Changes to biodiversity net gain that took effect on 6 August 2026 have removed many smaller developments from the mandatory BNG regime. While the headline change is a new exemption for sites of 0.2 hectares or less, its practical effect is likely to be more significant than the threshold alone suggests.

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For developers and landowners bringing forward smaller sites, the changes could remove biodiversity metric preparation, gain-plan discharge, habitat-unit purchases and long-term management obligations. But whether a scheme benefits depends on more than simply being a “small development”.

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For planning applications made on or after 6 August, development on a site no larger than 0.2 hectares is exempt from mandatory BNG unless it affects onsite priority habitat. Importantly, the threshold is based principally on the red-line site area rather than the number of homes proposed, meaning the exemption can apply across residential and commercial development.

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The Government estimates that this change will remove around half of residential permissions previously subject to mandatory BNG, while reducing demand for offsite biodiversity units by approximately 10%. For individual schemes, particularly small infill developments, the effect could be a meaningful reduction in both cost and programme risk.

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The exemption is not, however, a general relaxation of ecological planning requirements. Priority habitat must still be considered, while protected species, designated sites, development plan policies and the NPPF mitigation hierarchy continue to apply. A scheme may therefore be exempt from the statutory 10% BNG requirement while still requiring ecological assessment and mitigation as part of the planning application.

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This distinction makes early analysis important. Applicants cannot safely assume that a site qualifies simply because its red-line area falls below 0.2 hectares. The presence of priority habitat needs to be established and the application boundary must properly reflect the development proposed. The exemption creates an obvious commercial incentive to understand site area accurately, but not to manipulate a red-line boundary simply to fall beneath the threshold.

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There are other changes too. Temporary development can now be exempt where the entire development is temporary, reinstatement is required and the total permitted period does not exceed five years, subject again to the priority-habitat safeguard. Conversely, the previous exemption for qualifying self-build and custom-build development has been removed, meaning larger self-build schemes may now face BNG requirements and costs that would previously have been avoided.

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For non-major development that remains subject to BNG, the biodiversity gain hierarchy has also become more flexible. Onsite habitat creation or enhancement and registered offsite gains now have equal preference, with statutory credits remaining the final option. For constrained minor sites, this could make an offsite solution commercially and practically more attractive than attempting to accommodate biodiversity units within an already tight layout.

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That flexibility should not be confused with the separate NPPF mitigation hierarchy. Significant ecological harm must still be avoided or mitigated before compensation is considered. Purchasing offsite units does not provide a route around ecological constraints that should properly influence the design of the development itself.

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Perhaps the most immediate strategic issue concerns applications already in the system. The new exemptions generally apply only to applications made on or after 6 August. An application submitted before that date does not gain the exemption simply because it remains undetermined.

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For some applicants, withdrawing and resubmitting could therefore be worth considering where a live application would now fall within the 0.2-hectare exemption. But the BNG saving needs to be weighed against the consequences of restarting the planning process, including delay, additional costs, validation requirements and any change in the policy or decision-making context. Transitional provisions and relevant section 73 applications also require particular care.

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The reforms should make many smaller developments simpler and cheaper to bring through the planning process, but the important planning judgement is not simply whether a site looks small enough to qualify.

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Application date, red-line area and habitat status now need to be established at the outset. For existing applications, there is an additional question: whether the potential BNG saving is significant enough to justify changing planning strategy.

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For smaller development, checking the exemption position should now come before commissioning a full BNG strategy. In some cases, that relatively simple exercise could remove a significant amount of unnecessary cost and process.