Sunlight to allotments and community gardens

If a proposed building will overshadow your allotment site or community garden, the test a planning officer is most likely to apply comes from BRE 209: at least half of an amenity area should receive at least two hours of direct sunlight on 21 March. Growing space is amenity space for this purpose, and a sunlight allotment planning application objection that cites that test, with a shadow plot to support it, carries far more weight than a letter saying the site will be in shade.

Two hours at the spring equinox sounds undemanding for a vegetable plot, and it is. The point of the test is that it is the recognised benchmark, so an objection built on it cannot be dismissed as opinion.

Why growing space is treated differently

A private back garden and an allotment are both amenity space, and the way they are used differs enough to matter. A garden is used for sitting out, mostly in summer afternoons. A growing site is used from the first sowings in March through to autumn harvest, and its value depends on direct sun reaching the soil across that whole period rather than on a pleasant evening in July.

That difference gives a community group two arguments rather than one. The BRE benchmark at 21 March is the formal test. The seasonal pattern across the growing season is the practical case, and it is the one that explains why a loss which looks modest at the equinox becomes severe in March and October when the sun is low.

Statutory allotments carry a further layer of protection. Where land is held by a local authority as statutory allotments, section 8 of the Allotments Act 1925 prevents disposal or appropriation without the consent of the Secretary of State. That does not stop a neighbouring development, and it is worth knowing if the proposal involves the allotment land itself.

The sunlight test applied to open space

BRE 209 handles sun on the ground separately from daylight to windows. The assessment plots the shadow cast by existing and proposed buildings across the area in question on 21 March and calculates the proportion receiving at least two hours of sun.

The guidance also addresses change rather than absolute value. Where the area receiving two hours on 21 March falls below about four fifths of its former extent, and below half the total area, the loss is treated as noticeable. Those two limbs work together, so a site already partly shaded is judged on the proportional reduction as well as the final figure.

Ask for that analysis. Where an applicant has submitted a Daylight and Sunlight Assessment, check whether the growing space was included as a receptor at all. It frequently is not, because the assessor was given a list of residential windows and gardens. A short written request to the case officer asking for the allotment site to be assessed as an amenity area is usually enough to get it added.

Seasonal variation and the growing season

The 21 March benchmark exists because it sits midway between the extremes, so it is a fair single test. It is not a description of the worst case.

On 21 December the sun in southern England rises to around 15 degrees above the horizon at midday, and further north it is lower still. A building that clears an allotment comfortably in June will lay a shadow several times longer across it in December, and in March and October the shadow is still long enough to remove the early and late parts of the day.

For a growing site that matters in specific ways. Seed beds and early sowings depend on soil warming in March and April. Greenhouses and polytunnels lose disproportionately because they depend on direct gain. Fruit trees and soft fruit set poorly in shade. Say which parts of the site do what, because an officer cannot weigh a loss described only as "the plots".

Figures in this table are approximate and vary with latitude. Use them to understand the pattern, not as evidence.

Measuring the affected proportion of the site

The practical method is a shadow plot, and a community group can produce a usable one.

1. Get a scaled site plan showing the allotment boundary, plot layout and any existing buildings and trees.
2. Get the applicant's proposed elevations with heights above ordnance datum or above ground level.
3. Establish true north on the plan, taking it from the applicant's drawings rather than a phone compass.
4. Plot the shadow outline at hourly intervals from 9am to 3pm on 21 March using the sun altitude and azimuth for your latitude.
5. Overlay the hourly outlines and shade the part of the site receiving fewer than two hours of sun.
6. Express the result as a percentage of the total growing area, before and after.

That produces a drawing an officer can check. It is the same method a consultant uses, without the software, and the arithmetic is public. Where the numbers are close or the geometry is complicated, an Overshadowing Study prepared properly is the more reliable route, and a group that has done the rough version first knows what it is buying.

Photographs help alongside the plot, and only if they are dated and timed. A set taken at the same hour on the same day each month over a season shows the existing pattern, which is the baseline the assessment will be argued against.

Evidence a community group can prepare

Beyond the shadow plot, four things carry weight and cost nothing.

A plan of the site showing what is grown where, with the greenhouse and fruit areas marked. A note of how many plots are let and how many people use them, which speaks to the number of people affected. Cropping records if the association keeps any. And a short statement of the association's tenure, because a site held on a long lease or as statutory allotments is a more durable receptor than one on a rolling annual licence.

Keep the material factual. A representation that sets out measurements and site facts is read differently from one that predicts the end of the site.

Raising it in a representation

Address the objection to the case officer, quote the application reference, and put the planning point in the first paragraph. Under section 70 of the Town and Country Planning Act 1990 the authority must have regard to material considerations, and loss of sunlight to an amenity area used by identified people is one.

Then structure it the way the officer's report is structured. What the policy says about amenity and about protecting open space. What the BRE benchmark is. What your shadow plot shows, with the before and after percentages. What the applicant's own assessment did and did not cover. And what you are asking for, which should be a specific design change rather than refusal, because a specific request is easier to grant.

Illustrative example: a four storey block proposed immediately south of a 38 plot allotment site. The group's shadow plot shows the proportion of the site receiving two hours of sun on 21 March falling from most of the site to a little over half, with the loss concentrated on the southern plots including the association greenhouse. The group asks for the southern range to be reduced by one storey rather than for refusal. Figures here are illustrative.

What mitigation can realistically achieve

Be honest with yourselves about what is achievable. Height reduction on the elevation nearest the site is the only measure that changes the sunlight result materially. Setting the building back helps in proportion to the distance gained. Stepping the massing down towards the boundary helps at the edges.

Things that do not help, whatever is offered: lighter external materials, a green roof, a contribution towards new raised beds, or relocating a few plots within the same overshadowed area. Reflected light from a pale wall is not direct sun and the two hour test measures direct sun.

Where an offer of replacement land is made, ask for the sunlight assessment of the replacement site before agreeing to anything. Land that is available is not necessarily land that grows.

For applicants reading this from the other side, the same analysis done early costs less than doing it after an objection. Browse the report types on PlanScope to see what an overshadowing study covers. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.