ADaylight & sunlight screening for UK planning
The BRE 209 screening battery — VSC, daylight factor, no-sky line, sunlight hours, garden amenity, overshadowing — computed on your real building geometry, and cross-checked against Radiance with the error bounds published.
Plus Part B, live against Radiance and IfcOpenShell: annual sDA/ASE matches Radiance two-phase exactly on the reference case; mesh and IFC per-point VSC agree to ≤ 0.27 pp on a real building; the reflected-light term is characterised and defaulted off.
BThe test battery
BRE 209 splits the work into daylight (sky) tests and sunlight (sun) tests. So do we — each verb below is one API call on your geometry, most of them fast enough to run on every massing option.
| Test | Family | What it answers | BRE 209 | Status |
|---|---|---|---|---|
| vsc / vsc-geom | Daylight | Vertical sky component at a neighbour's window — analytic walls or full 3D mesh | §2.2 | Live |
| daylight-factor / df-avg | Daylight | Room daylight factor — sky component and the Lynes average-DF method | §2.1 | Live |
| df-grid | Daylight | Per-point DF across the working plane — mean, median, % above target, heatmap data | §2.1.12 | Live |
| nsl | Daylight | No-sky-line contour — which part of a room sees any sky at all | App C | Live |
| apsh | Sunlight | Annual & winter probable sunlight hours at a window — plus the §3.2 before/after verdict on whether a development costs a neighbour noticeable sunlight | §3.2 | Live |
| sun-amenity | Sunlight | The 2-hour / 50%-of-area garden test on 21 March | §3.3 | Live |
| overshadow | Sunlight | Transient shadow plots at chosen hours and dates | §3.3.17 | Live |
| annual | Daylight | Annual sDA / ASE on a grid with EPW weather and four sky models | — | Live |
| glare-verdict / ocular-hazard | Sunlight | DGP glare class (EN 17037) and SGHAT specular-reflection ocular safety | — | Live |
| mesh-import | Geometry | OBJ / glTF / IFC upload — store-nothing: analysed in memory, deleted after the reply | — | Live |
Every verb above is live and cross-checked against Radiance and published references — see Sheet 02 §D.
CWorked example
Real output from the validated engine on this geometry. The same before/after pair drives the §3.2 sunlight verdict at the window — annual and winter APSH, and whether the neighbour loses noticeable sunlight. Change the extension depth and re-run in seconds — that's the point: screen every option before the consultant's assessment, not after refusal.
DWho this is for
A full daylight & sunlight assessment costs £800–2,500 and lands after design freeze. Failing it means redesign at ten times that. This API exists so the first time your scheme meets the BRE numbers isn't the last week before submission.
Architects & designers — test every massing option against the neighbours' windows while it's still cheap to change. Planning consultants — pre-screen applications and objections with defensible numbers. Developers — feasibility on a site in an afternoon, not a fortnight.
This is a screening tool, not a certified daylight & sunlight assessment. Planning authorities and courts expect assessments from a qualified consultant taking professional responsibility. What we provide: the same physics, validated in the open, at design speed — so the certified assessment holds no surprises. Our methodology, references and error bounds are public on Sheet 02.
EAccess
| Route | What you get |
|---|---|
| API | Every verb over HTTPS — JSON in, JSON out. IFC / glTF / OBJ upload, store-nothing. Grids sized for heatmaps. See the API sheet. |
| Screening report Coming | The full battery on your site, as a document: per-window VSC, DF grids, sunlight hours, amenity, methodology appendix with citations. |
We onboard practices and consultancies one to one: an evaluation key, and your first study run with you on your own geometry. Tell us the practice, the kind of schemes you screen, and the geometry format you work in — IFC, glTF or OBJ — and we'll set you up. hello@kairoico.com