Openness of the Green Belt: spatial and visual

Openness of the Green Belt is not a synonym for visual impact, and treating it as one is the fastest way to lose a Green Belt appeal. The courts have settled that openness is a broad policy concept with a spatial dimension, concerned with the absence of built development, and that visual impact may or may not be relevant depending on the case. So an assessment that consists of photographs and viewpoints, with no measured account of what is being built where, is answering half the question.

The Framework treats openness and permanence as the essential characteristics of Green Belts. Everything else in Green Belt policy sits on top of those two words.

What openness means in policy

The starting point is that openness is about the absence of built development rather than about visual amenity or landscape quality. Land can be open and ugly. Land can be attractive and not open.

Two propositions from the case law do the heavy lifting.

Openness is not exclusively a visual concept. The Court of Appeal in Turner in 2016 confirmed that it has a spatial aspect as well as a visual one, so a scheme can harm openness even where it is well screened.

Visual impact is not necessarily implicit in openness. The Supreme Court in Samuel Smith Old Brewery (Tadcaster) in 2020 held that openness is a broad policy concept and that whether visual impact is relevant in a given case is a matter of planning judgement for the decision maker rather than a legal requirement.

Read together, those two decisions tell you that a decision maker must consider the spatial dimension, and may consider the visual one. An applicant arguing openness on screening alone is relying on the weaker limb.

The spatial dimension and how to measure it

Spatial openness is measurable, and measuring it is what separates a persuasive assessment from an assertion. Five metrics do the work on most sites.

Footprint, meaning the area covered by buildings and permanent structures, existing and proposed.

Built volume, which captures height in a way footprint does not.

Height, stated as maximum and typical, with the relationship to surrounding development.

Spread, meaning the extent of the site over which built form is distributed. Two schemes of identical volume, one in a compact block and one strung along a frontage, have very different effects on spatial openness.

Permanence and activity, covering hardstanding, boundary treatments, lighting columns, parked vehicles and the duration of any activity on the land. The Supreme Court accepted that the duration of activity and the spread of built development can be relevant to openness.

Present these as a table with existing and proposed figures side by side. An officer or an inspector asked to judge harm to openness needs numbers to reason with, and they will take the objector's figures if you supply none.

The visual dimension and its limits

Visual effects are worth assessing, and they are not a substitute.

Where the site is seen from public vantage points, a viewpoint analysis showing the existing and proposed situation helps. Where the site is enclosed by mature hedgerows, saying so is legitimate. What does not work is an argument that screening removes harm to openness, because the spatial effect remains whether or not anyone can see it.

Screening also has a time dimension that applicants tend to ignore. Deciduous hedges are transparent for half the year, and hedgerows can be removed lawfully by whoever owns them. An assessment relying on existing vegetation should say what happens if it is not there, and secure its retention by condition if that is the case being made.

Where the scheme is large enough to warrant it, a landscape and visual impact assessment prepared to the recognised guidelines covers the visual dimension properly, and in a built-up fringe a townscape and visual impact assessment may be the better fit. Councils expect a suitably qualified author for either, and professional review is strongly advised.

Comparing volume, footprint and spread

Several Green Belt exceptions turn on a comparison with what is already there. Extensions and alterations to a building are capable of being appropriate development provided they do not amount to disproportionate additions over and above the size of the original building. Replacement buildings have to be in the same use and not materially larger. Redevelopment of previously developed land turns on whether the effect on openness would be greater than the existing development.

Three drafting points for that comparison.

Define the original building precisely. It means the building as it stood at the relevant date, not the building as extended since, and the difference is often decisive.

Give both footprint and volume. Authorities' supplementary planning documents commonly set percentage tests, and those tests are expressed in different units in different districts, so provide both and work to whichever the local guidance uses.

Deal with spread separately from quantum. A replacement dwelling of identical volume relocated to a more prominent part of a plot can increase harm to openness even though no test on size is breached.

Reduced harm is not no harm

This is the point most often misunderstood. Showing that a scheme has less effect on openness than some alternative does not show that it has no effect.

Where a proposal is inappropriate development, the policy requires substantial weight to be given to any harm to the Green Belt, and very special circumstances have to be demonstrated, meaning the harm is clearly outweighed by other considerations. A reduction in harm relative to a notional worse scheme does not feed into that at all.

Where the proposal falls within one of the exceptions, the test is different and the comparison does matter, because the exception itself is framed as a comparison. So the first thing an assessment should establish, before any measurement, is which side of that line the scheme sits on. Applicants frequently write a careful comparative analysis and never state whether they say the development is appropriate or inappropriate, which leaves the officer to decide the most important question in the case without their input.

The December 2024 edition of the Framework introduced the grey belt concept, identifying Green Belt land that does not strongly contribute to certain Green Belt purposes, and the policy has been carried through subsequent editions. Check the current wording and any associated guidance at the time of writing rather than relying on a summary, because this is the part of Green Belt policy that has moved most recently.

Evidence for an openness assessment

A workable package on a small or medium scheme looks like this.

A measured schedule of existing structures with footprint, volume and height, supported by a topographical survey rather than scaled from aerial imagery.

The same schedule for the proposal, with percentage changes.

A plan comparison showing site coverage and spread, existing and proposed.

A section through the site showing heights against the surrounding context.

Photographs from public vantage points with a viewpoint plan, and an honest statement of seasonal variation in screening.

A short written analysis stating whether the development is appropriate or inappropriate, the harm to openness in spatial and, where relevant, visual terms, and the case on very special circumstances if one is needed.

That analysis belongs in the planning statement rather than in a separate document, with the measured schedules as appendices.

How inspectors have approached it

Appeal decisions are indicative of approach rather than binding precedent, and two patterns are worth knowing. Inspectors tend to give short treatment to openness arguments resting only on screening, and they tend to engage closely with measured comparisons where both parties have provided figures.

The other pattern is less comfortable for applicants. Where an appellant has not stated whether the scheme is appropriate development, inspectors generally decide that it is inappropriate and move straight to very special circumstances, which is the harder ground to fight on.

So state your position on appropriateness first, then measure, then deal with the visual dimension as a supporting argument. The full report index sets out the supporting documents a Green Belt application typically needs.

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.