Updated October 2026
Greenmount sits right where Great Eastern Highway starts to climb the scarp, and it is one of the localities named on the primary record as sitting at the Darling Scarp's western edge. The Welcome to Perth Hills signs go up on Greenmount Hill for a reason. We connect you with builders who cover the 6056 area.
Common wall situations in Greenmount
Blocks that step up or down from the street, older housing stock, and a lot of walls built in the 1960s and 1970s that are reaching the end of their life. The jobs are driveway cuttings, terracing, and replacing failed walls, often with tight access between the house and the boundary.
The Shire of Mundaring's strategy named Greenmount among the foothills suburbs with unsewered residential areas, and recommended the Shire lobby for reticulated sewerage to be extended to them. So it is worth establishing which your block is on before the wall is designed, because an on-site system constrains where the wall and its drainage can go.
The ground under Greenmount
Rock, not sand, is what decides a price here. The City of Kalamunda has it in writing that hard granite sits close to the surface across the Hills and is costly to dig through, which is exactly the problem a post hole or an engineered footing runs into. Rock drilling or coring takes longer and costs more, and it is the most common reason a Hills quote reads above the Perth average.
Water is the failure mode. On ground where rock stops it draining down, it runs along the rock until it finds the back of a wall. A quote that does not itemise ag-pipe, gravel backfill, fabric and a discharge point is a cheaper wall that fails sooner.
What a wall costs in Greenmount
Guide pricing only: roughly $200 per metre at the timber end up to $700 or more per metre for stone and engineered block, for a wall about a metre high, from published Australian cost guides. Ground conditions and access move it more here than almost anywhere. See the retaining wall cost guide.
Approval, and who to ask in Greenmount
Approval in WA turns on 500mm of retained ground, not on the height of the wall, and the exemption only applies where the wall is also clear of other building work and is not holding up or affecting the land next door. All three have to be true at once. A wall on or at a boundary is dealt with separately under the Building Act and needs the neighbour's consent or another authority whatever its height. Development approval under the local planning scheme can apply as well, so confirm the position with the Shire of Mundaring before anything is quoted.
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 a homeowner can apply to their 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. Have the builder lodge a free Before You Dig Australia (BYDA) enquiry before anything is dug.
Frequently asked questions
Is Greenmount hilly?
Yes. It is one of the sixteen localities named on the primary record as sitting at the scarp's western edge, and the highway climbs through it. The level suburbs in this service area are further out on the plain.
Is my Greenmount block on sewer?
Worth checking. The Shire of Mundaring's strategy named Greenmount as having unsewered residential areas and recommended lobbying for sewerage to be extended, so both situations exist here. The Shire holds the records.
Tight access between the house and the fence. What are my options?
Smaller units placed by hand, usually, which trades material cost for labour cost. A builder will assess whether any machine can get to the wall line before quoting a method.
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