Class ZA: demolishing a building and rebuilding as homes
Class ZA of Schedule 2 Part 20 covers demolition of a qualifying detached building and its replacement with flats or a single dwelling, under prior approval rather than a full application.
Class ZA of Part 20 lets you demolish a single detached building and put new homes in its place without a full planning application, subject to prior approval. The class za demolition rebuild route is narrow by design. The building has to be the right kind, the right age, the right size and properly empty, and even then the council can refuse prior approval on any of a long list of matters that reads much like a planning application in miniature.
It is worth knowing what it is not. This is not the Part 11 demolition prior approval that deals with knocking a building down and leaving the site clear. Class ZA is a single consent covering demolition and replacement together.
What the class actually permits
The permitted development right is the demolition of a qualifying detached building and the construction of a new detached block of flats or a single detached dwellinghouse on the same site. The new building goes up in place of the old one, within the old footprint.
Because both halves sit in one right, you cannot demolish first and decide later. Prior approval has to be granted before any demolition happens, and the whole development has to be completed within three years of the date of that approval. Sites cleared in advance fall outside the class entirely.
Read the current text of Schedule 2 Part 20 on legislation.gov.uk before you commit. Part 20 has been amended several times since it was introduced in 2020, and the limits below are the ones to verify first.
The buildings that qualify
Three tests bite at once. The building must be detached. It must have been constructed before 1 January 1990. And it must have been in a qualifying use, broadly a purpose-built detached block of flats or a building in the former office, research and development or light industrial uses, at the reference date set out in the Order.
The exclusions remove most of the interesting sites. Class ZA does not apply on land in a conservation area, a National Park, the Broads, a National Landscape or a World Heritage Site. It does not apply to a listed building or a building within its curtilage, to a scheduled monument, or to a site of special scientific interest. Safety hazard areas and military explosives storage areas are out as well.
That combination means the typical Class ZA candidate is a 1970s or 1980s office block or light industrial unit on an unremarkable edge-of-centre site with no designation over it. If your building sits inside a conservation area boundary by ten metres, the route closes and you are back to a full application.
Size, height and footprint limits
| Limit | What the Order sets |
|---|---|
| Footprint of the old building | No more than 1,000 m² |
| Height of the old building | No more than 18 metres |
| Footprint of the new building | No greater than the footprint of the old building |
| Height of the new building | No more than 18 metres, and no more than 7 metres above the old building |
| Completion | Within three years of prior approval |
The footprint constraint is the one that catches schemes out. Since the new building cannot spread beyond the old one, the only way to add homes is upward, and the seven metre allowance gives you roughly two extra storeys on a low building. On a single storey light industrial shed the arithmetic rarely works, because the ground floor plate that suited a workshop makes an awkward residential floorplate.
New dwellings created under Part 20 are also expected to meet the nationally described space standard. Check the current conditions in the Order, since that requirement was added by later amendment rather than appearing in the original text.
Vacancy and how you evidence it
The building has to have been vacant for a continuous period immediately before the prior approval application is made. Councils treat this as a factual test and they do check.
Evidence that works: business rates records showing the empty property rating position, terminated lease documents or a surrender deed, utility bills or meter readings showing negligible consumption, and dated photographs of the interior. Evidence that does not work: a statement from the applicant that the building has been empty for a while.
A caretaker arrangement, a storage licence or a short-term occupier moved in to keep the building secure can break the period. If the building was occupied at any point in the qualifying window, say so and recalculate rather than hoping the point goes unnoticed, because a prior approval granted on wrong facts is vulnerable.
The prior approval matters
Part 20 gives the council a broad list of matters on which it can require prior approval, and Class ZA carries one of the longest. Expect to address transport and highways impacts, contamination risk, flooding risk, the design and external appearance of the new building, the provision of adequate natural light in all habitable rooms, the effect on the amenity of the new building and of neighbouring premises including overlooking, privacy and loss of light, noise from any nearby commercial premises, heritage and archaeological impact, the method of demolition, and landscaping. In some locations air traffic, defence assets and protected views are added.
Two of those deserve early attention on a former industrial or office site. Contamination is a near certainty on a light industrial building of that age, so a desk study and, where it flags a plausible pollutant linkage, intrusive investigation. Commission a Land Contamination assessment from a suitably qualified and experienced person working to BS 10175. This is one of the report types where professional input is legally expected rather than optional.
Natural light is the other. The condition on adequate natural light in habitable rooms is a hard requirement, and a deep floorplate inherited from an office building can fail it. A Daylight and Sunlight Assessment using the current BRE guidance settles the question before the council does.
Highways impact is usually lighter work. On a small scheme a Transport Statement covering access, parking and refuse and servicing arrangements is normally proportionate, with a full assessment reserved for larger replacements.
When a full application beats the prior approval route
Class ZA is attractive because it removes the principle of development from the argument. It is a poor fit when the scheme you want is bigger than the old building, when you need to change the footprint to get a decent layout, or when affordable housing policy would not otherwise apply and the site is large enough that a council will look hard for a reason to refuse.
A full application also lets you deal with the site as a whole rather than one building on it, and it gives you conditions you can discharge in stages. Where the numbers are close, price both routes. The prior approval application fee is lower, and the determination period is 56 days from a valid application, so the timetable is attractive. But a refusal costs you the same time as a refused full application and leaves you starting again.
Assembling the submission
The prior approval application needs a plan showing the site, the existing building and the proposed building, together with written evidence on each matter the council can consider. A Planning Statement structured against the Class ZA conditions, taking each limitation in turn and showing it is met, is the document that makes an officer's job easy.
Include the demolition method statement and the restoration proposals for the site, because both are named matters. Add the vacancy evidence as an annex with dates. Serve the notices the Order requires on adjoining occupiers and display the site notice, and keep proof of both, since a procedural failure here is a straightforward reason to refuse.
This is general guidance, not legal advice, and a lawful development certificate is the only formal way to confirm that works are lawful. Check the position with your local planning authority or a qualified professional before relying on it.
Working out which reports a Class ZA scheme needs? Enter the postcode on PlanScope and the constraint check will show what the site triggers.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Does Class ZA apply to a terraced building?
No. The building has to be detached. A terraced or semi-detached office or workshop falls outside the class however well it otherwise fits, and so does a building that shares a party wall with a neighbouring structure. Where the building is attached, a full planning application for demolition and replacement is the route.
Can the new building be larger than the one demolished?
Not in footprint. The replacement must sit within the footprint of the old building. Height is the only direction with any headroom, limited to 18 metres overall and to seven metres above the old building. That constraint is why single storey industrial units rarely work under this class.
How long must the building have been empty?
The Order requires a continuous period of vacancy immediately before the prior approval application. Check the current wording, and evidence it with empty property rating records, lease surrender documents, utility consumption and dated photographs. A short-term occupier or storage licence during the window can break the period and defeat the application.
How long does the council have to decide?
Prior approval applications under Part 20 run to a 56 day period from receipt of a valid application. If the authority does not notify a decision within that period the development may proceed in accordance with the details submitted, but that outcome depends on the application having been valid and complete from the start.
Is contamination assessment really needed for a small scheme?
Contamination is a named prior approval matter under Class ZA, and former light industrial and office sites of pre-1990 construction commonly have a plausible pollutant linkage. Expect a Phase 1 desk study as a minimum, prepared by a suitably qualified and experienced person, with intrusive investigation where the desk study identifies a credible risk.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.