ON 18 June
By: Natalie McMurdo
Retaining walls are a key part of landscaping and construction, providing support for soil and helping manage level changes on your property. Whether you’re planning a simple garden wall or a large structural system, it’s important to get the design and materials right from the start. At 21 Timbers, we supply quality timber, concrete and composite sleepers, posts, and hardware for long-lasting retaining walls—built to meet Australian standards.
Here’s what you need to know when building a retaining wall, including a quick look at AS 4678-2002, the Australian Standard for Earth-Retaining Structures.
What is AS 4678-2002?
AS 4678-2002 is the Australian Standard that outlines the design requirements for retaining walls supporting soil or other materials. It provides engineers and builders with guidelines on:
- Structural design
- Drainage
- Soil pressure
- Stability against sliding, overturning and collapse
It covers retaining walls over 800mm high or any wall that supports significant loads—such as driveways, buildings or slopes. If your wall is over 1 metre, most councils will require engineering approval and building permits, in line with this standard.
Things to Consider When Building a Retaining Wall
Retaining walls under 1 metre high often don’t need council approval (check with your local council).
Walls over 1 metre, or supporting additional loads (like fences, driveways, or structures), usually require:
- Engineering certification
- Compliance with AS 4678-2002
- Drainage plans
Soil Type and Site Conditions
- The type of soil on your site affects drainage, pressure, and stability.
- Clay soils hold water and exert more pressure on walls.
- Sandy or well-drained soils are easier to manage.
Drainage is Essential
Water build-up behind a wall is the biggest cause of failure. Proper drainage is a must:
- Use ag drains behind the wall
- Include weep holes to release water pressure
- Backfill with free-draining material like gravel
This helps avoid hydrostatic pressure and prolongs the life of your wall.
Materials Matter
At 21 Timbers, we supply a range of retaining wall materials to suit your project and budget:
- Treated Pine Sleepers – cost effective and ideal for low to medium height walls
- Treated Hardwood Sleepers – strong and naturally durable
- Concrete Sleepers – ideal for structural walls, resistant to rot, fire and termites
- Composite Sleepers – strong, durable and low maintenance
- Galvanised Steel Posts (H & C Channels) – designed to fit sleepers and resist corrosion
Correct Construction Method
Key construction elements include:
- Footings or post holes set to correct depth
- Posts spaced correctly to support sleepers (usually 2.0 m or 2.4 m centres)
- Using landscape fabric (geo fab) to separate soil and drainage gravel
Need Help Getting Started?
At 21 Timbers, we’re here to help you choose the right products for your retaining wall—whether it’s a weekend project or a large-scale build. Our team can guide you through:
- Timber and concrete sleeper options
- Composite sleeper options
- Galvanised steel posts
- Hardware, tools and advice
Contact us or visit the yard to get started on your retaining wall project.
📞 07 3801 1122
🏫 60 Cairns Street, Loganholme QLD 4129
📧 admin@21timbers.com.au
🌎 www.21timbers.com.au
Project by Evscavations – Expert Retaining Wall Builders
The retaining wall featured in this article was completed by Evscavations, a trusted name in earthworks and retaining wall construction. If you’re looking for professional retaining wall builders or excavation services, contact Gold Coast’s most trusted retaining wall builder Evscavations on 0422 560 061 or visit them at https://www.instagram.com/evscavations/
