Class AB: flats above terraced commercial buildings

Class AB permits one or two new storeys of flats above qualifying terraced or semi-detached commercial or mixed-use buildings, subject to the roof heights of every other building in the row.

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 building qualifies?

Class AB applies to a terrace building, including a semi-detached building, currently used for a specified former A1 shop, A2 financial and professional service, A3 restaurant or café, B1(a) office, betting office, payday loan shop or launderette, or relevant commercial and C3 mixed use. The former use-class names are defined by the Use Classes Order as it stood on 5th March 2018; modern Class E is not a universal shortcut.

The building must have been constructed from 1st July 1948 to 5th March 2018 inclusive and been used on 5th March 2018 for those specified commercial or mixed uses, or as a C3 dwellinghouse. A later change from an unlisted 2018 use will not meet the historic-use test. Part 3 Class MA dwellings are excluded, and the building cannot already have had an additional storey added above its original roof.

What can be added?

A one-storey building may receive one new storey of flats; an existing building of two or more storeys may receive up to two. The flats 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 for a one-storey building or 7 metres for a taller one; 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 storey of the principal part. No window may be inserted in a side wall or 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.

Replacement or additional plant is only within the Class AB right if plant already exists; its height cannot exceed the specified height of the existing plant.

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

Prior approval covers highways and transport; air traffic and defence assets; contamination and flooding; external appearance of principal and highway-facing side elevations, including access and storage; adequate natural light; the amenity of existing and neighbouring premises; commercial noise affecting occupants; impacts of residents on surrounding businesses; and protected views. 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 AB, AB.1 and AB.2, Paragraph B and the eligibility table.

Class AB legislation (checked 24th September 2026)

The following reproduces the consolidated Class AB, AB.1 and AB.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

AB.—(1) Development consisting of works for the construction of new dwellinghouses immediately above the topmost storey on a terrace building to which sub-paragraph(2) applies, where that development comprises—

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

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

together with any development under sub-paragraph (3).

(2) This sub-paragraph applies to a building which is—

(a) used for any purpose within Class A1 (shops), Class A2 (financial and professional services), Class A3 (restaurants and cafes) or Class B1(a) (offices) of the Schedule to the 1987 Order, or as a betting office, pay day loan shop or launderette;

(b) in a mixed use combining—

(i) two or more uses within paragraph (a); or

(ii) a use falling within Class C3 (dwellinghouses) of the Schedule to the 1987 Order, together with one or more uses within paragraph (a).

(3) Development consisting of any or all—

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

(b) works for the replacement of existing plant or installation of additional plant on the roof of the extended building reasonably necessary to service the new dwellinghouses;

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

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

(4) In relation to Class AB, “the 1987 Order” means the Use Classes Order as in force on 5th March 2018.

Development not permitted

AB.1. Development is not permitted by Class AB 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 or mixed use within paragraph AB(2)(a) or (b); or

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

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

(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 building;

(e) the new dwellinghouses are not flats;

(f) the height of the highest part of the roof of the extended building (not including plant) 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 (not including plant, in each case);

(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 building (not including plant, in each case) by more than—

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

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

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

(j) development under Class AB(3)(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 AB(3)(a) would consist of engineering operations other than works within the existing curtilage of the building to—

(i) strengthen existing walls;

(ii) strengthen existing foundations; or

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

(l) in the case of Class AB(3)(b) development there is no existing plant on the building;

(m) in the case of Class AB(3)(b) development the height of any replaced or additional plant as measured from the lowest surface of the new roof on the principal part of the extended building would exceed the height of any existing plant as measured from the lowest surface of the existing roof on the principal part of the existing building;

(n) development under Class AB(3)(c) would extend beyond the curtilage of the existing building;

(o) development under Class AB(3)(d) would—

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

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

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

(p) the land or site on which the building 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

AB.2.—(1) Where any development under Class AB 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 AB(3)(c) or (d);

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

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

(h) impacts of noise from any commercial premises on the intended occupiers of the new dwellinghouses;

(i) impacts of the introduction of, or an increase in, a residential use of premises in the area on the carrying on of any trade, business or other use of land in the area;

(j) 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) In sub-paragraph (1)(h), “commercial premises” means any premises in the building or the surrounding area which are normally used for the purpose of carrying on any trade or business, and includes any premises licensed under the Licensing Act 2003 or any other place of public entertainment..

(3) Any development under Class AB is permitted subject to the condition that the development must not include a window in any wall or roof slope forming a side elevation of the building.

(4) Any development under Class AB 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.

(5) Any development under Class AB 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.

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

(7) The notification referred to in sub-paragraph (6) 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.

(8) 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