Receptor selection for a daylight study in a terraced street

Daylight receptor selection decides the result of a study before any modelling happens, and in a terraced street it is the part most often done badly. The task is to identify every window in a neighbouring property that serves a room with a reasonable expectation of daylight and could be affected by the proposal, then to say for each one which room it serves and on what evidence. Miss a receptor and the council's consultant will find it. Include a bathroom window as a habitable room receptor and you have inflated your own harm figures.

The BRE guidance in Site Layout Planning for Daylight and Sunlight gives the numerical criteria. It does not choose your receptors for you.

Fixing the zone of influence first

Run the screening test before you build a model. From the centre of the lowest window of each neighbouring property facing the site, measure the angle to the horizontal subtended by the proposed development. Where that angle is less than 25 degrees, the BRE guidance treats diffuse daylight as remaining adequate and no further calculation is needed for that window.

In a terraced street this usually resolves quickly. A two storey rear extension affects the immediate neighbours on both sides and, depending on the back-to-back distance, the properties facing across the rear gardens. It rarely affects the house two doors along, because the intervening building blocks the geometry.

Apply the test honestly at the boundaries of the zone. Where a window is marginal, include it and report the result rather than excluding it and inviting an argument. A schedule that contains three windows passing comfortably is stronger evidence than a schedule that quietly omits them.

Record the screening on a plan with the 25 degree lines drawn. That plan is the first figure in the Daylight and Sunlight Assessment and it saves the reviewer an hour.

Deciding which rooms count

The guidance ranks rooms by expectation. Main living rooms have the highest expectation of daylight, bedrooms come next, and kitchens have a lower expectation again. Bathrooms, cloakrooms, WCs, halls, landings, stores, utility rooms and garages are not treated as having a requirement for daylight at all.

Two refinements matter in terraced housing. A kitchen and dining space that is plainly the main living area of the house should be treated as a living room, because that is what it is, and in a great many small terraces the rear kitchen-diner is exactly that. And a room that has been converted in a way you can see from the outside, such as a former garage with a new window, should be treated according to its present use rather than its original label.

Where the use of a room is unknown, adopt the more sensitive assumption and say so. Treating an unidentified ground floor rear room as a living room is defensible. Treating it as a store because that produces a better result is not, and a case officer who visits the street will notice.

Do not forget windows in the flank wall of an outrigger. In a back-addition terrace these serve the rooms most affected by a neighbour's rear extension, and they are the receptors that fail.

Windows serving more than one room

A single window can serve a combined space, most commonly a through-lounge formed by removing the wall between front and rear reception rooms. Treat the combined space as one room, because that is what it now is, and assess the daylight distribution across the whole of it.

The consequence is usually unfavourable to the applicant. A through-lounge is deep, the no sky line test looks at how much of the working plane can see the sky, and a deep room with windows at both ends behaves very differently from two separate rooms each with its own window. Model the actual geometry rather than a nominal room.

Where the space is served by windows in two different elevations and only one elevation faces your site, the room still has to be assessed as a whole for daylight distribution while the vertical sky component is assessed window by window. Mixing those two up is the single most common technical error in this area.

If you cannot establish whether a wall has been removed, say which assumption you have used and run a sensitivity check on the alternative. Two numbers with an explanation beat one number with a footnote.

Rooms with more than one window

Separate the two tests in your head and in the report.

Vertical sky component is a property of a window. Each window gets its own value and its own before and after comparison, so a room with three windows generates three vertical sky component results.

Daylight distribution, the no sky line test, is a property of a room. It is assessed once for the room using all of its windows together, and it is the test that reflects what the occupant actually experiences.

That asymmetry produces results which look contradictory until they are explained. A rear window can lose well over 20 per cent of its vertical sky component while the room retains almost all of its daylit area, because a side window continues to light the space. Explain the combination in the text instead of leaving the reader to reconcile two tables.

Annual probable sunlight hours follows a third rule again: it is assessed for windows within 90 degrees of due south, and only where the room has an expectation of sunlight, which in practice means main living rooms.

Obscured, secondary and non-habitable openings

Obscure glazing does not by itself take a window out of the study, because the window may still serve a habitable room. What matters is the room, not the glass. A bathroom window with obscure glazing is excluded because it is a bathroom.

Conservatories and glazed lean-tos are treated as less sensitive than the main building, and results for them should be reported separately rather than mixed with habitable room results. The same goes for rooflights and dormers in a converted loft, where the geometry is unusual and the criteria for a roof window differ from those for a vertical window.

Secondary windows to a room already well lit from another elevation are worth including and reporting, because their inclusion demonstrates that you assessed the whole property. Exclusions, on the other hand, need a stated reason each. A single line per excluded window is enough.

Recording assumptions where access is refused

Internal access to neighbouring property is normally refused, or simply never granted, and the study has to proceed anyway. The method is to reconstruct the internal layout from the best available evidence and to be explicit about it.

The sources worth working through, in order of reliability: drawings from previous planning applications on the neighbouring property, held on the council's public register. Sale particulars and letting particulars carrying floor plans. External observation of window positions, cills, lintels, flues and soil pipes, which together indicate where kitchens and bathrooms sit. The age and type of the terrace, where a standard plan form is well established. And finally street-level imagery for window arrangements that have since changed.

Then write an assumptions table. One row per property, stating the layout assumed, the evidence relied on, and the effect if the assumption is wrong. Offer to revise the study if the occupier provides access during the consultation period, and say so in the report. Councils respond well to that offer and it costs nothing.

Where a refusal on daylight grounds is already on the table, the assumptions are the first thing the other side will test, which is why our note on preparing a statement of case for a householder appeal puts the evidence trail first.

An illustrative receptor schedule

The following schedule is illustrative only, for a terrace of eight houses numbered 2 to 16 with a proposed two storey rear extension at No 10.

Eight receptors, four exclusions with reasons, and a screening line that explains the rest of the street. That is the level of transparency a reviewer needs.

Where the concern is shadow on gardens rather than light into rooms, the receptor logic changes entirely and an Overshadowing Study with sun-on-ground plots is the right document. And the reasoning behind the layout belongs in the Design and Access Statement, where the design response to neighbour amenity can be explained rather than defended.

PlanScope can draft the assessment narrative and the receptor and assumptions schedules around the modelling output your consultant produces. Councils usually expect a suitably qualified author for daylight work, and professional review is strongly advised. This is general guidance rather than legal advice, so 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.