Why concrete sleepers suit Wollondilly blocks
Concrete sleepers are termite-proof and rot-proof, which matters on blocks where timber walls have already failed. They go up quickly between galvanised H-beam or C-channel posts, and they make a solid base for boundary fencing mounted on top.
On reactive clay, the posts do the real work. Post holes should be bored to suit the wall height and soil class so the wall doesn’t lean forward when the clay swells after heavy rain.
What a properly built sleeper wall includes
- ✓40–50 MPa steel-reinforced concrete sleepers
- ✓Hot-dip galvanised H-beam or C-channel posts
- ✓Post holes bored and concreted to suit wall height and soil
- ✓Slotted 100 mm ag-pipe in a geofabric sock, bedded in washed 20 mm aggregate
- ✓Gravel backfill so water drains instead of building up behind the face
- ✓Fence brackets or post extensions if a fence is going on top
Typical cost
As a guide, supply and installation of engineered steel-post and concrete sleeper retaining walls typically ranges from $450 to $750+ per square metre of wall face. Site access, rock in the excavation, drainage and whether a fence is mounted on top all move the price. You’ll get an itemised quote from the builder after a site measure.
Drainage and approvals
Every retaining wall needs a way for water to escape: slotted 100 mm ag-pipe in a geofabric sock, bedded in washed 20 mm aggregate, relieves water pressure behind the wall. Walls over the NSW exempt height (generally 600 mm, and at least 1 m from a boundary), or walls supporting a structure, need structural engineering and CDC/DA approval. More on retaining walls in Wollondilly.
Frequently Asked Questions
How high can a concrete sleeper wall be without approval?+
Under the NSW Exempt and Complying Development Codes, retaining walls up to 600 mm high (and at least 1 m from a boundary) generally qualify as exempt development. Higher walls, or walls supporting a structure, need structural engineering and CDC/DA approval.
Can I put a fence on top of a sleeper wall?+
Yes, it’s common on new estate boundaries, but the posts and footings have to be designed for the extra wind load. Mention it when you request a quote so it’s priced in.
How Wollondilly Wall Co works
Wollondilly Wall Co is a local lead-matching service connecting Wollondilly property owners with independent, licensed structural landscapers and retaining wall contractors. When you call or send a request, we pass your details to a local builder who contacts you to arrange a site measure and quote. The builder you’re matched with is responsible for the work, its pricing and any warranties.