Block retaining walls in the Perth Hills
Updated October 2026
Block covers two quite different jobs that often get quoted as if they were one. At the low end, dry-stacked interlocking garden block builds a terrace or a planter in an afternoon with no mortar and no footing. At the high end, core-filled reinforced masonry on an engineered strip footing holds back a driveway, a pool surround or a cut into a slope. Both are block walls. They are not the same wall.
Interlocking garden block
The system most people picture: cast blocks that key into each other, laid dry, usually rated by the manufacturer for walls up to somewhere around 500 to 900mm depending on the product and the batter. No mortar, no steel, no concrete footing on most systems, which is why it is quick and cheap.
It is a genuinely good fit for the flatter end of this service area, the terracing, driveway edges and pool surrounds in Forrestfield, High Wycombe, Maida Vale, Wattle Grove, Midvale and Bellevue, where there is no slope to retain and the job is levelling a garden rather than holding a hillside. Work to the manufacturer's height rating, build to its setback and drainage detail, and it will last.
What it is not is a structural wall. If anything will drive, park or sit on the ground above it, the answer is the reinforced version below.
Core-filled reinforced masonry
The serious option. Reinforced block laid on an engineered strip footing, vertical steel through the cores, cores filled with concrete, and the whole thing designed for the load it is carrying. This is what holds up a driveway cut on a Lesmurdie or Roleystone block, and it is the material of choice where a wall has to be strong and have a clean rendered or painted finish.
On Hills ground the footing is the question. The Darling Plateau here is lateritic duricrust and pea gravel over weathered granite, and an engineered strip footing has to found properly in it. That can mean rock excavation, which costs more and takes longer than digging soil but gives you a footing that will not settle. It is also the reason an engineer gets involved earlier here than a Perth cost guide would suggest.
Drainage, which is not optional on either
Block holds soil. It does not hold water. Ag-pipe at the base, free draining gravel backfill, geotextile fabric to stop the gravel silting up, and a legal discharge point. On a reinforced wall, weep holes or a drainage layer behind the face as well. The Shire of Mundaring names heavy soils and perched water tables as Hills constraints, which in plain terms means water sits behind a wall here instead of soaking away. Our retaining wall drainage page explains the mechanics.
Where a property runs its own septic tank and leach drains or a secondary treatment system, the tank, the drains and the irrigation area decide where the wall and its drainage can go. Worth raising on the quote visit.
Guide pricing
As a rough 2026 guide, block and reinforced masonry walls in Australia typically run around $300 to $750 per metre for a wall about a metre high, interlocking garden systems at the lower end and core-filled reinforced work at the top, with some guides pricing engineered masonry above the range per square metre of face. Guide pricing only. The retaining wall cost guide covers what moves it, including how rock changes a Hills number.
Approvals, engineering and registration
In WA a retaining wall is exempt from needing a building permit only where it retains no more than 500mm of ground, is not tied to other building work or to holding up the land next door, and is not work of a kind that affects adjoining land. The measurement is the ground retained, not the wall height, and all three conditions have to be met, so a wall on or near a boundary needs a permit at any height. Note how that interacts with interlocking block: a product rated to 900mm does not exempt a wall retaining 900mm of ground. Development approval under the local planning scheme can be a separate question again. Confirm your wall with the Shire of Mundaring, the City of Kalamunda, the City of Swan or the City of Armadale, whichever is your permit authority, and have your builder lodge a free Before You Dig Australia (BYDA) enquiry before digging.
On who may carry out the work, WA draws the line by how the work is classified under the building legislation, not by a dollar threshold you can apply to your own job, and the position for a standalone retaining wall is not something to take from a website. Ask any builder what registration or licence they hold and verify it with Building and Energy, and ask your permit authority what your wall requires.
How the referral works
Perth Hills Retaining Walls is a referral service. Tell us what you need through the form and we pass it to an experienced, insured local builder who works your suburb. They call you back with a free quote, no obligation. Comparing options? See concrete sleeper walls and limestone retaining walls.
Frequently asked questions
How high can interlocking garden block go without engineering?
It depends on the product, and the manufacturer's rating is the number that matters, commonly somewhere around 500 to 900mm for dry-stacked systems with the correct batter and drainage. That is a structural rating, not an approval. In WA a wall retaining more than 500mm of ground needs a building permit regardless of what the block is rated to, so the two questions have to be answered separately.
What is the difference between block and concrete sleeper for the same job?
Block gives you a continuous masonry face that can be rendered or painted and sits flush at the ends, which suits walls people look at. Concrete sleeper is usually faster and cheaper to build at the same height because the posts do the structural work. Where access is tight, sleepers often win. Where the finish matters, block often does.
Does a reinforced block wall need an engineer?
Nearly always, and certainly if anything will sit, drive or park on the ground above it. Walls carrying a surcharge generally need engineering whatever their height, and several WA councils ask for a structural engineer's design on any wall needing a permit. That is applied through the permit application, so ask your permit authority what yours requires.
Can a block wall be built straight onto rock?
Often, and a sound rock foundation is as good as it gets for a masonry wall. The engineer decides how the footing keys into it. Budget for rock excavation, because that is the Hills cost nobody warns you about.