What daylight modelling outputs to submit

A daylight and sunlight submission is judged on whether an officer can check it, and most cannot be checked. The outputs a council needs are a consistent window numbering system tied to annotated elevations, result tables for every assessed window and room in both the existing and proposed conditions, plans and sections showing the model extent, a stated set of assumptions for reflectance, transmittance and room depths, and an offer to release the model. Submit those and the consultation runs smoothly. Submit a summary with a conclusion and an appendix of unlabelled numbers and you will get a request for further information, three weeks in.

The assessment methodology is a separate matter. This is about the deliverables.

What an officer needs to check a result

The council's reviewer, whether an in-house urban designer or an external consultant, is trying to answer three questions. Which windows and rooms were assessed, and were any omitted. What were the results before and after. And are the assumptions reasonable.

Everything in the report should serve one of those three. A page of methodology quoting BRE 209 at length serves none of them, and a reviewer who cannot find the numbers assumes the numbers are unfavourable.

Structure the document so the reader moves from a plan showing the assessed properties, to a table per property, to the per-window results, with nothing to hunt for.

Window numbering and its consistency

This is the single most common failure. Adopt one numbering convention, apply it everywhere, and annotate it on photographs of each affected elevation.

A convention that works: property reference by address or plot, then floor level, then window number running left to right as viewed from outside, then room reference. So 12 Mill Road, first floor, W3, bedroom R2. The same string appears on the elevation, in the table, in the model and in the text.

Where a window serves two rooms, or a room has two windows, say which in the table rather than leaving the reviewer to work it out from a plan. Where you have renumbered between the pre-application submission and the application, provide a concordance table. Officers who checked the earlier version will notice.

Result tables by room and by property

Report the existing value, the proposed value and the ratio for each test you have used, with the criterion alongside it so nothing has to be looked up. For neighbouring amenity that normally means vertical sky component, daylight distribution against the no-sky line, and annual probable sunlight hours split into the total and the winter component.

Sort the tables so the most affected windows appear first within each property, rather than in numerical order. An officer writing a report wants to see the worst case immediately, and hiding it in the middle of a 200 row appendix reads as evasion when it is found.

Where a result does not meet the benchmark, give the value, the margin and one sentence of context in the same row or directly beneath it. Our note on the 0.8 rule for retained daylight and how it works explains the ratio the tables turn on, and daylight to a north-facing habitable room covers the cases where the numerical criterion needs qualifying.

Plans, sections and the model extent

Include a plan showing the site, every property assessed, and every building included in the model, with a clear line around the model extent. State how the surrounding context was captured: measured survey, aerial photogrammetry, published mapping with heights, or a combination, and give the date.

Two sections through the most sensitive relationships do more work than any amount of text. Draw them at a stated scale through the affected windows, showing the existing obstruction, the proposed obstruction and the angle to the sky.

Where a consented but unbuilt scheme sits adjacent, model it as a separate scenario and say so. Reviewers ask about consented context on almost every urban site, and pre-empting the question saves a round of correspondence.

Reflectance, transmittance and room assumptions

List every assumption in one table with its source. Visible transmittance of the glazing, frame factor, maintenance factor, internal surface reflectances, external surface reflectance for obstructions, and ground reflectance.

Then deal with what you could not see. Internal layouts of neighbouring properties are usually unknown, so state the assumed room depth, the assumed use and how they were derived, whether from planning records, from estate agents' floor plans, from an external survey of window positions, or from a standard assumption. Show the assumed layouts on a plan.

Where access was requested and refused, record the request and the date. That single line protects the assessment from an objection that the assumed layout was convenient.

Kitchens, bathrooms, circulation and stores are treated differently from living rooms and bedrooms, so the room use column does real work. Do not classify a room as non-habitable without saying why.

Sunlight outputs and amenity space

Sunlight to windows and sunlight to ground are reported differently, and both get lost in submissions that concentrate on daylight. For windows, give annual probable sunlight hours with the winter figure alongside the annual one, since a window can hold its annual total while losing almost all of its winter sun. For gardens, courtyards and communal amenity space, give the percentage of the area receiving two hours of sunlight on 21 March in the existing and proposed conditions, with the analysis grid spacing stated.

Present the sun-on-ground work as plots rather than as a single number. A plan shaded to show where the two hour criterion is met, existing beside proposed, is understood immediately by a committee member who will never read a table.

Releasing the model for third party review

Offer the model. Say in the report that it can be provided to the authority or its reviewing consultant on request, name the software and version, and give a contact route through the applicant's agent.

Councils increasingly appoint an independent reviewer on larger schemes, and their first request is the model file. Volunteering it shortens that exchange and changes the tone of the consultation. Where commercial sensitivity is raised, the usual answer is a model containing only geometry.

Appendices that avoid a further information request

The pack that tends to clear validation and consultation without follow-up questions:

1. Drawing register listing every drawing and revision the assessment relied on.
2. Annotated elevation photographs of each affected property with window numbering.
3. Full result tables for all tests, existing and proposed.
4. Sun-on-ground plots for gardens and amenity space, with the analysis grid stated, as covered in the Overshadowing Study guidance.
5. Assumptions schedule with sources.
6. Plan of model extent and context data sources.
7. Correspondence log for access requests to neighbouring properties.

Where the scheme also needs internal daylight results for the new units, keep them in a separate section with their own criteria, because the standards differ from the neighbour tests, as daylight inside new flats compared with neighbours sets out. Mixing the two in one table is the fastest way to confuse a committee.

Draft the supporting document structure for your Daylight and Sunlight Assessment on PlanScope, then have the modelling and the result tables prepared by a qualified consultant before submission.

For specialist technical reports, qualified professional input may be required. This is general guidance, 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.