What counts as the principal elevation of a house

The principal elevation of a house is not defined in the General Permitted Development Order 2015, which is awkward, because several of the most useful householder rights depend on it. The working principal elevation definition permitted development practice uses comes from the government's technical guidance: the elevation that fronts the main highway serving the house, directly or at an angle, usually containing the main architectural features such as a bay window or a porch, and usually but not always containing the main entrance door.

Get the identification wrong and you can build an extension forward of a wall that turns out to be the principal elevation, which is not permitted development at all.

Why the definition decides several separate limits

The term appears across Part 1 and beyond, and in each place it removes a right rather than granting one.

Under Class A, an extension that would extend beyond a wall forming the principal elevation is not permitted development, and nor is one extending beyond a side elevation wall that fronts a highway. That single restriction is why forward extensions almost always need an application. Class B prevents a roof extension protruding beyond the plane of an existing roof slope that forms the principal elevation and fronts a highway, which is why rear dormers are often permitted development and front dormers are not. Class E prevents an outbuilding being situated on land forward of a wall forming the principal elevation, which catches garden offices placed in a front garden and garden structures on corner plots.

The term also appears in restrictions on designated land, in the chimney and flue class, and in the solar classes under Part 14, where equipment on a wall forming the principal elevation that fronts a highway loses its permitted development status in a conservation area or other Article 2(3) land.

So the identification is not an academic question. It governs the forward building line, the roof, the position of outbuildings and the location of equipment, all at once.

The interpretation used in practice

The technical guidance gives three indicators and they are applied together rather than individually.

The elevation fronts the main highway serving the house, directly or at an angle. The main highway is the one that sets the usually accepted frontage line on the street, which on a normal residential road is obvious and on a corner plot is not. The elevation contains the main architectural features, such as the principal bay windows, the porch or a decorative gable. And it usually, though not invariably, contains the main entrance door.

Note the word usually in each of those. The guidance is guidance rather than law, and an inspector deciding an appeal is entitled to reach a different view from the one in a householder's design statement. Where the answer matters, record the reasoning rather than asserting the conclusion.

Corner plots with two street frontages

Corner plots are where the argument happens, and the stakes are high because a side elevation that fronts a highway brings its own restrictions.

Where a house addresses one road with its front door, bay window and front garden path, and simply has a flank wall along the other road, the first is the principal elevation and the flank is a side elevation fronting a highway. The practical consequence is that side extensions and outbuildings along the flank are constrained by both the forward projection rule relative to the principal elevation and the side elevation restrictions.

Harder cases arise where a house has been designed to address a corner, with a canted bay or an entrance on the chamfer, or where the two frontages carry comparable architectural emphasis. The guidance acknowledges that a view has to be taken where two elevations have the character of a principal elevation. In that situation the architectural features usually carry more weight than the door position.

One point regularly misunderstood. A highway includes a public footpath or bridleway as well as a road used by vehicles, so a flank wall facing a public footpath can be a side elevation fronting a highway. Check the definitive map rather than assuming that a narrow alley does not count.

Houses set at an angle or behind another building

Estates built in the 1960s and 1970s produce plots where the house sits at 45 degrees to the road, or behind a neighbour, or at the end of a shared drive.

Where the house is set at an angle, the elevation that fronts the highway at an angle is still capable of being the principal elevation, because the guidance includes the words directly or at an angle. The architectural features then do most of the work: whichever elevation carries the main windows and the entrance is the strongest candidate.

Backland and flatted plots are harder. Where a dwelling is reached by a private drive and faces no highway at all, the highway indicator gives no answer and the identification falls back on the architectural features and the elevation the house was designed to address. That is a judgement, and reasonable people differ, which is a good reason to settle it formally rather than argue it after the works.

The same reasoning affects outbuildings, because the forward of the principal elevation rule has to be applied to a line that somebody has drawn. The relationship with the other Class E limits, including the fifty per cent curtilage test, means the position and the size questions have to be resolved together.

Where the original front door has moved

Houses are altered, and a door moved 40 years ago does not change which elevation the house was designed to present to the street.

Two scenarios recur. A house whose original front door has been blocked up and replaced by an entrance on the side, often during a 1980s extension, where the original elevation still carries the bay windows and the frontage line. The original elevation remains the principal one in almost every reading, because the architectural features and the frontage relationship survive the alteration.

And a house converted from something else, such as a former chapel, barn or shop, where the entrance now faces a car park. Here the architectural features may point one way and the current use another, and the honest answer may be that two elevations have a claim.

Evidence helps. Historic photographs, the original estate layout drawing, historic Ordnance Survey mapping showing the frontage line of the street, and the pattern of neighbouring houses all support a reading. Works to a front access raise the same identification question, which is why dropped kerbs and access under Part 2 Class B depend on where the frontage line is taken to be.

Flank walls that read as a front

A flank wall can acquire the character of a front over time, and councils occasionally argue it has.

Where a flank has been given a bay window, a porch and a path from the pavement, and the original front now faces a garden, an officer may treat the flank as the principal elevation. That is a reading of the current physical situation rather than of the original design, and it is contestable, but it is not unreasonable.

The practical risk runs in one direction. An applicant who treats the flank as a side elevation, and extends forward of the original front, finds that the extension is beyond a wall forming the principal elevation and therefore unlawful. The reverse mistake, treating the flank as principal when it is not, merely results in an unnecessary planning application.

On designated land the stakes rise again, because several classes remove rights in relation to a principal or side elevation fronting a highway, and side extensions are excluded altogether. The way those restrictions interact is set out in the treatment of side extensions under Class A in a conservation area.

Settling it with a certificate before you design

The cost of getting this wrong is a retrospective application, an enforcement notice or an unsellable house. The cost of settling it is a fee and a few weeks.

A Lawful Development Certificate under section 192 of the Town and Country Planning Act 1990 is the only formal way to confirm that proposed works are lawful, and it binds the council. Where the identification of the principal elevation is finely balanced, particularly on a corner plot or a dwelling set at an angle, apply for one before you spend money on detailed design.

What the application needs is not long. A location plan showing the highways serving the house and the frontage line of neighbouring properties. Elevations of all sides, with the architectural features annotated. Photographs from the public highway. A short Planning Statement setting out which elevation you say is the principal one and why, addressing each of the indicators in turn, and then demonstrating compliance with every limit of the class you are relying on.

And if the answer remains unclear, say so in the statement and give the alternative. A council that can see you have considered both readings is far more likely to engage with the reasoning than one presented with a bare assertion.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. Enter your postcode on PlanScope to see which documents a householder application would need. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.