Demolition and rebuild under Part 20 Class ZA
Class ZA allows a detached commercial building or block of flats to be demolished and rebuilt as homes. Here are the gates most sites fail and the evidence needed.
Class ZA of Part 20 of the General Permitted Development Order 2015 allows a single detached building to be demolished and replaced with homes, subject to prior approval. It is the most demanding permitted development right in the Order to use, and the reason is arithmetic rather than policy. The replacement has to sit within the footprint of the building it replaces, and it can only go so much taller, so the scheme that works is one where the old building was already close to the shape you want.
Most sites fail on eligibility before anyone reaches the design. Work through the gates in order and you will know within an hour whether the right is available.
What the right permits
Class ZA covers demolition of a single detached block of flats, or a single detached building last used for commercial, business or service purposes, and the construction of a replacement building in its place for residential use. It can also be used to replace the building with a single dwellinghouse.
Two applications in one, in effect. The demolition and the rebuild are authorised together, and the prior approval application has to describe both. The council cannot refuse on the principle of losing the commercial floorspace, because the Order has already granted that permission. What it can do is refuse prior approval on any of the listed matters, and the list is long enough that a poorly evidenced application fails.
The eligibility gates
Run these checks before spending money on drawings.
- The building must be detached, standing alone rather than sharing a wall with anything else.
- It must have been constructed before 1 January 1990.
- Its footprint must not exceed 1,000 square metres.
- It must have been in the qualifying use immediately before it became vacant, and vacant for a continuous period before the prior approval application is made.
- The land must not be in a conservation area, a National Landscape, a National Park, a World Heritage Site or the Broads, and the building must not be listed, within the curtilage of a listed building, or a scheduled monument.
- The site must not be in a site of special scientific interest, a safety hazard area or a military explosives storage area.
Agricultural buildings are outside the right entirely. So is anything already residential other than a detached block of flats.
The vacancy requirement is the one that produces arguments. Evidence it properly with business rates records, utility accounts showing no consumption, dated photographs and any marketing particulars. Councils ask for this and a bare assertion in a covering letter will not do.
Footprint, height and the shape of the replacement
The replacement building must be built within the footprint of the old one. Not the same area somewhere else on the site, and not a rearranged footprint of equivalent size. That single rule kills most conversions of low-rise industrial sheds into flats, because a 900 square metre single-storey footprint makes a poor residential plan.
Height is capped two ways. The new building can be taller than the old one by a limited margin, and it is subject to an overall ceiling that keeps the right below the height at which the higher-risk building regime bites. Read the current consolidated text of Class ZA for the exact figures before you fix a storey count, because Part 20 has been amended since it was introduced in 2020.
Time limits apply at the other end. The development has to be completed within three years of the date of prior approval, covering both the demolition and the new building. That is a genuine constraint on a scheme needing vacant possession, a demolition contractor and a funding package.
The homes themselves must meet the nationally described space standard and every habitable room must have adequate natural light, requirements that apply to permitted development homes generally. Single-aspect flats in the middle of a deep plan will not satisfy the second.
The prior approval matters
The council considers a defined list, and each one needs evidence in the submission rather than a promise to supply it later.
- Transport and highways impacts, including parking and servicing
- Contamination risk on the site
- Flooding risk on the site
- Design and external appearance of the new building
- The impact of the greater number of homes on the provision of services, where relevant
- Impact on the amenity of the new and neighbouring premises, including overlooking, privacy and light
- Natural light in all habitable rooms
- Impact on heritage and archaeology
- The method of demolition and the restoration of the site
- Landscaping, including tree planting
- Air traffic and defence asset safeguarding
- Protected views where they apply
Design deserves attention. A prior approval for external appearance is not a rubber stamp, and officers have refused Class ZA schemes on massing, materials and fenestration. Submit proper elevations, a materials schedule and a contextual street elevation, and treat the design section as you would on a full application.
Contamination and demolition method go together on former commercial sites. A Phase 1 desk study identifying the previous uses, followed by intrusive investigation where the desk study indicates it, is the expected sequence. Land contamination work is one of the areas where a suitably qualified and experienced author is required rather than preferred, and a contaminated land assessment should be prepared in accordance with BS 10175 by such a person. The same applies to an asbestos survey before demolition, which sits under health and safety law rather than planning.
Where the site drains poorly or sits near a watercourse, expect a request for a Flood Risk Assessment covering both the site and any change in run-off from the new footprint.
Practical obstacles in delivery
The right looks attractive on paper and disappoints in practice for reasons that have nothing to do with planning.
Vacant possession has to be real and continuous, which means holding an empty building through the application period while paying rates. Demolition of a detached building in a tight urban plot needs scaffolding, hoarding and often a party wall or adjoining owner agreement despite the building being detached, because the works affect neighbouring land.
The levy is payable. Class ZA development is chargeable development for Community Infrastructure Levy purposes, and the notices and deadlines apply exactly as they do on a full permission. Higher-risk building duties under the Building Safety Act apply where the finished height crosses the threshold, and the height cap in Class ZA is set to keep most schemes below it.
Finance is the quiet obstacle. Lenders are cautious about schemes whose consent depends on a prior approval that has conditions attached, and a three-year completion requirement leaves little room for a stalled build.
When a full application is the better route
Choose a full application where the footprint you want differs from the one you have, where the site is in a conservation area or otherwise excluded, where you want more height than the right allows, or where you want to build more than one building.
A full application also lets you argue the planning merits of a better scheme, and on a site with genuine potential the difference in value usually outweighs the extra determination time. It brings affordable housing policy and a different fee with it, so run the numbers both ways. Where the case turns on policy rather than on the right, the argument belongs in a Planning Statement.
For anyone following how Part 20 and the rest of the permitted development regime continue to change, the planning law timeline collects the updates.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
Which buildings qualify under Class ZA?
A single detached block of flats, or a single detached building last used for commercial, business or service purposes. The building must have been constructed before 1 January 1990, have a footprint not exceeding 1,000 square metres, and have been vacant for a continuous period before the application. Agricultural buildings and buildings in conservation areas are excluded.
Can the replacement building be bigger than the old one?
Not in footprint. The new building must be constructed within the footprint of the building it replaces, which rules out rearranging the plan across the site. Additional height is allowed within limits, subject to an overall cap. Check the consolidated text of Part 20 for the current figures, because the Order has been amended since 2020.
How do I evidence that the building is vacant?
Business rates records showing an empty property, utility accounts showing no consumption, dated photographs of the interior and exterior, and any letting or marketing particulars. Councils test this point, and a statement in the covering letter without documents behind it is the most common reason a Class ZA prior approval application is refused or returned.
Does Class ZA development pay the Community Infrastructure Levy?
Yes, where the charging authority has adopted a levy. Class ZA schemes are chargeable development, so the liability notice, assumption of liability and commencement notice requirements all apply, along with the surcharges for missing them. Existing floorspace deductions may reduce the amount where the building has been in lawful use.
When is a full application the better route?
Where you want a different footprint, more height than the right allows, more than one building, or where the site sits on excluded land such as a conservation area or National Landscape. A full application also allows the design to be argued on its merits, which on a site with real potential usually outweighs the longer determination period.
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.