Class ZA: demolition and rebuild as new dwellings

Class ZA of Part 20 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015 lets you demolish a single detached building and rebuild it as homes, subject to prior approval. It arrived in August 2020, it applies to a narrow set of buildings, and it is used far less than the attention it received would suggest. The Class ZA permitted development route works for a vacant detached office or light industrial block, or a detached block of flats, built before 1990 and no larger than 1,000 square metres in footprint.

Read that sentence again. Most buildings people want to demolish fail one of those tests, and the ones that pass usually have a better route available.

What the class permits and for which buildings

The right covers demolition of a qualifying building and construction of a new building in its place, either as a single dwellinghouse or as a block of flats. Both the demolition and the rebuild are authorised together, which is the point of it.

The qualifying building must be detached, and it must have been either a block of flats or a building in office, research and development, or light industrial use as at 12 March 2020. Buildings in retail, hospitality, storage, distribution or general industrial use do not qualify, however convenient that would be.

The building must also have been constructed before 1 January 1990. That cut-off excludes a large part of the stock people most want to replace, including a generation of 1990s business park sheds that are now obsolete.

The qualifying conditions on the old building

Three further conditions do most of the filtering:

• the footprint of the old building must be no more than 1,000 square metres
• the building must have been vacant for a continuous period of at least six months immediately before the date of the prior approval application
• nothing of the old building may remain, since the right authorises demolition rather than partial retention

The six month vacancy period is a real commercial cost. Holding an empty building through a vacancy period, empty rates and all, before you can even apply is a decision to take deliberately rather than to discover.

Height and footprint limits

The new building has to sit within the footprint of the old one. That single condition explains most of why Class ZA is rarely used, because it removes any possibility of gaining floor area at ground level. You can go up, within limits, and you cannot go out.

Upwards is capped twice over. The new building must be no more than 18 metres in overall height, and it must be no more than two storeys taller than the building it replaces. A single storey building therefore becomes at most three storeys, which on a 1,000 square metre footprint is not a large scheme.

The 18 metre figure lines up with the higher-risk building threshold in the building safety regime, and a scheme designed to sit just under it is making a decision with consequences well beyond planning, as set out in what the higher-risk building threshold changes at planning.

Prior approval matters

Prior approval under Class ZA covers a wider list than most permitted development rights, which is one reason the process is less predictable than the word "permitted" suggests. The matters include transport and highways impacts, contamination risk, flooding risk, the design and external appearance of the new building, the impact on the amenity of neighbouring premises including overlooking, privacy and loss of light, noise from commercial premises affecting future occupiers, heritage and archaeological impact, the method of demolition, landscaping, and impacts on protected views and on air traffic or defence assets.

Design and external appearance being in that list matters. It means the council can engage with how the building looks, which is exactly what most permitted development routes prevent, and it means the submission needs proper elevations rather than a massing diagram.

Prepare the technical material up front. A desk study feeding a contaminated land assessment where the site history warrants it, and, where the building or its setting has historic interest, a Heritage Statement addressing the heritage and archaeology matter. Councils refuse prior approval applications on incomplete information more readily than they refuse full applications, because there is less scope to negotiate.

Where the right cannot be used

Class ZA does not apply on article 2(3) land, which takes out conservation areas, National Parks, National Landscapes, the Broads and World Heritage Sites in one line. It does not apply to listed buildings or land within their curtilage, or to scheduled monuments. Sites of special scientific interest, safety hazard areas and military explosives storage areas are excluded.

An Article 4 direction can remove the right, and some authorities have made them.

Add those exclusions to the pre-1990, detached, 1,000 square metre and six month vacancy tests, and the population of eligible buildings is small.

Why the right is used rarely

The honest assessment is that Class ZA solves a problem most developers do not have.

If the building is in Class E use, which includes offices, research and development, light industrial, retail and much else, a conversion under Class MA now delivers homes without demolition, without a footprint cap and without the vacancy period that Class MA lost in 2024. Conversion keeps the embodied carbon, avoids the demolition cost, and reaches a wider set of buildings.

If the site can take more than the old footprint, a full planning application is the only way to get it, and on a site worth developing that extra area is usually worth more than the certainty Class ZA offers.

Where Class ZA earns its place is the obsolete detached building on a constrained plot, where conversion cannot work because of floor to ceiling heights, structure or plan depth, and where the owner wants a defined process rather than a policy argument about density and affordable housing. That is a real category. It is just not a large one.

Interaction with conservation areas and with a full application

Because article 2(3) land is excluded outright, a building in a conservation area cannot use Class ZA at all, and demolition in a conservation area is a separate question with its own consent requirements.

Where a full application is the better route, the trade is predictability for flexibility. A full application opens up floor area, layout and design, and it brings in affordable housing policy, density policy and the full development plan test. It also allows negotiation, which prior approval does not. A scheme that is nearly compliant with Class ZA will be refused rather than amended, and the applicant then has to start again.

One practical suggestion: run the Class ZA tests as a checklist at the outset, on paper, before anyone draws anything. Pre-1990, detached, qualifying use on 12 March 2020, footprint under 1,000 square metres, vacant six months, not on article 2(3) land, not listed. Five minutes of that saves a wasted feasibility study.

This is general guidance, not legal advice. Permitted development rights are amended frequently, so check the current text of Part 20 and the position with your local planning authority before relying on it. A Lawful Development Certificate is the only formal way to confirm that works are lawful.

Follow changes on the UK planning law updates timeline, and browse the report types a prior approval submission is likely to need. PlanScope's drafts should be reviewed before submission, and we do not guarantee planning approval.