How to build a timber retaining wall

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How to build a timber retaining wall

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Building a retaining wall is a great way to add function and visual appeal to your garden. It not only supports the soil bed, but also makes an impressive decorative feature that will last for many years to come. It’s a project that you can do yourself, all you need is some basic D.I.Y. skills and a little bit of elbow grease.

Tools and materials

Circular saw

Concrete

Cordless drill

Ear muffs

H4 treated pine sleepers

Impact driver

Pencil

Safety glasses

Scoria

Shovel

Spirit level

Spray paint

Square

String line

Tape measure 

Tools and materials needed to create a timber retaining wall

1. Make a plan

Before you start, plan out the length and height of your retaining wall. We are replacing an old retaining wall, but the same principles apply to one that you start from scratch. Our retaining wall will be two sleepers high, but you can make it lower or higher depending on your requirements.

2. Measure the area

Use a tape measure to work out the length of your wall and how much timber you’ll need. Make sure you leave some space at the back for a drainage pipe.

Using a tape measure to work out the length of the retaining wall

3. Choose your timber

Choose timber with a minimum rating of H4. We’ve gone for treated pine sleepers, which are designed to go in ground, and will last longer out in the weather and soil.

6 lengths of H4 treated timber

4. Mark out the posts

Depending on the length of your wall, the sleepers are going to need joiner posts to keep them in place. So, measure and mark the points where the posts will go.

Using marking spray paint to show where a post will be placed

5. Set up a string line

Lay out where you are going to build your retaining wall by running a string line between two stakes at either end. Make sure you set your string line to the back of the retaining wall. This will help you keep your posts in line and your retaining wall straight.

Using a nail to anchor in a string line

6. Dig holes for the posts

Dig holes for the posts the same depth as the height you want the posts to be above ground. We are also digging a bit further out from the string line because our posts will be in front of the wall.

Digging a post hole outside the string line

7. Measure the posts

Measure the height of your posts from the bottom of the hole to the top of the string line. We will be cutting enough timber for three posts, but you may need more.

Measuring the depth of the post hole with a measuring tape

8. Cut your timber to size

Now it’s time to cut your timber to the sizes you need for the wall and posts. Measure and mark your timber using a pencil and square, then use a circular saw or handsaw to cut the timber.

Cutting the timber sleepers with a circular saw

9. Position the posts

Once you have your timber cut to size, put the posts into position. Make sure they are far enough out to go in front of the wall.

Inserting the post into the previously dug hole

10. Attach sleepers to the posts

Place a wall sleeper behind the first end post, and attach it using your drill. Then attach the other end to the next post. Repeat this process with each sleeper until the bottom row is completed. Then, work your way down the same way for the top row of sleepers.

Using a drill to secure the post to a length of sleeper

11. Level the posts

Use a pencil and square to mark the height you need for the posts to be flush with the wall. Then, use your saw to cut off the tops of each post.

Cutting down the post to size

12. Pour the conrete

Now, mix up some concrete according to the directions on the packaging and pour it into the holes around the base of each post. Cover each hole with soil and let the concrete set. It’s a good idea to brace your posts first, so that they stay in line when you’re pouring the concrete, and while it’s setting.

Filling in the remaining post hole with concrete

13. Install drainage

Pour a layer of scoria behind the wall and place your drainage pipe directly on top. Cover the pipe with another layer of scoria and then cover that with soil. Make sure to run the end of the pipe to a spot where it can be accessed. Direct it to a suitable stormwater drain on-site or into a garden area.

Filling in the gap behind the retaining wall with scoria and placing in a drainage pipe

14. Cap it off

You can also attach single sleepers face down on top of your wall. They not only look good but also double as seating when you want to spend some time out in the yard with your family and friends. Then, all you have to do is stain or paint your wall.

A Bunnings team member sitting above a completed timber retaining wall

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