Retaining walls on a site boundary and who approves them
A boundary retaining wall often needs planning permission, highway authority consent and a party wall notice, and nobody checks the structure unless you ask.
A retaining wall on a boundary is usually several approvals rather than one, and the planning permission is often the easiest of them. Whether you need planning permission for a retaining wall turns on height, position relative to the highway, and whether the works are better described as an engineering operation than as a means of enclosure. Separately, a wall near a street may need the highway authority's consent under section 167 of the Highways Act 1980, and the excavation behind it may be notifiable under the Party Wall etc. Act 1996.
Sort out which approvals apply before the groundworker quotes, because the structural design and the drainage detail drive the cost far more than the blockwork does.
When a retaining wall needs planning permission
Schedule 2 Part 2 Class A of the General Permitted Development Order permits the erection, construction, maintenance, improvement or alteration of a gate, fence, wall or other means of enclosure, up to one metre above ground level where it is adjacent to a highway used by vehicular traffic or a footway of such a highway, and up to two metres elsewhere. The right does not apply within the curtilage of a listed building.
Two things complicate that for a retaining structure. First, a wall whose purpose is to hold back ground may not be a means of enclosure at all, in which case Part 2 Class A does not help and the question becomes whether the works amount to development as an engineering operation under section 55 of the Town and Country Planning Act 1990. Second, the regrading itself is development even where a wall might be permitted, because cutting into a slope or building up a terrace alters the land.
Height measurement is the usual argument. Height is taken above ground level, and on a retaining wall the ground is at two different levels. Which one applies is a point to settle with the authority in writing rather than to assume, because a wall that is 900 millimetres on the upper side and 1.8 metres on the lower side is either permitted or not depending on the answer.
Where you want certainty, a lawful development certificate under section 192 of the 1990 Act is the only formal way to confirm that proposed works are lawful without permission.
Walls near a highway and section 167
This is the provision that catches self-builders. Section 167 of the Highways Act 1980 gives the highway authority control over retaining walls near a street. A retaining wall within four yards of a street, where the wall exceeds four feet six inches in height measured from the lower ground level, needs the authority's consent, and the section also deals with liability for maintenance and for repair where the wall becomes defective.
Two practical consequences. The consent is separate from planning permission, so a permission does not dispense with it. And the maintenance liability attaches to the wall, which means a wall built to retain a driveway above the footway is a long term obligation on the property rather than a one off cost.
Where the wall retains the highway itself, rather than retaining land above it, expect the highway authority to require a design check by its own engineers and sometimes a commuted sum. Get that conversation started early, because highway authorities are slower than planning departments.
Building regulations, structure and who checks it
A freestanding garden retaining wall is generally not building work within the Building Regulations, so there is no building control application and nobody checks the structural design on your behalf. That surprises people, and it is the single biggest risk in the whole exercise.
The position changes where the wall forms part of a building or supports one. A basement retaining wall, a wall built into a house extension, or a wall whose failure would undermine a dwelling is within the regulations and Part A applies. Where the wall is close to but not part of the building, the question is whether its failure would affect the building, and the honest answer on a steep plot is usually yes.
| Situation | Planning permission | Highway consent | Building control |
|---|---|---|---|
| 900 mm wall, rear boundary, not near highway | Usually permitted development | No | No |
| 1.8 m wall retaining a terrace, rear garden | Usually needed | No | Not usually |
| 1.5 m wall retaining a new driveway above the footway | Usually needed | Yes, under section 167 | Not usually |
| Retaining wall forming part of a basement or extension | Needed with the main scheme | Depends on position | Yes |
| Wall retaining the public highway | Needed | Yes, with a design check | Depends on arrangement |
Because nobody is obliged to check a freestanding wall, commission the design properly. A structural engineer working to Eurocode 7 will size the base, the reinforcement and the drainage for your soil and your surcharge, and the fee is a fraction of the cost of rebuilding a failed wall. A Geotechnical Assessment is the document that supplies the ground parameters the engineer needs.
Surcharge from adjoining land
Surcharge is the additional load on the retained face from whatever sits above and behind it. A lawn surcharges a wall very little. A parking space, a shed on a concrete base, a neighbour's extension or a delivery vehicle on an access road surcharges it a great deal, and the design load has to reflect the heaviest realistic case over the life of the wall.
Ask three questions before the design is fixed. What is above and behind the wall now, what could be there in future given the neighbour's own permitted development rights, and what construction plant will stand there during the build. A wall designed for a garden and then loaded by a neighbour's hardstanding is a dispute with no easy answer.
Where the neighbouring land is higher and already built on, the loading assumptions need the neighbour's cooperation to verify, which is one reason to raise the project with them before the application rather than after.
Drainage behind the wall
Water pressure behind a retaining wall is what pushes most failed walls over. A wall designed for earth pressure alone, with no drainage, can see loads far above its design case after a wet winter.
The standard arrangement is granular backfill behind the wall, a perforated land drain at the base laid to a fall, a filter geotextile to stop the drain silting, and a discharge point that actually goes somewhere. The last item is where domestic schemes fail: a land drain that discharges into the subsoil at the low end of the garden simply moves the problem.
Where the discharge needs to reach a surface water sewer or a watercourse, that is a connection question with its own permissions. Our note on building over or near buried infrastructure covers the constraints where pipes and sewers are involved.
Illustrative example: a sloping plot requires a 1.6 metre reinforced concrete retaining wall along the rear boundary to form a level terrace. The engineer designs for a 10 kilonewtons per square metre surcharge to allow for a future neighbour hardstanding, with 300 millimetres of granular backfill, a 100 millimetre land drain and a discharge to a new soakaway tested on site. All figures are illustrative.
Support, excavation and the Party Wall Act
Land has a natural right of support from adjoining land, and removing that support gives rise to a claim at common law whatever the planning position. That principle is the reason a cut into a slope at a boundary is a legal question as well as an engineering one.
The Party Wall etc. Act 1996 adds a procedure. Section 6 requires notice where you excavate within three metres of an adjoining owner's building or structure to a lower level than its foundations, or within six metres where the excavation would cut a line drawn downwards at 45 degrees from the bottom of those foundations. Serve notice, appoint surveyors if the neighbour dissents, and get the award before you dig.
Notice is not a formality. A party wall award records the condition of the neighbour's property before work, which is the evidence that protects you if cracks appear afterwards. Where piling or vibration is involved, the method matters too, and our note on piling methods beside sensitive neighbours sets out the options.
Conditions on level changes
Where permission is needed, expect conditions requiring approval of existing and proposed levels, cross sections through the site at stated intervals, details of the retaining structure, surface water drainage details, and sometimes a structural certificate before the wall is backfilled.
Submit the sections at the application stage rather than waiting for the condition. A pair of cross sections showing existing ground, proposed ground and the wall, annotated with levels relative to a fixed datum, answers most of the officer's questions and most of the neighbour's. Where the wall affects a boundary with a building, a Structural Survey recording the existing condition is worth having before work starts.
Get the levels surveyed and the sections drawn before anything else. Enter your postcode on PlanScope to see which ground and structural documents your site is likely to need, and have any draft reviewed before submission.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance, not legal advice, so check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
Do I need planning permission for a retaining wall?
Often yes. Part 2 Class A of the General Permitted Development Order permits a means of enclosure up to one metre adjacent to a vehicular highway and two metres elsewhere, but a structure whose purpose is to retain ground may not be a means of enclosure, and regrading a slope is development in its own right as an engineering operation.
How is the height of a retaining wall measured?
Above ground level, which on a retaining wall exists at two different levels. Which one applies decides whether the wall is permitted development, so confirm the convention with your local planning authority in writing. Where certainty matters, a lawful development certificate under section 192 of the Town and Country Planning Act 1990 is the formal route.
What is section 167 of the Highways Act 1980?
It gives the highway authority control over retaining walls near a street. A wall within four yards of a street exceeding four feet six inches in height measured from the lower ground level needs the authority's consent, and the section also addresses maintenance and repair liability. The consent is separate from planning permission.
Are retaining walls covered by building regulations?
A freestanding garden retaining wall is generally not building work, so there is no building control application and no independent structural check. Where the wall forms part of a building, supports one, or would undermine one if it failed, Part A applies. Commission a structural design to Eurocode 7 either way.
When does a retaining wall need a party wall notice?
Section 6 of the Party Wall etc. Act 1996 requires notice where you excavate within three metres of an adjoining owner's building or structure to a lower level than its foundations, or within six metres where the excavation cuts a line drawn at 45 degrees downwards from those foundations. Get the award before digging.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.