What is Class A Part 20?
Class A of Part 20 of the GPDO allows a qualifying block of flats to be extended upward, creating new homes without a full planning application. Part 20 contains several upward-extension rights for different building types, and Class A is the one for blocks of flats.
The right suits a freeholder, landlord or developer looking to add new homes and value to a building they already own, and it's particularly relevant to post-war blocks where there's scope to go higher. Cheffins can assess whether a building qualifies and advise on the best way to realise that potential.
Does your building qualify?
Class A Part 20 only applies to certain purpose-built, detached blocks of flats, so the building itself is the first thing to check. The building generally needs to:
be a purpose-built, detached block of flats of at least three storeys above ground level, excluding any accommodation within the roof
have been built between 1 July 1948 and 5 March 2018
not have gained its residential use solely through certain permitted development rights, including Class MA
meet the other qualifying criteria and restrictions in the GPDO
A block originally built for another purpose and later converted into flats won't usually qualify. Cheffins can review a building's planning history and characteristics against the relevant constraints, and establish whether Class A Part 20 is a realistic option.
How much you can add, and what are the limits?
Class A Part 20 allows up to two additional storeys directly above the existing top residential storey. The main limits are:
the roof height can't increase by more than 7 metres
the extended building can't exceed 30 metres overall, excluding rooftop plant
each new storey's internal floor-to-ceiling height can't exceed 3 metres, or the height of an existing storey where that's lower
The new accommodation has to be self-contained flats that meet the residential space standards. Each flat needs a gross internal floor area of at least 37 square metres and has to comply with the nationally described space standard, which sets higher minimum floorspace according to the number of bedrooms and occupants. Further restrictions apply to where the new storeys sit and to the construction works involved.
Cheffins can work out how many flats a building could take and in what layout, alongside architects and other specialists.
Where Class A Part 20 does not apply
Class A Part 20 includes restrictions that protect specific buildings and designated areas. The right can't be used:
in conservation areas, National Landscapes, National Parks, the Broads, World Heritage Sites or Sites of Special Scientific Interest
on listed buildings or land within their curtilage
on scheduled monuments or land within their curtilage
in safety hazard areas or military explosives storage areas
on land within three kilometres of an aerodrome
A council can also remove permitted development rights from a building through an Article 4 direction, so that's worth checking too. Cheffins can advise on an alternative route to permission where the right isn't available.
What does the council assess?
Class A Part 20 grants planning permission for qualifying upward extensions, subject to the requirements of the GPDO, including prior approval from the council on a defined set of matters s. The matters include:
transport and highway impacts
air traffic and defence asset impacts
contamination and flood risk
the external appearance of the extended building
natural light to the proposed flats
the impact on existing residents and neighbours, including privacy, overlooking and loss of light
protected views
fire safety, where the building is tall enough for it to apply
The council also looks at the external wall construction of the existing block as part of the fire safety assessment on a taller building. Cheffins can pin down which matters are relevant to a proposal, pull together the supporting information and prepare a case that addresses what the council is entitled to consider.
The process and timescales
Class A Part 20 needs prior approval from the council before any work starts. Cheffins can check a building's eligibility, prepare and manage the application and pull together the supporting information it needs.
The council has eight weeks to determine the application. Class A Part 20 doesn't carry the deemed approval that some permitted development rights have, so if the council doesn't decide within those eight weeks, you can either appeal against non-determination or wait for its decision.
The development has to be completed within three years of approval. A report on how construction will be managed, and its effect on existing occupiers and neighbours, has to go to the council before work begins, and the council must be notified in writing once the development is finished.
When do you need full permission instead?
A scheme that falls outside the qualifying criteria or limits of Class A Part 20 may still be possible through a full planning application. A full application can cover a building that doesn't qualify on its age, original construction or location, or a scheme that wants more height or more storeys than the right allows.
Full permission can also be the better route where a scheme needs more extensive alterations to the existing building, or where you want more flexibility over the design and layout of the new flats. Cheffins can weigh up the options and advise on the most realistic route to permission.
Why Cheffins?
Cheffins does more than secure the consent. The firm has land and new homes teams alongside the planning consultancy, so a single enquiry can run from prior approval right through to the sale of the finished flats, all under one roof. Our planning and development team advises on permitted development across the region, led by Kennedy Durrant MRTPI, Director, and Andy Brand MRTPI, Director.
Recent work includes a Class A Part 20 approval at Wembley (Brent), where Cheffins secured prior approval for six new flats above an existing block.
Frequently asked questions
Can I build flats on top of an existing block of flats?
Yes, potentially. Class A Part 20 lets qualifying purpose-built, detached blocks of flats be extended upward to create new homes. Whether a building qualifies depends on factors such as its age, height, construction and location, along with the other requirements of the right.
What is Class A Part 20 permitted development?
Class A Part 20 is a permitted development right that lets qualifying detached, purpose-built blocks of flats be extended upward by up to two storeys to create new flats, subject to set limits and prior approval from the council.
How many storeys can I add to a block of flats?
Class A Part 20 allows up to two additional storeys, as long as the roof height stays within 7 metres of the existing roof and the extended building stays within 30 metres overall, excluding rooftop plant. Other restrictions apply too.
Does Class A Part 20 apply in a conservation area or to a listed building?
No. Class A Part 20 can't be used in a conservation area, or for a listed building or land within its curtilage. A full planning application may be an alternative route, subject to the relevant planning policy and heritage considerations.
Do I need prior approval for an upward extension?
Yes. Class A Part 20 needs prior approval from the council before work can begin. The council normally has eight weeks to decide, and development can't go ahead without approval or a successful appeal.
Speak to the planning team
Thinking about adding flats on top of an existing block? Send us the building's details and we'll check whether it qualifies for an upward extension and set out your options. Get in touch with the planning team, or request a call back.
A note for readers
The information here is a general introduction rather than a statement of the law. Permitted development rules are detailed and change regularly, with many rights subject to conditions and a prior approval requirement, so it's worth confirming the current position for your building with us or the local planning authority.