What a retaining wall has to do
A retaining wall holds back soil so you can have a level terrace, patio or drive on a sloping plot. Unlike a garden wall, it is pushed sideways all the time by the ground behind it, and that push rises sharply when the soil is wet. Every retaining wall type is really an answer to two questions: how does it resist that push, and how does it get the water out.
As a rough rule, low walls holding back a small step in level are straightforward. Taller walls, walls near a house or a road, and walls with a drive or building above them need an engineer's design.
Brick retaining walls
A brick retaining wall is built thick, often two bricks or brick-faced blockwork, on a wide concrete footing. Its weight and width resist the soil. It looks the most finished and can match the house, which is why it is popular for front gardens and terraces close to the building.
The brick must be a frost-resistant grade suited to being in contact with damp soil, and the back face should be waterproofed so water does not soak through and stain the face. Weep holes near the base let trapped water out.
Reinforced blockwork
For taller walls, hollow concrete blocks are laid with steel reinforcing bars running up through the cores, tied into the footing, and the cores are filled with concrete. The result acts like a single stiff cantilever. It can be faced with brick, rendered, or left as a clean block finish at the back of a garden.
This is the type most often specified by engineers where the level change is significant, because the reinforcement does the work rather than sheer mass.
Timber sleeper walls
Sleeper walls use heavy treated timbers laid horizontally or set upright in the ground. They are quick to build, suit informal gardens and raised beds, and are forgiving on uneven sites. Their weakness is life span: even treated timber eventually rots where it is in contact with wet soil, and taller sleeper walls need posts concreted deep into the ground to stop them leaning.
King post walls
A king post wall uses steel H-section posts concreted into deep holes at regular spacing, with concrete or timber panels dropped into the slots between them. The posts carry the load down into the ground, so the wall needs less excavation behind it than a mass wall. That makes king post walls useful on tight sites, along boundaries and where you cannot dig a big footing without disturbing a neighbour.
They look more utilitarian, but the panels can be faced or planted in front of, and they are quick to install once the posts are set.
Drainage, whichever type you choose
Most retaining walls that fail do so because of water, not design. Behind the wall there should be a layer of free-draining gravel wrapped in membrane, with a perforated pipe at the base carrying water to a soakaway or drain, plus weep holes through the face. Skipping this is the most common shortcut on cheap jobs, and it is the one that causes bulging and cracking a few winters later.
How we can help
Retaining walls and steps are part of the hardscaping work we list on this site. We have more than 26 years' building experience, NVQ Level 2 brickwork, FMB membership and full insurance. For the step-by-step planning and build process, read the retaining wall guide; this page is only about choosing the type.
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Questions people ask
Which retaining wall type lasts longest?
Properly drained brick and reinforced block walls last the longest. Timber sleepers have the shortest life because the timber eventually rots in wet soil.
Does a retaining wall need planning permission?
Usually not in a back garden if it is low, but walls next to a road, tall walls and anything in a conservation area can need consent. Check with the council first.
When is an engineer needed?
For taller walls, walls close to a house or road, or where a drive or structure sits above the retained ground.