Class AC: flats above terraced houses

Class AC permits new flats above a qualifying terraced or semi-detached building now used as a single C3 house. Its historic use, date, neighbouring roof heights and design conditions are decisive.

This permitted development right applies in England under Part 20 of Schedule 2 to the GPDO. Establish the current and historic building use, protected-land position and written prior approval before committing to a scheme.

Which house qualifies?

Class AC applies to a terrace building, including a semi-detached building, now used as a single Class C3 dwellinghouse. A shop, restaurant or office that remains in commercial use does not qualify under Class AC. It may qualify after a lawful change to a single C3 home, subject to the separate historic-use and other tests. The building must have been built from 1st July 1948 to 5th March 2018 inclusive. On 5th March 2018 it must have been in C3 use or one of the commercial or mixed uses described in Class AA(2). A home whose dwellinghouse permission comes only from Part 3 Class MA is excluded.

The original house must not already have been extended upwards by adding a storey, whether under Part 1 Class AA or another permission.

What can be added?

A one-storey home can gain one additional storey of new flats; one with two or more storeys can gain up to two. They must sit immediately above the topmost storey on the principal part. The new roof must remain no higher than 18 metres; rise no more than 3.5 metres above a one-storey house or 7 metres above a taller house; and be no more than 3.5 metres higher than the roof of every other building in the row. Each new storey’s internal floor-to-ceiling height is limited to the lower of 3 metres and the height of any principal-part storey.

Exterior materials must have a similar appearance to the existing house. Keep the principal part’s roof pitch the same. Do not install windows in a side wall or side roof slope.

Structural strengthening is restricted to existing walls or foundations within the curtilage, along with permitted service works. Visible external supports are not permitted on completion. New access and ancillary storage or waste facilities must remain within the curtilage, with the latter kept behind the specified principal and highway-facing side walls.

Where the right is excluded

The site cannot be article 2(3) land, a site of special scientific interest, a listed building or land within its curtilage, a scheduled monument or land within its curtilage, a safety hazard area, a military explosives storage area, or land within 3 kilometres of an aerodrome perimeter. Article 2(3) land includes conservation areas, National Parks, the Broads, areas of outstanding natural beauty (National Landscapes) and World Heritage Sites. Check any Article 4 Direction and conditions on earlier permissions as well.

Prior approval issues

The authority considers highways and transport; air traffic and defence assets; contamination and flood risk; external appearance, including principal and highway-facing side elevations, access and facilities; natural light in habitable rooms; neighbouring amenity, overlooking, privacy and loss of light; and protected views where relevant. A construction-management report must be provided before starting.

For Classes A to AD, provide a description, a scaled north-pointing site plan, scaled floor plans showing each new flat’s total floor space, room dimensions and use, windows, doors and walls, existing and proposed elevations, the number of new dwellings, and addresses of flats and other premises already in the building. A site-specific flood risk assessment is needed where Paragraph B requires Environment Agency consultation. The authority may seek reasonably necessary supporting assessments. Notices go to neighbours and relevant existing occupiers.

Every new home must meet the GPDO article 3(9A) minimum of 37 square metres gross internal area and the nationally described space standard. The development must be completed within three years from prior approval, and the local planning authority must be notified in writing of completion. Every dwellinghouse in the building following the development is subject to the statutory Class C3 use condition.

Application and decision

Apply for prior approval before work starts. Paragraph B sets out the application information, consultation and publicity procedure. The authority can refuse if eligibility is not demonstrated or if information is insufficient, and must refuse prior approval where adequate natural light is not provided in every habitable room of the proposed new dwellinghouses. Work must await a written notice granting prior approval; there is no automatic consent after 56 days. Approved plans and any reasonable conditions must be followed. Check the latest consolidated legislation before making a proposal.

Legislation and related guidance

Read Class AC, AC.1 and AC.2, Paragraph B and the eligibility table.

Class AC legislation (checked 24th September 2026)

The following reproduces the consolidated Class AC, AC.1 and AC.2 text as checked on 24th September 2026. Read the official Part 20 text for the legal source and any subsequent amendments. Contains public sector information licensed under the Open Government Licence v3.0.

Permitted development

AC.—(1) Development consisting of works for the construction of new dwellinghouses immediately above the topmost storey on a terrace building in use as a single dwellinghouse within the meaning of Class C3 of the Schedule to the Use Classes Order, where the development comprises—

(a) up to two additional storeys, in the case of an existing dwellinghouse consisting of two or more storeys;

(b) one additional storey, in the case of an existing dwellinghouse consisting of one storey,

together with any development under sub-paragraph (2).

(2) Development consisting of any or all—

(a) engineering operations reasonably necessary to construct the additional storeys and new dwellinghouses;

(b) works for the construction of appropriate and safe access to and egress from the new and existing dwellinghouses, including means of escape from fire, via additional external doors or external staircases;

(c) works for the construction of storage, waste or other ancillary facilities reasonably necessary to support the new dwellinghouses.

Development not permitted

AC.1. Development is not permitted by Class AC if—

(za) the permission to use the building as a dwellinghouse has been granted only by virtue of Class MA of Part 3 of this Schedule;

(a) the building was constructed before 1st July 1948 or after 5th March 2018;

(b) on 5th March 2018 the building was in a use other than—

(i) a use falling within Class C3 (dwellinghouses) of the Schedule to the Use Classes Order; or

(ii) a use or mixed use within paragraph AA(2)(a) or (b) of this Part;

(c) the additional storeys are constructed other than on the principal part of the dwellinghouse;

(d) the floor to ceiling height of any additional storey, measured internally, would exceed the lower of—

(i) 3 metres; or

(ii) the floor to ceiling height, measured internally, of any storey of the principal part of the existing dwellinghouse;

(e) the new dwellinghouses are not flats;

(f) the height of the highest part of the roof of the extended building would be greater than 18 metres;

(g) the height of the highest part of the roof of the extended building would exceed by more than 3.5 metres the height of the highest part of the roof of every other building in the row of terrace buildings of which it forms part;

(h) the height of the highest part of the roof of the extended building would exceed the height of the highest part of the roof of the existing dwellinghouse by more than—

(i) 3.5 metres, where the existing dwellinghouse consists of one storey; or

(ii) 7 metres, where the existing dwellinghouse consists of more than one storey;

(i) the existing dwellinghouse has been enlarged by the addition of one or more storeys above the original dwellinghouse, whether in reliance on permission granted under Class AA of Part 1 or otherwise;

(j) development under Class AC(2)(a) would include the provision of visible support structures on or attached to the exterior of the building upon completion of the development;

(k) development under Class AC(2)(a) would consist of engineering operations other than works within the existing curtilage of the dwellinghouse to—

(i) strengthen existing walls;

(ii) strengthen existing foundations; or

(iii) install or replace water, drainage, electricity, gas or other services;

(l) development under Class AC(2)(b) would extend beyond the curtilage of the existing dwellinghouse;

(m) development under Class AC(2)(c) would—

(i) extend beyond the curtilage of the existing dwellinghouse;

(ii) be situated on land forward of a wall forming the principal elevation of the existing dwellinghouse; or

(iii) be situated on land forward of a wall fronting a highway and forming a side elevation of the existing dwellinghouse; or

(n) the land or site on which the dwellinghouse is located, is or forms part of—

(i) article 2(3) land;

(ii) a site of special scientific interest;

(iii) a listed building or land within its curtilage;

(iv) a scheduled monument or land within its curtilage;

(v) a safety hazard area;

(vi) a military explosives storage area; or

(vii) land within 3 kilometres of the perimeter of an aerodrome.

Conditions

AC.2.—(1) Where any development under Class AC is proposed, development is permitted subject to the condition that before beginning the development, the developer must apply to the local planning authority for prior approval of the authority as to—

(a) transport and highways impacts of the development;

(b) air traffic and defence asset impacts of the development;

(c) contamination risks in relation to the building;

(d) flooding risks in relation to the building;

(e) the external appearance of the building, including—

(i) the design and architectural features of—

(aa) the principal elevation; and

(bb) any side elevation that fronts a highway; and

(ii) the impact of any works under paragraph AC(2)(b) or (c);

(f) the provision of adequate natural light in all habitable rooms of the new dwellinghouses;

(g) impact on the amenity of the neighbouring premises including overlooking, privacy and the loss of light;

(h) whether, because of the siting of the building, the development will impact on a protected view identified in the Directions Relating to Protected Vistas dated 15th March 2012 issued by the Secretary of State,

and the provisions of paragraph B (prior approval) of this Part apply in relation to that application.

(2) Any development under Class AC is permitted subject to the following conditions—

(a) the materials used in any exterior work must be of a similar appearance to those used in the construction of the exterior of the existing dwellinghouse;

(b) following the development, the roof pitch of the principal part of the building must be the same as the roof pitch of the principal part of the existing dwellinghouse; and

(c) the development must not include a window in any wall or roof slope forming a side elevation of the dwellinghouse.

(3) Any development under Class AC is permitted subject to the condition that it must be completed within a period of 3 years starting with the date prior approval is granted.

(4) Any development under Class AC is permitted subject to the condition that before beginning the development, the developer must provide the local planning authority with a report for the management of the construction of the development, which sets out the proposed development hours of operation and how any adverse impact of noise, dust, vibration and traffic on occupiers of the building and adjoining owners or occupiers will be mitigated.

(5) The developer must notify the local planning authority of the completion of the development as soon as reasonably practicable after completion.

(6) The notification referred to in sub-paragraph (5) must be in writing and must include—

(a) the name of the developer;

(b) the address or location of the development; and

(c) the date of completion.

(7) Following the development, every dwellinghouse in the building must remain in use as a dwellinghouse within the meaning of Class C3 of the Schedule to the Use Classes Order and for no other purpose, except to the extent that the other purpose is ancillary to the primary use as a dwellinghouse.

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Page updated: 24th September 2026