Updated October 2026
Boya is a small locality at the western edge of the scarp below Darlington, named on the primary record among the localities sitting at the scarp's edge. Small suburb, real slope. We connect you with builders who cover the 6056 area.
Common wall situations in Boya
Blocks that step, older stock, and walls that went in without drainage behind them. The jobs are terracing, driveway edges and cuttings, and replacement work. Access varies a lot block to block here, so it is the first thing a builder looks at.
The Shire of Mundaring's strategy named Boya among the foothills suburbs with unsewered residential areas and recommended lobbying for reticulated sewerage to be extended to them. Establish which your block is on, because an on-site system decides where the wall and its drainage can sit.
The ground under Boya
Perth is a sand city. Up here it is not. The ground is ironstone and laterite gravel over weathered granite, and the City of Kalamunda records in its Local Planning Strategy that reticulated sewerage is constrained in the Hills because hard granite sits close to the surface and is costly to dig through. That same rock is what a post hole has to get through, so ask any builder how the quote prices a hole that hits it.
Drainage is the thing that actually matters. Water that cannot soak away through rock travels sideways and arrives behind the wall, and the Shire of Mundaring names heavy soils and perched water tables as Hills constraints for that reason. Ag-pipe, free draining gravel, geotextile fabric and a lawful discharge point are not optional line items.
What a wall costs in Boya
As a rough guide, most residential walls run from around $200 to $700 or more per metre for a wall about a metre high, depending on material, height, access and engineering. Those are published Australian guide figures rather than a quote, and rock is the reason a Hills number can sit above them. Read the retaining wall cost guide and then get a price for your block.
Approval, and who to ask in Boya
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 the wall retains, not the height of the wall, which catches a lot of people out. All three conditions have to be met, so a wall on or near a boundary needs a permit whatever its height. Development approval under the local planning scheme can be a separate question again, and the rules change, so confirm your wall with the Shire of Mundaring before you build.
Who is allowed to build it is a statutory question in WA, and it turns on how the work is classified under the building legislation rather than on a figure you can look up and apply yourself. We are not going to settle that on a web page. What is worth doing is simple: ask the builder what registration or licence they hold, check it with Building and Energy, and ask your permit authority what your particular wall requires before you sign anything. Before any digging, your builder should lodge a free Before You Dig Australia (BYDA) enquiry so underground services are located.
Frequently asked questions
Is Boya on the scarp?
Yes. It is one of the localities named on the primary record as sitting at the Darling Scarp's western edge, alongside Greenmount, Swan View, Helena Valley and Darlington.
What is under the soil here?
Likely laterite and ironstone gravel over weathered granite, with rock possible in the post holes. It is not the soft ground that Perth cost guides assume.
Who do I ask about approval?
The Shire of Mundaring, as the permit authority. A wall retaining more than 500mm of ground needs a building permit, and so does a wall on or near a boundary at any height.
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We also cover nearby Greenmount and Darlington.