Class ZA demolition and rebuild: what the right covers

Class ZA of Part 20 of Schedule 2 to the General Permitted Development Order 2015 permits the demolition of a single detached building and its replacement with a block of flats or a single dwellinghouse, subject to prior approval. It was introduced in August 2020 alongside the upward extension classes, and it has been used far less than the attention it received suggested it would be.

The reason is in the qualifying conditions. Most buildings that would benefit from redevelopment fail one of them, and the schemes that do qualify usually cannot increase floorspace enough to pay for the demolition.

What the class permits and on which buildings

The right covers demolition of a detached building and construction in its place of a new building used as a block of flats or as a single dwellinghouse. The old building has to be either a purpose-built detached block of flats or a detached building last used for office, research and development or light industrial purposes.

That is a narrow list. A detached retail unit does not qualify. A terraced or semi-detached building does not qualify, because the class requires a detached building. A mixed-use building with a shop at ground floor does not qualify on the office limb.

The class also carries a footprint limit on the old building, expressed in square metres, which excludes anything of real scale. Read the current text on legislation.gov.uk before advising, because Part 20 has been amended since it was made and the limits are the whole of the commercial question.

Vacancy and the qualifying dates

Two date-based conditions do most of the exclusion work.

The old building must have been constructed before a stated date in 1990, which rules out the 1990s and 2000s office stock that is otherwise the most obvious candidate for residential conversion. And the building must have been vacant for a continuous period immediately before the prior approval application, measured in months rather than weeks.

The vacancy condition is harder to satisfy than it looks. Evidence of vacancy means business rates records, utility readings, lease documentation and photographs across the whole period, and a building with a caretaker, a mast licence or a storage tenant is arguably not vacant. Holding an income-producing asset empty for the qualifying period also costs money, and that cost sits in the appraisal.

Assemble the vacancy evidence before you apply. A prior approval application refused on vacancy grounds cannot be rescued by producing the evidence afterwards, because the period is measured to the application date.

Height, footprint and volume limits

The dimensional limits are what stop the numbers working.

• The footprint of the new building must not exceed the footprint of the old building
• The new building must not exceed a stated overall height limit, set at 18 metres
• The new building must not be more than a stated number of metres higher than the old building
• The new building must sit within the footprint of the old one rather than shifting across the site

The footprint restriction is the commercially fatal one. You are demolishing a building and rebuilding on the same footprint, so the only additional floorspace comes from added height, and the added height is capped. On a two-storey office you may gain a couple of storeys. On a four-storey block you may gain very little.

There is a related design problem. A residential floorplate that matches an office footprint often produces poor unit layouts, deep plans and single-aspect flats, and natural light is itself a prior approval matter.

Prior approval matters the council may consider

The list of matters is long enough that the process resembles a planning application in everything but the policy test. Expect the authority to consider transport and highways, contamination, flood risk, the external appearance of the new building, the effect on amenity of both the new building and neighbouring premises including overlooking, privacy and light, the effect on heritage and archaeology, the method of demolition, landscaping, and the provision of adequate natural light to all habitable rooms.

Two of those deserve dedicated evidence. Contamination on a former light industrial site means a Contaminated Land Assessment prepared by a suitably qualified and experienced person in accordance with the relevant British Standard. Amenity and natural light mean a Daylight and Sunlight Assessment covering both the proposed units and the neighbouring windows.

Because the authority cannot refuse on general policy grounds, the argument usually runs through these matters instead. Officers who dislike a scheme find their objection within the prior approval list, and design and amenity give them room to do it.

Where the right is unavailable by designation

The class does not apply on article 2(3) land, which covers conservation areas, National Parks, National Landscapes, World Heritage Sites and the Broads. Listed buildings and their curtilage are excluded, as are scheduled monuments and sites of special scientific interest, and there are exclusions related to safety hazard and military explosives storage areas.

An Article 4 direction can also remove the right for a defined area. Authorities have made directions covering permitted development changes where they consider the effects unacceptable, and the national policy test for making one is tighter than it used to be. Check the local land charges register and the council's published list of directions, and read how Article 4 directions work against the national policy test before assuming the right survives.

Even where the class applies, the other regimes do not disappear. Community Infrastructure Levy liability arises on the new floorspace. The biodiversity gain condition applies to prior approvals in the same way as to planning permissions. Building control, the demolition notice procedure and asbestos obligations all run in parallel.

Why the class is used less than expected

Put the conditions together and the eligible universe is small: a detached, pre-1990, sub-threshold, currently vacant office or flat block, outside every designation, on a site where adding a small number of storeys on the same footprint produces a viable residential scheme.

Compare that with the alternative routes. A conversion under Class MA keeps the building and avoids demolition cost entirely, and the changes to Class MA following removal of the floorspace cap widened its reach. A full planning application has no dimensional limits, allows a larger footprint and permits a scheme designed for residential use from the outset, at the cost of a policy test and affordable housing.

For most sites the full application wins on value even after allowing for the risk. Class ZA earns its place where the building is unlettable in its current form, the site is unconstrained, and the applicant wants certainty of principle rather than maximum floorspace.

Evidence to submit with the application

Build the application around the qualifying conditions first and the prior approval matters second, because a scheme that fails a condition is refused without the matters being reached.

1. Evidence of the date of construction, from historic records, building control files or a dated survey.
2. Evidence of the last lawful use, with the use class and the supporting documents.
3. Continuous vacancy evidence covering the full qualifying period.
4. A measured survey establishing the existing footprint and height, and drawings showing the proposed building within those limits.
5. Technical reports addressing contamination, flood risk, transport, daylight, amenity and the demolition method.
6. A demolition method statement, including hours, dust and traffic management.

Keep the timeline visible on the front of the submission, because the case officer's first question is whether the building qualifies at all. Following how the class has been amended is easier through the planning law updates timeline than through the Order itself.

This is general guidance rather than legal advice. Check the current text of the Order and the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.