A free-standing garden wall carries only its own weight and wind load. A retaining wall holds back earth and the water in it, which is a structural job — and water pressure is what fails them, not the masonry. Any retaining wall over about a metre, or supporting a surface that is loaded, should be designed rather than guessed.
- Retaining walls fail from water pressure behind them, not from weak brickwork.
- Weep holes and a free-draining backfill are not optional details.
- Free-standing walls need movement joints and a coping; both are routinely left out.
- Over about a metre, or retaining a driveway, get it designed.
Two different structures
These get discussed as if they were the same job with a different location. They are not.
A free-standing wall — a boundary wall, a planter surround, a low wall edging a patio — carries its own weight and resists wind. The loads are modest and predictable. It needs a sensible foundation, the right mortar, movement joints at intervals and a coping to keep water out of the top.
A retaining wall holds back ground. The soil behind it pushes outwards, and that push increases sharply when the soil is saturated, because water adds its own pressure. That is a structural problem, and it is solved by managing the water and by designing the wall to resist what remains — not by building the same wall slightly thicker.
The distinction matters because a retaining wall built as if it were a garden wall will lean, crack and eventually fail. We see it regularly: a single-skin wall holding back half a metre of a raised bed, bowing outwards after two wet winters.
Why retaining walls fail
| Symptom | Usual cause | Remedy |
|---|---|---|
| Wall leaning outwards at the top | Water pressure behind it | Drainage behind; often rebuild |
| Horizontal crack partway up | Overturning — wall too slender | Structural assessment |
| Bulging in the middle | Single skin retaining too much | Rebuild to a designed section |
| Water weeping through the face | No drainage route — the only way out | Add weep holes and a drain |
| Mortar washing out | Saturation plus the wrong mortar mix | Repoint; fix the drainage first |
| Settlement at one end | Inadequate or uneven foundation | Underpin or rebuild that section |
| Coping lifted or missing | Frost in a saturated wall top | Replace with a proper overhanging coping |
Four of those seven come back to water. That is the point of this page: the drainage is the structure, as much as the masonry is.
What goes behind a retaining wall
- A foundation sized for the height and the ground conditions, taken below any made ground.
- A free-draining backfill — clean angular stone against the back of the wall, not the clay that came out of the hole. Clay backfill holds water and expands.
- A perforated land drain at the base of that stone, laid to a fall, taking water to somewhere it can go.
- Weep holes through the face at the base, so any water that does accumulate has a route out rather than building pressure.
- A geotextile between the stone and the soil, so fine material does not migrate into the stone and block it.
- A waterproof coating on the buried face, where the wall backs onto a patio or structure.
- A coping that overhangs with a drip, keeping water out of the top of the wall.
Points two, three and four are the ones omitted from cheap work, and they are precisely the ones that decide whether the wall survives. None of them is visible once the job is finished, which is exactly why they go missing.
When you need it designed
There is no single height at which a retaining wall becomes a structural matter, because the loads depend on what is behind it as much as how tall it is. As a working guide, get a design where any of the following apply.
Over about a metre of retained height. The pressure increases faster than the height, so a 1.5m wall is carrying considerably more than one and a half times what a 1m wall carries.
Anything is loaded above it. A retaining wall supporting a driveway, a parking space or a building is carrying the weight of vehicles or the structure as a surcharge on top of the soil pressure. That changes the calculation substantially.
It supports or is close to a neighbouring property, a boundary or a highway. Failure then affects someone else, and the consequences are not just yours.
Ground conditions are poor — made ground, a high water table, or soft clay.
A retaining wall can also be a Building Regulations matter where it affects a building or the public, and work affecting a party boundary can engage the Party Wall etc. Act. Worth establishing before you start rather than afterwards.
Where a wall is retaining more than a metre and nobody has calculated anything, the honest answer is that nobody knows whether it is adequate. That is a reason to ask, not a reason to assume the worst.
Free-standing walls: the details that get left out
Movement joints
Masonry expands and contracts. A long wall with no movement joints cracks, and it cracks in the place of its own choosing rather than at a joint you designed. Vertical joints at sensible intervals, with the wall free to move at that point, prevents it. Routinely omitted on garden walls, and the commonest cause of the vertical cracks people later point at.
The coping
The top of a wall is its most exposed surface. An overhanging coping with a drip throws water clear of the face; a flush brick-on-edge finish lets water run straight down it and soak in. Saturated masonry then spalls in frost, and the damage starts at the top and works down. A proper coping is inexpensive and it is the single best thing you can do for a wall's lifespan.
The right mortar
Stronger is not better. A mortar harder than the brick forces any movement to crack the brick rather than the joint, and in older soft brickwork a cement-rich mortar traps moisture and causes the face to blow off. The mortar should be weaker than what it bonds, which on garden walls in exposed conditions is a balance rather than a formula.
A damp-proof course
A free-standing wall draws moisture up from the ground. A DPC at the base stops that rise, keeping salts and saturation out of the visible brickwork. Cheap, invisible, and left out of most garden walls.
Mistakes Coventry homeowners keep making
- Backfilling with the spoil. The clay that came out holds water and swells. Clean stone goes back, and the clay goes away.
- Building a single-skin wall to retain. A half-brick wall is a garden wall. It is not a retaining structure at any useful height.
- No weep holes, then surprise when water finds its way through the mortar instead.
- Raising ground level against the house. A raised bed built against an external wall bridges the damp-proof course and puts wet soil against brickwork. It is one of the most common causes of internal damp we find.
- Repointing a wall that is wet for structural reasons. The mortar washed out because water is passing through. Repointing without fixing that just restarts the clock.
- Sleeper walls with no drainage. Timber sleepers are popular and they retain earth like anything else. The drainage requirement does not go away because the material changed.
- Assuming a wall that has stood for years is fine. Retaining walls fail progressively. A lean that has been there for a decade is still a lean.
What it costs
These are the figures published across this site that apply to walling work:
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Day rate | £150–£250/day | Per landscaper |
| Landscaper, hourly | £15–£40/hr | Task dependent |
| Patio | £80–£150 per m² | Material dependent |
| Fencing | £80–£150 per panel | Supplied & fitted |
Walls are priced per job because the foundation, the retained height and the drainage dominate the cost rather than the visible brickwork. A quote that does not mention backfill, a land drain or weep holes on a retaining wall is quoting for the wrong job.
We look at where the water is going first, because on a retaining wall that is usually what caused it.
Frequently asked questions
What is the difference between a garden wall and a retaining wall?
A garden wall carries only its own weight and wind load. A retaining wall holds back earth and the water within it, which pushes outwards — sharply more when saturated. That is a structural job solved by drainage and design, not by building the same wall slightly thicker.
Why is my retaining wall leaning?
Almost always water pressure behind it. If there is no free-draining backfill, no land drain and no weep holes, water accumulates behind the wall and pushes it outwards. The masonry is usually fine. Rebuilding without fixing the drainage repeats the failure.
Do retaining walls need weep holes?
Yes. They give water a route out at the base instead of building pressure behind the wall. They work alongside a clean stone backfill and a perforated land drain — weep holes alone cannot drain a clay backfill. All three are invisible once finished, which is why they get left out.
How high can a retaining wall be before it needs designing?
As a working guide, over about a metre of retained height, or at any height where something is loaded above it — a driveway, a parking space, a building. Pressure rises faster than height, and a surcharge above changes the calculation substantially. Poor ground or a boundary nearby are also reasons to have it designed.
Can I build a raised bed against my house wall?
Not without dealing with the damp-proof course. Soil piled against an external wall bridges the DPC and puts wet earth in contact with brickwork above it, which is a common cause of internal damp. Either keep the bed clear of the wall with a drained gap, or line and waterproof the retaining face.
What mortar should a garden wall use?
One weaker than the brick it bonds. A mortar harder than the masonry forces movement to crack the brick rather than the joint, and on older soft brickwork a cement-rich mix traps moisture and blows the face off. Stronger is not better, and matching the existing wall matters on repairs.
The drainage is the structure
On a retaining wall we specify the backfill, the land drain and the weep holes in writing, because those are what decide whether it stands. Free survey.