Why the principal elevation is excluded from Class A

Class A permits nothing forward of the principal elevation. The wording in paragraph A.1(d) of Part 1 of Schedule 2 to the General Permitted Development Order 2015 excludes any enlargement that would extend beyond a wall forming the principal elevation of the original dwellinghouse, and also beyond a wall that fronts a highway and forms a side elevation. So a front extension always needs planning permission, and on a corner plot one of the side elevations may be closed off as well.

The exclusion exists because the front of a house is the part the street sees. Rear extensions affect a neighbour or two. Front extensions change the building line and the rhythm of a road, and the Order leaves that judgement to the council.

How the Order treats the front and the sides

Three separate limbs work together, and they are easy to conflate.

The principal elevation limb excludes any enlargement extending beyond the wall that forms the principal elevation of the original dwellinghouse. The measurement is taken from the plane of that wall, not from the building line of the street, so a house set back behind its neighbours gains nothing from the setback.

The side elevation limb excludes any enlargement extending beyond a wall that fronts a highway and forms a side elevation. A flank wall facing a road, a public footpath or a bridleway is caught. A flank wall facing a private drive that is not a highway is not.

The word "original" carries its usual meaning here: the house as built, or as it stood on 1 July 1948 for anything predating that date. An earlier front porch does not move the datum forward.

Outbuildings are treated the same way. Class E does not permit a building, enclosure or container on land forward of a wall forming the principal elevation, which is why a garden office cannot go in the front garden without permission.

Two things are still permitted at the front. A hard surface under Class F, subject to the porous surfacing or drainage requirement where the area exceeds five square metres. And a porch under Class D, which has its own limits: a ground area not exceeding three square metres measured externally, a height not exceeding three metres, and no part within two metres of any boundary of the curtilage that fronts a highway.

Identifying the principal elevation

The Order does not define it. The government's technical guidance on householder permitted development rights does, in substance: the principal elevation is normally the one containing the main architectural features, such as a principal bay window or the entrance, and it will usually be the elevation facing the highway. A house has one principal elevation, not two.

Where the front door and the architectural treatment point to different walls, the architectural treatment normally wins. A house whose entrance is on the flank, with a symmetrical front elevation containing bay windows facing the road, has its principal elevation facing the road.

Awkward cases and how they are usually resolved:

• A house turned side-on to the road, with its entrance and main windows facing a side garden. The elevation with the architectural treatment and the entrance is the principal elevation, even though it does not face the highway.
• A bungalow on a plot with no highway frontage, reached by a private track. There is still a principal elevation, identified by the treatment and the entrance, and the side elevation limb simply does not bite because there is no highway.
• A converted barn or former commercial building with no obvious front. Argue it from the treatment, the entrance and the address, and expect the council to have a view.
• A house that has been extended so heavily that the original front is hard to read. Go back to the original drawings or historic mapping.

Where the answer matters financially, a Lawful Development Certificate for proposed works under section 192 of the Town and Country Planning Act 1990 is the only way to settle it formally.

Corner plots with two frontages

On a corner plot, both the front and one flank commonly front a highway, which leaves a narrower envelope than owners expect.

The practical position is usually this. Nothing can come forward of the principal elevation. Nothing can extend beyond the flank wall that fronts the side road. A rear extension within the depth and height limits remains available, and a side extension is available only on the elevation that does not front a highway, subject to the single storey, four metre height and half-width limits that apply to side extensions generally.

Outbuildings are further constrained, because the land forward of the principal elevation is excluded and a corner garden is often largely in that zone.

Two points that catch people out. A verge or a grass strip between the flank wall and the carriageway is usually part of the highway, so the flank still fronts it. And a footpath running along the side of the plot is a highway for these purposes even though no vehicle uses it.

What "extend beyond" means in practice

The test is geometric and unforgiving. Any part of the enlargement that projects past the plane of the relevant wall takes the whole works outside Class A.

Stepped frontages are the hard case. Where the front of the house is not a single plane, because of a projecting bay, a recessed entrance or a two-storey forward wing, more than one wall can be said to form the principal elevation. The cautious reading, and the one most councils apply, is that filling in a recess to the line of a projecting element extends beyond a wall forming the principal elevation and therefore needs permission.

Bay windows, canopies and small projections have their own treatment, and the position on those is set out in our note on bay windows, canopies and small projections.

Where the works turn the corner from the side towards the front, Class A applies both limbs at once and the design usually has to stop at the front plane, as our note on wrap around extensions and the Class A limits explains.

Applying for a front extension

A front extension is not a lost cause. It is a planning judgement, and the arguments that work are about the street rather than about the house.

What councils assess:

1. The established building line, and whether the proposal breaks it in a way visible from the street.
2. The rhythm and pattern of the street, including whether other properties have been extended forward and how consistently.
3. The proportion of the front garden retained, and whether parking, turning and any visibility splay still work.
4. Subordination: whether the addition reads as an addition rather than as a rebuilt frontage.
5. Effect on the neighbour, particularly where the extension is close to a shared boundary and to their front window.
6. In a conservation area, whether the character and appearance of the area is preserved or enhanced.

Designs that get permission tend to be modest in depth, set down from the eaves, set in from at least one side, and built in materials that match. A full-width two-storey front extension on a uniform 1930s road rarely succeeds. A single storey entrance addition, 1.2 m deep, on a road where three other houses already have them, usually does.

Make the case in a short Planning Statement with a street elevation drawing showing the proposal alongside its neighbours. Where a Design and Access Statement is required, the building line analysis belongs in it rather than in a covering letter.

Evidence that settles the elevation question

Assemble this before you argue with a case officer:

• The original as-built drawings, where the council's file holds them.
• Historic Ordnance Survey mapping showing the original footprint and orientation.
• Photographs of all elevations, with the architectural treatment visible.
• The postal address and which road the property is numbered from, which is persuasive rather than decisive.
• The adopted highway extent, available from the county or unitary highway authority, to establish whether a flank wall fronts a highway at all.
• Any earlier permission or certificate for the property that records the council's previous view.

The highway extent is the document most often missing and most often decisive on a corner plot. A flank wall that appears to face a road may in fact face a strip of private land, which changes the answer entirely.

This is general guidance, not legal advice. Permitted development rights turn on the precise wording of the Order, on whether rights have been removed by condition or by an Article 4 direction, and on the facts of the building, 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.

Enter your postcode on PlanScope to see which documents a front extension application is likely to need. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.