Winter is on the way, and while WA’s cooler months are pretty mild compared to other parts of the world, we still get our fair share of wind and rain. This kind of weather doesn’t just make working in the garden cold and unpleasant; it can also destabilise your garden beds and generally leave things looking distressed, untidy and dishevelled.
Building a retaining wall is a great way of keeping the soil in your garden and yard stable. Helping to ensure your garden is able to withstand the howling wind and driving rain without the need for maintenance, retaining walls can add an extra element of eye-catching structure and appeal to your outdoor spaces.
Before you get started on your retaining wall project, there are a few things you need to be aware of. As the name suggests, these walls are designed to retain large amounts of earth, which means there are considerable forces involved. Getting it wrong can lead to hazardous collapses.
That’s why we’ve put together this expert guide. Autumn is the perfect time to embark on outdoor home improvement projects like these as the weather is cooler but hasn’t turned too nasty just yet. Have a read if you’re thinking of upgrading your garden with a retaining wall before winter arrives.
What You Need To Know Before You Start
- Retaining walls should never be installed above their maximum specified height or into cuttings where the base soil or backfill is not firm, or consists of expansive clay. (Click here to download our brochure to find out more).
- Most local councils have their own height limits when it comes to retaining walls that can be built without engineer approval. Before you install your retaining wall, we recommend consulting with your local council, as some require retaining walls to be designed and certified by a qualified engineer if they exceed a certain height.
What You’ll Need To Get The Job Done
- Protective gloves
- Eye protection (such as goggles)
- Feet protection (like steel cap boots)
- A shovel
- A spirit level
- Drainage material (such as gravel or blue metal)
- Stakes & string
- An agricultural drain (like 100mm subsoil pipe)
- A wheelbarrow
- Coarse sand for the levelling pad
- A hammer
- A small broom
- Black builders plastic
Step 1: Choose Your Building Product
At Midland Brick we have a number of different products to choose from when it comes to building retaining walls. Choosing the right one depends on your specific project and personal design tastes.
Heathstone’s mortarless design makes it ideal for low, vertical landscaping and retaining walls. It can also be used to separate and highlight entertaining areas, BBQ areas, paths, garden beds, hedges or to create and differentiate levels in your outdoor space.
With a stunning textured look that just oozes rugged appeal, Gardenwall lets you easily and simply create curved walls, steps, terraces and raised garden beds. It also has the added bonus of not needing mortar or concrete footings, which means no bricklaying skills are required to work with it.
Solid, simple and effective, these bevelled concrete blocks are ideal for building sturdy retaining walls. They’re also lighter, easier and safer to handle when compared to other similar products.
Step 2: Check With Your Local Council
Before you start on your retaining wall project it is highly advisable to consult your local council and check up on any design regulations that you need to be aware of. As we mentioned before, retaining walls over a certain height and walls located near surcharge loading (such as a house or driveway) are generally required to be designed and certified by a qualified engineer, so you want to make sure that you’re not putting yourself at risk of any negative legal consequences.
Step 3: Work Out How Many Blocks You Require
This step involves a little bit of maths - but stick with us - it’s actually pretty simple. Just multiply the length of your wall by the height to determine the overall area (in m2) and then simply multiply the m2 by the number of units per m2. (This can be found on the online product profile.)
Pro Tip: It’s often worth ordering an extra 5% onto your order to allow for wastage if you’re going to be cutting product.
Step 4: Preparing The Site
Thoroughly level the area for the base (or foundation) course by removing any roots, debris or soft earth. Create a shallow trench by levelling the ground and tamping down the earth to a flat and level finish.
Next, compact the ground either manually or with a mechanical compactor (if you have access to one). Fill the trench with coarse sand or road base if required, then compact and level until it forms a 100mm thick levelling pad. This will mean that your first course should be partially sunken.
Step 5: Locate Your Wall
Mark out the location of your retaining wall with stakes and a string line. Alternatively, you can mark a line on the ground with spray paint.
Step 6: Lay The First Course
Getting the first course right is an essential part of building a structurally sound retaining wall, so take your time and make sure you get it right.
Place the blocks side by side and align them on the levelling pad using a string line along the back. Then level each unit back to front and side-to-side with a spirit level to make 100% sure that everything is perfectly in place.
We highly recommend placing black builders plastic along the back of the wall to reduce the flow of water draining through it. This will cut down on efflorescence (a white, powdery substance) or mineralisation from the soil that can discolour the face of your retaining wall.
If your soil has poor drainage, it may be necessary to install appropriate agricultural drainage behind the first course and surround it with gravel.
Pro Tip: Spend extra time and attention levelling the first-course units. Get this wrong and your whole wall will not be level, which can look awful and cause instability further down the line.
Step 7: Backfill & Compact
If it’s required, now is the time to place your drainage material (gravel or blue metal sized at 12-20mm is best practice) behind your first course. Shovel and compact the backfill (existing site soil) behind the drainage material to ensure that it all stays in place.
Pro Tip: Making sure the soil behind your retaining wall can drain is very important. If it doesn’t drain properly, water will build up behind it and weaken the construction.
Step 8: Adding The Additional Courses
To build the rest of your retaining wall, sweep the top of each course clean and then place the next course on top in a half bond pattern (this means with the vertical joints from the previous course halfway across the units of the next course).
Lay the additional courses using this method. You’ll need to backfill on at least every other course to ensure your wall is sturdy and secure. Continue stacking and backfilling until your wall is complete.
Step 9: Step Back & Admire
Once all the hard work is done, it’s important to step back and admire what you’ve achieved! Chances are, your garden/outdoor space looks that much more composed and orderly, and it’ll continue to do so no matter what the winter weather throws at it.
Click here to browse our range of retaining wall materials online, or get in touch if you need some additional information.