Daylight and sunlight for schools and healthcare buildings

Daylight in schools planning cases is assessed on two separate questions, and mixing them up is the fastest route to a consultation response you did not expect. The first is whether the proposed building gives its own occupants enough daylight. The second is whether it takes daylight away from a neighbouring school, clinic or ward. Residential schemes usually only face the second question. Sensitive non-domestic uses face both, with different standards behind each.

The internal question is not really a planning matter at all in most authorities, until a policy or a design code makes it one.

Why non-residential rooms are assessed differently

The BRE guide on site layout planning for daylight and sunlight, now in its 2022 edition, sets the neighbour tests most English authorities apply: vertical sky component, no-sky line, and annual probable sunlight hours. Those numerical guidelines were derived with dwellings in mind and the guide says so.

For non-domestic buildings the guide takes a different position. It identifies uses where occupants have a reasonable expectation of daylight, schools and hospitals among them, and says the same tests can be applied where that expectation exists. It also says the guidelines should be applied flexibly, with the character of the area and the nature of the room taken into account.

That flexibility cuts both ways. An objector can argue that a classroom deserves protection equivalent to a living room. An applicant can argue that a store, a corridor or an examination room with controlled lighting does not. Both arguments are available on the same page of the same guide, and the officer has to pick.

Which spaces are treated as sensitive

Work through the room schedule before the assessment is scoped. The distinction that matters is whether daylight forms part of the intended function of the space.

Getting this schedule agreed with the case officer before modelling starts saves a round of consultation. Where the neighbouring building is a school, the school itself will often be a consultee in practice through the local authority's education team, and a room schedule they recognise is easier to accept.

Standards applied to teaching and clinical spaces

For the internal performance of the new building, BS EN 17037 is the reference. It expresses daylight provision as target illuminance achieved over a proportion of the reference plane for a proportion of daylight hours, and it also covers sunlight exposure, view out and protection from glare. Its UK National Annex sets lower illuminance targets for dwellings, so for a school or clinic the standard's own levels apply.

Alongside that sits sector guidance. Schools procured through central programmes are designed to the Department for Education output specification, which has historically been expressed through a daylight factor target for teaching spaces, and healthcare projects work to the relevant CIBSE lighting guidance for hospitals and health care buildings. Cite whichever the client is actually contracted to, and say which edition.

A practical warning. Daylight factor and the EN 17037 illuminance method give different answers on the same room, particularly where the room is deep or the glazing is high in the wall. Present one method as the primary assessment and note the other, instead of switching between them to find the flattering result. Officers and their consultants notice.

Glare and its treatment alongside daylight

Glare is the reason teachers close blinds and then switch on the lights, which wastes the daylight the design was assessed on. Any assessment of a teaching or clinical space that reports illuminance without reporting glare control is incomplete.

Three things carry weight at planning stage because they are visible externally and cannot be added later without a further application:

• External shading depth and position, including brise soleil and reveal depth
• The height of the window head, which drives depth of daylight penetration
• Orientation of the principal glazed elevation

Internal blinds are a mitigation the council cannot see or secure, so they are worth mentioning and not worth relying on. Where a design leans on solar control glass, state the light transmittance, because a low transmittance coating chosen for overheating can pull the daylight result below target.

Assessing effects on a neighbouring school or clinic

Where your development sits next to an existing sensitive building, run the same neighbour tests you would for housing, applied to the rooms identified as sensitive.

1. Establish the existing situation with a measured survey or accurate drawings of the neighbouring facade, including window head heights and any existing obstruction.
2. Model vertical sky component at each relevant window, before and after.
3. Where the internal layout is known, run the no-sky line test for daylight distribution across the working plane.
4. Apply the annual probable sunlight hours test to windows facing within 90 degrees of due south, where sunlight matters to the room.
5. Test external amenity areas, including playgrounds and therapy gardens, against the two-hour sunlight criterion on 21 March.
6. Report absolute retained values, not just percentage reductions.

Point six decides more cases than any other. A classroom window that keeps a vertical sky component of 24 per cent after the development has good daylight, whatever the percentage change says. A window falling from 12 to 8 per cent is a real loss even though the arithmetic looks similar. The methodology behind these tests is set out further in our note on daylight distribution and the no-sky line, and the playground question follows the same approach as the two-hour test on 21 March.

Internal layouts of a neighbouring school are often unavailable. Where that happens, state the assumption you have made about room depth and use, and test the sensitivity of the result to it.

Evidence expected with an application

A Daylight and Sunlight Assessment for a scheme of this kind should contain the modelled context extent and its source, the room schedule with sensitivity classified, the results tables with absolute and relative values, and a clear statement of which guidance edition was used. Where playgrounds or courtyards are affected, an Overshadowing Study presenting shadow plots at the equinox and both solstices makes the effect legible to members who will not read a results table.

Include the transient effect during construction if the programme is long. A three-year build next to a primary school is a material consideration in its own right.

Conditions that follow

Expect conditions fixing the external shading as drawn, the glazing specification including light transmittance, and sometimes a requirement to submit a post-completion daylight verification for the new teaching spaces. That last one is rare and worth resisting where the modelling was done properly, because measured verification depends on sky conditions on the day.

Where the scheme includes a replacement school building on the same site as the one it replaces, the sequencing condition matters more than the daylight one: a phasing plan showing that no teaching space is left below target while the old building is still in use.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. Councils usually expect daylight modelling of this kind from a suitably qualified author, and professional review is strongly advised.

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