Navigating the paradox of Green Belt openness: The complete assessment framework

Stand on a bridleway where Birmingham dissolves into Worcestershire and pause. 

What strikes you first isn't the birdsong or the scent of wild grass - it's the breathing room. Sky vaults overhead, hedges crouch low, horizons stretch endlessly. This quality, this freedom from urban containment, is what planning law calls “openness of the Green Belt.”

Together with permanence, openness forms the philosophical cornerstone protecting 1.6 million hectares of English countryside from the relentless march of suburbia. Yet for all its importance, openness remains a maddeningly elusive concept - a principle everyone cites but few truly master.

Here's the paradox that keeps developers awake at night and leaves landowners perplexed: why might a modest agricultural shed fatally compromise openness, while a 40-hectare solar array is deemed to enhance it? Such outcomes reveal a sophisticated interplay between policy, perception, and professional judgment that defines contemporary practice.

The landscape has shifted seismically. 

The High Court's rigid, volumetric approach in Timmins (2014) gave way to the Court of Appeal's revolutionary Turner decision (2016), which insisted openness has both spatial and visual dimensions.

The Supreme Court's Samuel Smith ruling (2020) then cemented this, declaring openness a “broad planning judgment” rather than a calculator-led test. 

Now, with the December 2024 National Planning Policy Framework (NPPF) introducing “Grey Belt” land and the February 2025 planning practice guidance (PPG) clarifying the new Green Belt rules, we are witnessing the most significant evolution in Green Belt policy for a generation.

If you are a landowner wondering why your neighbour's scheme sailed through while your barn conversion failed, or an architect whose elegant design for a Paragraph 84 house was crushed by outdated volumetric calculations, this guide is your blueprint for understanding - and winning - the openness argument.

This comprehensive guide maps every contour of this evolving landscape. We will:

By the final page, your perspective on Green Belt openness will have evolved from outdated calculations to a sophisticated grasp of modern planning judgement, ready to confidently balance the crucial spatial and visual aspects that define today’s arguments for Green Belt developments.

Navigating policy to achieve planning permission in the Green Belt requires precision. Understanding the hierarchy of planning law and policy is the first step to building a compelling case.

Under section 38(6) of the Town and Country Planning Act 1990, planning decisions must be made in accordance with the development plan "unless material considerations indicate otherwise." 

Since local development plans invariably drape Green Belt land in highly protective policies, the challenge for applicants is almost always to demonstrate that national policy - specifically the NPPF - or other compelling factors provide a justification to override that restrictive local starting point.

Think of it as a high-stakes chess match where the local plan holds the opening advantage. Your countermove is to deploy the NPPF's exceptions and the new Grey Belt provisions with surgical precision.

Chapter 13 of the NPPF distills Green Belt protection into 19 carefully crafted paragraphs. 

For assessing openness, these are the ones that matter most:

Updated on 25 February 2025, the PPG crystallises decades of case law into a practical assessment framework. It confirms that when assessing the impact on openness, decision-makers can and should consider:

These four bullets have transformed abstract legal theory into a practical methodology now embedded in officer reports and appeal decisions across the country.

The PPG (paragraph 64-001) provides the all-important definition: Grey Belt land is a parcel of Green Belt land that does not make a "strong contribution" to at least three of the five Green Belt purposes. The guidance specifically points to purposes (a) sprawl prevention, (b) merger prevention, and (d) historic setting preservation as the key considerations.

Development on these sites must then pass the tests in NPPF paragraph 155 and must not "fundamentally undermine" the purposes of the remaining Green Belt across the plan area. Early Grey Belt appeal examples are already showing that this creates a different, more nuanced balancing exercise than the traditional, hard-line approach.

The concept of openness has been forged in the courts. Understanding this evolution is not just an academic exercise; it provides the intellectual firepower to justify a planning judgment. Inspectors reflexively cite these cases - so should you.

In what now seems like a distant era, the High Court ruled that visual impact was irrelevant when gauging openness. Green J declared it "wrong in principle to arrive at a specific conclusion as to openness by reference to visual impact." This led many local planning authorities to rely on mechanistic, cubic-metre maths alone, ignoring design quality, landscape context, or the actual lived experience of the space.

The Court of Appeal confirmed that buildings for agriculture and forestry are deemed "appropriate" development by policy and therefore, in principle, cannot be harmful to openness. The judgment separated the black-and-white policy definition from the on-the-ground experience, with Lindblom LJ clarifying: "The concept of 'openness' here means the state of being free from built development, the absence of buildings - as distinct from the absence of visual impact."

This was the ruling that changed everything. Sales LJ, in a landmark Court of Appeal judgment, declared that openness is an “open-textured” concept that goes far beyond simple maths. He established two critical limbs for its assessment:

His memorable phrase - that Green Belts exist so "the eye and the spirit should be relieved from the prospect of unrelenting urban sprawl" - eloquently shifted the focus from arithmetic to human experience.

The Supreme Court provided the final word, endorsing Turner while refining its application. Lord Carnwath established three key principles:

This ruling empowers decision-makers, giving them the latitude to weigh the different aspects of openness based on the evidence before them, rather than slavishly following a rigid formula.

In a crucial clarification for cases where harm is found, the Court of Appeal confirmed that when conducting the very special circumstances (VSC) balancing act, all harm - Green Belt harm (including to openness) and any "other harm" (e.g., to landscape character, highways, or amenity) - must be placed on the negative side of the ledger. This ensures intellectual honesty in the final planning balance.

These cases are now the reflexive language of inspectors. As we will see, Inspector K Townend’s Upper Austby Farm decision explicitly cites Turner for its spatial and visual limbs and Samuel Smith to justify her holistic judgment, concluding that a new, well-designed bungalow improves perceived openness compared to eight lawful shipping containers.

So, how do you translate these legal principles and policy bullets into a robust, evidence-based assessment? The PPG’s four-bullet test can be expanded into a practical, five-dimension model that covers every angle.

This is the quantitative core of the assessment, addressing the physical presence of development.

This addresses the Turner visual limb - what people will actually see and experience.

This captures the PPG's "degree of activity" bullet, recognising that openness is also about tranquillity.

This dimension considers the permanence of the impact.

Linked to duration, this assesses whether the land can realistically be returned to an open state.

A winning openness case is built on a foundation of irrefutable evidence, woven into a compelling narrative. Our advice? Follow this six-step process:

Establish the lawful planning position comprehensively. This is your factual starting point. Don't just assess the empty field; assess what could lawfully be there.

Run the numbers. Calculate and compare the existing versus proposed footprints, volumes, and heights. Critically, map the pattern of development to show how a proposal might consolidate a scattered, messy site into a tight, coherent form.

Move from numbers to perception. Select representative public viewpoints and produce accurate, verifiable photomontages. Never forget to consider seasonal changes and the cumulative impact alongside other developments.

Quantify the change in human presence. Compare current and proposed vehicle movements and operational characteristics. For temporary schemes, detail the permission length, restoration methodology, and financial guarantees.

This is where analysis becomes advocacy. Weave the evidence from the five dimensions into two or three tight, plain-English paragraphs. Link the numbers to the lived experience. For example, connect a reduction in footprint (spatial) to the opening up of a key view (visual).

Inspector Townend’s July 2025 decision is the perfect template. The Inspector noted the proposal was technically "inappropriate" but then concluded: "The proposal would result in the removal of the existing containers and other units. This would be beneficial to both the spatial and visual aspect of openness." This demonstrates a holistic judgment where a clear visual and spatial improvement outweighed a definitional policy breach.

The principles of openness apply universally, but their emphasis shifts depending on the type of development.

Under paragraph 154(g), PDL redevelopment is not inappropriate, provided it does not have a greater impact on openness. The bar is high, but the path is clear.

Post-Lee Valley, new buildings for agriculture are appropriate by definition. However, this is not a free pass.

Solar farms and wind turbines are often controversial. Their success on openness grounds leans heavily on the final two dimensions of our model.

This appeal decision is a masterclass in contemporary openness assessment. The Inspector, K Townend, allowed a new bungalow on the basis that it improved openness compared to the lawful baseline of eight large shipping containers.

Inspector Townend’s reasoning directly mirrors Turner ("spatial and visual aspects") and cites Samuel Smith to justify making a holistic, evidence-based planning judgment. This decision is now a powerful precedent for schemes that swap lawful, unsightly clutter for high-quality, consolidated design.

The introduction of Grey Belt land in the 2024 NPPF is the most significant strategic shift in Green Belt policy in decades. It creates a new pathway for development that avoids the high bar of very special circumstances.

The route via NPPF paragraph 155 requires satisfying four cumulative tests:

If a scheme passes these gateways, it is not inappropriate development. The crucial consequence, confirmed in Footnote 55, is that the automatic "substantial weight" against the proposal is removed. The assessment becomes a standard planning balance under section 38(6).

This policy shift creates a two-tier system for assessing openness. The key question for a Grey Belt site is not whether there is any harm to openness, but whether the harm is so significant that it "fundamentally undermines" the purpose of the remaining Green Belt in the area.

Here’s how we have applied this framework to one of our Grey Belt projects at Urbanist Architecture.

"[...], the proposed development fully accords with national and local policy, delivering a significant enhancement to the site and the character of the area. The proposal is brought forward under the grey-belt provisions of paragraph 155 of the National Planning Policy Framework (NPPF). As the scheme satisfies the requisite gateway tests for development on such land, it is not considered inappropriate development. Consequently, as clarified by the crucial guidance in footnote 55, the automatic “substantial weight” that is typically applied against development in the Green Belt under paragraph 153 is not engaged here. This distinction is fundamental to the planning balance for this site.[...]”

"[...] The assessment of any impact on openness must be guided by the principles established in binding case law. The Supreme Court’s judgment in Samuel Smith confirms that determining openness is a matter for broad planning judgment, not the application of a rigid volumetric formula. This moves the assessment away from simple arithmetic and towards a qualitative appreciation of a place. Furthermore, the Turner judgment directs that this assessment must consider both spatial and visual dimensions. It is through this sophisticated lens that this proposal must be viewed, comparing the proposed condition not with an idealised green field, but with the lawful reality of the site’s existing state as an expansive, sterile car park.[...]”

"[...] When subjected to this proper analysis, the proposal delivers a clear and demonstrable net improvement to the openness of the Green Belt. Spatially, the scheme dramatically reduces the extent of hard surfacing, consolidating the built form into a tight, inward-looking courtyard on the northern portion of the site. This paring back of the footprint restores a significant area to landscape, enhancing permeability. Visually, this translates into a profound betterment. The eye no longer perceives a sprawling expanse of asphalt and associated clutter, but rather a coherent, modest, and vernacular built edge that frames new views across a newly created pocket park. The activity on site also shifts from sporadic, commercial vehicle movements to a quieter and less intrusive domestic pattern. While the dwellings are permanent, a neutral factor on duration, the minor drawback associated with remediability is overwhelmingly outweighed by the immediate and lasting public benefits secured by the development.

"[...]These wider public benefits add considerable positive weight to the planning balance. The proposal will deliver nine new dwellings, making a valuable contribution to the borough’s housing need. Furthermore, the creation of a meadow swale will deliver a significant biodiversity net gain, while the integrated sustainable drainage system (SuDS) represents a tangible betterment for surface water management. The gifting of a new, high-quality, and publicly accessible recreational open space provides a vital new amenity for the local community where none currently exists.[...]”

"[...] In conclusion, any residual harm is extremely limited and could not be considered substantial, let alone the ‘fundamental’ harm that would be required to refuse a grey-belt scheme. The proposal does not fundamentally undermine the residual openness of the Green Belt; on the contrary, it enhances it. By replacing an impermeable slab with a permeable, landscaped, and structured development, the scheme leaves the Green Belt reading more open to the eye and spirit alike. It meets every gateway test in NPPF §155 and, as such, attracts none of the automatic sanctions of §153. Given the positive net effect on openness and the delivery of much-needed housing and green infrastructure, the application represents a clear enhancement over stagnation. In line with the principle established in Samuel Smith that planning judgment should favour such betterment, the application merits a grant of full planning permission.”

Before finalising any Green Belt planning application, it is vital to test the robustness of your case on Green Belt openness. This final review translates the complex principles of planning judgement, as required by the Supreme Court in Samuel Smith, into a practical acid test. 

The following checklist distills the entire assessment framework, from quantifying the spatial and visual aspects of openness to evidencing how you are enhancing openness, into five critical questions. 

A confident 'yes' to each is the hallmark of a defensible submission, ready to withstand scrutiny and effectively counter claims of harm to openness, whether you are arguing for very special circumstances or proceeding under the Grey Belt land policy.

The trajectory of recent case law points towards one clear conclusion, a principle that directly shapes our work as Green Belt architects and planning consultants: A demonstrable improvement to the visual and spatial aspects of openness now carries more weight than rigid, outdated assessments. 

A robust case, as confirmed by the checklist, answers the technical questions of impact; high-quality design then addresses the qualitative experience. It is the primary tool for mitigating any residual visual harm and for delivering the tangible betterment that can transform a defensible planning application into a truly compelling one.

Excellent design cannot make an inappropriate scheme appropriate, but it can be the decisive factor in borderline cases by mitigating harm and delivering tangible betterment.

Openness has travelled a remarkable journey: from the crude spreadsheets of cubic-metre calculations, through the twin limbs of Turner's spatial and visual analysis, to the sophisticated planning judgment demanded by Samuel Smith, and now to the pragmatic recalibration offered by the Grey Belt route.

This journey reflects the planning system's maturation. Today's successful practitioners - be they architects, planners, or developers - understand that assessing openness combines rigorous, forensic analysis with creative, persuasive professional judgment.

The Supreme Court confirmed openness is a planning judgment, not a legal formula. The PPG provides the assessment framework. Turner and Samuel Smith supply the intellectual architecture. Grey Belt offers new, targeted opportunities. Your role is to apply these tools with skill, integrity, and creativity.

Remember Inspector Townend's wisdom from the Upper Austby Farm appeal: sometimes, eight ugly shipping containers create far less openness than one well-designed rural dwelling. The ultimate test isn't about arithmetic - it's about the breathing space between our cities and our countryside, the visual and spiritual relief that the Green Belt exists to provide.

Master the five dimensions. Document your baseline forensically. Design with a landscape-first mentality. Argue your case with clarity and conviction. In this lies both the challenge and the immense opportunity. Those who truly understand openness hold the keys to unlocking sustainable development that can enhance the very qualities the Green Belt was created to protect.

We believe that it is in the nature of things that many hard problems are best solved when they are addressed backward. While the concept of inversion has been applied mostly to mathematics, the model is one of the most powerful in our toolkit for formulating planning and design strategies for complex planning cases.

That’s why, when we take on a Green Belt project, we begin by drafting the refusal letter we never want to receive. Setting out every policy reason the scheme could be turned down—loss of openness, landscape harm, inadequate very special circumstances—exposes the exact places where the design must work hardest. 

Each identified risk then directs a design response: volumes are set low to preserve baselines, building lines follow existing hedgerows, habitat corridors are drawn first and architecture follows, and transport measures are woven into the site layout rather than appended later.

By the time the application is submitted, objections have been pre-empted, consultees are onside, and the determination often feels inevitable. And, if it goes to appeal, our evidence is already written.

If you believe your project would benefit from an inversion-led, design-first approach built to satisfy policy tests upfront, we’d be glad to discuss how we can help.