How to Build a Retaining Wall: Materials and Method Guide

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What is a retaining wall used for?

A retaining wall is built to hold back soil where there is a difference in ground level. It can be used to create raised beds, level out a sloped garden, form terraces or support landscaped areas around a property or commercial site. 

A garden retaining wall is often used to improve the layout of an outdoor space, but it still needs to be built with the right support and drainage. Even smaller retaining walls can fail if water pressure builds up behind them or the base is not prepared correctly. 

For taller walls, walls near buildings, or walls supporting driveways and heavy loads, specialist advice may be needed before installation. 

Retaining wall materials

The best materials will depend on the size of the wall, the ground conditions and the finished appearance required.

Retaining wall blocks

Retaining wall blocks are a popular choice because they are designed to create strong, consistent walling. They can be used for straight or curved walls, depending on the block type, and can provide a neat finish for landscaping projects.

Concrete retaining wall blocks are often chosen where strength and durability are important. Always check the product guidance, as some systems may require specific installation methods, reinforcement or backfill.

Retaining wall sleepers

Sleepers can create a natural timber appearance and are often used for garden retaining walls, raised beds and landscaping features. A sleeper retaining wall can work well for lower walls where a softer finish is preferred.

Timber sleepers should be suitable for external use, and any cut ends should be treated where required. Brackets, fixings and drainage should also be considered as a part of the specification. 

Concrete and masonry options

Concrete blocks, bricks and masonry walling can also be used for retaining walls, depending on the project. These may need proper foundations, mortar, drainage and in some cases reinforcement.

For trade projects, the wall should be specified around the load it needs to retain, not just the finished appearance.

What materials do you need to build a retaining wall?

The exact materials will depend on the wall type, but most retaining wall projects will need a combination of structural materials, drainage materials and installation tools. 

This may include:

• Retaining wall blocks, concrete blocks or sleepers

• MOT type 1 or suitable sub-base material

• Sharp sand or bedding material

• Gravel or clean stone for drainage

• Perforated drainage pipe 

• Geotextile membrane 

• Mortar, adhesive or suitable fixings 

• Support brackets when using sleepers

• Spirit level, string line and tape measure 

• Spade, shovel, saw or cutting tools 

• Plate compactor 

• Appropriate PPE 

Drainage materials are especially important. A retaining wall needs to manage water behind the structure, otherwise pressure can build up and affect stability.

How to prepare for a retaining wall

Before building starts, the area should be measured and marked out. Check the full wall length, finished height, ground levels and any changes in direction. It is also worth checking for materials and tools, especially if bulk materials need to be moved around the site. 

The ground should be cleared of loose soil, roots, vegetation and debris. The base needs to be firm and level, as movement at the bottom of the wall can affect the full structure.

You should also plan where water will drain. Retaining wall drainage is not something to leave until the end of the job. It should be included from the start, with suitable gravel, drainage pipe or weep points where needed. 

How to build a retaining wall

The installation method will depend on whether you are using retaining wall blocks, sleepers or masonry. However, most retaining walls follow a similar basic process. 

1. Mark out the wall

Use a string to mark out the position of the retaining wall. Check the line, levels and any corners before excavation begins. For curved walls, mark the curve clearly so the base can be prepared accurately.

2. Excavate the base

Dig out the trench for the wall base. The depth and width will depend on the wall height, material and ground conditions. The trench should allow space for a compacted sub-base and the first course of blocks or sleepers.

Remove soft or loose material and make sure the base is even before adding sub-base.

3. Add and compact the sub-base

Add a suitable sub-base material and compact it properly. This helps create a stable foundation and reduces the risk of movement. Use a spirit level to check the base, as the first course sets the line for the rest of the wall.

4. Lay the first course

The first course needs to be level, straight and secure. For retaining wall blocks, follow the product guidance for laying and spacing. For a sleeper retaining wall, make sure the sleepers are positioned correctly and fixed securely. 

Take time with this stage, as errors in the first course can become more visible as the wall gets higher. 

5. Build up the wall

Continue building the wall course by course. Check the level and alignment regularly. If the wall system requires staggered joints, reinforcements. Adhesive or specific fixings, follow the recommended method. 

For retaining wall sleepers make sure each sleeper is properly secured and that fixings are suitable for outdoor use. 

6. Add drainage behind the wall

Place gravel or clean stone behind the wall to help water drain away. A perforated drainage pipe may also be needed at the base, depending on the wall design and site conditions. 

A geotextile membrane can help separate the drainage stone from the soil, reducing the risk of the drainage area becoming blocked. 

7. Backfill and finish

Backfill behind the wall in layers, compacting carefully as you go. Avoid placing heavy pressure directly against the wall too quickly. Once the wall is complete, check the finish, top level and surrounding ground. 

Common retaining wall mistakes to avoid

A retaining wall needs careful preparation. Common mistakes can lead to movement, cracking, leaning or drainage issues. 

Mistakes to avoid include:

• Building on soft or uneven ground 

• Not compacting the sub-base properly 

• Ignoring retaining wall drainage 

• Using materials that are not suitable for retaining soil 

• Not checking levels during installation 

• Back filling too quickly or unevenly 

• Underestimating the load behind the wall 

• Building a tall or load-bearing wall without suitable advice 

Taking time to check the specification, base and drainage can help reduce problems later. 

Which retaining wall material should you choose?

Retaining wall blocks are a strong option where a neat, consistent finish is needed. Concrete retaining wall blocks can suit projects where durability and structural performance are key considerations.

Sleepers are often chosen for garden retaining walls and landscaping features where a timber finish is preferred. They can work well for lower walls, raised beds and stepped outdoor areas. 

The right choice depends on the wall height, soil conditions, drainage needs, finish and level of support required. For more complex projects, specialist design advice should be considered before materials are ordered. 

Retaining wall FAQs

What is the best material for a retaining wall?

The best material depends on the project. Bricks and concrete retaining wall blocks are often chosen for strength, while timber sleepers can suit lower garden retaining walls where a timber finish is preferred.

How important is retaining wall drainage?

Retaining wall drainage is very important. Without suitable drainage, water can build up behind the wall and increase pressure on the structure. 

Can you build a retaining wall with sleepers?

Yes, a sleeper retaining wall can be used for many landscaping projects, especially lower garden retaining walls and raised beds. The sleepers, brackets and fixings should be suitable for outdoor use.

Do retaining walls need a foundation?

Most retaining walls need a stable, well-prepared base. The type and depth of foundation will depend on the wall height, material and ground conditions.

When should you get specialist advice for a retaining wall?

Specialist advice may be needed for taller retaining walls, walls close to buildings, walls supporting driveways or walls holding back a large amount of soil.

Final thoughts

Building a retaining wall starts with choosing the right materials and preparing the ground properly. Retaining wall bricks, concrete retaining wall blocks and retaining wall sleepers can all be suitable, but the best option depends on the project.

For a strong and long-lasting finish, plan the base, drainage, backfill and installation method before work begins. As a builder’s merchant, Travis Perkins offers a range of landscaping, building and drainage materials to support retaining wall projects.