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Class AA: adding extra storeys to your house
Class AA can allow you to add an extra storey, or sometimes two, above an existing house in England. The new accommodation must remain part of the house. This is different from the Part 20 routes for creating additional homes.
You must obtain written prior approval before building. Meeting the height limits alone is not enough: the council also considers the matters specified in Class AA, including neighbouring amenity and external appearance.
Need help with permitted development?
Permitted development can avoid a full planning application, but only if the right applies and every relevant limit and condition is met. Planning Geek can check the planning history, Article 4 directions and other restrictions, and help with a lawful development certificate or prior approval where needed.
How many storeys can you add?
- If the existing house has one storey, Class AA can permit one additional storey
- If it has two or more storeys, it can permit up to two additional storeys
For this calculation, a basement storey below ground and accommodation within the roof do not count as storeys. A new storey replacing existing roof accommodation can count as an additional storey under the right.
The work must sit immediately above the topmost storey of the principal part of the house. That means the main house excluding lower front, side or rear extensions, even if those extensions were original. An extra storey above a lower rear extension is not brought within Class AA simply because it is attached to the house. Check Class A separately for that type of proposal.
Does your house qualify?
- It must have been constructed on or after 1st July 1948 and on or before 28th October 2018
- It must not be on article 2(3) land or a Site of Special Scientific Interest
- It must not already have had one or more storeys added above the original house, whether through Class AA or a different planning permission
- Its permission to be used as a house must not have arisen only through Part 3 Classes G, M, MA, N, O, P, PA or Q
- It must be a dwellinghouse for Part 1 purposes, rather than a flat, maisonette or building containing flats
Article 2(3) land includes conservation areas, National Parks, the Broads, National Landscapes and World Heritage Sites. Check relevant Article 4 directions, planning conditions and the lawfulness of the existing building and use too.
There is no separate blanket listed-building exclusion in Class AA. However, all its eligibility tests still apply, and listed building consent is required for works affecting the building’s special character. Many listed houses will fall outside the construction-date window.
All the height limits apply together
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| Check | Limit |
|---|---|
| Height of the resulting house | The highest part of its roof must not exceed 18 m |
| Existing single-storey house | The highest roof point may rise by no more than 3.5 m |
| Existing house with more than one storey | The highest roof point may rise by no more than 7 m |
| Semi-detached house | The new highest roof point must not be more than 3.5 m above the highest roof point of the building it adjoins |
| Terrace house | Apply the additional 3.5 m comparison with the highest roof of the other buildings in the row, as set out in AA.1(g)(ii) |
| Internal floor-to-ceiling height of an added storey | No greater than the lower of 3 m and the internal floor-to-ceiling height of any storey of the existing principal part |
The 3.5 m or 7 m allowance is an increase in the highest roof point, not the total permitted height of the resulting house. The separate 18 m cap still applies. Nor does the 3 m internal ceiling limit give you a universal 3 m allowance where the existing ceilings are lower. Where existing storeys have different ceiling heights, show each on the drawings and address AA.1(h) explicitly.
Class AA has its own definitions of detached, semi-detached and terrace houses. A terrace is a row of three or more buildings meeting the shared or adjoining-main-wall definition; the row need not consist entirely of houses. The precise building relationships matter.
Design and structural restrictions
- External materials must have a similar appearance to the exterior of the existing house
- The development must not include a window in a side-elevation wall or roof slope
- The principal part’s resulting roof pitch must be the same as the existing house’s roof pitch
- No visible support structure may remain on or attached to the exterior when the work is finished
- Permitted engineering operations are limited to work within the curtilage strengthening the existing walls or foundations
The side-window rule is stricter than Class A. Obscure glazing or a high opening does not make a new side window acceptable under Class AA.
Planning permission does not establish that the existing structure can carry extra floors. Have the load, foundations and proposed strengthening assessed by an appropriate structural specialist, alongside Building Regulations.
What does the council assess?
Before beginning development, apply for prior approval of:
- Effects on the amenity of adjoining premises, including overlooking, privacy and loss of light
- The external appearance of the house, including the design and architectural features of its principal elevation and any side elevation fronting a highway
- Air traffic and defence asset impacts
- Impacts on protected views identified in the Protected Vistas Directions dated 15th March 2012
The external-appearance wording should not be read as a guarantee that every design inside the dimensional limits must be approved. The council must have regard to the NPPF so far as relevant to the subject matter of prior approval.
What to submit
- A written description, including details of the proposed works
- A site and proposal plan at an identified scale, showing north
- Scaled existing and proposed elevations
- The positions and dimensions of proposed windows
- The required application fee
The council may refuse a proposal which does not comply or where there is insufficient information to establish compliance. It can require further reasonable information, including assessments, mitigation and details of the works. Use our fees guide for current charges.
Unless the application is refused under the early compliance provision, adjoining owners and occupiers must be notified and allowed at least 21 days for representations. Relevant aviation, defence and protected-view consultations also apply. Public holidays are excluded when calculating the specified minimum representation and consultee periods.
Before starting and after completion
- Obtain the council’s written prior approval and comply with its relevant conditions
- Before starting, provide a construction management report covering working hours and mitigation of noise, dust, vibration and traffic impacts on adjoining owners or occupiers
- Build in accordance with the approved details and complete within three years of the prior approval grant
- Notify the council in writing as soon as reasonably practicable after completion, giving the developer’s name, property address and completion date
Silence is not permission to start. AA.3(13) requires receipt of written prior approval. Do not import the larger rear-extension 42-day rule from Class A.
The house must remain in C3 use
After development, the house must be used as a dwellinghouse within Use Class C3, with other purposes only so far as ancillary to that main use. This continuing condition means you should not assume a subsequent move to C4 HMO use can simply rely on Class L.
Class AA enlarges the existing home. It does not grant permission to divide the property into separate flats. Different proposals need the appropriate planning route.
Sources and Class AA legislation
Checked against the current GPDO Part 1 and article 2 definitions. The government householder technical guidance provides explanations and examples, but must be read with subsequent amendments to the legislation.
Read the Class AA legislation
Class AA – enlargement of a dwellinghouse by construction of additional storeys
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 G, M, MA, 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.
together 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; 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, 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.
Interpretation of Class AA
AA4.—(1) For the purposes of Class AA—
“defence asset” means a site identified on a safeguarding map provided to the local planning authority for the purposes of a direction made by the Secretary of State in exercise of the powers conferred by article 31(1) of the Procedure Order or any previous powers to the like effect;
“detached”, in relation to a dwellinghouse, means that the dwellinghouse does not—
(a)share a party wall with another building; or
(b)have a main wall adjoining the main wall of another building;
“principal part”, in relation to a dwellinghouse, means the main part of the dwellinghouse excluding any front, side or rear extension of a lower height, whether this forms part of the original dwellinghouse or is a subsequent addition;
“semi-detached”, in relation to a dwellinghouse, means that the dwellinghouse is neither detached nor a terrace house;
“technical sites” has the same meaning as in the Town and Country Planning (Safeguarded Aerodromes, Technical Sites and Military Explosives Storage Areas) Direction 2002;
“terrace house” means a dwellinghouse situated in a row of three or more buildings, where—
(a)it shares a party wall with, or has a main wall adjoining the main wall of, the building on either side; or
(b)if it is at the end of a row, it shares a party wall with, or has a main wall adjoining the main wall of, a building which fulfils the requirements of paragraph a.
(2) In Class AA references to a “storey” do not include—
(a)any storey below ground level; or
(b)any accommodation within the roof of a dwellinghouse, whether comprising part of the original dwellinghouse or created by a subsequent addition or alteration,
and accordingly, references to an “additional storey” include a storey constructed in reliance on the permission granted by Class AA which replaces accommodation within the roof of the existing dwellinghouse.
Explore GPDO Part 1
Choose the work you are planning. These guides explain the English rules for houses.
- Part 1 overview
Start here for permitted development at a house - Class A: house extension and alteration
Rear and side extensions, windows and doors - Class AA: additional storeys
Build upwards above an existing house - Class B: roof enlargement
Dormers and hip-to-gable enlargements - Class C: other roof alteration
Rooflights and other roof alterations - Class D: porch
Porches outside an external door - Class E: outbuilding
Garden buildings, pools and other incidental development - Class F: hard surface
Driveways, paths and patios - Class G: chimney and flue
Chimneys, flues and soil and vent pipes - Class H: satellite dish
Microwave antennas on the house or in its curtilage - Paragraph I: definitions
Terms used in Part 1
Page Updated: 25th September 2026