Sunlight to a north facing garden
A garden on the north side of a house sits in its own shadow, so the absolute sun on ground test is often failed before anything is built. The case then turns on how much of the remaining sunlit area a proposal removes.
North facing garden sunlight planning objections turn on one published test: whether at least half of the garden still receives two hours or more of sunlight on 21 March. If your neighbour's garden already falls short of that before anything is built, the test shifts to whether the proposal reduces the sunlit area to less than 0.8 times what it was. That second limb is the one that decides most north facing cases, because a garden on the north side of a house is already shaded by the house for much of the day.
Which means the argument is rarely about whether the garden is sunny. It is about how much of the little sun it gets you are taking away.
How garden sunlight is assessed
The relevant published guidance is the BRE document on site layout planning for daylight and sunlight, which sets out a sun on ground method for gardens and amenity areas. A plan of the garden is prepared, the shadow cast by existing buildings, fences and the proposal is plotted through the day, and the area receiving two hours or more of direct sun is measured.
The date used is 21 March, the spring equinox, chosen because it sits midway between the extremes and gives a reasonable representation of the year. Some assessments add 21 June and 21 December plots for context, and on a contested case those extra plots are worth having, because they show what the garden is actually like in the months people use it.
Nothing in national policy requires this test. It is guidance, and councils apply it as a tool for judging amenity harm. Officers treat a numerical failure as a strong indicator rather than as an automatic refusal.
The proportion and duration tests applied
Two numbers do the work.
The proportion: at least half the area of the garden or amenity space. The duration: two hours or more of direct sunlight on 21 March. Both limbs have to be satisfied for the garden to pass.
Where the garden already fails before the development, the comparison becomes relative. A reduction that leaves the sunlit area at less than 0.8 times its previous extent is treated as a noticeable loss. That is a 20 per cent reduction in the sunlit area, not a 20 per cent reduction in the garden.
The distinction matters when a small shadow falls across an already small sunlit patch. A single-storey extension on the right boundary can remove a quarter of the remaining sunlit area of a garden that was barely passing, and the test picks that up even though the extension looks modest on a plan.
Why north facing gardens are already marginal
A garden on the north side of a house sits in the house's own shadow for a large part of the day, because the sun is in the southern sky in the United Kingdom all year round. In March the sun is low, the shadows are long, and a two-storey house casts a shadow across much of a modest garden through the middle of the day.
The practical consequence is counter-intuitive but important. The baseline is poor, so the absolute test is often failed before anything is proposed, and the case runs on the relative test instead. That usually favours the applicant on a small extension and goes against them on anything tall near the boundary.
The other consequence is that the sun these gardens do get arrives at the ends of the day, from the east in the morning and the west in the afternoon. Development on the east or west boundary therefore does more harm than development of the same size on the south, which is the opposite of what most people assume.
Boundary fences, trees and existing shade
| Feature | Effect on the baseline | How to treat it |
|---|---|---|
| 1.8 m boundary fence | Shades a strip along the southern boundary | Include in the baseline model, since it exists lawfully |
| Mature tree in or near the garden | Can dominate the shadow pattern | Include, but note deciduous canopy varies by season |
| Neighbour's own extension | Part of the existing situation | Include at its as-built extent |
| Proposed tree planting | Not part of the baseline | Do not use it to improve the result |
| An unlawful structure | Not part of the lawful baseline | Exclude, and say why |
The fence point comes up repeatedly. A garden whose southern boundary carries a 1.8 metre close-boarded fence already has a shaded strip, and including that correctly lowers the baseline, which helps an applicant on the relative test. Leaving it out overstates the existing sunlight and makes your own proposal look worse.
Trees cut both ways and need a stated assumption. Model them in leaf and out of leaf, or state which condition you used and why.
Preparing a simple shadow study
- Measure the garden, the house, the boundary treatments and anything else that casts a shadow. Scale off a measured survey rather than from an aerial image, because heights cannot be scaled from a photograph.
- Build a simple three dimensional model, including the neighbouring house and fences.
- Set the location by latitude and generate shadows at hourly intervals on 21 March, from early morning to late afternoon.
- Overlay the hourly shadows to produce a plan showing the area receiving two hours or more.
- Repeat for the proposed situation.
- Measure both sunlit areas and express the result as a proportion of the garden and as a ratio of before to after.
A householder can produce that with free modelling software and an afternoon. For a contested case, or where the garden is small and the proposal is close to the boundary, an Overshadowing Study prepared by someone who does this routinely carries more weight, and councils generally expect a suitably qualified author where the issue is finely balanced.
The same method applied to other kinds of amenity space behaves identically, as our note on sun on ground for allotments and community growing space sets out.
What officers accept as mitigation
Reducing the projection depth is the measure that moves results most on a rear extension, because the shadow length scales with the mass nearest the boundary. Lowering the eaves comes second, and on a single-storey extension dropping the eaves by 300 mm can matter more than losing half a metre of depth.
A roof that slopes away from the boundary helps, and a flat roof with a low parapet often performs better than a pitched roof with a gable facing the neighbour. Setting the extension off the boundary helps on the east and west sides more than on the south.
What does not work: planting, which is not part of the baseline and is not secured in perpetuity, and rooflights, which change nothing outside. Offering to paint a flank wall a light colour is a daylight argument rather than a sunlight one and will not shift a sun on ground result.
Where the objection is likely to succeed
Four situations where an objection on garden sunlight has real prospects. A small garden, under about 50 m², where any new shadow removes a large share of the sunlit area. A two-storey or first floor extension close to the shared boundary on the east or west side. A proposal that takes the sunlit area below the 0.8 ratio from an already failing baseline. And a garden that is the only amenity space for a family dwelling, where the loss has nowhere else to go.
Against that, objections rarely succeed against a modest single-storey rear extension built within permitted development limits, because there is no application to object to, and the shadow effects of that kind of extension are usually small on gardens to the north. Our note on daylight and a single-storey rear extension covers the related window tests.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. If you are putting an application together, enter your postcode on PlanScope to see which documents the council is likely to expect.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What is the sun on ground test?
A method in the BRE site layout guidance asking whether at least half of a garden or amenity area receives two hours or more of direct sunlight on 21 March. Where the area already falls short, a reduction leaving the sunlit area at less than 0.8 times its previous extent is treated as a noticeable loss.
Why do north facing gardens fail the test already?
Because the sun is in the southern sky throughout the year in the United Kingdom, so a garden on the north side of a house sits in the house's shadow for much of the day. In March the sun is low and shadows are long, and a two-storey house shades much of a modest garden through the middle of the day.
Which boundary matters most for a north facing garden?
The east and west ones. The sun these gardens receive arrives at the ends of the day, so an extension on the east or west boundary removes more of it than the same extension on the south boundary. That is the opposite of what most people assume when looking at a plan.
Should I include the boundary fence in the assessment?
Yes, if it exists lawfully. A 1.8 metre fence along the southern boundary already casts a shaded strip, and including it lowers the baseline, which helps an applicant on the relative test. Leaving it out overstates the existing sunlight and makes the proposal look worse than it is.
What mitigation do officers accept?
Reducing the projection depth, lowering the eaves, sloping the roof away from the boundary, and setting the extension off an east or west boundary. Planting is not accepted because it is not part of the baseline and is not secured. Rooflights change nothing outside, and light-coloured walls are a daylight point rather than a sunlight one.
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.