Class AA – enlargement of a dwellinghouse by construction of additional storeys

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What does the legislation say?

Permitted development

AA. The enlargement of a dwellinghouse consisting of the construction of—
(a) up to two additional storeys, where the existing dwellinghouse consists of two or more storeys; or
(b) one additional storey, where the existing dwellinghouse consists of one storey,
immediately above the topmost storey of the dwellinghouse, together with any engineering operations reasonably necessary for the purpose of that construction.

Development not permitted

AA.1. Development is not permitted by Class AA if—
(a) permission to use the dwellinghouse as a dwellinghouse has been granted only by virtue of Class M, N, O, P, PA or Q of Part 3 of this Schedule (changes of use);
(b) the dwellinghouse is located on— (i) article 2(3) land; or
(ii) a site of special scientific interest;
(c) the dwellinghouse was constructed before 1st July 1948 or after 28th October 2018;
(d) the existing dwellinghouse has been enlarged by the addition of one or more storeys above the original dwellinghouse, whether in reliance on the permission granted by Class AA or otherwise;
(e) following the development the height of the highest part of the roof of the dwellinghouse would exceed 18 metres;
(f) following the development the height of the highest part of the roof of the dwellinghouse 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;
(g) the dwellinghouse is not detached and following the development the height of the highest part of its roof would exceed by more than 3.5 metres
(i) in the case of a semi-detached house, the height of the highest part of the roof of the building with which it shares a party wall (or, as the case may be, which has a main wall adjoining its main wall); or
(ii) in the case of a terrace house, the height of the highest part of the roof of every other building in the row in which it is situated;
(h) 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;
(i) any additional storey is constructed other than on the principal part of the dwellinghouse;
(j) the development would include the provision of visible support structures on or attached to the exterior of the dwellinghouse upon completion of the development; or
(k) the development would include any engineering operations other than works within the curtilage of the dwellinghouse to strengthen its existing walls or existing foundations.


AA.2.—(1)Development is permitted by Class AA subject to the conditions set out in sub-paragraphs (2) and (3).
The conditions in this sub-paragraph are as follows—
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;
the development must not include a window in any wall or roof slope forming a side elevation of the dwelling house;
the roof pitch of the principal part of the dwellinghouse following the development must be the same as the roof pitch of the existing dwellinghouse; and
following the development, the dwellinghouse must be used 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.
The conditions in this sub-paragraph are as follows—
before beginning the development, the developer must apply to the local planning authority for prior approval as to—
impact on the amenity of any adjoining premises including overlooking, privacy and the loss of light;
the external appearance of the dwellinghouse, including the design and architectural features of—
(aa) the principal elevation of the dwellinghouse, and
(bb) any side elevation of the dwellinghouse that fronts a highway; (iii) air traffic and defence asset impacts of the development; and
(iv) whether, as a result of the siting of the dwellinghouse, the development will impact on a protected view identified in the Directions Relating to Protected Vistas dated 15th March 201245 issued by the Secretary of State;
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 adjoining owners or occupiers will be mitigated;
the development must be completed within a period of 3 years starting with the date prior approval is granted;
the developer must notify the local planning authority of the completion of the development as soon as reasonably practicable after completion; and
that notification must be in writing and include— (i) the name of the developer;
(ii) the address of the dwellinghouse; and (iii) the date of completion.

Our Views on Class AA

Class AA Development is essentially brand new and is intended to allow homeowners to grow their properties upwards in recognition of the limited space avaliable within the UK for extensions to existing houses.

At the time of writing it remains still relativity untested at appeal but has already seen uptake in some of the London Borough’s as well as elsewhere in the Country. Regrettably at the time of writing levels of refusals appear to be as high as 90% *based on research conducted by Planning Magazine.

The use of Class AA has been encouraged by the Government but has no technical guidance to accomplay it and so it is left to the LPA’s and the Planning Inspectorate to provide decision making behaviour.

Class AA development may not be used on HMO’s or on properties which are:

A designated heritage asset, Area of outstanding natural beauty (AONB), Wildlife protection area, The Broads, A National Park, Site of special scientific interest, Safety hazard area, Military explosives storage area; or Within 3 kilometres of the perimeter of an aerodrome.

Class AA is not excluded by other development within Part 1 and is a prior approval matter requiring assessment by the LPA.

Class AA is immune from the imposition of the National Floor-space Standards as the development does not result in a new dwelling.

The ‘existing dwelling’ provision is set in law as the day the property was constructed or the 1st July 1948 (whichever the sooner).

How to Use Class AA

Class AA permitted development should be explored first before engaging with a planning permission and careful consideration to the key criteria should be given before engaging in a Class AA application. You must seek prior approval before using Class AA.

*Correct at time of writing.

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