Objecting to a planning application for loss of light: daylight, sunlight and the 45 degree rule

How councils assess loss of daylight and sunlight from an extension, what the 45 degree and 25 degree tests mean, and how to write a loss of light objection that gets weighed.

Daylight, sunlight and outlook are three different things

Daylight is the general light a room receives from the sky. Sunlight is direct sun, which matters for rooms and gardens facing within 90 degrees of south. Outlook is the sense of openness from a window or garden, and an overbearing extension can harm it even when light is unaffected. A strong objection separates the three, because officers assess them separately and a local plan amenity policy usually covers all of them.

The 45 degree test

Most councils use a version of the Building Research Establishment guidance, often simplified in a design guide as the 45 degree rule. Take the centre of the nearest habitable room window on the neighbouring house (a kitchen, living room, dining room or bedroom; not a bathroom, hall or garage). Draw a line at 45 degrees from that point, in plan and in elevation. If the proposed extension crosses that line, it is likely to cause a noticeable loss of daylight and the council will look at it closely. Some councils apply the test in plan only, some in both planes, and some use a 25 degree test for windows directly facing the new wall. Your council's householder design guide will say which.

What to put in the letter

• Which room and which window: "the only window serving my kitchen, on the flank elevation facing the site".
• The distance from that window to the proposed wall, taken from the block plan.
• The depth and height of the extension along the shared boundary.
• The orientation: an extension to the south or west of your window takes afternoon and evening sun.
• Whether the room has any other window, because a room lit from two sides is less affected.
• The policy: the local plan's residential amenity or design policy, and in England the national policy on living conditions.
• What you want: refusal, or a reduced depth, a set-in from the boundary, or a lower eaves height as a condition.

What not to do

Do not claim the extension will make the room dark unless the geometry supports it; officers test the claim against the drawings. Do not cite a rights to light case, which is a private legal matter with no role in the planning decision. Do not rely on a percentage figure you have not measured. Where the case is finely balanced, ask the council to require a daylight and sunlight assessment before deciding: that is a reasonable request and it puts the burden on the applicant.

How Curtilage helps

Curtilage asks you for the window, the distance and the orientation, writes the ground in those terms, cites your council's actual amenity policy, and lists the facts that would make the case stronger so you can add them before you submit.

Updated 2026-09-14. Curtilage is not legal advice.