Sunlight to a north facing window: what to expect
A north facing window is not assessed for sunlight under BRE guidance at all. The test that does apply measures skylight, and it is the one a neighbour objection should cite.
If your kitchen window faces north, the planning system will not assess it for sunlight. BRE guidance on site layout planning for daylight and sunlight applies its sunlight test only to windows that face within 90 degrees of due south, on the straightforward basis that a north facing window receives almost no direct sun whatever the neighbour builds. Objecting to an extension because it will block the sun from a north facing room therefore lands on an assessment that was never going to be made.
That is not the end of the argument. It moves it. What a north facing window does receive is diffuse skylight from the whole sky dome, and that is measured, tested and frequently decisive. Make the objection about daylight and it has somewhere to go.
The two tests, and which window each applies to
Sunlight is assessed as annual probable sunlight hours, a figure for how many hours of direct sun a window receives across the year at that orientation and latitude, with a separate figure for the winter months between 21 September and 21 March. BRE guidance treats a window as adequately sunlit where it receives at least a quarter of annual probable sunlight hours including at least 5 per cent in winter. A loss becomes noticeable where the retained value falls below those figures, drops below 0.8 times its former value, and the annual reduction exceeds 4 per cent.
Daylight is assessed first at the window, using the vertical sky component. That measures how much of the sky is visible from the centre of the window as a percentage of an unobstructed vertical surface, with 27 per cent as the benchmark for a well lit window and a reduction to less than 0.8 times the former value as the point where the change is noticeable. A second test looks inside the room, checking how much of the working plane can still see the sky.
Orientation decides which applies. South, south east and south west facing windows get both. East and west facing windows get both, since they sit within the 90 degree arc. North, north east and north west facing windows get the daylight tests only.
Why the arc is drawn where it is
The sun in England never rises far north of due east in midsummer and never reaches due north at all. A window facing 20 degrees east of north sees the sun for a short period on summer mornings at a very low altitude, when it is usually blocked by whatever is already there. Testing it produces a number that changes with obstruction but says nothing useful about how the room feels.
BRE guidance is explicit that the numerical targets are advisory and should be applied with regard to context, particularly in dense urban areas where the figures were never intended to set an absolute floor. Councils generally adopt them through a design guide, which is where the local variations live, and some authorities set alternative targets in dense urban areas to reflect what is achievable. The point to take from that flexibility is that a small shortfall on one test rarely decides an application on its own.
Making a daylight objection that works
If an extension next door will darken a north facing room, the useful evidence is a vertical sky component calculation, before and after. That requires a model of the existing situation and the proposal, which in turn needs measurements.
What helps a case:
- The window serves a habitable room. Kitchens count in most authorities' guidance, bathrooms, halls and utility rooms generally do not.
- The room has no other window. A single aspect room loses more, proportionately, than a room lit from two sides.
- The existing vertical sky component is already modest, so the proportional loss is larger.
- The proposal projects well beyond the boundary line of the existing rear wall, which is what drives the obstruction angle.
What weakens it: a room with a large patio door on another elevation, an objection based on garden sunlight when the garden retains sun for most of the day, and an assertion of loss with no measurement behind it.
Where the neighbour will not allow access to measure the room, there are accepted ways of working from external dimensions and standard assumptions, and the approach to modelling a neighbouring room without access is worth understanding before paying for a survey nobody can complete.
Gardens and amenity space are tested differently
Sunlight to open space has its own test, and it does not depend on window orientation. BRE guidance asks that at least half of an amenity area should receive at least two hours of sunlight on 21 March. Where the proposal reduces the sunlit area to less than half, and to less than 0.8 times its former value, the loss is treated as noticeable.
That is the test to run where the complaint is about the garden rather than the room, and it is often the stronger case for a north facing property, because the garden of a house with north facing rear windows is a south facing garden belonging to somebody else. The same method covers sunlight to amenity space in a courtyard or a shared garden, and an overshadowing study sets it out with shadow plots at the standard dates.
Getting the assessment done, and when it is worth it
On a two storey rear extension between terraced houses, a full daylight and sunlight assessment costs more than the argument is usually worth, and most authorities decide these on the 45 degree rule and a site visit. The assessment earns its cost when the proposal is larger, when the relationship is unusual, or when the application is heading for appeal and the officer report has already accepted the loss.
Commission it early enough to change the design. A report produced after the drawings are fixed can only describe the harm. A study run during design can move a rear wall 600 millimetres, drop a roof pitch, or angle a flank, and recover most of the loss for very little money.
An illustrative situation
Illustrative example. A terraced house with a single north facing kitchen window at the rear. The neighbour proposes a three metre deep single storey rear extension with a flat roof at 3 metres. The sunlight test does not apply to that window. The vertical sky component falls from a figure typical of an unobstructed terrace rear to roughly three quarters of its former value, which crosses the 0.8 trigger and supports an objection on daylight. The garden retains sun through the afternoon, so the amenity test does not assist. Figures are illustrative and a measured study governs.
Before you write to the council, check which way the window actually faces with a compass rather than from memory. It decides which half of the guidance you are arguing about.
Check your address on PlanScope to see which supporting documents an application at your property is likely to need.
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.
Frequently asked questions
Is sunlight to a north facing window protected in planning?
Not through the sunlight test. BRE guidance applies its annual probable sunlight hours assessment only to windows facing within 90 degrees of due south, because windows outside that arc receive little or no direct sun regardless of what is built nearby. Daylight, which is diffuse skylight rather than direct sun, is assessed for every orientation.
What is the vertical sky component?
A measure of how much of the sky dome is visible from the centre of a window, expressed as a percentage of unobstructed horizontal sky. BRE guidance uses 27 per cent as the point above which a window is well lit, and treats a reduction to less than 0.8 times the former value as the point at which a loss becomes noticeable to occupants.
Does the council have to follow BRE guidance?
No. It is guidance, not policy, and its own text says the numerical targets should be applied flexibly according to context. Councils use it because it gives a consistent method, and many adopt it through a design supplementary planning document. An inspector will expect a reasoned departure rather than an assertion that the figures do not matter.
What about the 45 degree rule my council mentions?
That is a local rule of thumb, not a BRE test. A line is drawn at 45 degrees in plan, and often in section, from the midpoint of the neighbour's nearest habitable room window. Where the proposed extension crosses it, the authority looks harder at the impact. Its value is speed rather than accuracy, and a proper assessment can displace it.
Is this the same as rights of light?
No. Rights of light is a private law matter, usually acquired by twenty years of uninterrupted enjoyment and enforced through the civil courts, with its own measure of adequate light. Planning assessment is a public law judgement about amenity. A scheme can be acceptable in planning terms and still face a rights of light claim.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.