Side extensions under Class A in a conservation area

A side extension conservation area permitted development claim almost never works. Class A of Part 1 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015 removes the right to extend beyond a wall forming a side elevation of the original dwellinghouse on what the Order calls article 2(3) land, and a conservation area is article 2(3) land. So the side extension needs a planning application. That is the whole answer, and everything below is about what to do with it.

The rule catches people because the same extension two streets away, outside the boundary, would be permitted development. Designation does not change the building. It changes the rights attached to it.

What article 2(3) land covers

Article 2(3) of the Order lists the designated areas where householder rights are cut back. They are conservation areas, National Parks, National Landscapes (the designation formerly called areas of outstanding natural beauty), the Broads, and World Heritage Sites.

Two things about that list are worth holding on to. It is fixed by the Order, so a council cannot add to it locally, and it applies to the whole of the land within the designation regardless of whether your particular house contributes anything to the special interest. A 1990s infill house inside a conservation area boundary loses the same rights as the Georgian terrace the designation was made for.

Article 4 directions are a separate mechanism. A direction can remove permitted development rights that the Order otherwise grants, and many councils have made directions covering front extensions, windows, roof materials and hard surfacing in conservation areas. Check both. The boundaries of a conservation area and the extent of a direction over it are not always the same, and the mapping is on the council's own website. A useful cross-check on what designation removes is set out in what article 2(3) land takes away.

The side elevation restriction

Outside designated land, Class A permits a side extension where it is single storey, no more than 4 m high, and no wider than half the width of the original dwellinghouse. On article 2(3) land that right disappears entirely: no part of the enlarged dwelling may extend beyond a wall forming a side elevation of the original house.

Three words in that do a lot of work.

"Original" means the house as it was on 1 July 1948, or as built if later. If a previous owner added a side extension in 1975, the wall you are measuring from is the 1948 wall, not the 1975 one.

"Side elevation" is not defined by width or by which way it faces. It is decided on the geometry of the original house. A rear projection on a Victorian terrace has its own side elevation, and extending into the side return goes beyond it, which is why side return extensions in conservation areas need permission even though they look like rear extensions from the street.

"Extend beyond" includes going out at all, by any amount. There is no de minimis.

The parallel restriction is that on article 2(3) land a rear extension of more than one storey is not permitted either, so the two-storey rear extension that would be allowed elsewhere within the depth limits also needs an application.

Cladding and materials on designated land

Class A also removes the right to clad the exterior of the house on article 2(3) land with stone, artificial stone, pebble dash, render, timber, plastic or tiles. That catches a lot of well-meant improvement work.

Rendering a tired brick side wall, adding timber boarding to a rear outshot, hanging tiles on a gable: each needs permission in a conservation area. Painting is treated differently from cladding and normally does not need permission on an unlisted house, although a direction can capture it, and the boundary between decoration and alteration is worth understanding before you start. The position on painting a house exterior sets out where that line falls.

Where an extension is permitted, Class A still carries conditions. The materials of the exterior must be of similar appearance to those of the existing house, and any upper floor window in a wall or roof slope forming a side elevation must be obscure glazed and non-opening below 1.7 m above floor level. Those conditions apply everywhere, not only on designated land, and breaching one takes the whole development outside the permission.

When an application is the only route

Assume it is, and plan for a householder application rather than hoping for a certificate.

The council determines it against the development plan and, in a conservation area, against the statutory duty to pay special attention to preserving or enhancing the character or appearance of the area. That duty sits in the Planning (Listed Buildings and Conservation Areas) Act 1990 and it is the reason officers scrutinise side extensions harder here than elsewhere. Side extensions close the gaps between buildings, and rhythm and spacing are often the thing a conservation area appraisal identifies as its character.

Expect eight weeks for a householder application, publicity that may include a site notice, and a consultation response from the council's conservation officer. On a semi-detached or detached house in a terrace-and-gap townscape, the gap itself may be the constraint that decides the case.

Design evidence that helps the case

The arguments that work in a conservation area are specific and visual.

Set the extension back from the front building line, typically by a metre or more, so the original elevation still reads as the primary form. Drop the ridge or eaves below those of the host dwelling. Keep the roof form the same and the pitch the same. Match the brick by sampling rather than by name, because a brick specified as a match on paper frequently is not. Keep window proportions and reveals consistent with the original.

The written case should do three things. Describe the conservation area's character in the terms the council's own appraisal uses. Identify what contribution the building and its plot make to that character. Then explain how the design responds, element by element.

Where the council asks for a heritage case, a Heritage Statement proportionate to the significance of the asset is what it wants: a short document on an unremarkable house in a large conservation area, a longer one where the building is identified as a positive contributor. Pair it with a Design and Access Statement if your council's validation list requires one for householder applications, which some do inside designated areas.

Street photographs of comparable extensions in the same conservation area are worth more than any amount of policy quotation. Officers respond to evidence that a form already exists locally and has not harmed the area.

Confirming lawfulness with a certificate

If you believe your works do fall within Class A, for example a single storey rear extension within the depth limits on a house in a conservation area, do not rely on that belief.

A certificate of lawfulness of proposed use or development under section 192 of the Town and Country Planning Act 1990 is the only formal way to confirm that works are lawful. It is determined on the facts and the law rather than on planning merits, so the council cannot refuse it because it dislikes the design. You need accurate drawings of the original house, evidence of what has been added since, and a measured statement against each limit in Class A.

The certificate matters most at sale. A buyer's solicitor asking why a side extension has no permission is a problem that surfaces years later and costs more to fix than the certificate fee. And where works have already been carried out without permission, a certificate under section 191 for existing development is a different application with a different evidence burden.

This is general guidance, not legal advice. Permitted development rights are removed by article 4 directions in many conservation areas, so check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Enter your postcode on PlanScope to see which documents a householder application in a conservation area is likely to need.