Last updated December 2022
Retaining walls are core structural features for a sloping garden or landscape. They create tiered spaces in functional and stylish levels and stop banks from eroding. Done right they solve many garden issues, but get the construction wrong and you could be facing a major problem.
Over the years we have seen many problems with retaining walls caused by poor drainage, foundation issues or badly executed construction. So if you are about to build a new retaining wall, or replace an existing one we have summarised six of the key problems and our recommended solutions to help make your new build or repair as seamless as possible.
HOW DO YOU KNOW IF YOUR WALL IS FAILING?
The most prominent signs that a retaining wall is not functioning includes leaning, cracking, or bulging. If there are weep holes and no water appears after rainfall this may also be a sign of a drainage issue. At worst-case scenario, a wall may collapse entirely. This can be very costly and time-consuming to repair and may be dangerous so if this occurs cordon of the area and contact a professional for advice.
Can you fix a leaning retaining wall? Yes, most retaining walls can be rehabilitated despite their initial issues, so the first task is identifying what is the cause of the failure. Below are some of the common causes of retaining wall failure and key considerations which can help you understand your issue (or avoid one if starting a new build!).
1: Ineffective or a lack of drainage
A lack of drainage behind retaining walls is a major problem. Wet, saturated soil behind a wall adds extra weight and this can put additional stress on a retaining wall, particularly if it is not constructed properly or is aging. Therefore it is important to add adequate drainage so the water can leave the structure – this includes using materials such as ag pipe and blue metal before backfilling behind the wall. Weep holes drilled horizontally along a wall at intervals can also assist with providing proper drainage.
2: Failure to use a sturdy footing
Installing a sturdy footing is critical for block walls to ensure the overall integrity of a retaining wall is maintained. To make sure the footing is sturdy it needs to be deep enough to resist any heavy weight. Depending on the wall material/size, footings may be constructed through a layer of crushed rock or a layer of concrete. If the wall is large enough to require engineering design, footing specifications will be provided as part of this and must be followed in the construction.
Sleeper walls require sturdy support posts installed at the appropriate depth with concrete – short cuts around this can result in the posts and then the sleeper wall leaning. The general rule of thumb is the height of wall above ground needs to be equal to the depth of posts below the ground.
3: Building too high without sufficient support
When building a retaining wall you need to make sure your wall is not too high and the height works with the soil type, footing dimensions and structural specifications of the structure.
In many areas, building a retaining wall also requires a building permit and possibly engineering certification (generally over 1m in height) so its best to check with your local council or approval authority before proceeding with any constructions or repairs.
4: Access
We are commonly asked to quote new retaining walls in housing estates where the walls are being constructed after the house has been finished. In many cases access constraints have not been considered and the job of installing or even repairing an old wall becomes very complex. If access is limited this can mean the wall has to be constructed manually which adds to the cost and may constrain the type of materials you can use.
Therefore, if building new retaining walls we highly recommend that you plan ahead and get walls installed before the house construction is completed. This will save money and guarantee a sound structure.
5: Using a contractor with a licence in structural landscaping
Retaining walls are structural landscaping works and require a Contractor with a licence in structural landscaping to build them. It is also worth checking that your contractor holds relevant domestic building insurance so that your project is covered by insurance – check out our Grow Dig Build Blog article from November 2022 for more information on this.
If you are paying someone to build your retaining wall, we recommend you do your research and communicate your wishes with the contractor. Also make sure you are on the same page and feel comfortable that your contractor will respond to any questions you have during the build process. At Grow Dig Build we are licenced and registered to provide insurance in Victoria and NSW giving our customers peace of mind.
6: Choosing the right material for your wall
Budget and aesthetics are typical considerations in the materials chosen for retaining wall construction. Common materials include concrete, hardwood or treated pine sleeper walls or block walls using materials such as rock, concrete blocks, chokka blocks, gabion baskets or sandstone blocks.
Take time choosing a material that, as well as being sturdy, will complement the surroundings for a harmonious look and suit your environment. This way, you can ensure a beautiful design and reduce the risk of issues or added expenses down the line. Beware that cheaper materials up front may result in more costs down the track if the materials chosen do not have longevity.
