Extending a house on a corner plot with two frontages

On a corner plot, permitted development for an extension is tighter than it is anywhere else, and the reason is a single phrase in Class A of Part 1 of Schedule 2 to the GPDO 2015. Rights are removed where the enlarged part would extend beyond a wall which fronts a highway and forms a side elevation of the original house. A corner plot has two walls fronting a highway. One is the principal elevation. The other is a side elevation fronting a highway, and building beyond it is not permitted development at all.

So the practical position for a corner plot extension is that a rear extension is usually available and a side extension usually is not.

Identifying the principal elevation with two highway frontages

The principal elevation is the one that gives the house its main architectural presentation, which in most cases is the elevation containing the front door and facing the address road. It is not defined by which road is busier.

Where the house was designed to address the corner, with a canted bay or a door on the chamfer, the answer is less obvious. Three indicators help.

• The postal address and the original plot layout, which usually reflect the designer's intention.
• The position of the front door, the front garden and the path from the gate.
• The architectural hierarchy: which elevation carries the better detailing, the bay windows, the string course, the porch.

Get this wrong and the consequence is serious. An extension built beyond what is in fact the principal elevation is not permitted development, and no amount of design quality cures that.

The second elevation is then the side elevation fronting a highway. Both restrictions bite: you cannot extend beyond the principal elevation, and you cannot extend beyond the side elevation that fronts the highway.

Side elevation restrictions that apply on both sides

It is worth separating the two side elevation rules, because people conflate them.

The first is the one just described: no extension beyond a side elevation that fronts a highway. That is an absolute bar within Class A, regardless of size or design.

The second applies to any side extension, whether or not the elevation fronts a highway. A side extension must not exceed 4 metres in height, must be single storey, and must not be wider than half the width of the original house. On a corner plot the inner side elevation, the one facing the neighbour rather than the road, is where that rule operates.

Add the eaves rule and the picture is complete. Where any part of the extension is within 2 metres of the boundary of the curtilage, its eaves cannot exceed 3 metres. Corner plots often have two boundaries close to the house, so the 3 metre eaves limit applies more often than on a mid-terrace plot. A wrap-around scheme has to satisfy all of these at once, and the interaction between the rear and side limits is the usual sticking point.

Boundary treatment heights next to a highway

Fences and walls have their own class and their own numbers, and corner plots run into them constantly.

Class A of Part 2 permits a gate, fence, wall or other means of enclosure up to 1 metre high where it is adjacent to a highway used by vehicular traffic, and up to 2 metres elsewhere. Adjacent to a highway does not mean only on the boundary line, so a fence set back a short distance from a footway can still be caught.

Two consequences on a corner. The 1 metre limit applies along both frontages, which is why corner gardens so often have low walls and hedges rather than close-boarded fences. And hedges are not caught by the class at all, because planting is not development, so a beech hedge at 1.8 metres beside the footway needs no permission even where a fence at 1.2 metres would.

Where privacy on the corner matters, the workable answer is usually a 1 metre wall with hedging behind it, or an application for a taller enclosure supported by the visibility analysis below.

Visibility splays at the junction

Highway visibility is what turns a corner plot application from a Class A question into a highways one.

The local highway authority will look at the sight line from a driver emerging from the side road, measured from a set-back point along the centre or edge of the minor arm to a point along the major road. Those distances come from the authority's own standards, and the design speed of the major road drives them, so ask for the local figures rather than assuming a national value.

What gets refused is anything that obstructs the splay above about 1 metre in height: a wall, a fence, a dense hedge, a substantial planter, a parked car in a new driveway, or a garage positioned across the corner.

Two design responses work. Keep the corner itself open and put the built form back from the chamfer, which also reads better. Or, where the splay crosses your land, offer to keep it clear by a condition or a section 106 obligation restricting planting and structures above a stated height within a defined area. Offering it is better than being asked.

Character of the street and openness of the corner

Where permitted development is unavailable and a full application follows, the argument is rarely about the extension itself. It is about the corner.

Corner plots read as gaps in a street, and a scheme that fills the gap has to answer three points an officer will raise. Whether the openness of the corner contributes to the character of the area. Whether the extension turns the corner properly, with active frontage and windows to both roads, or presents a blank flank to the side road. And whether the result looks like a house that was designed for the corner or a house with something bolted onto it.

The blank flank is the most common refusal reason on corner extensions and the easiest to design out. Put a window in it. Break up the mass with a setback, a change of plane or a subordinate roof.

Where the order is unavailable and a full application follows

Assume a householder application for anything beyond a rear extension on a corner plot. The documents needed are modest.

1. Existing and proposed plans and elevations at a recognised scale, including a street elevation showing the neighbouring houses.
2. A site plan showing the visibility splays with dimensions, and any land within your ownership that falls inside them.
3. A short planning statement dealing with the character of the corner, the side road elevation and highway safety.
4. A design and access statement where the site is in a conservation area or the authority's checklist requires one.
5. A heritage statement where the house is listed or in a conservation area.

Photographs of the street from both directions are worth including even where nobody asks for them, because they set the context the officer is judging.

Design approaches that succeed on corners

Illustrative example: a 1930s corner house with the front door on the address road and a long side elevation to the side road. A side extension was not available under Class A. The approved scheme took the form of a single storey rear extension within the permitted limits, plus a separate householder application for a subordinate two storey element set back 1.2 metres from the side elevation, with a hipped roof dropping below the main ridge, two windows to the side road and a 1 metre wall with hornbeam hedging behind it along both frontages. The visibility splay was kept clear by condition.

Four moves recur in schemes that get through.

Set back rather than align, so the addition reads as secondary. Drop the ridge, because a subordinate roof does more for acceptability than any material choice. Give the side road a proper elevation with windows and a door where the plan allows. And keep the corner itself open, in plan and in boundary treatment.

Enter your postcode on PlanScope to see which documents a corner plot extension is likely to need before you apply.

This is general guidance, not legal advice, and a lawful development certificate is the only formal way to confirm that works are lawful. Check the position with your local planning authority or a qualified professional 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.