What to submit with a daylight and sunlight assessment

A daylight and sunlight assessment is refused validation or sent back for clarification more often because of what is missing from the submission than because of what the numbers say. The deliverables are not complicated: a window and room numbering plan tied to the drawings, results tables showing existing and proposed values with the ratio, the extent of the context model, and a plain statement of every assumption that could not be measured. Get those four right and the reviewer can check your work. Leave one out and they cannot.

The target figures themselves come from the BRE guidance on site layout planning for daylight and sunlight, third edition 2022, and from BS EN 17037 with its UK national annex for internal daylight provision. What follows is about the submission rather than the method.

The window and room numbering plan

Every number in a results table has to be traceable to a window on a plan, and the plan has to be readable at the size the council will print it.

Number windows by property, then by floor, then in a consistent direction. Show the room each window serves and the room use assumed, because the test applied depends on it. A kitchen, a living room and a bedroom are treated differently, and an assessor who labels every room as a living room is making a judgement that needs stating.

Where a neighbouring property's internal layout is not known, say so and say what you assumed it from. External observation, historic planning drawings held on the authority's public register, estate agent floor plans and energy performance certificate plans are all legitimate sources, and all of them are weaker than a measured survey. The one thing you cannot do is present an assumed layout as a surveyed one.

Rooms excluded from the assessment need to be on the plan too, marked as excluded with the reason. Bathrooms, circulation space, storage and non-habitable rooms are the usual exclusions. An objector reviewing the report will look for a habitable room that quietly left the schedule.

Results tables and their conventions

A reviewer wants to read a row and reach a conclusion without arithmetic.

For each window, show the existing value, the proposed value and the proportional retained value. For daylight distribution, show the existing and proposed no sky line areas and the proportion retained. For sunlight, show annual probable sunlight hours and the winter component separately, because a window can pass on the annual figure and fail on the winter one.

Three conventions make the tables usable.

State the test threshold in the table header rather than in a paragraph three pages earlier. Flag every result that falls below the guidance target, rather than only summarising how many did. And keep the same row order as the numbering plan so the two documents read in parallel.

Where results are reported for a property as a whole, give the window-level data as well, in an appendix if necessary. A summary that says most windows comply is not something a case officer can rely on in a committee report.

Model extents and the surrounding context

The context model decides a surprising proportion of the results, and it is the input most often challenged. Include every building that could meaningfully obstruct light to the assessed windows, which in a dense urban setting means more than the immediate neighbours.

State the extent you modelled and why. A plan showing the modelled envelope, with a boundary marking where the model stops, lets a reviewer judge whether anything influential was left out. Where a neighbouring site has an unimplemented planning permission or an allocation, say whether you modelled the existing situation, the consented situation or both, since that choice can change the answer completely.

Trees are a recurring argument. The BRE guidance treats deciduous trees as having limited effect for daylight purposes, so most assessments exclude them, and that exclusion should be stated rather than silent. Evergreen screening close to a window is different.

Boundary treatment, existing walls, projecting bays and rooflights all belong in the model if they obstruct or admit light. A model built from a planning drawing alone usually misses at least one of them.

Assumptions and limitations stated at the front

Put the assumptions near the beginning, not in an appendix. A short section listing them makes the document reviewable and protects the author.

The list should cover the drawing revisions the model was built from, the surface reflectances and glazing transmittance used, any maintenance factor applied, the assumed room uses, the source of each neighbouring layout, the treatment of trees and boundary features, and anything that could not be surveyed because access was refused. Where access was refused, record when it was requested and by what means, because that question comes up at appeal.

Say what the assessment does not cover. Most do not assess rights of light, which is a civil matter between landowners and uses a different test from the planning assessment. Confusing the two in a planning submission invites an objection that the author has misunderstood the exercise, and the distinction is worth a sentence. The same care is needed when answering a neighbour's daylight objection, where the objector has often read a rights of light article rather than planning guidance.

Drawings the model was built from

Record the drawing numbers, revisions and dates of every drawing used, and keep them consistent with the drawings submitted for determination. This sounds like housekeeping. It is the single most common reason an assessment is queried.

When the scheme changes during determination, the assessment has to be revised or formally confirmed as unaffected. A letter from the assessor saying the amendment does not alter the modelled envelope, with the superseded and new drawing numbers listed, is usually accepted. An assessment that silently refers to a superseded revision is not.

Where the proposal is small, the same rule applies in miniature. Even for daylight evidence on a rear dormer in a terrace, the officer needs to know which section drawing the obstruction angle was taken from.

Whether to supply the model file

Most authorities do not require the model file for validation, and most do not have the software to open it. Some, particularly those with in-house assessment capability or a retained consultant, will ask.

Offering it is usually the right call. A line in the report stating that the model is available on request, with the software and version named, removes an argument about transparency at no cost. Where the model contains third party survey data with licensing restrictions, say that instead of staying silent.

What you should always supply, model file or not, is enough geometric information for the results to be reproduced: floor levels, window head and cill heights, room depths and the position of obstructions relative to the assessed facades. A reviewer with that information can spot check a vertical sky component by hand, which is often all they want to do.

Keeping the submission consistent with the rest of the application

A daylight and sunlight assessment does not sit alone. The Daylight and Sunlight Assessment has to agree with the design and access statement on room uses, with the accommodation schedule on unit mix and layout, and with any Overshadowing Study on the modelled envelope and the dates assessed.

Where internal daylight provision is assessed under BS EN 17037, state the target illuminance for each room type from the UK national annex, the proportion of the reference plane assessed and the proportion of daylight hours, and keep the room areas identical to those in the accommodation schedule. Mismatched areas between the two documents are an easy objection.

One last point on tone. Assessments that present every shortfall as acceptable before the officer has formed a view read as advocacy rather than analysis. Report the results, identify the windows that fall below the targets, and then make the planning case for why the impact is acceptable in a separate section that is clearly labelled as judgement rather than measurement. Officers trust the numbers more when the author has not already decided what they mean.

This is general guidance, not legal advice. Daylight and sunlight assessment is a technical discipline and councils usually expect a suitably qualified author, so professional review is strongly advised before submission.

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