Daylight to a north facing habitable room

North facing room daylight is assessed differently from daylight to any other elevation, and the difference works in your favour more often than people expect. The sunlight tests in the standard guidance simply fall away for a window facing more than 90 degrees from due south, because such a window receives very little direct sun in any case. The daylight tests stay, in full.

So if a neighbour objects that your extension will take the sun from their north facing kitchen, the technical answer is that there was no sun to take. Their daylight argument may still be a good one.

Why orientation changes which tests apply

Daylight and sunlight are two different things and are measured separately.

Daylight is diffuse light from the whole sky dome. It arrives from every direction, all day, in all weather, and a north facing window receives it much like any other window of the same size with the same obstruction in front of it.

Sunlight is the direct beam. In the northern hemisphere it comes from the southern half of the sky, so a window facing north never receives it except for a short period around midsummer very early and very late in the day, when the sun swings round behind the building.

The guidance reflects that physics. Assessment of sunlight to existing windows is carried out only where the window is within 90 degrees of due south. Everything else is assessed for daylight alone.

The sunlight test and the 90 degree rule

Where the test does apply, it measures annual probable sunlight hours at the window: the proportion of the sunlight available across the year that reaches it, with a separate check on the winter months from late September to late March.

The usual criteria are a retained 25 per cent of annual probable sunlight hours with at least 5 per cent in winter, or, if those are not met, a retained value of no less than 0.8 times the former figure with the loss amounting to more than 4 per cent of annual hours before it counts as material.

The 90 degree rule removes that whole exercise for a north facing window. It is a simple orientation check made from the plan, and it is not a matter of judgement.

Two qualifications. The rule applies to the window being assessed, so an extension can affect a south facing window on one elevation and a north facing one on another, and only the first gets a sunlight assessment. And gardens and amenity areas are assessed separately for sunlight regardless of which window looks onto them, using the area receiving at least two hours of sun on 21 March.

The daylight tests that still apply

None of the daylight tests care about orientation.

Both are proportional as well as absolute, which is what makes them bite on tight urban sites. A north facing kitchen window that currently achieves a vertical sky component in the low twenties can be taken below the 0.8 ratio by a modest extension, and the fact that the room never had sunlight is not an answer.

Daylight distribution is the test that usually decides a householder dispute, because it reflects what people actually notice: the back of the room going dark. It needs the internal layout of the affected room, and where that is unavailable there are recognised ways of proceeding, though they should be stated openly.

Room use matters here too, since a room counted as a kitchen is treated differently from one counted as a utility, which is the subject of our note on room use assumptions and how they change results.

Designing a north facing room that works

North light has real virtues. It is even, it does not produce glare across a screen or a worktop, it does not fade finishes, and it brings almost no solar gain, which means the room does not overheat in July. Artists' studios face north for a reason.

The design problem is quantity, not quality. Practical responses, roughly in order of effectiveness:

1. Increase the head height of the window rather than its width. Daylight entering high reaches further into the room than the same area of glazing set low.
2. Keep the room shallow. Depth is the enemy of a north facing room more than glazing area is.
3. Use pale finishes on the wall opposite the window and on the ceiling, because internal reflectance carries the light to the back of the space.
4. Avoid deep reveals and heavy frames, which cut the visible sky.
5. Set any canopy, overhang or balcony above the window as high and as shallow as the design allows.

A rear extension with a north facing garden is the common case. Here the fix is usually overhead rather than vertical, which brings us to the next section.

Rooflights and borrowed light

A rooflight sees the whole sky dome rather than the slice a vertical window sees, so it delivers considerably more daylight per square metre than a north facing window in the same room. On a single storey extension it is the most effective move available.

Three practical points. Flat rooflights in a flat roof outperform pitched lanterns of the same plan area, although the lantern often looks better from the garden. Deep upstands around the opening cut the angle of sky the room can see, so keep the build up shallow. And a rooflight over the deepest part of the plan is worth more than one over the part of the room already next to the doors.

Borrowed light, meaning light reaching a room through internal glazing or a wide opening into an adjacent space, is useful and limited. It improves how a space feels. It does not turn an internal room into a habitable one, and a council will not count a room with no external window as a bedroom.

Glazed links, where the new roof is broken by a band of glazing against the original rear wall, are the usual way of keeping light to a retained room behind an extension.

What councils accept in dense streets

The published criteria were written with suburban conditions in mind, and the guidance itself accepts that different targets may be appropriate in dense urban areas where existing daylight is already well below the numerical values.

That does not mean the tests are ignored. It means an assessment can propose an alternative target, provided it explains the local context, applies it consistently, and shows what the existing condition is. Some London boroughs publish their own expectations on this, so check the local plan and any design guidance before assuming.

For a householder scheme the practical position is simpler. Officers tend to look at daylight distribution and at the 45 degree and 25 degree rules of thumb in the council's own design guide, rather than commissioning a full technical assessment. Where the neighbour relationship is difficult, a proper assessment is still worth having, because it moves the argument onto measurable ground.

Overshadowing that comes and goes across the day is assessed differently again, as our note on transient overshadowing explains.

Evidence to submit

For most householder applications the following is enough, and it is more than most applications carry.

Existing and proposed plans and elevations. A section through the affected boundary showing the 45 degree line from the centre of the neighbour's nearest habitable room window in both plan and elevation. A roof plan showing rooflight positions. And, where the case is contested, a Daylight and Sunlight Assessment covering vertical sky component and daylight distribution for the affected windows, with the orientation of each window stated so the reader can see which tests apply.

Put the reasoning in the Design and Access Statement rather than leaving the drawings to speak. A paragraph explaining that the affected window faces north, that the sunlight test therefore does not apply, and that the daylight results are within the criteria, saves the case officer the work of reaching the same conclusion.

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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.