Planning and approvals
Do I need a building permit?
Retaining walls are building work in Western Australia. A building permit is commonly needed once a wall retains more than about 500 mm of ground, and some walls need one regardless of height because of where they are or what they hold up. Permits are issued by the City of Mandurah for lots in the City, and by the Shire of Murray for Pinjarra, Ravenswood, the Yunderups and nearby areas. Requirements change, so confirm with the council before work starts.
Does a boundary wall need anything extra?
Often. Walls and fill near a lot boundary can be affected by the Residential Design Codes, which deal with how close retaining and changes in ground level can be to the boundary. A wall that does not meet the standard settings may need a planning approval as well as a building permit. Talk to your neighbour early; work from their side may be needed, and a dividing fence often sits on top.
When does a wall need an engineer?
Taller walls, and walls that hold up a driveway, a building, a pool or other load, usually need a design from a structural engineer. Many concrete sleeper and segmental block products come with engineering tables for set heights and soils. Outside those, an engineer designs the footing and reinforcement.
What about underground services?
Before You Dig Australia is a free enquiry service that shows where registered underground services run. Your contractor should check it before digging. Private items such as septic tanks, leach drains, soak wells and reticulation are not on the register, so point them out.
Materials and design
Which wall type should I choose?
It depends on height, load, budget, look and the ground. As a rough guide:
- Low garden walls and terraces: limestone or timber.
- Straight boundary runs and pool surrounds: concrete sleeper.
- Tall or loaded walls: engineered block.
Why does sand keep leaking from my wall?
Because the joints are open and there is no fabric behind them, so every time water moves through the soil it carries fine sand out. The cure is geotextile fabric behind the wall. On an existing wall that usually means taking down and re-laying the affected section. See repairs and rebuilds.
Does every wall need drainage?
Practically, yes. Water behind a wall adds pressure and makes the soil heavier. A slotted pipe in drainage gravel at the base, with an outlet to somewhere suitable, is standard practice. In clay-loam around Pinjarra and on lots with high water tables, it is even more important.
Can a wall be built right next to the house?
Yes, but the wall must not interfere with the house footings, damp-proofing or termite management, and it should not direct water towards the slab. The contractor will consider how close the excavation can safely go.
Canal, estuary and coastal lots
I live on a canal. Can I fix the wall at the water's edge?
Possibly not on your own. Who owns and maintains water-facing walls differs between estates. Some are on the private lot; others are managed by the City or form part of shared canal infrastructure. Check with the City of Mandurah before any work on or near a canal or estuary wall. Our guide to sandy and canal-side blocks covers this in more detail.
Does salt air affect retaining walls?
It affects steel more than masonry. Steel posts, reinforcing near the surface, and fixings corrode faster near the ocean and on canal lots. Heavier galvanising, stainless fixings and good drainage help.
Working with the contractor
Who builds the wall?
This is a referral service. Walls are built by independent local contractors. We ask the contractors we work with to hold the licences and insurance the job needs. Ask to see them before work starts.
What should be on the quote?
The wall type and finish, length and height, footing, drainage, fabric, backfill, spoil handling, making good, and who handles permits and engineering. Our cost guide has a checklist.
Is the quote free?
Yes. Quotes are free, given on site, and there is no obligation to go ahead.