Retaining walls: when you need a permit.

Under the Western Australian Building Regulations 2012, a retaining wall is exempt from needing a building permit only if it satisfies both of two tests. It must be less than 500mm high, and it must be not supporting a surcharge. People remember the first and forget the second, and the second is where the trouble lives.

A surcharge is any additional load sitting behind the wall on top of the soil's own weight. A driveway is a surcharge. A pool is a surcharge. A shed, a slab, a retaining wall further up the slope, a parked car, and a slope that keeps climbing behind the wall are all surcharges. So is your neighbour's soil, which is why boundary walls are almost never exempt. In practice this means a modest 400mm garden edge holding nothing but a flat garden bed is exempt, while a 400mm wall holding up the edge of your driveway is building work needing a permit from the City of Greater Geraldton. Same height, completely different legal position.

This matters far more in Geraldton than in a flat suburb, because so much of our work is on slope. Mount Tarcoola is elevated and sloping almost throughout, so the walls there are frequently structural, frequently over 500mm, and frequently carrying a driveway or a level pad above them. Around Drummond Cove the blocks fall away toward the dunes, which is the same problem in the other direction. If a contractor looks at a sloping Geraldton block and tells you no permit is needed without asking what is behind the wall, that is your signal to get another quote.

What a permitted wall actually involves.

Once you are over the line, there is a sequence, and it is not as painful as it sounds. First a structural engineer designs the wall to AS 4678, the Australian Standard for earth-retaining structures. They will want to know the height, the length, the surcharge, the soil, and the drainage. Block and masonry work also has to satisfy AS 3700, and the National Construction Code sits over the top of both.

Then a building permit application goes to the City of Greater Geraldton. There are two routes. A certified application is lodged with a Certificate of Design Compliance from a registered building surveyor, and the City has a shorter statutory window to determine it, broadly 10 business days. An uncertified application, which is available for this class of work, is assessed by the City's own building surveyor, and the statutory window is longer, broadly 25 business days. Neither clock starts until the application is complete, and both pause if the City asks a question.

The corrosion detail everyone inland gets to ignore.

Here is the piece of local grounding that generic advice will never give you. Geraldton sits in a severe marine atmospheric environment. Within roughly a kilometre of the surf, out at Tarcoola Beach, Glenfield and the northern beaches, the airborne salt load is high enough that ordinary galvanised steel is on a much shorter clock than it would be in Perth's eastern suburbs, let alone somewhere inland. Any steel in the wall, whether it is post-and-panel uprights, reinforcement in a core-filled block wall, or the fixings, needs a corrosion spec written for that environment.

This is a real, expensive failure mode. A wall whose blocks are perfect and whose internal steel has rusted is a wall that fails without warning, and it fails from the inside where you cannot see it coming. An engineer who does not ask which part of Geraldton the wall is going in is not asking enough questions. The same salt driver is why we spec paving the way we do, which is covered on the coastal wind guide.

Your neighbour, and why fencing law does not help.

Boundary retaining is the most common source of genuine disputes we see. Two things to know. First, if any part of the work, including the footing, the drainage layer or just the excavation batter, will encroach onto or affect the adjoining land, you need that owner's written consent before a permit can issue under the Building Act 2011. Not a chat over the fence. Written consent, lodged with the application.

Second, and this surprises people every time: the Dividing Fences Act does not cover retaining walls. There is no automatic 50-50 cost-sharing the way there is for a colorbond fence. Whoever needs the retaining generally pays for the retaining. If your neighbour is happy to contribute, wonderful, get it in writing before the job starts rather than after. Sorting this out early is free. Sorting it out after the blocks are on site is not.

A worked example: the 12 metre Mount Tarcoola wall.

Take a common one. A 12 metre long limestone block wall, 900mm high, holding back the cut for a level driveway on a sloping Mount Tarcoola block. The wall face is 12 times 0.9, so 10.8 square metres. At $350 to $650 per square metre of face, with drainage, that is roughly $3,800 to $7,000.

It is over 500mm and it carries a driveway surcharge, so it is permitted work. Add $800 to $2,200 for the engineer's design and the City of Greater Geraldton building permit application. The permit fee itself is set by state regulation as a percentage of the estimated value of the work with a minimum charge, and WA adds a Building Services Levy plus a Construction Training Fund levy on work valued over $20,000. Your total lands around $4,600 to $9,200, and the paperwork is roughly 10 to 25 percent of it. Then the driveway paving on the level pad above is a separate line at $75 to $170 per square metre. The full rate card is on the pricing page.

Timing, and the mistake to avoid.

Allow four to eight weeks from first call to first dig: one to three weeks for the engineer, then the City's statutory determination window, then a buffer for questions. The mistake we see constantly is homeowners choosing block colours and booking a start date before the design exists. Start the engineering first. It runs on its own clock and it does not care what the weather or your calendar is doing, which is worth knowing when you are planning around the best paving season. One more thing: before anyone excavates, services need locating. That is not a formality on a Geraldton verge.