Assessing Green Belt openness in a planning application

A green belt openness assessment is a written argument, not a measurement. It has to say what openness means on this site, how the proposal changes it spatially and visually, how that bears on the purposes of including land in the Green Belt, and what weight the decision-maker should give the result. Officers and inspectors rarely disagree with the numbers. They disagree with the conclusion drawn from them, which is why the reasoning has to be visible.

What openness means in policy and in case law

National policy treats openness and permanence as the essential characteristics of the Green Belt. Openness is not defined, and the courts have repeatedly declined to reduce it to a formula.

Two judgments do most of the work. The Court of Appeal in Turner v Secretary of State established that openness has a visual dimension as well as a spatial one, so a scheme can harm openness through the way it appears even where the footprint is unchanged. The Supreme Court in Samuel Smith Old Brewery (Tadcaster) then confirmed that openness is a broad policy concept rather than a purely visual one, that visual impact is not always a mandatory consideration, and that what falls within it in any given case is a matter of planning judgement.

The practical reading is that both dimensions are available to you and neither is compulsory in every case. Say which dimensions matter here and why. An assessment that recites both judgments and then measures only volume has missed the point of citing them.

The National Planning Policy Framework was re-issued on 17 August 2026 with policy-coded chapters, so quote the code from that edition. The December 2024 edition introduced the grey belt concept and the associated development requirements, and how the current edition carries those forward needs checking against the published text rather than a summary.

Spatial and visual dimensions of openness

Separate the two in the drafting, because they lead to different evidence.

Spatial openness is about the absence of built form. The evidence is quantitative: site area, existing and proposed footprint, existing and proposed volume, building heights, hardstanding, and the proportion of the site that remains undeveloped. Where the site already contains buildings, set out the baseline honestly, including agricultural buildings and hardstanding that may not appear on the title plan.

Visual openness is about how open the land reads to a viewer. The evidence is a set of viewpoints, an analysis of screening and topography, and a judgement about whether the development will be perceived as built form intruding into open land. Photographs taken in winter, from publicly accessible positions, with the viewpoint locations shown on a plan.

Duration matters as well. A temporary structure removed after five years affects openness differently from a permanent building, and the permanence characteristic of Green Belt policy makes that distinction relevant.

So does activity. Vehicle movements, external storage, lighting and the comings and goings associated with a use all contribute to the sense of a site being developed rather than open, and they can be conditioned.

Measuring volume, footprint and built form

Set the baseline before you measure anything. For extensions the comparator is the original building, meaning as built or as it stood on 1 July 1948, not as extended since. Getting that wrong is the most common technical error in Green Belt statements, and the disproportionate additions test for extending a house in the Green Belt turns entirely on it.

Present the figures in a table, with the method stated:

Say how volume was calculated, because external volume measured to the outside face of walls and to the roof surface gives a different answer from internal volume, and reviewers will check. Include drawings that show the measured envelope.

Percentages need care. A 60 per cent increase on a small cottage may be modest in absolute terms, while a 30 per cent increase on a large house may add more built form than the entire original cottage. Give both figures and comment on the difference rather than leaving the officer to spot it.

Assessing effects on the purposes of including land

Openness is one question. Harm to the five Green Belt purposes is another, and a competent assessment addresses each purpose separately rather than treating them as a block.

Check unrestricted sprawl of large built-up areas: is the site on the edge of a large settlement and does the proposal extend built form outwards? Prevent neighbouring towns merging: how wide is the gap and what proportion of it does the proposal occupy? Safeguard the countryside from encroachment: does the proposal introduce built form or domestic paraphernalia into open countryside? Preserve the setting and special character of historic towns: is the site in a relevant setting at all? Assist urban regeneration: this one rarely turns on an individual application and can usually be dealt with in a sentence.

Be willing to conclude that a purpose is not engaged. An assessment that finds harm to all five purposes on a garden extension reads as unserious and damages the credibility of the rest of the document.

Where a proposal is not inappropriate development

Before arguing very special circumstances, check whether the proposal falls within one of the exceptions in national policy, because an exception avoids the harm by definition and changes the entire structure of the case.

The exceptions cover buildings for agriculture and forestry, facilities for outdoor sport and recreation, cemeteries and burial grounds and allotments where openness is preserved and purposes are not conflicted with, extensions or alterations that are not disproportionate additions over and above the size of the original building, replacement buildings in the same use that are not materially larger, limited infilling in villages, limited affordable housing for local community needs, and limited infilling or redevelopment of previously developed land in defined circumstances.

Several of those carry an openness condition built into the exception itself, and the openness assessment therefore does double duty. Structure the statement so that the openness analysis appears once and is then applied to the exception test, rather than repeating it under a second heading.

Where the exception applies, say so clearly and early. Many refusals proceed on the assumption that development in the Green Belt is inappropriate unless the applicant proves otherwise, and the wider guidance on how openness is assessed helps in framing that argument.

Building the very special circumstances case

Where the proposal is inappropriate, substantial weight must be given to the harm, and very special circumstances exist only where that harm and any other harm are clearly outweighed by other considerations.

Two drafting disciplines help. First, identify and weigh every harm, including openness, purposes, landscape, highways and heritage, rather than dealing only with the Green Belt point. An inspector who finds an unaddressed harm will assume it was avoided deliberately. Second, make each benefit specific and secured, with a mechanism and a weight attached, and be honest where a benefit is modest.

Benefits that have carried weight in decisions include the removal of existing unsightly development, biodiversity gain well above the mandatory minimum, delivery of specialist accommodation for an identified need, and the resolution of a long-standing enforcement problem. Benefits that rarely carry weight on their own include ordinary market housing, private need and the personal circumstances of the applicant, although personal circumstances can tip a finely balanced case and can be secured by a personal condition.

The pattern of decisions on appeal is instructive rather than binding. Reading what inspectors have said about very special circumstances in Green Belt refusals is a better use of an afternoon than redrafting the same paragraph.

Presenting the balance clearly for the officer

Give the balance its own section with a heading the officer can find. Set out the finding on inappropriateness, the finding on openness with its spatial and visual elements, the findings on each purpose, every other harm with its weight, every benefit with its weight and its securing mechanism, and the conclusion.

Write it so it can be lifted into a delegated report. Officers are working to a deadline, and a passage they can quote saves them an hour. That is a practical observation about how decisions get written.

Keep the Planning Statement consistent with the drawings and the other supporting documents. Where the landscape evidence says the site is well screened and the openness section says the development will be prominent, someone will notice.

PlanScope drafts a Planning Statement structured to UK planning policy with the Green Belt tests set out in sequence, flagging the site-specific measurements for you to supply. Enter your postcode on PlanScope to see which reports your site is likely to need.

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.