Retaining walls close to a highway boundary
Planning permission and section 167 approval are two different consents, and the highways one bites at a lower height than most self-builders expect. Here is what each covers and what the drawings must show.
A retaining wall near a highway boundary is usually subject to two separate approvals that people conflate. Planning permission deals with whether the structure is acceptable in land use and appearance terms. Section 167 of the Highways Act 1980 deals with whether the highway authority is content with a wall that could fail onto the street, and it bites at a lower height than most self-builders expect. Clearing one does not clear the other, and the highways consent is the one more often missed.
The planning position is also less settled than the permitted development guides suggest, because a retaining wall is not obviously a means of enclosure.
When a retaining wall needs planning permission
Class A of Part 2 of Schedule 2 to the General Permitted Development Order 2015 grants rights for the erection of gates, fences, walls or other means of enclosure. The height limits are 1 metre where the structure is adjacent to a highway used by vehicular traffic, or a footway of such a highway, and 2 metres elsewhere. The rights do not apply where the structure would be within the curtilage of a listed building, and an Article 4 direction can remove them.
The wrinkle is the phrase "means of enclosure". A wall built to hold back ground is doing something different from a wall built to mark a boundary, and it is arguable that its construction is an engineering operation within section 55 of the Town and Country Planning Act 1990 rather than the erection of an enclosure. Authorities take different views, and the answer often turns on whether the structure is also the boundary.
Two things follow. First, do not assume the 1 metre allowance covers a retaining structure by the road. Second, if the works are marginal and you intend to rely on permitted development, apply for a lawful development certificate under section 192 of the 1990 Act. A certificate is the only formal way to confirm that proposed works are lawful, and it costs a fraction of what an enforcement dispute costs.
Regrading a front garden to form a parking area, which is the commonest reason a domestic retaining wall appears, brings its own issues. The engineering operation, the hard surface and the new vehicle crossing are three separate matters, and the crossing needs a separate application to the highway authority under section 184 of the Highways Act 1980.
What the highway authority consent covers
Section 167 of the Highways Act 1980 restricts the erection of retaining walls on land adjoining a street. The controlling figures are expressed in imperial units in the statute: a wall within 4 yards of the street, any part of which stands more than 4 feet 6 inches above the ground level at the boundary of the street, may not be erected except in accordance with plans and sections approved by the council. In metric terms that is roughly 3.7 metres from the street and about 1.4 metres of height.
Read that carefully, because two details catch people. The distance is measured to the street, which includes the footway, not to the carriageway edge. And the height is measured against ground level at the street boundary, so a wall that looks modest from inside a raised garden can be well over the threshold when viewed from the pavement.
Approval under section 167 is an approval of the plans and sections by the highway authority. It is a structural review, not a design one. The authority wants to see the wall geometry, the retained height, the ground conditions assumed, the loading including any surcharge from vehicles, the drainage, and the calculations. Expect it to be handled by a structures team rather than by the development management officer who deals with the planning application.
Where the wall supports the highway itself, rather than merely standing near it, the position is more onerous again and the authority may require an agreement dealing with future maintenance liability. Establish who owns and maintains the wall before you design it. Ownership of a retaining wall between two levels is frequently unclear on the title, and unclear ownership at design stage becomes a dispute at failure stage.
Ground conditions and the structural case
The design cannot start from a height and a block type. It starts from the ground.
A retaining wall fails in one of a small number of ways: sliding, overturning, bearing failure beneath the base, deep-seated slip through the soil behind, or structural failure of the stem. Which of these governs depends on the soil, the groundwater and the surcharge, so a modest ground investigation is proportionate even on a domestic job. On sloping or made ground, or anywhere with a history of instability, a Geotechnical Assessment informed by boreholes or trial pits is the document the highway authority will want alongside the calculations.
Surcharge is the item most often left out of a domestic calculation. A wall retaining a garden is one thing. The same wall with a car parked on the fill behind it, or with a delivery vehicle mounting the verge above, is carrying a load the original design never contemplated. State the assumed surcharge on the drawing and, where the fill will not be trafficked, say so and fence it.
Where the excavation comes within the notifiable distances of a neighbouring structure, the Party Wall etc. Act 1996 applies and notice must be served. That is a separate statutory process running in parallel with planning and with section 167, and it has its own timescales.
Drainage behind the wall
Water pressure is what kills retaining walls. A wall designed for drained conditions and then built without functioning drainage carries loads far beyond its design.
The standard arrangement is a free-draining granular backfill, a geotextile separation layer to stop fines migrating into it, a perforated land drain at the base laid to fall, and an outlet to a positive destination. Weep holes through the stem help but are not a drainage system on their own, and they discharge onto the footway unless you plan otherwise, which the highway authority will notice.
The outfall is the detail that gets lost. Discharging land drainage into the highway drain usually needs the authority's agreement, and discharging to a sewer needs the undertaker's. Where the wall sits within a wider scheme, tie the detail into the Drainage Strategy rather than showing it only on a structural section.
Frost and root action matter too. A drain outlet at the base of a wall below a mature hedge will silt or block, so allow a rodding point and show maintenance access on the plan.
Design life, maintenance and the long view
Ask what happens in thirty years. A gravity wall in engineering brick with a sound foundation and working drainage has a long and boring life. A crib wall or gabion structure has a shorter one, and a timber sleeper wall retaining more than modest heights beside a footway is a liability rather than a saving.
Set out a design life and a maintenance regime in the submission. Inspection access, the ability to rod the drain, and a note of who holds responsibility all belong in the documents. Where the wall is close to a highway, the authority may well condition or require them.
Construction stage risk sits alongside this. Temporary works to hold the face open during excavation are a designed element under the Construction (Design and Management) Regulations 2015, and on a constrained frontage the sequencing may need to be agreed with the authority alongside the Construction Traffic Management Plan. Where an existing wall is being replaced, a Structural Survey of what is there tells you whether you are underpinning, propping or demolishing.
What to show on the drawings
For a wall near a highway, submit the following as a minimum.
- A site plan with the wall, the street boundary, the footway and the measured distance between them.
- Existing and proposed ground levels on both sides, at the street boundary and at the top of the retained ground.
- A cross section through the wall showing retained height, foundation depth, backfill, drainage and outfall.
- The assumed surcharge and what is proposed on the fill behind.
- Materials and finish on the exposed face, since appearance is a planning matter even where structure is not.
- A statement of who will maintain the wall and how access is obtained.
Then send the section 167 submission to the highway authority in parallel with the planning application rather than after it. The structures team works to a different timetable from development management, and discovering a geometry problem after permission is granted means redesigning both.
This is general guidance, not legal advice. Check the position with your local planning authority, the highway authority and a chartered structural or geotechnical engineer before relying on it.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.
Frequently asked questions
Is a retaining wall permitted development?
Not reliably. Class A of Part 2 of Schedule 2 to the General Permitted Development Order 2015 covers gates, fences, walls and other means of enclosure, with a 1 metre limit adjacent to a highway used by vehicles. A structure whose purpose is to hold back ground may be an engineering operation rather than a means of enclosure. Apply for a lawful development certificate if you intend to rely on the rights.
What does section 167 of the Highways Act 1980 require?
A retaining wall on land adjoining a street, within 4 yards of the street and more than 4 feet 6 inches above ground level at the street boundary, may not be erected except in accordance with plans and sections approved by the council. In metric terms that is about 3.7 metres from the street and about 1.4 metres of retained height. The review is structural rather than aesthetic.
Is the distance measured to the road or the pavement?
To the street, which includes the footway rather than only the carriageway. That catches many domestic walls that sit back from the kerb but close to the pavement edge. The height is measured against ground level at the street boundary, so a wall that looks modest from inside a raised garden may be well over the threshold when viewed from the pavement.
Does drainage behind a retaining wall need to be shown?
Yes. Water pressure is the commonest cause of failure, so a section should show free-draining granular backfill, a geotextile separation layer, a perforated land drain laid to fall and a positive outfall. Weep holes alone are not a drainage system and they discharge onto the footway unless routed otherwise. Discharging to a highway drain or a sewer needs the relevant authority's agreement.
Who is responsible for maintaining a retaining wall by a road?
It depends on ownership, which is frequently unclear on the title where a wall separates two levels. Establish the position before you design, because the highway authority may require a maintenance agreement where the wall supports the highway itself. Set out a design life, an inspection regime and how access for maintenance is obtained in the submitted documents.
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.