Nothing here is a guess.

Freegovernment10 min for Schedule 4Perth / WA
Building Regulations 2012 (WA) — Schedule 4, building work that does not require a building permit
Parliamentary Counsel's Office, Government of Western Australia
Why this oneThe primary source for the number everybody quotes and almost nobody reads. Download the current consolidated version and go to Schedule 4 item 6, which exempts a retaining wall only if it retains ground no more than 0.5 m in height, is not associated with other building work or with the protection of adjoining land, and is not work to which sections 76, 77, 78 or 79 of the Building Act 2011 relate. Those three conditions are cumulative, which is why so many sub-500 mm walls still need a permit.
Change this for Perth
The version current when this was checked started on 23 July 2026, suffix 04-ae0-01. Always download the version marked Current rather than a cached PDF, and read the exemption alongside your local government's planning rules, which are separate and often tighter.
Link checked 2 Aug 2026
Freegovernment20 minPerth / WA
Retaining walls and site works
City of Joondalup
Why this oneThe clearest local-government explanation in Perth of the two separate approvals — development (planning) approval and a building permit — and how they interact. It publishes the setback table most people never see, where the minimum setback to a property boundary equals the retained height (0.5 m retained needs 0 m, 1 m needs 1 m, 3 m needs 3 m), states that the party who altered the natural ground level is the party responsible for the wall, confirms a dividing fence does not qualify to retain soil, and sets out the dispute process including a contour and feature survey.
Change this for Perth
This is one council's policy. The 0.5 m building permit trigger comes from state regulation and is the same everywhere in WA, but the setback table, street-setback heights and screening rules are Joondalup's own. Get your own council's equivalent page in writing before you design.
Link checked 2 Aug 2026
Freegovernment1 h for the relevant sectionsPerth / WA
Excavation: code of practice
WorkSafe WA, Department of Energy, Mines, Industry Regulation and Safety
Why this oneThe only excavation safety document written for WA ground, and it names our soils directly. It gives safe batter slopes by soil type — 1.5 horizontal to 1 vertical for poorly graded sands such as Bassendean sand, 1 to 1 for the angular well-graded Karrakatta and Spearwood sands — plus the rule that nobody works in an excavation 1.5 m or more deep unless it is shored or cut back, the requirement for a second person in the immediate vicinity at that depth, and the 600 mm minimum clearance for spoil from the edge (two metres where possible).
Change this for Perth
Published 2014 and last updated November 2024, so it still cites the old Occupational Safety and Health Regulations 1996 numbering (regulations 3.111, 3.112) rather than the Work Health and Safety (General) Regulations 2022 that now apply. The regulation numbers have moved; the engineering advice and the soil-specific batter slopes have not.
Link checked 2 Aug 2026
Freegovernment15 minPerth / WA
Managing crystalline silica dust in the workplace
WorkSafe WA, Department of Energy, Mines, Industry Regulation and Safety
Why this oneRead this before you put a blade into a block. It names the exact tasks that generate respirable crystalline silica — angle grinding, jack hammering and chiselling of concrete or masonry, brick, concrete or stone cutting, and dry concrete cutting — gives the silica content of the materials (concrete less than 30 per cent, engineered stone up to 97 per cent), and sets the control hierarchy: wet cutting first, on-tool extraction second, respiratory protection only as a supplement.
Link checked 2 Aug 2026
Freestandard2 h+Australian
Retaining structures technical manuals (RW01, RW02, RW03, TP14)
Concrete Masonry Association of Australia
Why this oneThe Australian industry body's own design manuals, written to AS 4678 and free once you create an account. RW03 covers gravity retaining walls, which is what a limestone block wall actually is; RW01 covers reinforced cantilever walls, which is what a core-filled block wall on a designed footing is; RW02 covers reinforced soil walls. If you want to understand what your engineer is doing rather than just paying for it, these are the documents to read.
Change this for Perth
Registration is required to download — the manuals themselves cost nothing. These are engineering design documents aimed at architects, engineers and builders, not step-by-step installation guides, and they assume you have already decided the wall needs designing.
Link checked 2 Aug 2026
Freearticle30 minOverseas — adapt it
Guide to Segmental Retaining Walls (SRW-TEC-005)
Concrete Masonry and Hardscapes Association
Why this oneThe best free document on the construction numbers nobody publishes: a levelling pad at least 150 mm thick extending about 150 mm past the toe and heel of the bottom unit, drainage gravel a minimum of 300 mm deep behind the units, a geotextile filter between the gravel and the soil backfill, and backfill compacted in lifts of 200 mm or less. Its most useful single rule is that within about 900 mm of the wall face you use only hand-operated or walk-behind compaction equipment — heavy plant that close pushes the wall out.
Change this for Perth
North American document in imperial units. Ignore the freeze-thaw and frost-depth material entirely. Substitute compacted crushed limestone for the crushed-stone levelling pad, since that is the Perth standard and it self-cements when laid damp and compacted in layers. Its drainage advice is if anything conservative for Perth sand — but the sand is exactly why the geotextile separation matters more here, not less.
Link checked 2 Aug 2026
Paid · $342.21 hard copy, web reader licences from $308.30 (checked 2 August 2026)standardAustralian
AS 4678-2002 Earth-retaining structures
Standards Australia
Why this oneThe standard your engineer will design to, and the one referenced by the National Construction Code for earth-retaining structures. It is 117 pages, currently listed as Pending Revision, and it is genuinely written for engineers rather than builders. Buy it only if you intend to check a design; otherwise the free CMAA manuals above summarise what it requires for the wall types you are likely to build.
Change this for Perth
AS 4678 applies to earth-retaining structures between 800 mm and 15 m in height, so it does not cover the sub-800 mm walls that make up most suburban landscaping. Below that height you are relying on the manufacturer's system limits and good practice, not a standard.
Link checked 2 Aug 2026
Freetool10 min to lodgeAustralian
Before You Dig Australia
Before You Dig Australia
Why this oneOne free enquiry returns plans from every participating utility for your work site instead of you contacting each one separately. A retaining wall footing is a continuous trench, often along a boundary, which is precisely where power, gas, water, comms and old irrigation mains run. Lodge it before you book machinery, not the morning you dig, because plans are indicative and you still have to pothole by hand to prove location.
Link checked 2 Aug 2026
Freegovernment15 minPerth / WA
Building on a residential property (working near Water Corporation assets)
Water Corporation
Why this oneWater Corporation names retaining walls explicitly alongside houses, sheds, garages, carports and pools as structures that must clear its sewers, and explains the two clearance regimes: structures without piles cannot come as close, while structures founded on piles or footings taken below the zone of influence may be allowed closer. If a sewer or an easement crosses your block, this determines where the wall can go before any design work starts.
Change this for Perth
The page points to the Residential Guidelines for Designers for the actual clearance dimensions rather than publishing them inline, so you will need to lodge an enquiry or read that document for the numbers that apply to your pipe and depth.
Link checked 2 Aug 2026
Freegovernment15 minPerth / WA
Owner-builder approval
Department of Local Government, Industry Regulation and Safety
Why this oneThe page that resolves the licensing question for retaining walls, and the answer surprises people. It confirms that a registered building contractor or owner-builder approval may be needed where a building permit is required and the work exceeds $20,000, but also states that 'incidental structures' — naming swimming pools, retaining walls, fencing and patios — are exempt from the need for occupational licensing. It also warns that work which is substantially one job must not be split into sub-$20,000 projects to dodge licensing.
Change this for Perth
Exempt from licensing is not exempt from a building permit. A wall retaining more than 0.5 m still needs a permit, still needs to satisfy the permit authority, and the owner still carries the liability if it moves.
Link checked 2 Aug 2026
Freesupplier5 minPerth / WA
Limestone blocks Perth — sizes and weights
Meteor Stone
Why this oneA published size and weight table for the reconstituted limestone blocks actually sold in Perth, which is the information you need to plan lifting and courses. The common 500 x 350 x 200 mm block is 63 kg, a 500 x 350 x 350 mm block is 115 kg, and a 1000 x 350 x 350 mm block is 225 kg. Those numbers decide whether the wall is a two-person job, a machine job, or a job you should not be doing.
Change this for Perth
This is a Perth stone supplier's own product page and it exists to sell blocks. The dimensions and weights are the useful part and match what the trade uses; price-check against other WA block yards, and note the page publishes nothing about footings, drainage or maximum heights.
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 retaining wall does not require a building permit in WA only if it satisfies all three conditions in Schedule 4 item 6 of the Building Regulations 2012: 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 on which it is located; and it is not work of a kind to which section 76, 77, 78 or 79 of the Building Act 2011 relates.
Building Regulations 2012 (WA), Schedule 4 item 6, consolidated version current from 23 July 2026 ↗ · checked 2 Aug 2026
A person responsible for work must ensure that no part of a building or incidental structure is placed beyond the boundaries of the works land, and that the work does not adversely affect land beyond those boundaries, without the consent of each affected owner or a court order. The penalty for each offence is a fine of $25,000.
Building Act 2011 (WA), sections 76 and 77, consolidated version current from 28 May 2026 ↗ · checked 2 Aug 2026
Retaining walls are 'incidental structures' and are exempt from the need for occupational licensing in WA, so neither a registered building contractor nor owner-builder approval is required to build one. Most other building work valued at $20,000 or more that requires a building permit must still be carried out by a registered builder, and from 1 July 2026 the threshold for Class 10a buildings such as sheds, carports and private garages rose to $50,000.
Department of Local Government, Industry Regulation and Safety, and Building and Energy ↗ · checked 2 Aug 2026
A person must not work in an excavation 1.5 metres or more deep that is not protected by shoring, and must not do that work without at least one other person present in the immediate vicinity, unless a competent person has assessed the sides as self-supporting by virtue of their slope or stability. Excavated material, plant and equipment should be kept at least 600 mm from the edge of an excavation, and two metres where possible.
WorkSafe WA, Excavation: code of practice ↗ · checked 2 Aug 2026
WA's crystalline silica substance provisions in the Work Health and Safety (General) Regulations took effect on 1 September 2024. A crystalline silica substance is any material containing at least 1 per cent crystalline silica by weight, and processing includes cutting, grinding and drilling with power tools.
WorkSafe WA, Crystalline silica substances regulations information sheet ↗ · checked 2 Aug 2026
Responsibility for constructing a retaining wall falls to the party altering the land's natural slope, whether by cutting or filling, and a dividing fence does not qualify to retain soil. Where planning approval is not triggered, the City of Joondalup requires a minimum setback to a property boundary equal to the retained height — 0 m at 0.5 m retained, 1 m at 1 m, 2 m at 2 m and 3 m at 3 m.
City of Joondalup ↗ · checked 2 Aug 2026