When a new building is proposed, planners do not only ask whether habitable rooms keep their daylight and sunlight. They also ask a simpler, more visible question: will the gardens and amenity spaces still get the sun? The BRE overshadowing test for gardens and amenity spaces answers exactly that, and for many householder and residential schemes it is the assessment that decides the application.
This guide explains how the overshadowing test works under BRE BR 209 (2022), what the two-hour rule and the 0.8 times threshold really mean, and how to design outdoor space that keeps its sunlight and keeps planners satisfied.
What the overshadowing test for amenity space measures
Daylight and sunlight assessments split into two families. One looks at light reaching windows — the metrics VSC, NSL and APSH covered in our guide to the three daylight and sunlight metrics. The other looks at sunlight reaching the ground: the open spaces people actually use. That second family is the overshadowing, or “sun on ground”, assessment.
The spaces it protects include private rear gardens, communal courtyards, children’s play areas, roof terraces, seating areas and any garden or amenity area whose enjoyment depends on sunlight. BRE guidance treats these as a genuine planning consideration because a scheme can technically meet window-based targets while casting a neighbouring garden into shade for most of the day.
The two-hour rule on 21 March
The core BRE recommendation is straightforward. On 21 March — the spring equinox — at least half (50%) of a garden or amenity area should receive at least two hours of direct sunlight. The equinox is chosen deliberately: it sits midway between the low winter sun and the high summer sun, so it represents an average, fair day for testing rather than a best or worst case. Our companion article on the 21 March equinox test explains why that single date carries so much weight.
The assessor builds a three-dimensional model of the site and its surroundings, then plots where shadows fall across the amenity space through the day on 21 March. The result is a percentage: how much of the usable ground receives two or more hours of sun. If it is 50% or more, the space passes the BRE recommendation. If it falls below, the space is judged to be poorly sunlit.
The 0.8 times rule for existing spaces
Where a proposal affects a neighbour’s existing garden or amenity area, BRE applies a change-based test as well. If, after the development is built, the sunlit area (the part receiving two hours on 21 March) falls to less than 0.8 times — that is, an 80% — of its former value, the loss is likely to be noticeable and is considered a significant adverse effect.
In plain terms: a neighbouring garden can lose up to a fifth of its well-sunlit area before the BRE flags a material impact. The same 0.8 multiplier appears throughout BRE guidance, and we unpack it in detail in the 0.8 times rule explained. Applied to amenity space, it gives officers a clear, numeric line to judge objections against.
Why this matters for planning
BRE BR 209 is guidance, not law. It is not part of national planning policy and its numerical targets are advisory. In practice, though, local authorities across England and Wales adopt the overshadowing test as a material consideration, and it is frequently cited in officer reports, neighbour objections and appeal decisions. Loss of sunlight to a garden is one of the most common grounds a neighbour raises against a rear extension or a new dwelling — precisely because it is easy to observe and easy to feel.
National policy reinforces the point indirectly. The National Planning Policy Framework (NPPF) expects new development to secure a high standard of amenity for existing and future occupiers, and access to sunlight in gardens and shared spaces is part of that standard. Many councils translate it through a residential amenity policy in their local plan, which is where the BRE numbers do their work.
Designing amenity space that keeps its sunlight
Overshadowing problems are far cheaper to solve on the drawing board than at appeal. A few design moves make the difference:
- Orientate the main amenity space to the south or west where possible, so it captures midday and afternoon sun rather than sitting in permanent shadow to the north of a building.
- Step back or reduce height on the elevation that faces a neighbour’s garden. Even a modest set-back can lift a garden back above the 50% two-hour threshold.
- Keep boundary structures modest. Tall close-boarded fences, outbuildings and dense evergreen screening all remove sun from the ground and count against the test.
- Test communal courtyards early. In flatted schemes, a courtyard hemmed in by tall blocks on several sides can fail badly; a single-aspect or open-corner layout usually performs far better.
Running the sun-on-ground study at concept stage, alongside the internal daylight checks under BS EN 17037, lets you find and fix these issues before the design is fixed.
How Fortress Associates can help
Fortress Associates prepares BRE-compliant daylight, sunlight and overshadowing assessments for planning applications across the UK. Our daylight and sunlight report service includes sun-on-ground modelling for gardens, courtyards and amenity areas, tested to the two-hour and 0.8 times BRE recommendations, with clear plots you can submit to your planning authority. Reports are typically ready in four to five working days, with no advance payment required. Explore our full range on the services page, or get in touch with your site details for a quote.
Sources & further reading
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