Curtilage and principal elevation in Class A cases

Most householder permitted development disputes are decided by three defined terms rather than by any measurement. Whether an extension is permitted under Class A of Part 1 of Schedule 2 to the General Permitted Development Order 2015 turns on what the curtilage is, what the original dwellinghouse was, and where the principal elevation runs. Get the principal elevation permitted development question wrong on a corner plot or an L-shaped cottage and a scheme that looks compliant on the dimensions is unlawful development.

The Order defines some of these terms and leaves others to guidance and case law, which is why two officers can reach different answers on the same plot.

Why the definitions decide more cases than the dimensions

Depth, height and eaves limits are arithmetic. An officer can check them from a dimensioned drawing in two minutes.

The defined terms are different. They ask what the plot looked like at a date in the past, what land belongs functionally to the house, and which face of the building the world reads as its front. Those questions produce a judgement, and a judgement is what an appeal or a lawful development certificate refusal is usually about.

Treat them as the first stage of any Class A assessment rather than as a footnote after the dimensions check.

Curtilage and the three-part test

The GPDO does not give a general definition of curtilage, so the courts fill the gap. The established approach asks three things: the physical layout of the land and buildings, the ownership of the land both now and historically, and the use or function of the land in relation to the house.

None of the three is decisive on its own. A paddock in the same ownership, fenced off and grazed, is usually outside the curtilage. A former stable yard enclosed by the same wall as the garden and used for domestic storage is usually inside it, even where the title is separate. Land bought from a neighbour and merged into the garden may sit outside the curtilage until it has been used domestically for some time.

Two Class A limits depend directly on the answer. The restriction on the proportion of the curtilage that may be covered by buildings other than the original dwellinghouse cannot be applied without a curtilage boundary, and the same is true of the outbuilding provisions in Class E. Draw the curtilage on the plan, colour it, and explain the reasoning in the supporting statement. A drawing with no curtilage line invites the officer to draw their own.

The original dwellinghouse and the 1948 date

The original dwellinghouse means the building as it was first built, or as it stood on 1 July 1948 if it was there before that date. Every later extension counts against the allowances, whoever built it and whether or not it needed permission.

That single rule accounts for a large share of refused certificates. A 1930s semi with a 1970s rear addition, a 1990s conservatory and a garage conversion has already used most of its Class A volume, and the current owner often has no idea. Historic mapping, aerial photography, old council tax or rating records and the deeds are the usual evidence. Where the house predates 1948, the question becomes what stood on the ground on that day rather than what the Victorian builder put up.

And demolishing a previous extension does not restore the allowance. The original dwellinghouse is fixed by history, and rebuilding elsewhere on the plot does not reset it. There is more on this in our note on what "original dwellinghouse" means in the GPDO.

Reading the principal elevation on an irregular plan

The principal elevation is not defined in the Order itself. The working test, set out in the Ministry's technical guidance for householders, is the elevation that forms the principal face of the building: normally the one containing the main architectural treatment and the principal entrance, and normally the one facing the highway.

On a standard terraced or semi-detached house the answer is obvious. On anything else, work through the indicators in order:

1. Which elevation contains the principal entrance used by visitors, as opposed to a back door or a boot room.
2. Which elevation carries the main architectural treatment, such as a bay, a porch, a decorative doorcase or the composed window rhythm.
3. Which elevation the building was designed to present to the street, judged from the original drawings or from the pattern of the street.
4. Which elevation faces a highway, including a public footpath or bridleway.

Where the indicators conflict, say so and explain which you have weighted and why. A farmhouse whose front door faces a yard and whose composed elevation faces a lane is a real argument rather than a trick question. A house turned 90 degrees to the street by a 1960s layout is another.

One point often missed. The principal elevation belongs to the original dwellinghouse, so a later extension that now presents the most prominent face to the road does not become the principal elevation.

Corner plots and two frontages

A corner plot commonly has one principal elevation and one side elevation, with both fronting a highway. Class A treats them differently.

Nothing may extend beyond a wall forming the principal elevation of the original dwellinghouse where that wall fronts a highway. A side extension is restricted where the wall it extends beyond forms a side elevation of the original dwellinghouse and fronts a highway, with tighter limits on height and width than apply elsewhere. The practical result is that the flank of a corner house is close to undevelopable under Class A, and a full application is often the honest route.

Check what the highway actually is. An adopted footpath running along the flank boundary counts, and a private driveway shared with three houses generally does not. The highway authority's adopted highway plan settles it, and a screenshot of that plan belongs in the certificate application.

Land forward of the principal elevation

Several classes in Part 1 restrict development on land forward of a wall forming the principal elevation. Class E outbuildings are the common example, and the restriction bites on front gardens.

The line runs along the plane of the wall, extended across the plot, rather than following the building footprint round a bay or a porch. Where the house sits at an angle to the boundary the forward area can be an awkward wedge, and a bin store that looks well behind the front of the house on a site plan can sit forward of that plane at one corner.

Hard surfaces are governed separately, with front garden paving subject to the porous surfacing condition in Class F. Fences and walls fronting a highway have their own height limit in Part 2. None of those provisions is affected by where the principal elevation runs, which is worth stating in the analysis so nobody conflates them.

Recording the analysis in a certificate application

An application for 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. The burden of proof sits with the applicant, on the balance of probability, so the evidence has to be assembled rather than asserted.

Include an existing site plan with the curtilage outlined and the principal elevation marked, a short written analysis of each defined term with the evidence relied on, historic maps or aerial images establishing the original dwellinghouse, the adopted highway plan for a corner plot, and a schedule of every previous addition with its approximate date. Where the point is arguable, set out the counter-argument and answer it. A Planning Statement framed that way reads as a professional assessment rather than an assertion, and officers respond to it accordingly.

Check for an Article 4 direction before any of this. A direction withdrawing Class A rights makes the whole analysis academic, and directions are common in conservation areas.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

You can see which supporting documents a householder application usually needs from a postcode. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.