Class AA - Additional Storeys

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Class AA – Additional Storeys on Houses

Class AA of the General Permitted Development Order (GPDO) allows you to add new floors on top of your house without needing full planning permission, provided you meet strict conditions. It’s one of the more powerful rights but also one of the most technical.

Our easy guide sets out what you can and can’t do with these rights. Scroll down for a quick reference table, and the full legislation included at the bottom of the page for reference.

✅ What you can do under Class AA

Add up to two new storeys on top of an existing detached house of two or more storeys.

Add one new storey on top of an existing detached house of a single storey.

Add one new storey on top of an existing terraced or semi-detached house of two or more storeys.

The new floors must be built directly above the existing top floor (you can’t add floors to garages, outbuildings, or single-storey side extensions).

Internal works (e.g. stairs, partitions) are generally allowed.

External materials must be of similar appearance to the existing house.

❌ What you can’t do under Class AA

No new floors on flats or maisonettes — this only applies to houses.

No use if the house is:

Listed; or
Within a Conservation Area, National Park, AONB, the Broads, or a World Heritage Site.

No extensions beyond the side/front walls of the house — the new storey must sit squarely above the existing footprint.

No raising the overall height by more than 7 metres above the original house.

The total height of the house (after extension) cannot exceed 18 metres.

No balconies, verandas, or raised platforms as part of the works.

No use if the house was built before 1 July 1948 or after 28 October 2018.

⚠️ Things you should be aware of...

Prior Approval is required: This isn’t a “do it tomorrow” right. You must apply to the council for Prior Approval, who will assess things like:

Impact on neighbours’ amenity (overlooking, loss of light, privacy).

Design and external appearance.

Impact on highways and air traffic safety.

Neighbour consultation: The council will notify your neighbours and take their comments into account.

Building Regulations still apply: Adding whole new floors means major structural work, so you’ll need Building Regs approval.

Party Wall Act: If you share a wall with a neighbour, expect to go through the Party Wall procedure.

Previous extensions count: You can’t “stack” Class AA on top of some existing additions (e.g. upward extensions already added under PD).

Summary

Class AA gives homeowners a way to add serious extra space — but it comes with lots of strings attached. It’s not as simple as building a loft dormer under Class B; this is essentially a full new floor or two, so the process is more controlled.

👉 If you’re thinking about an upward extension and want to know if your house qualifies, contact me and I’ll help you check the conditions, prepare the Prior Approval application, and make sure you stay on the right side of the rules.

Quick Reference Table

House type
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Detached
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Detached
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Semi-detached
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Terraced

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Flats / Maisonettes

Number of storeys
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1 storey
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2+ storeys

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2+ storeys

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Any height

..

What Class AA allows
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Add 1 extra storey
________________________________
Add up to 2 additional storeys

________________________________
Add 1 extra storey

________________________________
Not permitted under Class AA

Class AA - The Legislation

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 [F2G,] M, [F3MA,] 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.

Conditions
AA.2.—(1) Development is permitted by Class AA subject to the conditions set out in sub-paragraphs (2) and (3).

(2) The conditions in this sub-paragraph are as follows—

(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)the development must not include a window in any wall or roof slope forming a side elevation of the dwelling house;

(c)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

(d)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.

(3) The conditions in this sub-paragraph are as follows—

(a)before beginning the development, the developer must apply to the local planning authority for prior approval as to—

(i)impact on the amenity of any adjoining premises including overlooking, privacy and the loss of light;

(ii)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 2012 issued by the Secretary of State;

(b)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;

(c)the development must be completed within a period of 3 years starting with the date prior approval is granted;

(d)the developer must notify the local planning authority of the completion of the development as soon as reasonably practicable after completion; and

(e)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.

Procedure for applications for prior approval
AA.3.—(1) The following sub-paragraphs apply where an application to the local planning authority for prior approval is required by paragraph AA.2(3)(a)

(2) The application must be accompanied by—

(a)a written description of the proposed development, including details of any works proposed;

(b)a plan which is drawn to an identified scale and shows the direction of North, indicating the site and showing the proposed development; and

(c)a plan which is drawn to an identified scale and shows—

(i)the existing and proposed elevations of the dwellinghouse, and

(ii)the position and dimensions of the proposed windows.

[F4together with any fee required to be paid.]

(3) The local planning authority may refuse an application where, in its opinion—

(a)the proposed development does not comply with, or

(b)the developer has provided insufficient information to enable the authority to establish whether the proposed development complies with,

any conditions, limitations or restrictions specified in paragraphs AA.1 and AA.2.

(4) Sub-paragraphs (5) to (8) do not apply where a local planning authority refuses an application under sub-paragraph (3); and for the purposes of section 78 (appeals) of the Act, such a refusal is to be treated as a refusal of an application for approval.

(5) The local planning authority must notify each adjoining owner or occupier about the proposed development by serving on them a notice which—

(a)describes the proposed development, including the maximum height of the proposed additional storeys;

(b)provides the address of the proposed development; and

(c)specifies the date, which must not be less than 21 days from the date the notice is given, by which representations are to be received by the local planning authority.

(6) Where the application relates to prior approval as to the impact on air traffic or defence assets, the local planning authority must consult any relevant operators of aerodromes, technical sites or defence assets and where appropriate the Civil Aviation Authority and the Secretary of State for Defence.

(7) Where an aerodrome, technical site or defence asset is identified on a safeguarding map provided to the local planning authority, the local planning authority must not grant prior approval contrary to the advice of the operator of the aerodrome, technical site or defence asset, the Civil Aviation Authority or the Secretary of State for Defence.

(8) Where the application relates to prior approval as to the impact on protected views, the local planning authority must consult Historic England, the Mayor of London and any local planning authorities identified in the Directions Relating to Protected Vistas dated 15th March 2012 issued by the Secretary of State.

(9) The local planning authority must notify the consultees referred to in sub-paragraphs (6) and (8) specifying the date by which they must respond, being not less than 21 days from the date the notice is given.

(10) When computing the number of days in sub-paragraphs (5)(c) and (9), any day which is a public holiday must be disregarded.

(11) The local planning authority may require the developer to submit such information as the authority may reasonably require in order to determine the application, which may include—

(a)assessments of impacts or risks;

(b)statements setting out how impacts or risks are to be mitigated, having regard to the National Planning Policy Framework issued by the Ministry of Housing, Communities and Local Government in [F5July 2021]; and

(c)details of proposed building or other operations.

(12) The local planning authority must, when determining an application—

(a)take into account any representations made to them as a result of any notice given under sub-paragraph (5) and any consultation under sub-paragraph (6) or (8); and

(b)have regard to the National Planning Policy Framework issued by the Ministry of Housing, Communities and Local Government in [F6July 2021], so far as relevant to the subject matter of the prior approval, as if the application were a planning application.

(13) The development must not begin before the receipt by the applicant from the local planning authority of a written notice giving their prior approval.

(14) The development must be carried out in accordance with the details approved by the local planning authority.

(15) The local planning authority may grant prior approval unconditionally or subject to conditions reasonably related to the subject matter of the prior approval.