New flats above commercial premises under Part 20

Part 20 of Schedule 2 to the General Permitted Development Order 2015 allows new flats to be built on top of existing commercial premises by prior approval rather than by planning application. For part 20 flats above shops the relevant classes are AA for a detached building in commercial or mixed use and AB for a building in a terrace, and the conditions are detailed enough that most sites fail on one of them. Reading the Order before drawing anything saves the cost of a refused prior approval.

The right exists. It is narrow, it carries a long list of prior approval matters, and the council can refuse on most of the grounds a planning application would be judged on.

Which buildings and which classes

The upward extension classes in Part 20 divide by building type.

For the commercial classes, the qualifying use is a use within Class E of the Use Classes Order, or use as a betting office, pay day loan shop or launderette, or a mixed use combining one of those with a dwelling. A building in Class B2 general industrial or B8 storage use does not qualify, and a sui generis use such as a hot food takeaway or a pub does not either.

The age restriction catches a great many high street buildings. For the commercial upward extension classes the existing building must have been constructed within a defined window, which excludes buildings put up before 1 July 1948 and those completed after an early March 2018 cut-off. A Victorian parade is therefore out, and so is a recently built retail unit. Verify the exact dates in the current text of the Order, because Part 20 has been amended since it was introduced.

Height limits and where they are measured from

Three separate height controls apply, and all three have to be satisfied.

The extended building must not exceed 18 metres in total height. That figure is the trigger for higher-risk building status elsewhere in the regulatory system, which is not coincidental.

The additional storeys must not raise the building above the stated maximum increase for the class, measured from the top of the existing roof excluding plant and apparatus.

Each new storey must have an internal floor-to-ceiling height no greater than three metres, and no greater than the floor-to-ceiling height of any existing storey in the principal part of the building.

That last limit is the one that defeats schemes on older buildings with generous ground floors and low upper floors. If the existing first floor has a 2.4 metre internal height, the new storeys are capped at 2.4 metres, which leaves very little once the floor zone and services are taken out.

Measuring from the correct point matters as much here as it does under Part 1, and the same arguments about ground level recur. Measuring height under Part 1 from adjacent ground covers the principle.

What the council may consider on prior approval

Prior approval under Part 20 is not a light touch procedure. The matters the authority may consider include transport and highways impacts, air traffic and defence asset safeguarding, contamination risk, flood risk, the external appearance of the building, the provision of adequate natural light in all habitable rooms of the new dwellings, the impact on the amenity of the existing building and neighbouring premises including overlooking, privacy and loss of light, and the impact of noise from any commercial premises in the building on the intended occupiers.

Fire safety is also a matter for the prior approval, and the Order requires supporting information on it. Check the current wording of the class, since the fire safety requirement was added by amendment and the scope of what must be submitted has changed. For a building that will reach 18 metres or seven storeys, the wider Building Safety Act framework and Planning Gateway One come into play, and a Fire Statement prepared by someone with fire engineering competence becomes necessary rather than optional.

Natural light is the ground that refuses the most schemes. The test is adequate natural light in all habitable rooms, and a top-floor flat with a single window onto a lightwell, or a bedroom lit only from a corridor, fails it. Submit room-by-room daylight analysis rather than asserting compliance.

Reports a Part 20 application realistically needs

Prior approval applications under Part 20 attract larger document sets than people expect. On a typical high street site:

1. Existing and proposed drawings, including sections showing the measured existing floor-to-ceiling heights and the proposed ones, because the height limits are proved on the section.
2. A structural appraisal of the existing building's capacity to take additional storeys, with the foundation assumption stated.
3. Fire safety information to the extent the Order requires, and a full fire statement where Gateway One applies.
4. Daylight analysis of the new habitable rooms, and of neighbouring windows where overlooking and loss of light are in issue.
5. A noise assessment of the commercial premises below and any plant, addressing internal levels in the new flats.
6. A flood risk screening, and a flood risk assessment where the site is in Flood Zone 2 or 3.
7. A transport and servicing note covering cycle parking, refuse storage and any loss of servicing space.
8. A construction management report, which the Order requires as a condition before development begins, covering hours, dust, noise and traffic.

New dwellings created under Part 20 must also meet the nationally described space standard, so the unit areas have to be scheduled against it.

The structural appraisal is where schemes quietly die. Adding two storeys to a two-storey Victorian-era building with shallow footings usually means a new internal frame, which changes the ground floor retail layout and often the economics.

Where the right is excluded

Part 20 does not apply on article 2(3) land, which takes out conservation areas, National Landscapes, National Parks, the Broads and World Heritage Sites. It does not apply to listed buildings or buildings within their curtilage, scheduled monuments or land within their curtilage, sites of special scientific interest, safety hazard areas or military explosives storage areas.

An article 4 direction can remove the right as well, and several authorities have made directions covering upward extension in parts of their area. Check the direction's wording and its area map rather than assuming a borough-wide effect.

One more trap. Where a previous permission on the site is subject to a condition restricting further development, the right may not be available, and article 3(4) of the Order prevents permitted development that would conflict with a condition on an earlier permission. Development contrary to a condition and article 3(4) sets out how that works in practice.

Choosing between the right and a full application

The prior approval route has a shorter determination period and a lower fee than a full application for the same number of units, and it limits the grounds of refusal. Those are real advantages.

Against that, the design is boxed in by the height and floor-to-ceiling limits, there is no scope to negotiate a better scheme, affordable housing policy does not apply but neither does any flexibility on unit mix, and a refusal means starting again. On a site where the age or height limits are marginal, a refused prior approval followed by a full application costs more than going straight to the application.

The screening question for larger proposals is worth settling early too, since prior approval does not sidestep environmental impact assessment. Prior approval applications and EIA screening explains where that bites.

Where the full application route is chosen, the Planning Statement should address the fallback position explicitly. A deliverable Part 20 fallback is a material consideration, and spelling out what could be built without permission is one of the stronger arguments available for a better-designed scheme.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. A Fire Statement at Planning Gateway One must be prepared by someone with the necessary fire engineering competence, so treat any draft as a starting point for that professional. This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.