Permitted Development Rights for Extensions

Permitted development is not an exemption from planning control. It is planning permission, granted in advance and nationally, by a statutory instrument rather than by your council. That sounds like a technicality until something goes wrong, at which point it turns out to be the whole thing. You cannot negotiate with it, and an extension that misses one condition by a hundred millimetres was never permitted development at all.

Where the rights actually come from

One statutory instrument, one schedule, one part of it. Everything else is commentary.

The Town and Country Planning (General Permitted Development) (England) Order 2015 does the work. Article 3 grants planning permission for the classes of development set out in Schedule 2. Householder work sits in Schedule 2, Part 1, headed development within the curtilage of a dwellinghouse, and Part 1 is divided into lettered classes. When a builder or a case officer says Class A, that is what they are pointing at.

The Order has been amended repeatedly since 2015, which is why advice found on a forum can be confidently and completely out of date. Amendments in 2019 made the larger home extension route permanent when it had been due to lapse. Amendments in 2020 added a new class allowing houses to be extended upwards. Anything written before those dates describes a different regime.

The classes, and which one your job sits in

Part 1 is not one right. It is nine, each with its own conditions and its own way of being lost.

A single job frequently uses more than one class, and each has to be satisfied independently. A wrap around extension with a dormer over it is Class A and Class B at the same time, and complying with Class A does nothing whatsoever for the dormer.

Part 1 also applies only to a dwellinghouse, and the Order is explicit that a dwellinghouse does not include a building containing one or more flats, or a flat inside such a building. Split a house into two flats and the Part 1 rights leave with the change of use. Gates, walls and fences sit elsewhere again, in Part 2 of the same schedule.

What Class A allows, and where it stops

The limitations are a list of circumstances in which the permission simply does not exist, and every one of them applies at once.

The depth figures are the ones everybody arrives already knowing, and they are worked through in how deep a single storey extension can be. The eaves rule is the one that gets left out of the summary most homeowners have read, and on a narrow plot it quietly determines the roof, because a 3 metre eaves cap forces either a flat roof or a pitch that runs the wrong way.

Those are limitations. Conditions behave differently. A limitation decides whether the permission exists; a condition attaches to a permission that does exist and has to be complied with as you build. Class A carries three. Exterior materials must be similar in appearance to those of the existing house. Any upper floor window in a side elevation must be obscure glazed, and fixed shut unless the opening part sits more than 1.7 metres above the floor of the room. Where the extension has more than one storey, the roof pitch must match the pitch of the original house so far as practicable. Breaching a condition is a breach of planning control just as squarely as building a metre too deep.

Article 2(3) land, which is broader than conservation areas

One phrase in the Order carries most of the restrictions people associate with heritage.

Article 2(3) defines a category of land where Part 1 rights are cut back. It covers conservation areas, National Landscapes (the designation until recently called an Area of Outstanding Natural Beauty), National Parks, the Broads and World Heritage Sites. Around here that means the conservation areas, and it means Dedham Vale, a National Landscape which carries the same reduction whether or not a conservation area also covers the village.

Within Class A, being on article 2(3) land removes three specific things: cladding any part of the exterior in stone, artificial stone, pebbledash, render, timber, plastic or tiles; any extension beyond a side wall of the original house; and any rear extension of more than a single storey. Class B, the roof enlargement class, is removed in its entirety, so a dormer is an application. Class C is not removed, which is the point most often reported wrongly. A rooflight sitting in the plane of the slope, projecting no more than 150mm and rising no higher than the highest part of the original roof, remains permitted development on article 2(3) land, front slope included, unless an Article 4 direction has taken it away.

What an officer then assesses is set out in extending a house in a conservation area. Green Belt is not article 2(3) land and does not reduce these rights, though it changes a great deal about what a planning application would face.

The four things that remove the rights outright

None of these is visible from the pavement, and three of them are free to check.

• The property is a flat or maisonette. Part 1 never applied. There is no depth to argue about.
• An Article 4 direction. A council can withdraw specified permitted development rights across a defined area, commonly windows, doors, roof coverings, cladding and front boundary walls in a conservation area. Directions are made property by property or street by street rather than nationally, so the only reliable check is against your own address.
• A condition on an earlier planning permission. Estate housing built from the 1980s onwards very often had Part 1 rights removed by a condition on the permission for the whole estate. Nobody is told at purchase. The check takes ten minutes on the council’s planning search and almost nobody does it.
• The house was created by a change of use. A dwelling formed out of an office, a barn or an agricultural building under the permitted development change of use rules does not necessarily arrive with the same Part 1 rights, and a house built under the upward extension provisions of the Order carries its own restrictions.

The roof: two classes that look like one job

Whether your loft conversion is Class B or Class C decides everything about how much you can do.

Class B covers enlargements of the roof that change its shape, which means dormers and hip to gable conversions. It is limited by volume rather than by dimension: the resulting roof space must not exceed the volume of the original roof space by more than 40 cubic metres on a terraced house or 50 cubic metres on anything else, and that allowance is cumulative across everything already added. No part may exceed the height of the highest part of the existing roof, and nothing may extend beyond the plane of a roof slope forming the principal elevation and fronting a highway. Its conditions matter before the design is fixed: materials similar in appearance, side facing windows obscure glazed and fixed below 1.7 metres, and the enlargement set back at least 200mm from the eaves, measured along the roof slope, so far as practicable.

Class C covers alterations that do not change the roof’s shape, which is where rooflights live, along with re-covering. Nothing may protrude more than 150mm beyond the plane of the original slope, measured perpendicular to it, and nothing may rise above the highest part of the original roof. Side facing roof windows are obscure glazed on the same 1.7 metre basis.

A rooflight conversion and a dormer conversion are therefore not the same planning question, even in the same roof on the same afternoon. One is a dimension test against the original slope, the other a volume calculation against everything the roof has already lost.

Porches and outbuildings, which have their own arithmetic

Two of the smallest jobs on the site carry two of the tightest sets of numbers.

A porch under Class D must have a ground area, measured externally, of no more than 3 square metres. No part may be more than 3 metres above ground level, and no part may sit within 2 metres of any boundary of the curtilage which fronts a highway. On a house set close to the pavement that last one binds long before the size does.

Class E covers outbuildings, and the governing word in it is incidental. The building has to be required for a purpose incidental to the enjoyment of the house as such, which a home office satisfies and a self contained annexe with somebody sleeping in it does not. Beyond that: single storey, eaves no higher than 2.5 metres, overall height no more than 4 metres with a dual pitched roof or 3 metres otherwise, dropping to 2.5 metres if any part sits within 2 metres of a boundary, and nothing forward of the principal elevation. Every square metre also counts towards the 50 per cent ground cover limit, which is how a large detached garage silently consumes the allowance for the extension you actually wanted.

None of this produces a document

Permitted development leaves no paper trail, and a sale is where that becomes a problem.

If the work genuinely is permitted development, there is no application, no decision notice and nothing on the public file. The way to fix that is a Lawful Development Certificate. The council determines whether the development you have described would be lawful and issues a certificate saying so. Two versions exist: one for proposed work, applied for before you build, and one for something already built, which is a harder application resting on evidence.

The burden of proof sits with the applicant, on the balance of probabilities, and that is worth understanding because it is not how a planning application works. Nobody is weighing whether your extension is a good idea. They are deciding whether the thing you have described falls inside the rules, which is why a certificate is only ever as reliable as the drawing behind it. There is more in Lawful Development Certificates.

What permitted development does not get you out of

The planning answer settles one question and no others.

Building Regulations approval is required whatever the planning position, and the fact that no application was needed is neither a defence nor a shortcut. The two systems are separate, run by different teams, with different fees and different timetables. The Party Wall etc. Act 1996 is separate again, triggered by cutting into a shared wall, building on the line of junction or excavating near a neighbour’s foundations, and it applies whether or not you needed permission. Restrictive covenants on your title are private law between you and whoever holds the benefit of them, invisible to the council, and entirely capable of stopping a project that needed no permission at all.

How to establish what rights this house has

The order matters, because each answer changes what the next one is worth. Establish whether the property is a house or a flat. Search the address on the council’s planning register for previous permissions and for any condition removing rights. Check it against the conservation area mapping and against any Article 4 direction. Then work out what the original house was, because every measurement in Class A that matters is taken from it rather than from the building standing today, and that has its own answer in what original house means in planning.

Only when those four are settled is it worth measuring anything. Where the design wants more depth than Class A allows, the larger home extension prior approval route is the middle path, and it takes these same checks as its starting point.

We run that sequence before anybody draws a line, on every job, because the answer determines the design rather than the other way round. If you want to know what your house still has left before you commission drawings, the survey and the quotation cost nothing.

The Order is amended frequently and how any of it applies depends on your specific property, its planning history and its designation. Treat this as an explanation of how the system is built rather than as confirmation of what you can build.

Last reviewed August 2026. Planning and Building Regulations change, and your property may differ.