Rear extension depth on a corner plot

A corner plot does not lose its rear extension rights. What it loses is the right to build anything that projects beyond the side wall facing the flank road, because Class A of Schedule 2, Part 1 to the General Permitted Development Order 2015 excludes an enlargement extending beyond a wall that fronts a highway and forms a side elevation of the original house. A straight rear extension within the normal depth limits is usually still permitted development. A wrap-around is not.

That distinction decides the design. The same 3 metre or 4 metre rear projection your neighbour in the terrace enjoys is available to you, but the moment the extension turns the corner you are making a full application.

What a corner plot actually loses

Two restrictions bite harder on a corner than anywhere else.

The first is the side elevation rule. Where a side wall of the original house fronts a highway, nothing permitted under Class A may extend beyond it. On a mid-terrace house the side walls are party walls and the rule is irrelevant. On a corner plot the flank wall faces the road, so the whole of the side garden is effectively off limits for a permitted extension.

The second is that a side extension under Class A is limited to a single storey, a maximum height of 4 metres, and a width of no more than half the width of the original house, and on designated land side extensions are not permitted at all. Combine that with the side elevation rule and the result on most corner plots is that the side garden, which is the space you actually have, cannot be used without an application.

"Highway" is broader than people expect. It includes public footpaths, bridleways and byways, so a side wall facing a narrow adopted alley is caught in the same way as one facing a carriageway.

Identifying the principal and side elevations

The principal elevation is the one with the main architectural emphasis, which is usually the one containing the front door and facing the road the house is addressed from. It is not automatically the elevation facing the busier road.

On a corner plot the house is often turned to address the junction, or set at an angle, and then the identification is open to real argument. The government's technical guidance on householder permitted development discusses the point, and appeal decisions on it are indicative of how inspectors approach the question rather than binding.

Work through it in this order:

1. Identify the original dwellinghouse, meaning the house as built or as it stood on 1 July 1948, ignoring later additions.
2. Decide which wall carries the principal architectural treatment: the front door, the bay, the porch, the main fenestration rhythm.
3. For each remaining wall, ask whether it fronts a highway. A wall separated from the road by a front garden and a low wall still fronts it.
4. Mark both the principal elevation and any side elevation fronting a highway on a plan, and draw the two planes you cannot project beyond.

Keep that plan. It is the drawing the planning officer or an enforcement officer will ask for, and the one that makes a lawful development certificate application straightforward. The same analysis governs why front extensions are harder than rear ones, and the plane you are drawing is the same plane.

Depth limits that still apply at the rear

Assuming the rear extension stays behind both protected planes, the ordinary Class A limits apply:

A two storey rear extension must also leave at least 7 metres between the rear wall of the extension and the rear boundary opposite. The larger projections of 8 and 6 metres need prior approval through the neighbour consultation scheme, which is not available on designated land, and the total coverage of buildings within the curtilage must stay at or below half the curtilage excluding the original house.

Measure the projection from the original rear wall, not from the back of a 1990s conservatory. That single error accounts for a large share of unlawful extensions.

The wrap-around extension problem

An L-shaped extension that fills the corner between the rear and the side is the layout most corner plot owners want, and it is the one Class A does not permit, because the side leg projects beyond the side elevation fronting the highway.

There are three honest routes. And the first one usually costs the least to build.

Keep the extension entirely behind the side elevation plane. On a wide plot the rear extension can still be generous, and a single storey addition stepped in from the flank wall by a metre reads better from the street in any case.

Or apply for planning permission for the wrap-around. Householder applications are determined in eight weeks and the fee for a householder extension is set by the national fee regulations, which are indexed, so check the current schedule on the Planning Portal before budgeting.

Or split the work: build the compliant rear extension under permitted development, and apply separately for the side element. That sequencing has a cost in groundworks and roof junctions, and it can weaken the design, so weigh it carefully rather than treating it as a shortcut.

Street scene from two directions

Officers assess a corner plot proposal from both roads, and the flank elevation that was a garden boundary becomes a built frontage. The objections that recur are a blank flank wall, loss of the openness at the junction, and an extension that closes a visual gap the street relies on.

The design responses that work:

• Step the extension in from the flank boundary and keep a planted margin, rather than building to the line.
• Articulate the flank elevation with a window, a recess or a change of material, so it reads as a designed face rather than a gable end.
• Keep the ridge below the main house and set the roof form back from the corner.
• Retain mature boundary planting, which does more for the street than any detail you can draw.
• Keep upper floor windows on the flank oblique or obscured where they would overlook, which is where the thinking on overlooking and terraces earns its place.

Materials matter more on a corner because two elevations are visible together. Rendering or cladding the extension in something different from the house is a common refusal reason, and the position on rendering or cladding a house applies to the extension as much as to the original.

Boundary walls, visibility and the dropped kerb

Corner plots carry highway constraints that mid-plots do not. A new wall, fence or gate adjacent to a highway used by vehicular traffic is limited to 1 metre in height under Part 2 of Schedule 2, against 2 metres elsewhere, and the highway authority will resist anything that obstructs the visibility splay at the junction.

A new or widened vehicle crossing needs the highway authority's consent under section 184 of the Highways Act 1980, and on a classified road it needs planning permission as well. Apply for both early, because a refusal from the highway authority can make a driveway-dependent design undeliverable after the extension is built.

When a full application is the better route

If the scheme needs the side garden, apply. Trying to engineer a design around the side elevation rule usually produces a worse house and a thinner argument.

A householder application needs the form, the ownership certificate, a location plan, a site plan, existing and proposed elevations and floor plans, and on a corner plot a street scene elevation showing both frontages is worth adding even though it is not required. A short Planning Statement addressing the two frontages, the junction openness and the neighbour relationships does more than extra drawings.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A Lawful Development Certificate is the only formal way to confirm that works are lawful.

To see which documents a corner plot extension is likely to need, enter your postcode on PlanScope and work through the guided questions. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.