walls look deceptively straightforward. Stack some blocks, backfill with soil, job done – right? Not quite. Every year, homeowners spend significant sums repairing walls that failed within a few seasons because of errors made during the build. Whether you’re planning to tackle it yourself or you’re overseeing a contractor, understanding where things go wrong is half the battle. Poor retaining wall installation is one of the most common and costly landscaping mistakes a homeowner can make – and most of it is entirely avoidable.
Here are the seven mistakes that come up time and again, and what you should do instead.
Mistake 1: Skipping the drainage layer
This is the single most common cause of retaining wall failure. Without proper drainage behind the wall, water builds up in the retained soil after rain. That water creates hydrostatic pressure – and over time, it pushes against the wall with enormous force.
A well-built retaining wall includes a gravel backfill layer and a drainage pipe (often called ag pipe or agricultural drainage pipe) that runs along the base behind the wall. This channels water away before it has a chance to accumulate and cause structural problems.
Skipping this step to save on materials is a false economy. Drainage systems are far cheaper to install during the build than to retrofit after a wall has started leaning or cracking.
Mistake 2: Underestimating the footing requirements
A retaining wall doesn’t sit on top of the ground – or at least, it shouldn’t. The base course of most retaining walls needs to be partially buried to provide stability. The exact depth depends on the wall’s height, the type of material used, and the soil conditions.
A common rule of thumb is to bury at least one unit of height for every seven units of finished wall height. So for a wall that rises 700mm above ground, the first 100mm should be below grade. For taller walls or softer soils, that requirement increases significantly.
Walls built without adequate footing tend to tip forward over time under the pressure of the retained soil. By the time it’s visible, the structural integrity is already compromised.
Mistake 3: Using the wrong materials for the job
Not all retaining wall materials are equal, and not all are suited to every situation. Sleepers, concrete blocks, natural stone, and poured concrete all have different load-bearing capacities, lifespans, and maintenance requirements.
Timber sleepers, for example, are popular for their look and relative affordability – but they’re not ideal for walls that are constantly exposed to moisture or where significant soil pressure is involved. They’ll degrade over time and may need replacing within a decade in wet conditions.
Choosing materials based purely on appearance or upfront cost, without factoring in the specific demands of your site, often leads to premature failure. The right material depends on wall height, soil type, load requirements, and local conditions – not just what looks best.
Mistake 4: Ignoring the batter (wall lean)
Most retaining walls are designed to lean slightly back into the slope they’re retaining – this is called the ‘batter.’ It’s a deliberate structural feature that helps the wall resist the pressure pushing against it from the soil side.
Homeowners who build walls perfectly vertical, thinking it looks neater, are inadvertently making the wall more vulnerable. A wall built to the correct batter angle – typically around 25–50mm per 300mm of height, depending on the material – is significantly stronger than one that stands straight up.
Always check the manufacturer’s specifications for block systems, or consult an engineer for walls using natural or poured materials.
Mistake 5: Building too high without engineering sign-off
In most regions, retaining walls above a certain height – commonly 600mm to 1 metre – require a building permit and an engineer’s assessment. This threshold exists for good reason: taller walls retain significantly more soil mass, creating forces that need professional calculation to manage safely.
Homeowners sometimes push past this threshold without permits, either unaware of the requirement or trying to avoid the cost and paperwork. This creates real risk – not just of wall failure, but of legal liability if the wall collapses and damages neighbouring property or injures someone.
If your wall needs to be taller than the permitted threshold in your area, do it properly. The engineering and permit costs are minimal compared to the consequences of getting it wrong.
Mistake 6: Poor compaction of the backfill
Once the wall is up, the area behind it needs to be backfilled – but how that fill is placed matters enormously. If soil is dumped in all at once without being compacted in layers, it will settle unevenly over time. That uneven settlement creates shifting pressure on the wall and can cause cracking or movement.
Best practice is to backfill in layers of around 200–300mm and compact each layer before adding the next. This applies to both the drainage gravel and the soil above it. It takes more time, but it produces a stable result that won’t shift and compromise the wall later.
Also worth noting: never backfill with clay-heavy soil directly against the wall. Clay retains water and expands when wet, adding to the pressure on the structure. Free-draining material is always preferable directly behind the wall.
Mistake 7: Treating it as a DIY project when it isn’t
There’s a clear line between retaining wall work that an experienced DIYer can handle and work that genuinely needs a professional. Low garden borders under 400mm on flat ground with well-draining soil? Manageable for many homeowners with the right materials and some research. A 1.2-metre wall on a steep slope with heavy clay soil and a neighbour’s fence nearby? That’s a job for a professional.
The issue isn’t just skill – it’s knowledge of what you can’t see. Soil conditions, underground water movement, root systems, and load calculations aren’t visible from the surface, but they have an enormous impact on how a wall needs to be built.
Misplaced confidence in a retaining wall project is expensive. Remediation work – pulling down a failed wall, addressing drainage issues, and rebuilding – often costs two to three times what a professional build would have cost originally.
Build it right the first time
Retaining walls are one of those projects where shortcuts tend to show up eventually – sometimes within a year, sometimes within five. The mistakes outlined above are all avoidable with the right knowledge, the right materials, and in some cases, the right professional.
Whether you’re planning to build yourself or engage someone to do it for you, go into the project informed. A wall that’s built properly will do its job quietly for decades. One that’s not will become a recurring problem that costs far more than it ever needed to.