Applications, appeals, permitted development, enforcement and planning strategy across England
Planning explanations, updates and practical guidance in video form
Class A: Commercial extensions and alterations
Class A of Part 7 includes commercial extensions, new windows, doors and other alterations. Class A applies to any building in Use Class E, but also to any building that is partially in use as Use Class E, as long as the alteration or commercial extension is not undertaken on those parts not falling within Use Class E. It is also important that any extensions or other alterations are solely for purposes of the business within Use Class E.
In other words if the upstairs was in Use Class B8 (storage) you could still alter the Use Class E element of the ground floor.
This page separates extensions from alterations because the limits are not identical. It also flags the interaction with Class MA where a later residential conversion is contemplated. The legislation itself is reproduced below and linked to the official source.
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.
What does Class A allow?
Class A permits the extension or alteration of a commercial, business or service establishment. In practical terms, the relevant building, or the relevant part of a mixed-use building, must be used for a purpose within Use Class E. Other uses can exist elsewhere in the same building, provided the part being extended or altered is within Class E.
The completed extension or alteration must then be used as part of, or for a purpose incidental to, that Class E establishment. Class A is therefore not a route for creating a separate unrelated use.
Commercial extensions under Class A
For an extension, the maximum additional floor space is:
- on protected land such as a conservation area, National Park, National Landscape, the Broads or a World Heritage Site, or on a site of special scientific interest: 25% of the gross floor space of the original building or 50 square metres, whichever is less
- in any other case: 50% of the gross floor space of the original building or 100 square metres, whichever is less
The building as extended must not exceed 4 metres in height.
The drafting needs care on storeys. The statutory conditions expressly say that an alteration must be at ground-floor level, while they do not repeat those words for an extension. However, the Government’s 2021 consultation outcome says the amended Class A right allows ground-floor, single-storey extensions. Planning Geek therefore treats Class A as a ground-floor, single-storey extension right. An upper-storey extension should not be undertaken in reliance on Class A without formal confirmation, normally through a proposed certificate of lawfulness.
On protected land, any extension must also use materials with a similar external appearance to those used for the building being extended. That materials condition does not appear in Class A simply because a site is an SSSI.
The 2 metre rule also needs care. If the land either adjoins premises used for a residential or institutional purpose within Part C of the Use Classes Order, is protected land, or is a site of special scientific interest, no part of the extension may be within 2 metres of any boundary of the curtilage.
That is wider than simply keeping 2 metres from the residential neighbour. Once the residential-adjoining trigger applies, the setback applies to every boundary of the commercial curtilage. This can make rear additions to mixed commercial and residential parades difficult to achieve under Class A.
No part of the Class A development may extend beyond the front of any existing building. This is wider than simply saying that an extension cannot project beyond the shop front.
Class A cannot be used at all where the development would be within the curtilage of a listed building. It also cannot be used for a verandah, balcony or raised platform. For Class A, a raised platform means one more than 0.3 metres high.
How is the Class A floor-space allowance calculated?
The percentage is measured against the original building, not simply the building as it exists today. For most non-Crown buildings, the GPDO treats a building that existed on 1st July 1948 as original in its form on that date; a building constructed later is treated as original as first built. Later extensions therefore do not create a fresh allowance and can use up some or all of the Class A capacity.
There is another easily missed rule. Where two or more original buildings are within the same curtilage and are used for the same undertaking, Class A requires them to be treated as a single original building when making measurements. That can materially change the percentage calculation and should be checked before assuming that each building has its own separate allowance.
Class MA conversions
If you intend to carry out Class A works and later rely on Class MA to convert commercial space to residential, assess the Class MA position separately before carrying out the works. Class MA has its own eligibility and prior approval requirements, so a Class A extension should not be assumed automatically to form part of a later residential conversion.
Other alterations to the building
Class A of Part 7 allows for other alterations. Like Class A of Part 1, this includes new windows and doors. However again there are a few limitations.
You cannot use the Class A alteration right on protected land such as conservation areas, National Parks, National Landscapes, the Broads and World Heritage Sites. This is different from an extension on protected land, which can still fall within Class A if it satisfies the stricter size, setback and materials requirements above.
Class A does not authorise the insertion or creation of a new shop front, the alteration or replacement of an existing shop front, or the installation or replacement of a security grille or shutter on a shop front. Those works would need to rely on another planning permission or permitted development right, if one is available.
Class A was recast around Use Class E in 2021, but the current shop-front restrictions still use the term “shop front”. Do not assume that moving between uses within Class E automatically changes whether an existing frontage is a “shop front” for Class A. The Order does not define “shop front” within Class A. Where the status of a frontage affects a proposal, formal confirmation through a proposed certificate of lawfulness may be sensible before work starts.
Finally, every alteration carried out under Class A must be at ground-floor level only. Class A therefore does not authorise new windows, doors or other alterations above ground-floor level.
Extra permission required?
Class A itself has no prior approval procedure. However, do not treat that as the end of the checks. An Article 4 direction or a condition on an existing planning permission can remove or restrict permitted development rights, and separate requirements such as building regulations may still apply. A proposed certificate of lawfulness can provide formal confirmation where the position is uncertain. Planning Geek can assist with the planning checks. Please contact us for any assistance or book a Zoom call today. You might decide upon a certificate of lawfulness either before or after the works if required. The team at Planning Geek can handle that for you.
Class A legislation
Class A – extensions etc of commercial, business or service premises
Permitted development
A. The extension or alteration of a commercial, business or service establishment.
Development not permitted
A.1 Development is not permitted by Class A if—
(a) the gross floor space of the original building would be exceeded by more than—
(i) in respect of an original building or a development on—
(aa) article 2(3) land, or
(bb) a site of special scientific interest,
25% or 50 square metres (whichever is the lesser);
(ii) in any other case, 50% or 100 square metres (whichever is the lesser);
(b) the height of the building as extended would exceed 4 metres;
(c) any part of the development (other than an alteration)—
(i) is on land which—
(aa) adjoins other premises which are used for a purpose falling within any of the classes in Part C (residential premises or institutions) of Schedule 1 to the Use Classes Order,
(bb) is article 2(3) land, or
(cc) is a site of special scientific interest, and
(ii) is within 2 metres of any boundary of the curtilage of the premises;
(d) the development would be within the curtilage of a listed building;
(e) any alteration would be on article 2(3) land;
(f) the development would consist of or include the construction or provision of a verandah, balcony or raised platform;
(g) any part of the development would extend beyond the front of any existing building;
(h) the development would involve the insertion or creation of a new shop front or the alteration or replacement of an existing shop front; or
(i) the development would involve the installation or replacement of a security grill or shutter on a shop front.
Conditions
A.2 Development is permitted by Class A subject to the following conditions—
(a) any alteration is at ground floor level only;
(b) any extension is, in the case of article 2(3) land, constructed using materials which have a similar external appearance to those used for the building being extended; and
(c) any extension or alteration is only to be used as part of, or for a purpose incidental to, the use of the commercial, business or service establishment.
Interpretation of Class A
A.3 For the purposes of Class A—
“commercial, business or service premises” means a building, or part of a building, used for any purpose within Class E (commercial, business and service) of Schedule 2 to the Use Classes Order and includes buildings with other uses in other parts as long as the other uses are not within the parts being altered or extended;
“raised platform” means a platform with a height greater than 0.3 metres,
and where 2 or more original buildings are within the same curtilage and are used for the same undertaking, they are to be treated as a single original building in making any measurement.
Legislation on legislation.gov.uk
Commercial extension Page Updated: 23rd September 2026