Expert Builder: Retaining Walls

May 10, 2023

What is a retaining wall and when are they used in Granny Flat Construction?

Retaining walls are a common feature in many Granny Flat builds or indeed any residential build, especially those that are constructed on sloping or uneven terrain. Retaining walls are designed to hold back soil and prevent erosion, which helps to create a level and stable foundation for the Granny Flat. Find out all about how and why we use retaining walls in your building projects, to ensure the structural integrity of the finished product.

Retaining Wall

What is a retaining wall?

A retaining wall is like a barrier that is built to hold back soil and prevent it from sliding or eroding away. Think of it like a fence that keeps your yard from spilling over onto your neighbour’s property. The wall is usually made of sturdy materials like concrete, brick, or stone, and is designed to resist the pressure of the soil pushing against it.

Retaining walls are commonly used by Cubitt’s in construction of your Granny Flat to create a level surface on a sloping or uneven terrain. For example, if you want to build a hill, we might need to construct a retaining wall to keep the soil in place and create a flat surface for the foundation of the home.

To ensure that a retaining wall is strong and stable, we will properly design and construct the using factors like the height of the wall, the type of soil, and the slope of the terrain to secure your home in spot. This will include working with engineers to ensure that the wall meets all local building codes and regulations.

What sort of retaining walls do Cubitt’s use?

There are several types of retaining walls that can be used in Granny Flat construction, including:

  • Sleeper walls: Can be made of timber or concrete. Horizontal wales are attached behind vertical posts inserted into concrete footing. This type of retaining wall is cost effective, can be easily constructed in tight spaces and provides aesthetic options in terms of timber used.
  • Gravity walls: These are walls that rely on their own weight to hold back the soil. They are typically made from concrete blocks, bricks, or stone and are ideal for smaller retaining wall projects.
  • Cantilever walls: These are walls that are anchored to a footing and extend outwards to hold back the soil. They are typically made from reinforced concrete and are ideal for larger retaining wall projects.
  • Sheet pile walls: These are walls that are constructed by driving interlocking steel sheets into the ground. They are ideal for retaining soil in areas with limited space and are often used in conjunction with other types of retaining walls.

Cubitt’s will assess your building project and make recommendations for appropriate retaining wall structures as required by your local building regulations

What are the alternatives to retaining walls?

Cut and fill. Cut and fill is a common earthmoving technique used in construction to level or prepare a site for building. It involves removing soil from high points on the site (known as "cutting") and using it to fill in lower areas (known as "filling").

During the cut phase, earthmoving equipment such as excavators or bulldozers are used to remove soil from high areas of the site to lower areas of the site where it is used to fill in depressions or level the terrain. The cut and fill process can also involve importing or exporting soil from or to the site, depending on the amount of material required.

The cost of earthmoving equipment for this procedure often makes a retaining wall process more desirable. It is important to properly manage the cut and fill process to ensure that the soil is properly compacted and stable to prevent future settlement or erosion. In some cases it could be possible to ‘cut and fill’ your site, although in most cases cut and fill implies a slope of land that will still require some sort of retaining wall.

Steel piers. Building on piers could be a construction technique that suits your block if a retaining wall is not suitable. Piers can be adjusted in height to provide a level foundation for the structure.

Building on piers can also be a cost-effective solution in areas where traditional foundations are difficult or expensive to install. For example, in areas with rocky or hard soil, it may be easier and less expensive to install piers than to excavate the soil and install a traditional foundation.

How will I know that a retaining wall is best for my Granny Flat?

Cubitt’s have a team of builders, working with engineers who are knowledgeable and skilled in all aspects of construction. When we conduct a feasibility study for you, one of our builders will attend the site to confirm aspects of the construction discussed in your Design Consultation and make recommendations on the most suitable structure for your soil and land shape. Our planning team often consult engineers early on in the process and are familiar with all the local building codes.

Whether we use a retaining wall, cut and fill, or piers, our team will ensure that the design and construction of the foundation and structure are done to the highest standards of safety and quality.

More Expert Building content from the Cubitt's Construction team:

  • Raft slab
  • Screw piers


Cubitt's are committed to making your building project stress free and simple. Responsible for your result, you can be assured that we will be aiming to complete your project with the best outcome for your long term use of the home. Building a home is a journey we are privileged to go on with our clients, and Cubitt's are committed to being completely transparent and delivering the highest standards of communication along the way.

We're working towards you enjoying your home for decades to come. We work with expert engineers who help us deliver your building plans to the most up to date local council regulations. At every step of the way we are working with the engineers guidelines to validate expected building conditions. When there are surprises, (which there mostly aren't) you can be assured that your building supervisor has the expert knowledge to guide the decisions you make next - and the team to back it up.


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About Harry Kim

Harry has worked on building sites since the young age of 16, both on commercial and multi high rise buildings, before moving into residential construction management with Cubitt’s. Harry leads a team of 10 site supervisors, 30 employee trades and a large, fluctuating group of longstanding subcontractors.