A retaining wall is a structural job dressed up as a landscaping job. It is holding back soil, water and sometimes the weight of a driveway or a building, and when one fails it usually fails all at once. MLS Contractors builds and rebuilds retaining walls across Surrey, Sussex, Kent and London — masonry, reinforced blockwork, concrete, gabion and timber sleeper — with the drainage and the foundation designed to match what the wall is actually being asked to hold.
What a Retaining Wall Is Actually Resisting
Soil behind a wall does not sit still. It pushes sideways, and that push increases with height, with the type of soil, and enormously with water. Clay is worse than sand. A saturated backfill can more than double the load on the wall. Add a surcharge — a car parked above, a shed, a patio, a neighbour’s structure — and the numbers climb again.
This is why a wall that looks identical to the one down the road can need a completely different design, and why we would rather ask questions about what is above and behind the wall than quote off a photograph.
Types of Retaining Wall We Build
- Mass masonry brick and block walls — traditional, good-looking, and appropriate at modest heights with a wide footing
- Reinforced blockwork and in-situ concrete stem walls — steel reinforcement tied into a concrete base, for greater heights or surcharge loads
- Segmental and crib walling — interlocking concrete units, often with geogrid reinforcement into the retained soil
- Gabion baskets — free-draining, quick to build and increasingly used on rural and level-change sites
- Timber sleeper walls — cost-effective for lower retention where the look suits the garden
- Underpinning and repair of existing failing walls, including rebuilding to the original appearance
Drainage Is What Keeps a Retaining Wall Standing
If we had to point at one reason retaining walls fail in the South East, it is water with nowhere to go. Our standard build-up includes free-draining granular backfill immediately behind the wall, a geotextile separator so the fines do not migrate into it and clog it, a perforated land drain at the base taken to a suitable outfall, and weep holes or a drainage channel where appropriate. On masonry walls the retained face is waterproofed and a damp-proof course keeps ground salts out of the visible brickwork.
Skipping any of that saves very little at the time and is the single most expensive false economy in garden construction.
When You Need a Structural Engineer
Low garden steps and planters are one thing. Once a wall is retaining much more than about 600mm, or is retaining anything with a load on top of it, or is close to a building, a boundary or a highway, it wants a structural engineer’s design rather than a rule of thumb. Building control involvement may be required where a failure would affect a building or means of access, and work near a boundary can trigger notice under the Party Wall etc. Act 1996.
We work with structural engineers as a matter of course on our foundations and groundworks projects and will tell you at quotation stage if we think your wall needs a designed solution. We would far rather have that conversation before we start than defend a wall that was never designed for the job.
Timber Sleeper Retaining Walls
Sleeper walls are popular for good reasons: they are quick, they suit an informal garden, and they cost less than masonry. They also have real limits. Timber has a finite life in contact with wet soil, and the retention height that a sleeper wall can safely manage is modest unless the posts are properly founded in concrete and, above a certain height, tied back into the retained ground. We will build a sleeper wall where it is the right answer and tell you when it is not — for example where a driveway, a building or a significant level change sits behind it.
Terracing a Sloping Garden
Many of the retaining walls we build are part of a bigger idea: turning an unusable slope into two or three usable levels. That normally means a combination of retaining walls, steps, drainage, and paving or planting, and it works far better designed as one job than as a wall followed later by a patio. We can deliver the whole thing alongside our hardscaping and landscaping work, and if you want a masonry finish that ties into your house, our garden wall and brickwork teams are the same people.
What Affects the Cost of a Retaining Wall
- Retained height. The single biggest driver — loads increase faster than height does
- Surcharge. Whether vehicles, structures or another garden sit above the wall
- Soil type and groundwater. Clay and running water both add cost
- Construction type. Sleepers, gabions, masonry and reinforced concrete are very different propositions
- Access and spoil. Whether machines can reach the line, and how much soil has to leave site
- Drainage outfall. How far the land drain has to run to somewhere it can legally discharge
- Design and approvals. Engineer’s design, building control and party wall notices where required
- Finish. Facing brick, stone cladding, coping and rendering
We survey the site, agree the design approach and then give you a fixed figure. We do not quote retaining walls by the metre over the phone, because the wall you need and the wall you asked for are not always the same thing.
Signs an Existing Retaining Wall Is Failing
Worth acting on early: a wall that is leaning or bulging outwards, stepped or diagonal cracking, courses that have moved out of line, mortar washing out, water seeping through the face rather than out of a weep hole, or ground sinking behind the wall. Any of those suggests either the drainage has blocked or the wall was never strong enough. We will come and look and tell you whether it needs monitoring, repair, or replacement.
Frequently Asked Questions
Do I need planning permission for a retaining wall?
Retaining walls are treated like other walls for planning purposes, so the two-metre limit — or one metre where it adjoins a highway used by vehicles — is the usual starting point, with conservation areas and listed buildings as exceptions. Planning is a separate question from structural approval, and a wall can need engineering input even when it needs no planning permission.
How high can a retaining wall be without an engineer?
There is no single legal figure, but as a practical rule anything retaining more than about 600mm, or retaining soil with a load above it, should be designed rather than estimated. Below that, a properly founded and drained masonry or sleeper wall is usually straightforward.
Why does my retaining wall need drainage behind it?
Because water trapped in the soil behind a wall dramatically increases the sideways pressure on it. Free-draining backfill, a geotextile and a land drain at the base let that water escape instead of building up, and they are the difference between a wall that lasts decades and one that leans within a few winters.
Are timber sleeper walls any good?
They are genuinely good value for lower retention in an informal garden, provided the posts are properly concreted, the timber is suitable for ground contact and the wall is drained. They are not the right choice for high retention, for holding up a driveway, or where a structure sits behind them.
Can you rebuild a wall that has started to lean?
Usually, yes — and often it is the drainage rather than the masonry that needs the real attention. Depending on the condition we can rebuild in the original brick or stone so the finished result matches the rest of the garden.
Get a Quote for Your Retaining Wall
Tell us the height, the length and what sits above and behind the wall, and we will come and look. Call 01293 225853, email info@mlscontractors.co.uk, or use our contact form.