The BRE Daylight and Sunlight Guidelines Explained

Most UK planning authorities judge daylight and sunlight using the Building Research Establishment guide Site layout planning for daylight and sunlight: a guide to good practice, known as BR 209. The current third edition was published in 2022. This page explains the main tests in plain English.

Is the BRE guide mandatory?

No. BR 209 is advisory, and the guide itself says its numerical values should be applied flexibly. Councils use it as the recognised benchmark, so a report showing how a proposal performs against it is often requested with a planning application. Falling short of a guideline is not an automatic refusal; the results are weighed against the site's context, such as a dense urban setting.

The 45-degree approach for extensions

For extensions close to a neighbour's window, a quick check draws lines at 45° on both the plan and the elevation from the centre of the nearest affected window. If the extension crosses both lines, it may cause a noticeable loss of skylight and a more detailed assessment is usually needed. Many councils also use their own version of the 45-degree rule. Read more in the 45-degree rule: the most misunderstood rule in planning.

The 25-degree test

For a new building facing existing windows, a line is drawn at 25° to the horizontal from the centre of the lowest affected window. If the new building rises above that line, further daylight and sunlight tests are needed.

Vertical Sky Component (VSC)

VSC measures how much sky is visible from the centre of a window. A window is unlikely to be noticeably affected if its VSC stays at 27% or more, or is not reduced below 0.8 times its former value (a loss of no more than 20%).

No Sky Line (daylight distribution)

The No Sky Line marks the point in a room beyond which the sky cannot be seen at working-plane height. If the area of the room that can see the sky is reduced to less than 0.8 times its former value, the change is likely to be noticeable.

Annual Probable Sunlight Hours (APSH)

APSH applies to main living-room windows facing within 90° of due south. A window may be adversely affected if it receives less than 25% of annual probable sunlight hours, or less than 5% between 21 September and 21 March, and less than 0.8 times its former sunlight, and the reduction over the year is greater than 4% of annual probable sunlight hours.

Gardens and open spaces

For sunlight to gardens and amenity areas to be adequate, at least half of the area should receive at least two hours of sunlight on 21 March. If a proposal leaves less than half the area meeting this and reduces it to less than 0.8 times its former value, the loss is likely to be noticeable.

Daylight inside new homes: BS EN 17037

The 2022 edition of BR 209 adopts BS EN 17037 for daylight in new buildings, replacing the older Average Daylight Factor method. The UK National Annex sets target illuminances of 100 lux for bedrooms, 150 lux for living rooms and 200 lux for kitchens, to be achieved across at least half of the room for at least half of the daylight hours. For sunlight, at least one habitable room, preferably the main living room, should receive at least 1.5 hours of sunlight on 21 March.

Class MA prior approval

Commercial-to-residential conversions under Class MA must show that every habitable room receives adequate natural light. An internal daylight assessment against BS EN 17037 is the usual way to evidence this.

Need an assessment?

We prepare BRE-compliant neighbour impact and internal daylight reports for planning applications across the UK. See our sample reports, read the FAQs, or get an instant fixed-fee price.

The BRE guide itself is published by BRE and can be purchased from them.