Retaining Walls – All You Need to Know

Retaining walls are a structure designed to retain back soil or other materials to prevent erosion or collapse of an elevated area.

Retaining walls are commonly used to create usable land, manage water drainage, and stabilise slopes in various landscapes, especially in areas prone to heavy rainfall or erosion. This is because erosion and water run-off can trigger soil movement on slopes which could potentially cause dangerous situations.

Typology of Retaining Walls

Retaining walls can be made from various materials such as concrete blocks, shotcrete, treated timber, natural stone, or brick, depending on the desired aesthetics, site conditions, and budget. There are several types of retaining walls, the most common include: gravity walls; cantilever walls; anchored retaining walls; and sheet pile retaining walls. Each of these designs offer stability and durability while accommodating the specific soil conditions and weather patterns.

Designing a Retaining Wall

Designing and constructing retaining walls can present various challenges.

Firstly, site analysis is crucial to determine the soil type, slope stability, drainage requirements, and potential hydrological issues. These factors influence the design and material selection for the retaining wall. Structural engineering calculations are necessary to ensure that the retaining wall can withstand the lateral soil pressure and any additional loads imposed by the site conditions. Moreover, soil erosion, groundwater movement, and weather conditions can impact the durability of retaining walls over time.

Proper drainage systems, including weep holes (gaps left that allow water to drain out from structure), and perforated drainage pipes (also known as ag-pipes, with holes throughout it that allow water to trickle down into the pipe and drain out around the wall), must be considered as part of the design process to prevent water build up behind the wall, which can cause pressure on the wall and could lead to collapse. The depth of the foundation for a retaining wall depends on the height of the wall, soil characteristics, and local climate conditions.

These are just some critical factors that will inform the height and the design of a retaining wall. When designing a retaining wall, it is vital to consult with a qualified structural engineer or retaining wall professional to ensure the wall’s effectiveness and compliance with the relevant legislative requirements for the area.

Obtaining Approval for a Retaining Wall

The construction of retaining walls is subject to certain regulations and approval processes, and in NSW the more common approval process is to obtain a Development Approval (DA) from the local Council. This is usually because retaining walls are proposed close to the property boundary, and complying development does not enable any building works closer than 900mm to boundaries.

While exempt development may be possible for some low-impact designs, a DA issued by Council is the most common planning pathway.

Each Council has specific guidelines to ensure the safety, durability, and environmental compatibility of these structures. It is important to consult with a qualified structural engineer or retaining wall professional who can navigate the approval process and ensure compliance with the relevant building codes and regulations.

Once a DA is approved, it is then necessary to also obtain a Construction Certificate (CC) from a Principal Certifier (this can be a Private Certifier or it can be through Council) in order to be able to commence building works on site.

While it is possible to build a small and low-height retaining wall as a DIY project, it is recommended to hire a professional for larger or more complex walls, especially if demolition works are involved, as retaining walls require proper engineering, construction techniques, and are required to adhere to local regulations to ensure their safety and longevity.

The cost of building a retaining wall varies on factors such as wall height, materials used, site conditions, and labour costs. It is advisable to obtain quotes from contractors or consult with professionals experienced in retaining wall construction to get an accurate estimate based on the specific project requirements and location.

Problems During the Planning and Construction Phases of a Retaining Wall

Often it is impossible to know the exact conditions of a site for a retaining wall prior to demolition of any existing structures, especially when the topography of a site limits visibility of ground conditions. This can sometimes lead to a revised construction methodology addressing the changed site conditions. Unfortunately, unforeseen circumstances like this can lead to a cost overrun, as the construction of a retaining wall can be a significant investment. It is worthwhile to plan ahead when preparing to carry out a retaining wall project in case unexpected soil conditions are encountered or additional engineering solutions are required as a result.

Common Disputes Relating to Retaining Walls

Disputes over retaining walls can occur due to various reasons, however, some common issues that can arise relate to encroachments over property boundaries, design and construction defects, drainage problems, maintenance and responsibility, and visual impact and aesthetics.

Property boundaries Disputes may arise when there is uncertainty about the exact location of the boundary lines in relation to the retaining wall. This can lead to conflicts over ownership, maintenance responsibilities, or encroachments. It is advisable to consult property or land surveyors to determine the accurate property boundaries. Legal documents such as Land Titles and surveys can help resolve these matters.

Design and construction defects

Issues may arise if the retaining wall was poorly designed or constructed, leading to structural problems, instability, or failure. This can pose safety risks and potential damage to adjacent properties. Engaging a qualified engineer and contractor to assess the wall’s design and construction is crucial. They can identify any defects and provide recommendations for repairs or modifications.

Drainage problems

Retaining walls require proper drainage to prevent water build up and pressure behind them. Inadequate drainage can lead to erosion, soil movement, or damage to the wall or adjacent structures. Implementing proper drainage solutions should be considered during the design process, otherwise the responsible party may be liable for damage caused.

Maintenance and Responsibility

Disagreements may arise regarding the maintenance and repair responsibilities of a retaining wall, especially when it services multiple properties or is located on a shared boundary. Establishing a shared maintenance agreement can avoid conflict in these instances. Visual impact and aesthetics Disputes may arise when a retaining wall negatively impacts the view or aesthetics of neighbouring properties, leading to disagreements over its design, height, or appearance. Engaging in open communication with each party can help in finding a mutually acceptable solution.

How Can Corona Projects Assist with a Retaining Wall

Corona Projects can provide valuable assistance throughout the design and approval stages of retaining walls. Our experience with all metropolitan Sydney Councils puts us in a position to help clients navigate the complexity of such projects, from initial design to final DA approval and CC approval to ensure compliance with regulations and environmental site conditions.

It’s important to select professionals with the right experience, expertise, and local knowledge to ensure that your development project is successfully executed. The Corona Projects team has more than 25 years of experience with your local council, so can not only meet your needs, but make sure your council approval process is smoothly executed.

Contact the Corona Projects team here.