Courtyard blocks and sunlight to shared amenity space

Courtyard amenity sunlight is assessed against a simple benchmark from the Building Research Establishment's site layout guidance: at least half the amenity area should receive at least two hours of sunlight on 21 March. Perimeter blocks fail it more often than any other residential form, and they fail it for reasons fixed at massing stage, long before a consultant is appointed to model the result.

For a developer, that ordering is the whole problem. The test costs little to run and a great deal to fail.

Why courtyards fail the amenity sunlight test

A perimeter block encloses its open space on all four sides. The southern range casts its shadow into the courtyard for most of the day in March, the eastern and western ranges cut the early and late sun, and what is left is a strip along the northern edge.

Three design moves make it worse, and all three arrive for good reasons. Height is pushed up on the southern edge because that is where the street frontage or the site boundary allows it. Courtyard width is squeezed because units are worth more than open space. And the courtyard is treated as residual, shaped by whatever the blocks leave over, rather than set out first.

The result is predictable. On a courtyard 20 metres wide with a six storey southern range, the shadow covers the space at the equinox and the two hour figure lands somewhere well below half.

That is a design outcome, not an assessment outcome. No amount of careful modelling recovers it.

Block height against courtyard width

The geometry is not complicated. At the spring equinox in southern England the sun reaches roughly 38 to 39 degrees above the horizon at solar noon, and lower further north. A building of height H casts a noon shadow of roughly 1.25 times H at that latitude, longer through the morning and afternoon and longer again in northern England.

So a courtyard needs a width comfortably greater than the height of its southern range if the middle of the space is to see sun in March. A one to one ratio of southern range height to courtyard width leaves most of the space in shadow at noon. Ratios approaching one and a half to one start to work.

Two qualifications matter. Sunlight availability is a function of time of day as well as noon geometry, so a wide east to west courtyard can pick up hours in the morning and afternoon that a square one does not. And the figures above are approximate: the actual solar altitude depends on latitude, so the modelling has to be site specific rather than taken from a rule of thumb.

Use the rule of thumb to shape the massing. Use the model to prove it.

Orientation and the sunlit edge

In a courtyard, the sunlit part is the northern edge, because it faces south and the southern range's shadow falls away from it. That single fact should drive the layout of everything inside the space.

Where the southern range steps down, or where the courtyard opens to the south through a break in the perimeter, the sunlit area grows considerably. A gap of one bay in the southern range, or a single storey element where the rest is five, can move the result past the halfway mark on its own.

East and west ranges matter less than developers expect at the equinox and more than they expect in winter. Long east to west courtyards perform better than square ones of the same area. Deep north to south slots perform worst of all.

There is a trade here that is worth naming rather than hiding. Stepping the southern range down loses units on the most valuable frontage. The alternative is an amenity space that fails the benchmark and gives the authority a reason to refuse or to demand a redesign at planning stage, which costs more.

Placing play space where sun reaches

Where the scheme generates a child yield, the play space requirement lands in the same courtyard. In London that is policy S4 of the London Plan, with its standard of ten square metres of play space per child, and most authorities outside London have an equivalent in their adopted plan or a supplementary planning document.

Put the doorstep play space on the sunlit northern edge. It sounds obvious. It is routinely got wrong, because play space is placed where it is least disruptive to ground floor flats rather than where children will use it.

The same logic applies to seating, to any communal growing space, and to the one part of the courtyard likely to be used for longer than a few minutes at a time. Circulation, bin stores, cycle stores and substations belong in the shaded parts. That is a free improvement to the assessed result, since the benchmark applies to the amenity area rather than to every square metre of open ground.

Where the courtyard sits over a podium, the depth of build-up available for planting becomes the other constraint, and it interacts with light: shallow soil and deep shade together rule out most of what a landscape architect would otherwise specify.

Planting that tolerates low light

A courtyard with a southern range of any height has a permanently shaded zone, and planting it as though it were an open garden guarantees a thin, patchy result within two seasons.

Shade tolerant species exist in quantity, and the landscape strategy should be written around them rather than treating shade as an exception. Ferns, hellebores, epimedium, sarcococca, hydrangea and several of the shade tolerant grasses will hold a planted edge under a five storey wall. Evergreen structure matters more in shade than in sun, because there is less seasonal interest to carry the space.

What does not work is lawn. Amenity grass under a tall southern range will not establish, and it is the single most common cause of a courtyard looking neglected a year after practical completion.

Trees in a courtyard need care of a different kind. A tree placed in the sunlit northern strip removes the one part of the space that passes the test, so tree positions should be set after the sunlight study rather than before it.

Testing options at massing stage

Run the sunlight study on the massing model, not on the developed design. Three or four variants tested early cost far less than one late redesign.

A practical sequence:

1. Model the base massing and plot the 21 March sunlight availability across the courtyard
2. Test a reduction of one or two storeys on the southern range only
3. Test a break or a lower bay in the southern range
4. Test widening the courtyard by moving the northern range back
5. Compare the amenity area passing the two hour benchmark in each case against the units lost

Shadow plots on the hour through 21 March, plus 21 June and 21 December for context, tell the design team more than a single percentage figure. They also show where the sunlit area actually sits, which is what the landscape design needs.

The output feeds directly into the formal Daylight and Sunlight Assessment submitted with the application, and where neighbouring gardens or open space are also affected, into a separate Overshadowing Study. The distinction between shadow that moves across a space during the day and shadow that never leaves it is the one explored in transient overshadowing versus permanent loss of sunlight, and it is the distinction that decides whether a courtyard result is survivable.

Reporting the result honestly

A courtyard that achieves 42 per cent against a benchmark of 50 per cent is not a disaster, and reporting it as a pass is. Officers and their consultants read these reports carefully, and an overstated conclusion undermines everything else in the document.

The stronger approach states the figure, explains the constraint that produces it, sets out the options tested and the reason the chosen one was preferred, and identifies where in the space the usable sunlight actually falls. The guidance itself is expressed as good practice rather than as a rule, and it invites flexibility where site constraints justify it, but that flexibility has to be argued rather than assumed.

Where the scheme includes roof terraces as additional amenity space, the sunlight case there is usually much stronger and worth making, though wind comfort then becomes the constraint, as set out in roof terraces, sunlight and wind comfort together. Where the surrounding context is already dense and the baseline is poor, the comparison against existing conditions carries more weight than the absolute figure, which is the argument developed in daylight assessment in low baseline conditions.

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. For specialist technical reports, qualified professional input may be required.

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