Materials for a retaining wall can include wood, concrete, steel or a combination of all three. To help you decide between a timber retaining wall, a steel retaining wall, or one made of concrete, we’ll tell you everything you need to know about the materials that go into building your own DIY retaining wall.
Follow along as we list the advantages and disadvantages of the materials for a retaining wall.
A sleeper retaining wall is any wall built to hold back soil, earth and other materials when there is an elevation difference – making them a fantastic choice for any DIY enthusiast looking to add a bit more nature in their backyard.
Builders install these walls to remove slopes or where landscaping is required, using additional materials such as timber, concrete or steel to form a physical structure.
A sleeper retaining wall uses retaining posts to support the soil laterally (from the sides) between two levels of earth on either side, binding it together. They’re called sleeper retaining walls because of the use of wooden or concrete planks traditionally used for railroad tracks.
Designed to resist pressure from soil, retaining walls are built to alter the ground elevation, going past the soil’s steepest angle, otherwise known as the angle of repose. This characteristic relates to the friction or resistance to movement between particles, i.e. the ground, and is integral to determining whether or not a slope is at risk of collapse. Increasing the height of the wall is one way to overcome this. However, the stronger the sleeper retaining wall, the more stable it will be.
Sleeper retaining walls are typically made of timber, concrete or steel.
Traditional sleeper walls used the same timber sleepers from railroads, making them a sustainable option back in the day. However, concrete and steel are the preferred option in the modern world, as they are not as prone to environmental stressors and rot. Many choose timber as their preferred materials for retaining walls for aesthetic reasons, without considering the need for regular maintenance and treatment to ensure their longevity.
- Fast installation
- Natural aesthetic
- Minimal footings required
- Susceptible to environmental stressors, e.g. moisture, temperature
- Vulnerable to rotting, mould and termites
- Low strength; not suitable for large-scale projects
- Low flexibility
Far more durable than timber sleepers, concrete is ideal for retaining wall construction.
Structural concrete sleepers, for example, are reinforced with steel to increase durability.
- Structural strength, durability and longevity
- Suitable for large-scale projects and high walls
- Various finish and colour options
- No risk of rot
- Low maintenance
Steel retaining wall sleepers made from hot-dip galvanised steel are ideal for landscaping and civil work thanks to their increased durability and corrosion resistance.
Many steel retaining products also come pre-drilled, eliminating the need to drill or weld on-site. Steel can also be manufactured into various products, allowing for more customised steel fabrication for landscaping designs.
- Inherent strength, durability and corrosion resistance (hot dip galvanised steel)
- Suitable for projects big and small
- Prefabricated/ pre-drilled product options
- No risk of mould, rot or termite damage
- Multiple steel post designs for a range of applications
- C section
- H section
- C section 45-degree
- C section 90-degree
- T channel
- More expensive than timber.
Several retaining walls are used in residential and commercial construction.
However, the most important types are gravity and cantilevered walls.
Typically made of stone, concrete and other heavy materials, gravity walls resist pressure from behind by leaning back towards the retained soil.
Reinforced with an internal stem of steel, cast-in-place concrete or mortared masonry, installing a cantilevered wall converts the horizontal pressures from behind the wall to vertical forces on the ground below.
When materials like soil are compacted and bound together in a retaining wall, they are still impacted by gravity, which can cause the material to move downslope, creating lateral earth pressure behind the wall. The force of this pressure is lower at the top of the wall and increases proportionally to a maximum value at the lowest depth.
These lateral earth pressures can push the wall forward or overturn it entirely if not correctly installed or fixed.
Any groundwater not properly dissipated by external drainage systems may add to the lateral earth pressure with hydrostatic pressure. Drainage will also help maintain the stability of the material behind the wall.
Getting council approval for any exterior home renovation project is always recommended. However, retaining walls that are generally under 1m in height do not require permission or an engineering certificate before commencement. If this is your first DIY retaining wall, we highly recommend employing an engineer to sign off on your build before construction begins on your steel retaining wall.
Council approval will be required if the retaining wall is to be built along property boundaries; neighbours would typically share the cost. Check with your local authority to determine which neighbour pays for a retaining wall for more unique situations.
All retaining walls start with a trench and post holes, which gives your steel retaining wall more support. You’ll need to dig a channel that is the same depth as the height of your retaining wall.
Once your steel posts are positioned in their holes, fill them with concrete and wait till it is set before installing steel sleepers.
Drainage and plastic membrane should now be added as required and backfilled to finish.
Stronger and more durable than timber, lighter than concrete and with far greater flexibility, steel is the ideal choice for your DIY retaining wall. Just make sure you have all the essential tools before you get started!