Adequate natural light as a Class MA prior approval matter

Adequate natural light is a prior approval matter for Class MA conversions, and it is the one that kills more office-to-residential schemes than transport, contamination, flooding and noise put together. The local planning authority must refuse prior approval where adequate natural light is not provided in all the habitable rooms of the proposed dwellings, and the applicant has to supply floor plans showing the dimensions and proposed use of each room together with the position and dimensions of windows.

There is no definition of adequate in the Order. That sounds like a gap and in practice it is the reverse: it hands the authority a judgement, and the applicant has to make the judgement easy.

Where natural light sits in the prior approval list

Class MA of Schedule 2 Part 3 to the Town and Country Planning (General Permitted Development) (England) Order 2015 permits a change of use from Class E to Class C3, subject to qualifying conditions and to prior approval of a defined list of matters.

The list covers transport impacts and site access, contamination, flooding, the impact of noise from commercial premises on the intended occupiers, the impact on the character or sustainability of a conservation area where the ground floor use would be lost, the effect of introducing residential use into an area important for industry or storage, the loss of certain health or education services, and the provision of adequate natural light in all habitable rooms.

Two features of the natural light matter make it different from the others. It carries a duty to refuse rather than a discretion to weigh, and it is assessed on the drawings rather than on a technical survey of the site. Everything turns on the plans you submit.

The qualifying conditions have also moved. Class MA originally carried a floorspace limit and a vacancy period, and the 2024 amendments relaxed the qualifying criteria. Read the current conditions from the consolidated Order rather than from an article or a council leaflet written against the 2021 version, because whether your building qualifies at all is settled before anyone looks at the light.

Separately, dwellings created under Class MA must meet the nationally described space standard, which interacts directly with the light question: a layout squeezed to hit the space standard often creates the deep room that fails on light.

What adequate means when the Order does not define it

No figure is prescribed. What authorities actually do falls into a pattern.

They identify the habitable rooms, which means bedrooms, living rooms and kitchen-dining spaces where cooking and sitting are combined. Bathrooms, WCs, utility spaces, hallways and storage are not habitable rooms, and a windowless bathroom is not a problem.

Then they look at whether each habitable room has a window to the outside, the size of that window relative to the room, how deep the room is from the window, and whether anything outside the window blocks the sky. A room lit only by a borrowed light from another room, by a rooflight in a position that serves a corridor, or by a window into an enclosed shaft, gets scrutinised hard.

Where applicants want to put numbers on it, two frameworks are in use. The average daylight factor targets of 1 per cent for bedrooms, 1.5 per cent for living rooms and 2 per cent for kitchens come from the withdrawn BS 8206-2 and are still widely quoted and widely accepted. BS EN 17037 and its UK national annex set illuminance-based targets instead, and a modern Daylight and Sunlight Assessment will usually report against those.

Either framework is better than none. An assertion that the rooms will be well lit, unaccompanied by a calculation, invites a refusal the authority is obliged to issue.

Deep floorplates and the recurring problem

The buildings that attract Class MA applications are often the ones least suited to it. A 1970s or 1980s office with a 20 metre floor-to-core depth, a central service core, and windows on two elevations gives you a band of usable depth around the perimeter and a dead zone in the middle.

The arithmetic is unforgiving. A habitable room much deeper than about two and a half times its floor-to-ceiling height from the window struggles to show acceptable daylight at the back, and the figure worsens where the window head is low, where the window is narrow, or where there is a deep reveal or a balcony overhead.

That produces three failure patterns:

• Internal bedrooms with no window at all, which fail outright
• Long thin living and dining rooms where the dining end is effectively unlit
• Habitable rooms looking into a narrow lightwell or a back-of-building shaft where the visible sky angle is very small

Single aspect units are the usual compromise, and they come with their own problems around overheating and ventilation as well as light. The techniques for improving daylight to single aspect flats apply directly to a Class MA layout, and some of them cost almost nothing at design stage and are impossible afterwards.

The evidence an authority expects

A prior approval submission on a conversion of any size should contain the following, and most refusals follow from one of them missing.

Add one short note explaining how the layout responds to the building's depth. An authority reading a layout that puts bathrooms, stores and circulation in the deep core, with every habitable room on the perimeter, can see that the problem was addressed by design and not by assertion.

How refusals on light are worded

Refusals of prior approval on this ground are usually short and specific. They identify the units and the rooms that fail, note that the authority is required to refuse where adequate natural light is not provided in all habitable rooms, and leave it there.

Three variations are worth recognising. Some refusals say the submitted information was insufficient to demonstrate adequate natural light, which is a different and more recoverable position than a finding that the light is inadequate. Some identify a small number of units, which means a layout change rather than a redesign. And some refuse on light together with another matter such as noise, in which case fixing the light alone will not get you a grant.

Read the refusal to see which of those you have. A refusal for insufficient information is answered with a calculation and a window schedule, and a resubmission can follow quickly.

Design responses that work

Five moves do most of the work, in rough order of cost.

1. Rearrange the plan. Push non-habitable space into the core and put every habitable room on the perimeter, accepting fewer and larger units.
2. Reduce the unit count. A deep floor that yields eight compliant flats instead of eleven is still a conversion.
3. Make combined kitchen-living rooms shallower and wider rather than long and thin, so the window serves the whole room.
4. Cut a lightwell or courtyard into the plan, which is a building operation needing separate consent and is usually worth it only on larger floorplates.
5. Enlarge window openings or lower cills on the existing elevations, which is operational development outside the Class MA right and needs its own permission.

Points four and five matter procedurally as well as physically. Class MA permits a change of use, not building works, so any new opening, new window, new lightwell or external alteration needs planning permission in its own right, and on a listed building it needs listed building consent. Schemes are regularly granted prior approval and then stall because the enabling works were never applied for.

Local plan amenity policies do not apply to a prior approval decision in the way they apply to a full application, and that distinction is worth understanding, because the way local plan amenity policies use BRE 209 sets a different and often higher bar on the full planning route.

Appealing a refusal on light grounds

Appeals against refusal of prior approval go to the Planning Inspectorate and run on written representations. The deadline is short, so diarise it from the date of the decision.

The appeal case has one job: to show the inspector that each habitable room has adequate natural light, on the evidence. That means the calculation, the window schedule and the context plan, presented room by room with the results in a table. Inspectors deciding these appeals work from the drawings and the numbers, and an appeal that argues about the meaning of adequate without supplying a calculation rarely succeeds.

Two tactical points. Submitting fresh daylight calculations at appeal is possible and is better done at the application stage, because an authority that has refused for insufficient information will often not resist a revised application. And where only part of the scheme fails, a revised application for a reduced unit count is usually faster than an appeal.

Browse the PlanScope report types to see which daylight and amenity reports a conversion needs, or enter your postcode to check the constraints on the building first.

This is general guidance and not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.