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Want to stop soil erosion or level out spaces like driveways, gardens or patios? A wood retaining wall might be the answer. It’s a great way to change the shape of slopes on your land and even though this job looks on the larger side, it’s actually not that hard or expensive to to get done by a professional.
Unlike concrete blocks, wood walls are kinder to the pocket. But they require a lot of work to put up. An electric drill is essential in the construction process for making holes, driving spikes, and connecting boards.
Before you start building a wood retaining wall, planning is important. First, choose the right location. Accurately laying out the wall location after excavation is a must for the stability and overall quality of the wall.
Consider the height and length you need. Also, know your area’s building laws and get the necessary permits.
Look for areas with steep slopes that are eroding. These areas need a strong retaining wall to hold back the soil. Signs of soil erosion are dead plants, changes in your garden, more bugs and muddy water. Exposed roots are another sign of soil erosion.
Avoid areas where water collects as it will damage the wall. Choose an area where the soil you dig out is the same as what you need to put back to minimise extra work.
Measurements are important. The first course must be perfectly in place and level to ensure the stability of the entire structure.
| Wall Height | Council Approval Required |
| Less than 1m | No |
| 1m to 1.5m | Yes, if less than 1.5m from a neighbouring building |
| Over 1.5m | Yes, and engineering consultation recommended |
Note: These regulations and guidelines change from one state to another. Always check with your local council before constructing a retaining wall.
Make sure to check local building codes and get the right permits. Most places need council approval for walls over 1m high and close to a neighbour. These rules vary so check yours. For walls over 1m it’s smart to talk to an engineer. Also, consider hiring a professional landscaper (like us) or big projects. We can make sure everything is done right.
Before you start, get all your materials and tools. This step is important for a hassle-free build. It will save you trouble later on.
For the wall, choose pressure-treated pine or fir for ground use. Ensure the timber is rated for ground contact to guarantee durability and stability.
This will ensure it can all withstand weather and decay, keeping your wall strong. Go for posts at least 75mm thick for stability. But for walls over 1m, talk to an engineer about thicker posts.
Need posts? The general rule is to put half in the ground, half out. For a 600mm high wall, use 1.2m posts. Space them 3 feet (0.91 m) apart. For a 40 feet (12 m) wall you’d use 14 posts.
Go for 50mm or 75mm thick hardwood or treated pine for your rails. They should be 2.4m long. Divide your wall’s length by 2.4 to find out how many rails you need. Don’t forget galvanised bolts, 20mm drainage gravel, geofabric, agg pipe and concrete mix or rapid set.
The right tools are a must. For your wall you’ll need:
A wood retaining wall can change the look of your yard and make it level for use. With the right tools and a little knowledge, this is doable. Here’s a step-by-step guide on how to install a timber retaining wall.
Clear the area and remove rocks and debris. Level the ground with a rake. Accurately laying out the wall location is crucial for its stability and overall quality. Mark where your posts will go with chalk, 3 feet apart. For a solid base, dig a trench and holes as needed, fill with concrete, and let it dry.
Next, install your posts and anchor the wall. Posts should be 2 to 3 feet apart. For a 40-foot wall, you’ll need around 14 posts. Secure the posts well so they are straight and stable. Use an electric drill to drive spikes and connect boards to ensure a sturdy construction. This will make your wall look good and strong.
After the posts, install the boards. Use bolts to attach 2×6 boards between the posts. Line up the boards with the posts. Put nails or screws as spacers. Ensure the first course is perfectly in place and level, as this is crucial for the stability of the wall.
Now, fill the soil behind the boards as you go. This backfill should be as high as your post holes are deep.
Drainage for Your Wood Retaining Wall
Drainage is key when building a wood retaining wall. Proper water drainage is essential to prevent hydrostatic pressure buildup, which can lead to wall failure. Without it, your wall will crack, collapse, or be damaged by water. This is because of the pressure of water that’s not drained well. Including drainage in your wall design will make it last longer and stay strong.
Drainage is crucial for timber retaining walls. Water buildup can push against the wall and make it fail. This is due to hydrostatic pressure. This is more important for walls over 1 meter high which an engineer may need to check especially in certain soil types. Proper drainage stops water damage, keeps soil from getting too wet, improves the wall’s strength and stops erosion.
To keep your retaining wall drained well use gravel for backfill not just soil. Soaked soil is heavy and can cause wall collapse. Here’s how to include drainage in your design:
Drainage for timber retaining walls includes French drains, weep holes, fabric, pipes and surface drainage. The process involves digging, using geotextile, adding gravel or rock, installing the drainage components and backfilling.
Using these drainage methods in your design will control water pressure. This will prevent damage and keep your landscaping project stable for a long time.
You must take care of your timber retaining wall to make it last long. Regular maintenance is a must. A well-built wood wall can last over 10 years if it’s of good quality and treated right.
Pressure-treated wood is good for the outer parts, but it’s best to use copper preservative on any cuts. Additionally, using a wood preservative to seal cut ends of timber will prevent decay and preserve the quality of the wood used in the retaining wall construction, especially if you’re looking to create a smaller one. This will stop decay and make your wall last longer.
Adding plants or grass to the wall will help too. They will keep the soil in place so the wall stays strong.
Also, check the wall often. Look for loose parts, cracks or if the soil is eroding. Fixing small problems early will save your wall from bigger damage.
Pressure treated pine and fir are the best woods for a wood retaining wall. They are meant to touch the ground. These woods can handle moisture and decay, perfect for outdoor use.
Your wood retaining wall should not be higher than 30 inches (76 cm). Walls higher than this will fall due to water pressure. For higher walls ask an engineer for design and build assistance.
For anchoring a wood retaining wall use four-by-four posts like a fence. Dig these posts into the ground and attach boards to them. This will add strength and stability to the wall.
Wood retaining walls last 10 years. But good quality wood that’s treated can last 20 years. Don’t forget to take care and fix on time to make it last longer.
Good drainage will stop water from damaging or toppling your wall. Use gravel not soil for the backfill and add an agg pipe at the base of the wall. Cover the back with geo fabric to keep the drainage clear.
For walls over 1m but under 1.5m near another building you usually need council’s okay. Rules can vary so always check with your local council first. If council or an engineer must be involved, it’s best to hire a pro for a correct and compliant build.
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