Understanding the new 20% housing land supply buffer and the tilted balance

The changes to the National Planning Policy Framework that took effect on 1 July 2026 introduced one of the most significant amendments to five-year housing land supply in recent years. While much of the discussion has focused on revised housing targets and plan-making, paragraph 78(c) has potentially far-reaching implications for planning applications and appeals by changing the circumstances in which a 20% buffer must be applied.

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For some authorities, the consequence may be immediate. A council that was previously able to demonstrate a five-year housing land supply may now find that the additional buffer places it below the required threshold. That, in turn, raises the prospect of the tilted balance being engaged under paragraph 11(d), fundamentally changing the policy context in which housing applications are determined.

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Understanding how these provisions interact is therefore likely to become increasingly important for developers, landowners and planning practitioners.

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Paragraph 78(c) introduces a new route to applying a 20% buffer. Previously, the principal trigger was poor housing delivery, measured through the Housing Delivery Test. The new provision is different. It applies where an authority's adopted housing requirement is 80% or less of its latest standard method local housing need, provided the relevant Local Plan falls within the transitional circumstances set out in the Framework.

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Importantly, the policy does not replace the adopted housing requirement with the latest standard method figure. The adopted requirement remains the basis for calculating five-year housing land supply. Instead, the latest standard method assessment acts as a benchmark. Where the adopted requirement falls sufficiently below current housing need, the authority must apply a larger buffer when demonstrating its five-year supply.

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That distinction is easily overlooked but is central to understanding the policy. The Government has not rewritten recently adopted Local Plans through paragraph 78(c). Rather, it has increased the level of confidence that authorities with comparatively low housing requirements must demonstrate when identifying deliverable sites.

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The practical effect, however, may be similar. The purpose of the buffer is to bring additional supply forward from later in the plan period into the immediate five-year calculation. An authority already operating close to the five-year threshold may therefore find that a change in the applicable buffer is enough to move it below the required supply without any reduction in the number of deliverable sites.

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This is where the policy becomes commercially significant.

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The ability to demonstrate a five-year housing land supply remains one of the key considerations in residential planning decisions. Where an authority cannot demonstrate the required supply, paragraph 11(d) of the Framework may become engaged. Commonly referred to as the tilted balance, this requires planning permission to be granted unless the adverse impacts of development would significantly and demonstrably outweigh the benefits, or specific policies in the Framework provide a clear reason for refusal.

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The tilted balance is frequently misunderstood. It is not a presumption that every housing application should succeed, nor does it remove the statutory primacy of the development plan. Site-specific constraints, Green Belt policy, heritage assets, flood risk, landscape impacts, design quality and infrastructure considerations all continue to carry substantial weight where relevant.

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What changes is the planning balance itself. Once the policies most important to determining an application are treated as out of date because the authority cannot demonstrate the required housing land supply, greater weight is often afforded to the benefits of delivering new homes. The result can be a materially different outcome, particularly on sites that are sustainable but previously sat in a more marginal planning position.

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The transitional arrangements are equally important. The Government recognised that many Local Plans were progressing through examination under earlier versions of the National Planning Policy Framework and therefore allowed those plans to continue under the previous policy regime. Paragraph 78(c) effectively bridges that transition. Authorities were not required to revisit emerging Local Plans simply because national policy changed, but from 1 July 2026 they are expected to demonstrate a more robust five-year supply where their adopted housing requirement sits significantly below current local housing need.

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That reflects a broader policy objective. The Government has sought to preserve certainty in plan-making while ensuring that decision-making reflects contemporary housing need. Authorities with relatively low adopted housing requirements are therefore not prevented from relying on their Local Plans, but they are expected to demonstrate greater resilience in their short-term housing supply.

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The immediate implication is that housing land supply calculations are likely to become a renewed focus of planning applications and appeals. Authorities that published five-year housing land supply statements before July 2026 may need to revisit those assessments to establish whether the revised buffer now applies. Equally, applicants should not assume that a published supply position remains correct simply because it is relatively recent.

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For developers and landowners, this means housing land supply should once again become a central part of site appraisal. Sites that previously appeared difficult to promote may warrant reconsideration if an authority's supply position has weakened under the revised Framework. Equally, applicants should carefully scrutinise the evidence underpinning any claimed five-year supply, including the housing requirement being used, whether paragraph 78(c) applies and whether the identified sites genuinely satisfy the definition of deliverable.

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Appeals are also likely to become more technically contested. The debate may no longer centre solely on whether a council has five years' supply, but whether it has applied the correct buffer in the first place. Questions about transitional status, housing requirements and deliverability are therefore likely to feature more prominently than they have in recent years.

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Ultimately, paragraph 78(c) represents more than a technical amendment to housing land supply calculations. It changes the threshold that some authorities must meet before they can demonstrate a compliant five-year supply and, in doing so, may alter the planning balance for residential development. While the full implications will emerge only as planning decisions and appeal decisions begin to interpret the new policy, it is already clear that developers, landowners and planning authorities alike will need to pay much closer attention to the interaction between housing land supply, the new buffer and the tilted balance.