How high are you building?
Height decides your materials, your posts, your engineering and whether you need council approval. Work out the height first and everything else follows from it.
Three bands, three different builds
One metre is the common trigger
Across most of South East Queensland, building approval is usually not required where the total height of the wall and of the fill or cut it retains is no more than one metre above natural ground, there is no surcharge load in the zone of influence, and the wall sits at least 1.5 metres clear of a building or another retaining wall.
Miss any one of those three conditions and you are generally into approval territory, even on a wall well under a metre. The bands below are a starting point, not a ruling on your site.
Garden terraces, raised beds and edging
The usual owner builder starting point and the easiest material to handle by hand. Walls at this height are typically about levelling a sloping yard or framing a garden bed rather than holding back serious ground.
- Common materials. Treated pine and hardwood timber sleepers, or composite for a longer life without the maintenance.
- Approval. Usually not required, provided nothing is loading the ground behind the wall and setbacks are clear.
- Still do the drainage. Height does not exempt you from water. Gravel, geo fabric and an outlet are what stop a low wall pushing forward.
Boundary and backyard walls
The most common residential wall we supply. Still under the one metre trigger in many South East Queensland councils, provided nothing is loading the ground behind it and the setbacks are clear. This is where post size and spacing start to matter properly.
- Common materials. Composite or concrete sleepers on galvanised steel C or H posts.
- Approval. Often not required, but this is exactly the height where a surcharge load, an easement or a nearby structure quietly pushes you over the line.
- Watch the setback. The 1.5 metre clearance from a building or another retaining wall is easy to miss on a narrow block.
Engineered territory
Above the one metre trigger you generally need an engineered design and building approval through a licensed private building certifier. The design is done for your specific site, and the post size, embedment depth and footing come from the engineer rather than from a rule of thumb. If you do not already have an engineer, contact us and we will recommend one who is available for your job and your area.
- Common materials. Concrete sleepers on galvanised steel posts. Our concrete sleepers are RPEQ certified.
- Approval. Expect an engineered design and building approval. Budget time for it before you order material.
- Heavy duty options. Larger walls move to UB and UC sections. We quote those to your engineer's specification.
- Heavy duty 150 series. Now priced online rather than quote only: 150UC23 H posts and 150PFC C channel in 19 lengths from 2.0m to 6.0m. Sections above the 150 series are still quoted to your engineer's specification. Walls that need 150 series posts are engineered walls, so confirm your own situation with your local council or a licensed private building certifier before you order material.
What else triggers approval
Height is the headline number, but it is not the only one. Any of these can put a short wall into approval territory.
Surcharge loads
Anything sitting on the ground in the zone of influence behind the wall. A driveway, a parking area, a shed, a pool, a slab, or another wall stepping above it.
Setbacks from structures
The common exemption requires at least 1.5 metres clear of a building or another retaining wall. Tiered walls close together are usually assessed together, not as two short walls.
Easements and services
Sewer and stormwater easements, service lines and council infrastructure all carry their own restrictions regardless of wall height.
Pool fencing and boundaries
A wall that forms part of a pool barrier or a boundary fence line brings additional requirements, and a fence on top adds wind load the wall has to be designed for.
Your council, and your state
Sunshine Coast Council requires a building permit for most retaining walls regardless of height. Northern New South Wales works to its own rules entirely.
Site conditions
Reactive or unstable soil, steep slopes, fill of unknown origin and poor drainage all change what the wall has to do, whatever the tape measure says.
Thresholds vary by council and the rules change. We do not publish a maximum retained height either, because every wall has its own conditions and the limit for yours depends on the soil, the surcharge behind it, the post size and spacing and the footings. Contact us with your wall dimensions and we will give you clarity on the specifications for your wall. Nothing on this page is a substitute for confirming your own situation with your local council or a licensed private building certifier before you order material. We would much rather you checked first than found out after the truck has been booked.
What happens next
Height sets the material. After that it is post size, spacing, embedment depth and drainage, and those all come out of the same measurement.
Post size and spacing
Taller walls need heavier posts at closer centres. Our installation guides cover the spacings for each sleeper length, and post depth by wall height.
Drainage behind the wall
Aggregate, geo fabric and agi pipe, with somewhere for the water to go. Water pressure behind a wall is what fails it, at any height.
Anything going on top
A fence adds load, including wind load. It has to be allowed for in the wall design rather than bolted on afterwards.
The take-off
Send us the length and the height and we work out the sleeper count, posts, gravel, geo fabric, wedges and caps, and price it with delivery.
Send us the wall and we will tell you
Length, height, your suburb and a couple of phone photos of the site. We come back with a tailored quote including delivery, usually within one business day, and we will flag anything that looks like it needs approval.