Overshadowing of allotments, orchards and growing space

Allotment overshadowing is assessed against the wrong test most of the time. The usual planning yardstick for outdoor space, taken from BRE 209, asks whether at least half of an amenity area receives two hours of sunlight on 21 March, and whether the sunlit area falls below 0.8 times its former extent. That is a reasonable measure of whether people can sit outside. It says very little about whether a plot can grow food.

Productive growing space needs more sun, over a longer season, and the dates that matter are not the dates a standard amenity assessment reports. If you are objecting to a scheme next to allotments, or designing one, that gap is the argument.

Why growing space needs a different test

Sitting out is an occasional activity that people move around to suit. Growing is fixed in place and cumulative. A bed that loses the morning sun in May does not catch up in August.

Horticultural practice treats full sun as roughly six hours or more of direct sunlight a day in the growing season for fruiting crops: tomatoes, courgettes, beans, most soft fruit, apples and pears. Leafy crops, rhubarb, gooseberries and currants tolerate part shade and will still yield. Below about four hours of direct sun, the range of what can be grown narrows sharply and the plot becomes a different proposition for the person who holds it.

So the honest framing is not that a scheme makes an allotment unusable. It is that a scheme changes what can be grown there, and by how much, which is a material planning consideration where the space is protected by policy or designated in a local or neighbourhood plan.

The dates and hours that matter for growing

Test the growing season rather than the equinox alone. A reasonable set of dates to model, and to ask for in a consultation response:

Report the proportion of the plot area receiving at least two, four and six hours of direct sun on each date, before and after the proposal. Percentages at three thresholds tell a reader far more than a single pass or fail against the two hour figure. And on a site with an existing orchard, ask for the same analysis at canopy height rather than only at ground level, since a tree shaded to half its height still fruits on the sunlit side.

Modelling shadow across a plot

The method is the same one used for any Overshadowing Study: a three dimensional model of the proposal and the surrounding context, a solar position calculation for the site's latitude, and an hourly analysis across the ground plane.

Three things make the output usable in a planning argument. A grid fine enough to show individual beds or plots rather than the whole site as one average, typically 1 m or finer on an allotment site. A plan showing the shadow pattern at hourly intervals rather than a summed total alone, because a plot that loses all its sun between 10am and 2pm is worse off than one losing the first and last hour. And a clear statement of what was included in the model, since existing boundary trees, sheds, a railway embankment and the neighbouring terrace all cast shadows that already exist.

Existing obstruction is the point most objections get wrong and most applicant reports get right. If a plot already sits in shade from a mature lime for three hours each afternoon, the new building's effect has to be measured against that baseline.

Boundary planting and hedge effects

Hedges are the awkward part. A new development's boundary planting, screening required by a landscape condition, or a hedge grown for privacy can shade a plot more than the building does, and it grows.

Worth checking on any layout: the height a proposed hedge or tree line will reach at maturity, its distance from the boundary, and whether the species is evergreen. Where a screening belt is proposed on the southern edge of growing space, ask for it to be moved, lowered, or specified as deciduous, and ask for the maintenance regime to be secured by condition rather than left to a future management company.

There is a separate statutory route once a hedge exists. Part 8 of the Anti-social Behaviour Act 2003 allows a complaint to the council about an evergreen or semi-evergreen hedge over 2 m high that adversely affects the reasonable enjoyment of domestic property. It is slow, it carries a fee, and it does not apply to deciduous trees or to allotments held under a tenancy rather than as domestic property. Better to fix the specification at application stage.

Mitigation and relocation options

The options, in the order a council is likely to consider them:

1. Reduce the height of the part of the building nearest the growing space, or step the upper floors back.
2. Move the massing north or reorganise the layout so the tall element does not sit on the southern boundary.
3. Change the orientation of the growing space itself, which works on a new site and rarely on an established one.
4. Provide replacement space with demonstrably equivalent sunlight, quantified with the same analysis, not simply an equal area.
5. Adapt the affected plots with raised beds, cold frames or a shift to shade tolerant cropping, funded through the scheme where the loss is unavoidable.

Replacement at an equal area with worse sunlight is the outcome to resist. Ask for the sun hours analysis of the replacement land, on the same dates, before agreeing that the loss is mitigated.

Evidencing loss in an objection or an application

A written objection carries more weight when it describes the growing use precisely. Number of plots affected, orientation of the beds, what is currently grown, the height of the proposed building and its distance from the boundary, and photographs taken from the plot towards the site with the date and time recorded.

Illustrative example. A four storey block proposed 8 m from the southern boundary of a 24 plot allotment site. The applicant's report showed 62 per cent of the site retaining two hours of sun on 21 March, which passes the standard amenity test. A resident's response asked for the June and August analysis at the four and six hour thresholds, which showed the six southernmost plots dropping below four hours through the whole season. The scheme was amended to step the top floor back and the two most affected plots were relocated within the site, with the sun hours for the replacement land reported.

That is how these cases move. Not by asserting harm, and not by counting square metres, but by asking for the analysis the applicant did not volunteer. The same approach applies to communal gardens in flatted schemes, where the reasoning on sunlight to communal amenity space sets out what a proper assessment contains, and to the smaller scale effects covered in amenity effects of a dormer on the neighbouring house.

Statutory allotments carry an extra layer of protection: disposal by a local authority generally needs the consent of the Secretary of State, and national policy resists building on existing open space unless it is surplus, or the loss is replaced by equivalent or better provision, or the development is for alternative sports and recreational provision. Say which of those limbs the applicant is relying on, and test it.

Where the analysis matters, ask the council to require a Daylight and Sunlight Assessment covering growing season dates as a validation requirement, rather than accepting a March only study. Put the request in during the consultation period, in writing, and copy the case officer.

To see which reports a scheme next to protected open space is likely to need, enter the postcode on PlanScope.

This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it.