Which windows and rooms to assess for daylight

Deciding which windows to assess for daylight is the part of the report that gets attacked, and it is settled before any modelling happens. A scope that omits a receptor an objector later identifies is worth less than a scope that includes it and explains why the effect is acceptable. So the scoping section needs to name every property considered, every room assumed, and the reason each one is in or out.

Two principles carry most of the work. Assess rooms that have a reasonable expectation of daylight, and assess them on the basis of what is lawfully there or consented, not on the basis of what is convenient.

Establishing the affected receptors

Start with a plan showing every building with a window facing the development within a radius set by the height of the proposal. The BRE guidance provides a useful screening test: where a line drawn at 25 degrees above the horizontal from the centre of the lowest affected window is not obstructed by the proposal, daylight is unlikely to be materially reduced and detailed assessment is not needed for that window.

Use the screening test to narrow the list, then record the result. A table listing each property, the orientation of its windows towards the site, and whether the screening line is broken is the evidence that the scope was set methodically rather than selectively.

But do not stop at the immediate neighbours. On a taller proposal the affected receptors can sit across a road or beyond an intervening low building, and a scope that covers three adjoining houses when the proposal is six storeys will be challenged at once.

Habitable rooms and which uses are protected

The guidance treats rooms differently according to use. Living rooms, dining rooms and kitchens have the strongest expectation of daylight. Bedrooms are treated as less demanding. Bathrooms, lavatories, hallways, landings, stores, utility rooms and garages are not normally assessed at all.

The difficulty is that you rarely know the internal layout of a neighbour's house. Where the layout is unknown, the defensible approach is to assume the room use from the window position and the building type, state that assumption, and test whether a different assumption would change the conclusion.

Sensitive non-residential uses need including. Schools, nurseries, care homes, sheltered housing and hospital wards have a legitimate daylight expectation. Offices, shops, warehouses and industrial buildings do not normally attract protection under the guidance, though a local policy may treat a specific case differently.

Windows serving two rooms and combined rooms

Open-plan kitchen, dining and living spaces are now the normal arrangement in new flats and in many refurbished houses, and they complicate the scope.

Where one room serves several functions, the more demanding criterion applies to the relevant part of the room. Where a room has two or more windows, all of them are modelled and the room result is derived from the combination rather than from the best window. Where a single window serves two separate rooms through an opening, describe the arrangement and say how it was modelled.

Conservatories and glazed extensions raise a different question. A room lit only through a conservatory is usually treated as receiving daylight through the conservatory glazing, which reduces it, and that condition existed before your scheme. Record it as part of the baseline rather than as an effect of the proposal. Our note on daylight to a north facing habitable room covers the related question of rooms that start from a low baseline.

Consented but unbuilt neighbouring schemes

This is where scopes most often fail. The baseline should be assessed against the existing built situation, and a second scenario should test the position with any consented but unimplemented neighbouring development in place.

Three situations arise and each needs stating:

1. A neighbouring site with a live permission for a taller building, which reduces the daylight your neighbours will actually receive regardless of your scheme.
2. A neighbouring site with a permission for residential conversion, creating future receptors that do not exist yet.
3. An allocated site with no permission, where the scheme is a material consideration but not a baseline.

Report the existing baseline as the primary case and the consented scenario as a sensitivity, with both results in the same table. Presenting only the consented scenario, because it makes the effect look smaller, is the single fastest way to lose credibility with a case officer.

Commercial and institutional neighbours

Offices and retail units are generally outside the guidance, which surprises objectors. Where a commercial neighbour objects, the honest answer is that the guidance does not set a daylight standard for that use, and that the effect is a general amenity consideration rather than a numerical failure.

Institutional uses are different. A nursery playroom, a classroom, a care home lounge and a day room in a hospital all have a daylight expectation, and some have separate standards under building guidance for that building type. Where such a use adjoins the site, assess it and say which criterion you applied.

Buildings with a permission to convert from commercial to residential occupy an awkward middle position. The future occupiers are real receptors and the conversion may never happen. Assess them in the sensitivity scenario and say so.

Access refused and the fallback assumptions

Internal access is often refused, and the assessment still has to be made. The workable method is to measure the facade externally, obtain internal layouts from the council's planning records where any application has been made, and otherwise assume a layout typical of the building type and age.

Then state, for each assumed room: the source of the layout information, the assumed room depth and width, the assumed use, and whether the assumption is cautious or optimistic. An assumption that produces a worse result for your scheme is easy to defend. One that produces a better result needs justifying.

Where the assumption materially affects the conclusion, run the sensitivity. A room assumed to be 4 metres deep that is actually 6 metres deep will perform differently, and showing both removes the argument.

Setting out the scope so it cannot be attacked

Put a receptor schedule at the front of the report, before any results. For each receptor give the address, the elevation, the window reference used in the modelling, the assumed room use, the source of the layout, the screening test result, and whether it was assessed in detail or scoped out with a reason.

Then add three short statements: the date of the survey, the base information used for the surrounding buildings, and the planning history searched for consented schemes with the search date.

That schedule is what a case officer reads first, as our note on what a case officer checks in a daylight report first sets out, and it is what an objector's consultant will test. A Daylight and Sunlight Assessment with a clear scope and some failures is a stronger document than one with a narrow scope and no failures. Amenity areas are scoped separately, and an Overshadowing Study deals with them.

This is general guidance, not legal advice. Daylight assessment is specialist work and councils expect a suitably qualified author, so professional review is strongly advised. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.