Class ZA demolition and rebuild: what it permits

Class ZA demolition rebuild prior approval lets you knock down a qualifying building and put homes on its footprint without a planning application, and the constraints are so tight that most sites fall out before the design starts. The class sits in Part 20 of Schedule 2 to the General Permitted Development Order 2015 and covers a single detached block of flats, or a single detached building last used for offices, research and development or light industrial purposes. The replacement has to sit on the same footprint, within a capped height increase, and the whole thing has to pass a long list of prior approval matters. Read the class text before you buy anything.

Which buildings qualify

Three filters remove most candidates immediately.

The building must be detached and must be a single building. A terrace, a semi-detached unit or a building joined to its neighbour by anything structural is outside the class.

The use must be right. A purpose-built detached block of flats qualifies. So does a detached building last in use as offices, for research and development, or for light industrial purposes, the uses that were Class B1 before the 2020 reorganisation of the Use Classes Order. A detached shop, a warehouse, a pub or a dwelling house does not.

The building must be old enough and empty enough. The class requires the building to have been constructed before 1 January 1990, and to have been vacant for a continuous period immediately before the prior approval application is made. It also sets a maximum floorspace and a maximum height for the existing building, so a large office block is outside the class even if everything else fits.

Those thresholds are expressed precisely in the Order and have been amended since the class was introduced, so take them from the current text rather than from a summary, including this one.

Footprint and height constraints on the replacement

Here is where the class stops being a development opportunity and becomes a design puzzle.

The new building has to be on the footprint of the old one, and its footprint must not exceed it. No stepping out to catch daylight. No reshaping the plan to get a better unit mix. A 1970s office with a deep plan and a central core gives you a deep plan to work with, and deep plans produce flats with poor outlook.

The new building must also be detached, and its height is capped twice: a maximum increase over the height of the old building, and an absolute height limit. Both caps apply, so the shorter answer governs.

The practical consequence on most sites is that the extra storeys you were counting on are the ones that make the numbers work, and they are also the ones most likely to run into the amenity and external appearance limbs of prior approval.

Where the class cannot be used at all

Class ZA is withdrawn on designated and sensitive land, and the list is long.

Check all of these before anything else. Running a feasibility study on a building inside a conservation area and discovering the position at week six is an avoidable cost, and the designations are published on the national planning data platform.

The prior approval matters

Prior approval under Class ZA is not a light-touch process. The list of matters the authority may consider is wide enough that the exercise resembles a full application in everything but name.

Expect the authority to consider transport and highways impacts, contamination risk, flood risk, the external appearance of the new building, the provision of adequate natural light in all habitable rooms, the impact on the amenity of neighbouring premises including overlooking, privacy and loss of light, noise from any commercial premises nearby, the method of demolition and how it will be managed, landscaping, impacts on heritage and archaeology, and air traffic and defence asset impacts.

Adequate natural light is the one that kills schemes on deep plan buildings. It is a stated prior approval matter, and a refusal on it is not arguable away with a floor plan showing a borrowed light.

New dwellings created under permitted development must also meet the nationally described space standard, which applies as a condition of the class rather than as a local policy choice.

Evidence of the existing building

Because every constraint is relative to the old building, you have to prove what the old building was.

Commission a measured survey before demolition, not after. Record the footprint, the height to the highest part of the roof, the gross internal floorspace and the number of storeys, and reference the height to a fixed datum rather than to ground level alone, because ground level is itself a defined term with its own complications. The article on measuring height against adjacent ground under Part 1 covers the measurement convention.

Prove the use and the vacancy as well. Rating records, utility accounts, lease documents, marketing particulars and dated photographs all help. A statutory declaration from the owner on its own is weak evidence.

Keep the survey and the evidence pack, because the prior approval is granted on the basis of them and an enforcement officer may want to see them years later.

Interaction with the levy and policy obligations

Permitted development does not escape the Community Infrastructure Levy. Where a charging schedule is in force, levy liability is calculated on net additional floorspace, with the usual provisions on existing buildings in lawful use for a continuous period, and those provisions interact awkwardly with a class that requires the building to be vacant. Take advice on the levy position before relying on an existing floorspace deduction.

Affordable housing is a different matter. Permitted development does not engage local plan affordable housing policy, because there is no planning application against which to apply it and no mechanism to secure an obligation. That is a large part of why the class exists, and also a large part of why councils resist it.

Environmental impact assessment is not switched off by the class. Where the scheme falls within Schedule 2 of the 2017 Regulations, screening is still required, and the piece on prior approval applications and EIA screening sets out how that works alongside a prior approval route.

Programme and the lapse period

The class sets a deadline for completing the development, running from the date of prior approval. Miss it and the permission granted by the class falls away, which on a demolition and rebuild means a half-built site with no consent. Check the deadline in the Order text and programme to it with contingency, because demolition programmes slip for reasons nobody controls.

Treat the planning route as the fallback rather than the afterthought. Where the site is marginal under the class, a full application often delivers a better building, since the footprint constraint disappears and the policy obligations are the price. Setting out that comparison honestly is one of the jobs a planning statement does well. Where contamination is in play on a former industrial building, a contaminated land assessment will be needed whichever route you take.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A lawful development certificate is the only formal way to confirm that works are permitted development.

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