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Class AD – new dwellinghouses on detached buildings in use as dwellinghouses

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This allowance is effected by the changes to the Use Classes Order and it is anticipated that this allowance will be tidied up in August of 2021 in line with the current government consultations. Reference to the Use Classes should be taken from the pre-2020 Use Classes Order.

What is allowed

Development consisting of works for the construction of new dwellinghouses immediately above the topmost storey on a detached building in use as a single dwellinghouse within the meaning of Class C3 of the Schedule to the Use Classes Order, where the development comprises—

  • up to two additional storeys, in the case of an existing dwellinghouse consisting of two or more storeys;
  • one additional storey, in the case of an existing dwellinghouse consisting of one storey,

together with any development listed below

  • engineering operations reasonably necessary to construct the additional storeys and new dwellinghouses;
  • works for the construction of appropriate and safe access to and egress from the new and existing dwellinghouses, including means of escape from fire, via additional external doors or external staircases;
  • works for the construction of storage, waste or other ancillary facilities reasonably necessary to support the new dwellinghouses.
Where can I use it

On existing purpose built terraced houses and subject to the following restrictions.

What is not allowed

Development is not permitted by Class AC if—

  • the building was constructed before 1st July 1948 or after 5th March 2018;
  • on 5th March 2018 the building was in a use other than—
  • a use falling within Class C3 (dwellinghouses) of the Schedule to the Use Classes Order; or
  • a use or mixed use as set out above
  • the additional storeys are constructed other than on the principal part of the dwellinghouse;
  • the floor to ceiling height of any additional storey, measured internally, would exceed the lower of—
  • 3 metres; or
  • the floor to ceiling height, measured internally, of any storey of the principal part of the existing dwellinghouse;
  • the new dwellinghouses are not flats;
  • the height of the highest part of the roof of the extended building would be greater than 18 metres;
  • the height of the highest part of the roof of the extended building would exceed by more than 3.5 metres the height of the highest part of the roof of every other building in the row of terrace buildings of which it forms part;
  • the height of the highest part of the roof of the extended building would exceed the height of the highest part of the roof of the existing dwellinghouse by more than—
  • 3.5 metres, where the existing dwellinghouse consists of one storey; or
  • 7 metres, where the existing dwellinghouse consists of more than one storey;
  • the existing dwellinghouse has been enlarged by the addition of one or more storeys above the original dwellinghouse, whether in reliance on permission granted under Class AA of Part 1 or otherwise;
  • development under Class AC would include the provision of visible support structures on or attached to the exterior of the building upon completion of the development;
  • development under Class AC would consist of engineering operations other than works within the existing curtilage of the dwellinghouse to—
  • strengthen existing walls;
  • strengthen existing foundations; or
  • install or replace water, drainage, electricity, gas or other services;
  • development under Class AC would extend beyond the curtilage of the existing dwellinghouse;
  • development under Class AC would—
  • extend beyond the curtilage of the existing dwellinghouse;
  • be situated on land forward of a wall forming the principal elevation of the existing dwellinghouse; or
  • be situated on land forward of a wall fronting a highway and forming a side elevation of the existing dwellinghouse; or
  • the land or site on which the dwellinghouse is located, is or forms part of article 2(3) land;
  • a site of special scientific interest;
  • a listed building or land within its curtilage;
  • a scheduled monument or land within its curtilage;
  • a safety hazard area;
  • a military explosives storage area; or
  • land within 3 kilometres of the perimeter of an aerodrome.
How do I use the allowance

This is a complex prior a approval permitted development allowance that should not be attempted without the support of a planning consultant and as such it is subject to an assessment of the following criteria:

  • transport and highways impacts of the development;
  • air traffic and defence asset impacts of the development;
  • contamination risks in relation to the building;
  • flooding risks in relation to the building;
  • the external appearance of the building, including—
  • the design and architectural features of the principal elevation; and any side elevation that fronts a highway; and
  • the impact of any works of Class Ab;
  • the provision of adequate natural light in all habitable rooms of the new dwellinghouses;
  • impact on the amenity of the existing building and neighbouring premises including overlooking, privacy and the loss of light;
  • whether, because of the siting of the building, 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, and
  • compliance with the National Standards from 6th April 2021
Our Notes

Early Part 20 applications have been universally refused (based on research carried out by Planner Magazine). It remains to be seen how effective Class AD is in reality and at the time of writing it is untested at appeal.

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