Sunlight to communal amenity space in a flatted scheme

Communal amenity space in a flatted scheme is assessed for sunlight on the ground rather than through windows, and the criterion is simple enough to check on a sketch. Building research guidance treats an amenity area as adequately sunlit where at least half of it receives at least two hours of sunlight on 21 March, the spring equinox. Communal amenity space sunlight results below that, or a reduction to less than about 0.8 times the previous value, are treated as noticeable.

That single test governs courtyards, podium gardens, roof terraces, play areas and the shared gardens of converted buildings. It is also the test most often left until the massing is fixed, when the only remaining lever is to redraw the landscape plan.

Which spaces are assessed

The guidance applies to open spaces where people sit, play or gather. In a flatted scheme that means the main communal garden or courtyard, any podium deck given over to amenity, designated play space, roof terraces intended for shared use, and any public open space the scheme creates.

Spaces that are incidental rather than usable are excluded, and the distinction matters commercially. A 2 m strip of planting against a boundary is not amenity space, and calling it amenity space in a schedule while excluding it from the sunlight assessment is inconsistent.

Neighbouring amenity space is assessed too. A new block that overshadows the shared garden of an adjoining building is assessed against the same criterion, with the before and after comparison carrying the argument.

State in the report which spaces have been assessed, which have been excluded and why. An officer reading a report that assesses only the courtyard, when the drawings show three terraces, will ask about the other two.

The sun on ground criterion applied to courtyards

Courtyards fail on geometry. The governing variables are the height of the southern range, the width of the courtyard and the orientation.

A courtyard enclosed on all four sides by blocks of equal height is sunlit at the equinox only where its width is generous relative to that height. Narrowing the courtyard or raising the southern range moves the result quickly, and the relationship is not linear: a storey added to the southern block can remove more than a storey's worth of sunlit area because the shadow is cast across the whole depth.

The strongest moves are all about the southern edge. Lower the southern range. Break it with a gap that lets low sun through. Angle the courtyard so its long axis runs closer to north-south. Or place the amenity space at the southern end of the site rather than in the middle of the block.

Our note on courtyard blocks and sunlight to shared amenity space works through the geometry in more detail.

Podium and roof level spaces

Podium gardens sit above the surrounding ground and below the towers, which usually improves the sunlight result and worsens the wind result.

Model them the same way, at the podium surface level, with all surrounding massing included and with any parapet, pergola or planting structure that casts shadow. Parapets are frequently omitted from models and they matter at low sun angles, particularly for a narrow terrace.

Roof terraces at the top of a block generally perform well on sunlight and badly on comfort. A terrace on the fifteenth floor with two hours of equinox sun and wind speeds that make sitting unpleasant for most of the year is not amenity space in any meaningful sense, whatever the assessment says.

Privacy screening complicates both. Screens added to resolve overlooking cast shadow and interrupt views, as our piece on roof terraces, privacy screens and conditions sets out.

Play space and its own requirements

Play space carries requirements beyond sunlight. Where a scheme generates a child yield, policy in many authorities requires a quantum of play space, with doorstep provision for the youngest children close to the dwellings.

Sunlight matters more here than anywhere else in the scheme, because a shaded play area in a British climate is used for a fraction of the year. Assess the play space separately rather than as part of a larger courtyard average, since averaging can hide a fully shaded play area inside a generally sunlit space.

Shade also has a positive role. Some shade in summer is desirable for young children, and the sensible design outcome is a space with equinox sun and summer shade from trees rather than from buildings.

A Play Space Assessment should state the child yield method, the quantum required by policy, the location of each element and the sunlight result for each, so the two arguments sit in one place.

Wind and comfort assessed alongside

Sunlight and wind have to be read together. A space that passes the sunlight test and fails a comfort criterion is not usable, and inspectors have been unimpressed by schemes that treat the two separately.

Comfort is assessed against established criteria that relate wind speed and frequency to activities, from walking through to long periods of sitting. Sitting areas demand the calmest conditions, which is exactly what a podium deck between towers struggles to provide.

Where a Wind Microclimate Assessment identifies an exceedance, the mitigation usually involves screening, canopies or planting, all of which cast shadow. Run the sunlight model again after the mitigation is added. A scheme that passes both tests in isolation and neither together is a common and avoidable outcome.

Layout changes that improve the result

In rough order of effectiveness:

1. Move the amenity space towards the southern or western part of the site.
2. Reduce the height of the range on the southern side of the space.
3. Open a gap in the southern range aligned with the space.
4. Widen the space relative to the enclosing heights.
5. Step the southern block back at upper levels.
6. Split one large space into two smaller ones positioned where sun reaches.

The last of those needs care, because splitting can conflict with the quantum requirements for usable amenity space set out in local policy.

Evidence for a planning submission

A submission that settles the point contains a sunlight on ground analysis for every amenity space at the equinox, expressed as the percentage of each space receiving two or more hours, with plans showing the sunlit area.

Add transient shadow studies at hourly intervals for 21 March, 21 June and 21 December. They are not the test, and they are what committee members actually look at, so include them and label them as illustrative of the shadow pattern rather than as the assessment.

State the model assumptions: the massing included, the surrounding buildings modelled, the ground and podium levels used, the treatment of planting, and the software. Where an existing building is being replaced, state the baseline used, since the comparison depends on it and the approach is discussed in our note on mirror image baselines and existing obstructions.

A Daylight and Sunlight Assessment covering both internal daylight and external amenity space in one document keeps the assumptions consistent. Councils expect a suitably qualified author and professional review before submission is strongly advised.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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