Uphill Neighbours' Half Share of One Failed Wall Topped Three Typical New Walls

Retaining wall approval heights by state

Queensland's Building Regulation 2021 lets an owner build a retaining wall without building approval when the wall and the fill or cut it holds total no more than 1 m. The wall must also sit at least 1.5 m from a building or another retaining wall, with no surcharge loading the soil behind it. Western Australia's Building Regulations 2012 set a lower bar. A wall needs no permit only if it retains no more than 0.5 m and is not tied to other building work or to protecting the neighbour's land. Some WA councils go further. The Shire of Capel requires a permit for any wall along a boundary whatever its height, and the Shire of Denmark requires both planning approval and a building permit over 500 mm.

In Tasmania, the Director's Determination on categories of building work (as at version 1.4, applying from April 2021) lets an owner build without a permit if the wall retains no more than 500 mm within 1.5 m of a boundary, road or right of way, or no more than 1.2 m elsewhere. The ACT runs two tests. ACT Planning says Schedule 1 of the Building (General) Regulation allows a wall up to 1.2 m without building approval, or up to 1.5 m if it complies with the exempt building code, but under the planning regulation a wall within 1.5 m of a side or rear boundary is exempt from a development application only up to 0.4 m. In South Australia, the Legal Services Commission's Law Handbook, which summarises the Planning, Development and Infrastructure Act 2016 and its 2017 regulations, says development approval is not usually needed for a wall retaining 1 m or less, though some zones and council areas set lower limits.

Victoria's Building Regulations 2018 exempt a retaining wall under 1 m from a building permit if it is not tied to other building work or to protecting an adjoining property, and Boroondara and Hume councils say the same. Some Victorian councils add their own boundary rules. The City of Greater Bendigo says a wall on or near a boundary needs a permit at any height. The NSW figure rests on council guidance, because the text of the State Environmental Planning Policy (Exempt and Complying Development Codes) 2008 would not load. Wollondilly Shire Council's fact sheet says that under the SEPP a wall is exempt only if it stands no higher than 600 mm above existing ground and at least 1 m from any boundary. The same typical retaining wall ($9,000) can be exempt in one state and need a permit in the next, depending on its height and how close it sits to the boundary.

When a retaining wall needs a structural engineer

The National Construction Code points to AS 4678 as the standard for earth-retaining structures, and its explanatory information says the standard covers walls from 800 mm to 15 m high. AS 4678 sorts walls by the consequence of failure. In Goulburn-Murray Water's reproduction of the standard's Table 1.1, Class A walls are those whose failure would cause minimal damage, typically under 1.5 m high.

States and councils set their own engineering triggers. In Victoria, Macedon Ranges council says a wall 1 m or higher needs a permit, with a structural engineer's design and certification in the application. Tasmania's Director's Determination allows a licensed builder to build a wall retaining up to 1.8 m as low-risk work only if an engineer designs it. In South Australia, the City of Onkaparinga generally limits moss rock, dry stone and modular block walls to 2 m and requires an engineer to certify the location and design.

Some NSW councils go further than the state. Muswellbrook Shire Council's policy says any wall on or within 1 m of a boundary and over 500 mm high must be designed and certified to AS 4678 by a practising structural engineer. That is a local rule, and owners elsewhere in NSW should check their own council. Going Rate tracks a structural engineer's hourly rate ($200) separately from the wall itself.

What a 60-year design life means for a retaining wall

The ABCB says a retaining wall tied to a residential dwelling must have a design life of at least 60 years under AS 4678, and that those provisions are normative, so they must be followed. A wall in the garden with no link to the house is a different matter, the ABCB says, and its designer has to settle on a design life another way. Goulburn-Murray Water also specifies a minimum design life of 60 years for retaining walls on waterway banks.

A design life is a requirement the engineer designs to. It does not guarantee the wall will stand for 60 years, and it does not apply to every garden wall. The ABCB's figure comes from its video explainer on AS 4678, and Going Rate did not review the standard itself.

Muswellbrook council turns the 60 years into a materials rule. For walls on or within 1 m of a boundary and over 500 mm high, it requires materials with a design life of at least 60 years, such as masonry, concrete or stone, and it does not permit treated pine. An owner planning a typical retaining wall ($9,000) next to the house should ask whether the design life requirement applies before choosing a material.

Sleeper, block or rock: what each material is rated for

Concrete sleeper systems come with manufacturer warranties. Bunnings lists Austral Masonry's Pioneer reinforced concrete sleeper with a 35-year warranty and markets it for walls up to 3 m high. That is a retail claim, Going Rate did not review the warranty terms, and a warranty on the sleeper does not cover the design or the installation. A 3 m wall is well above the approval height in every state covered here. A typical concrete sleeper wall ($10,300) sits under the same height rules as any other material.

Brickworks says standard units in the Keystone KeyMass segmental block system work as a gravity wall for low, non-critical walls up to 1.2 m, and up to 4.4 m with no-fines concrete backfill. Those are manufacturer figures for one product system. Above the state approval heights, a typical besser block wall ($11,500) needs the same permit and engineering checks as a sleeper wall.

Rock walls face their own limits in some council areas. In Onkaparinga, moss rock and dry stone walls are generally capped at 2 m and need an engineer to certify the location and design, so a homeowner there pricing a typical rock wall ($11,500) should allow for that sign-off. Timber is harder to rate. WoodSolutions lists the AS 5604 natural durability classes, from more than 25 years in-ground for Class 1 down to under 5 years for Class 4, but those ratings apply only to heartwood. Sapwood counts as non-durable whatever the species, and no official source gives a lifespan in years for treated pine sleepers.

When a boundary retaining wall fails, who carries the bill

Fangyuan v Stockwell shows the size of a failure bill. The wall was timber, about 13 m long and 1.6 to 2.4 m high, built along a Wishart boundary in 2004 without approval. Part of it collapsed after heavy rain in about February 2022. The court found that work by the uphill neighbours, the Stockwells, contributed, including six added sleepers, at least 400 mm of extra soil, trees and a large deck, and that decayed post bases were also a cause. The parties agreed the replacement would cost $61,006, and in November 2024 the District Court apportioned 50% responsibility to the Stockwells. It found the previous owner who built the wall was also at fault. The court gave judgment for the downhill owner and asked for submissions on the form of the orders and costs, so the judgment sets no final amount and does not say anyone has paid.

At Going Rate's prices, the Stockwells' half share comes to more than three times a typical retaining wall ($9,000), and the full agreed cost to nearly seven. Measured against a typical concrete sleeper wall ($10,300), the half share is nearly three. The Fangyuan wall was much bigger than a typical wall and well above every state's approval height, so the ratio shows the scale of a failure bill. It does not compare like with like.

Three Queensland tribunal decisions put the cost on whoever benefits from the wall. In Ramsay v Earl in 2025, QCAT's appeal tribunal said responsibility for a retaining wall rests upon a party who has the benefit of it, and refused leave to appeal an order that the applicant pay the entire cost of a new concrete wall replacing old timber sleepers. In Zacaropoulos v Davison in 2022, QCAT found the wall benefited the applicant's property and ordered him to pay all of the removal and the new wall. In Neate v Zillotti in 2022, the appeal tribunal removed an order for a neighbour to pay 50% of a retaining wall below a 62 m fence, because the tribunal had no jurisdiction to order a contribution to that work. In ABC News' 2023 Law Report live blog, Peter Clarke said that in most cases each neighbour is jointly responsible for a failed boundary fence and wall, and a neighbour who wants to avoid paying half needs proof of what caused the failure.

Dividing fence laws and retaining walls

In most states the dividing fence rules stop at the wall. The NSW Dividing Fences Act 1991 excludes retaining walls from its definition of a fence, except for a footing or support the fence needs, Wollondilly council's fact sheet says. Legal Aid NSW says NCAT will not hear a retaining wall matter without evidence the wall is needed to support a dividing fence, so most disputes go to the NSW Supreme Court. The State Library of NSW says section 177 of the Conveyancing Act 1919 creates a duty not to remove the support of neighbouring land.

South Australia splits the cost by what each side's land puts on the wall. The Law Handbook says that where one party fills and the other excavates, each is liable in proportion to the fill or excavation the wall supports. In Western Australia, the City of Canning says the person who fills above or cuts below natural ground level at the boundary is responsible for a suitable retaining wall.

Queensland adds licensing. Business.gov.au says a QBCC structural landscaping licence is needed for work valued over $3,300, and a typical retaining wall ($9,000) at Going Rate's prices is more than two and a half times that threshold. The QBCC says an unlicensed man was convicted and fined a total of $8,000 over a retaining wall, fence, landscaping and drainage job on the Sunshine Coast between April and October 2023, and was ordered to pay the homeowner compensation.

Home insurance and collapsed retaining walls

Neither home policy checked here covers retaining walls in a flood. AAMI's home building key facts sheet, prepared in October 2024, gives no flood cover for retaining walls, sea walls, garden borders or free-standing outdoor walls. CHOICE reports that NRMA's Standard home policy gives no cover for retaining walls under flood, storm and cyclone, storm surge and accidental damage. Owners should read the full product disclosure statement before relying on any cover.

Collapses tend to follow rain or digging. In 2019 the St George and Sutherland Shire Leader reported that about 20% of a wall on a steep Woronora site collapsed after prolonged heavy rain, and Sutherland Shire Council required the owner to re-engineer the design. In June 2026, ABC News reported Burnie residents beside a Homes Tasmania excavation describing land slipping and a two to three metre drop at the edge of one backyard.

A rebuild can involve more than the wall. Clearing slumped soil and reshaping the ground is excavation work, priced by Going Rate as a typical excavation job ($7,750), and restoring the garden above is landscaping, priced as a typical landscaping job ($17,500). Without insurance, those costs fall on the owners and on how a court or tribunal splits the responsibility.

Common questions