Finding the principal elevation on a corner plot
On a corner plot a house may have two principal elevations, and the land forward of either is outside Part 1 rights. Here is how the definition works and how to get it confirmed.
On a corner plot a house can have two principal elevations, and that single point removes most of the permitted development rights homeowners assume they have. The Town and Country Planning (General Permitted Development) (England) Order 2015 hangs several of its householder limits on the phrase "principal elevation", including where an extension may go and where a shed or garden room may stand. The government's own technical guidance for householders says that where two elevations both have the character of a principal elevation, both are treated as one. A corner house with a front door on one road and a long glazed flank facing the other is the standard example.
Work this out before you draw anything. It changes what is possible in the garden.
What the Order means by principal elevation
The Order does not give a tidy dimensional test. The technical guidance published by government explains that the principal elevation is usually the part of the house fronting the main highway that serves it, the elevation the address relates to, and the one carrying the main architectural features: the main entrance, a bay window, a porch, the chimney arrangement, the decorative detail.
Two points follow from that. First, "front" is about character and setting rather than compass direction, so a house set at 45 degrees to the road still has a principal elevation facing it. Second, the assessment is made on the original dwellinghouse as it stood on 1 July 1948 or as first built if later, so a later extension does not create a new principal elevation.
The original house is the reference point throughout Part 1. People lose arguments over this more often than over anything else.
Why a corner plot can appear to have two
A typical 1930s corner house was designed to address both roads. The builder put a front door and bay on the short frontage and gave the long flank a projecting gable, a second bay, or windows to the main rooms. Neither elevation reads as the back of the house.
Where that is the case, the honest answer is that there are two principal elevations, and the land forward of either is out of bounds for the rights that depend on the phrase. Councils differ in how readily they accept a second principal elevation, and the argument turns on the drawings and the photographs rather than on policy.
Three patterns come up repeatedly:
- A genuine dual frontage, with matching architectural treatment on both roads. Two principal elevations.
- A blank or near-blank flank wall with only secondary windows, facing the side road across a fence. One principal elevation, with the side elevation rules still applying.
- A wrap-around plot where the house faces one road and the garden turns the corner. One principal elevation, but a long stretch of garden fronting a highway.
The third pattern is the one that catches people, because the garden is large and looks unconstrained until you read the outbuilding rules.
The side elevation fronting a highway rule
Class A of Part 1 allows a single-storey rear extension and, separately, a side extension, subject to limits. Among them, an extension is not permitted development where the enlarged part would extend beyond a wall which either forms the principal elevation of the original dwellinghouse, or fronts a highway and forms a side elevation of the original dwellinghouse.
The second limb is the one corner plots hit. If your flank wall faces a road, you cannot build out past it under Class A, even where the flank is plainly the side of the house.
"Highway" is broad. It takes in public footpaths, bridleways and byways as well as carriageways, so a plot bounded by an adopted footpath at the side is caught in the same way as one bounded by a street. A private drive serving a handful of houses is usually not a highway, but the status of a lane is a matter of fact to check with the highway authority rather than assume from the way it looks.
Roof extensions under Class B and the upper-storey rights under Class AA carry their own restrictions tied to the principal elevation as well, so the answer you reach here follows you up the building.
Where an outbuilding may and may not sit
Class E covers outbuildings and other structures incidental to the enjoyment of the dwellinghouse. It is not permitted development where the building would be situated on land forward of a wall forming the principal elevation of the original dwellinghouse.
On a corner plot with two principal elevations, that rules out the whole of the garden forward of either. A garden room tucked into the corner of a wrap-around plot, visually behind the house on one road but plainly in front of it on the other, is outside Class E even where the neighbours cannot see it.
Two further limits bite on corner plots more than elsewhere. Any outbuilding within two metres of the boundary of the curtilage is limited to 2.5 metres in overall height, which on a narrow corner garden usually means a flat or very shallow roof. And the total area covered by buildings, enclosures and containers must stay within half the area of the curtilage excluding the original house, a calculation that gets awkward where the boundary has moved over the years. Where land has been added to the garden, the curtilage question needs settling first, and measuring curtilage when a garden has been enlarged sets out how.
Extensions forward of the principal elevation
Nothing in Part 1 allows a domestic extension forward of a principal elevation. Not a porch beyond the Class D limits, not a bay, not a single-storey utility room across the front.
Class D does allow a porch, within tight limits: no more than 3 m2 of external ground area, no more than three metres above ground level, and not within two metres of any boundary of the curtilage with a highway. On a corner plot the two metre rule frequently defeats a porch on the side road frontage even though the porch itself would be small.
Designated land narrows things further. In a conservation area, a National Landscape, a National Park, the Broads or a World Heritage Site, side extensions are not permitted development at all, and rear extensions of more than one storey are excluded. Where the house is listed, Part 1 rights are heavily curtailed and listed building consent is a separate requirement, which is covered in permitted development rights in a listed building curtilage.
| Proposal on a corner plot | Class | Usual answer where the flank fronts a highway |
|---|---|---|
| Single-storey rear extension behind both frontages | A | Permitted, subject to depth and height limits |
| Side extension beyond the flank wall | A | Not permitted |
| Garden room forward of either principal elevation | E | Not permitted |
| Garden room behind both, within 2 m of boundary | E | Permitted at up to 2.5 m height |
| Porch on the side frontage | D | Usually not permitted, two metre rule |
Drawings and evidence that settle the question
The dispute is factual, so answer it with facts. A site plan at 1:200 with both highway boundaries marked, elevations of the original house, and photographs of each frontage taken square-on will usually settle it in one exchange with the case officer.
Add the historic evidence where the house has been altered. An old sale plan, a pre-extension survey or a dated aerial photograph showing the original footprint lets you argue from the original dwellinghouse rather than the current one. Where the council's view is that both elevations are principal and you disagree, the reasoning to put in writing is architectural: which elevation carries the main entrance, which carries the primary fenestration, which one the address relates to, and what the original design intent was.
Appeal decisions on dual frontage cases go both ways and are indicative of how inspectors weigh those features rather than any kind of precedent. Do not present one as binding.
Getting the point confirmed before you design
Two routes give certainty. A pre-application enquiry gives you an officer's informal view quickly and at modest cost, and is worth the fee where the answer decides the whole design. A Lawful Development Certificate for proposed use or development under section 192 of the Town and Country Planning Act 1990 gives a formal, binding determination that the works would be lawful, and it is the only way to be sure.
The certificate route costs a fee and takes eight weeks, and it is far less painful than an enforcement notice on a finished garden room. Where a certificate is refused, the fall-back position may still help a subsequent planning application, and using a permitted development fall-back in an application explains how that argument works.
If the answer turns out to be that you need permission, the supporting narrative is short: what the house is, what the two frontages look like, why the proposal respects both, and how the street scene is affected. You can draft that Planning Statement in PlanScope in minutes and have it reviewed before you submit.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
Can a house have two principal elevations?
Yes. The government's technical guidance for householder permitted development says that where two elevations both have the character of a principal elevation, for example on a corner plot, both are treated as principal. The consequence is that land forward of either wall falls outside the rights in Part 1 that depend on the phrase, including outbuildings under Class E.
Does a public footpath count as a highway for permitted development?
Yes. Highway takes in public footpaths, bridleways and byways as well as roads, so a flank wall facing an adopted footpath is a side elevation fronting a highway. That blocks a side extension beyond it under Class A. The status of a lane or private drive is a question of fact, so check it with the highway authority.
How is the principal elevation decided if the house has been extended?
Part 1 works from the original dwellinghouse, meaning the house as it stood on 1 July 1948 or as first built if later. A later extension does not create a new principal elevation and does not move the existing one. Use old sale plans, survey drawings or dated aerial photographs to show the original footprint if the point is disputed.
Can I put a garden room in the corner of a wrap-around garden?
Only if it sits behind both principal elevations. On a wrap-around plot the corner of the garden is often forward of the flank frontage, which takes it outside Class E even where it is screened from view. Within two metres of any boundary the height limit is 2.5 metres overall, which usually rules out a pitched roof.
What is the safest way to confirm the position before building?
Apply for a Lawful Development Certificate for proposed development under section 192 of the Town and Country Planning Act 1990. It gives a binding determination that the works would be lawful, takes around eight weeks and costs a fee. A pre-application enquiry is quicker and costs less, but the officer's view is informal and not binding.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.