Biodiversity Net Gain for Small Sites in 2026: What Applies Now and What Changes in July

Biodiversity Net Gain is still part of the planning baseline for most development in England. The current requirement remains in force, and developers should continue to follow the existing BNG legislation and guidance unless and until the new 2026 changes are brought into effect through secondary legislation.

That distinction matters. A lot of recent commentary has treated the April 2026 government announcements as though they are already fully in force. They are not. The April 2026 government response sets out a package of reforms intended to make BNG easier to operate for minor, medium and brownfield development, but many of those changes are still expected to come forward later in 2026, subject to parliamentary scheduling.

For small-site applicants, the real question in 2026 is therefore twofold: what applies today, and what is likely to change from summer 2026 onwards. In practice, both matter because they affect how schemes are scoped, costed and programmed now.

What applies now?

At present, the existing mandatory BNG regime remains in place. Developers still need to consider whether a scheme is exempt, whether the small sites metric can be used, and how the proposal will achieve at least 10% biodiversity net gain where BNG applies. Government guidance continues to say that developers should use the current rules and guidance until the proposed reforms are implemented.

The current exemption framework still includes developments below the de minimis threshold, householder applications, and certain self-build and custom-build applications, among others. Existing guidance also continues to apply to pre-12 February 2024 applications and other exempt categories.

For smaller developments that are not exempt, the small sites metric remains an important route. Government guidance says that, where a development qualifies to use the Small Sites Metric, it can use that simpler tool rather than the full statutory biodiversity metric. Guidance also says that, except for small developments using the Small Sites Metric, a developer or land manager should hire a competent person such as an ecologist to use the tool and advise on the calculations.

The practical implication is straightforward: for a live project being prepared now, BNG still needs to be treated as a current design and application issue, not a future reform issue. Applicants should not assume that the April 2026 announcements automatically remove or relax today’s requirements.

What is expected to change from July 2026?

The most significant proposed change for small sites is a new area-based exemption. The April 2026 government response says government intends to introduce an exemption for developments with a red-line boundary of 0.2 hectares or below, except where the development impacts on-site priority habitat. Government says it expects this to exempt around 50% of residential planning permissions that currently fall within mandatory BNG. The intention is for this change to come into force before 31 July 2026, subject to parliamentary scheduling.

That is a major shift. The question for many smaller residential schemes will no longer simply be whether they fall within the old de minimis thresholds, but whether they are within the new 0.2 hectare threshold once the legislation is in force. In practice, that could materially reduce the number of small residential developments needing to go through the full BNG process.

At the same time, government says it intends to remove the current self-build and custom-build exemption as part of the same reform package. The reasoning is that many of those schemes are expected to fall within the new 0.2 hectare exemption instead. Until the change takes effect, however, the current exemption guidance still applies.

Government also says it intends to create a new exemption for temporary developments where the whole development is granted planning permission for five years or less. It further says it expects to bring forward exemptions later in 2026 for developments whose primary objective is to conserve or enhance biodiversity, along with certain works relating to parks, playing fields and public gardens.

What changes for non-exempt minor development?

For minor development that remains within the BNG regime, the government response introduces a potentially important shift in the gain hierarchy. Government says it will amend the approach so that, for non-exempt minor development, off-site biodiversity gains will have the same preference as on-site habitat creation and enhancement.

That is a more practical change than it may first appear. Under the current system, small urban schemes can struggle to deliver meaningful on-site gains without compromising layout efficiency, access or unit numbers. Giving off-site options equal standing for minor development should make it easier for smaller applicants to use the off-site market without feeling that on-site enhancement must always be pushed further first.

This does not mean on-site biodiversity stops mattering. Site layout, retention of habitat and the overall planning strategy will still be important. But for constrained minor sites, the change should make the route to compliance more commercially workable.

What is happening on brownfield sites?

Brownfield remains one of the most sensitive parts of the BNG framework, particularly where urban sites contain open mosaic habitat or other higher-value ecological features. The April 2026 government response says government will update the metric definition, guidance and condition assessment for open mosaic habitat, and will also explore changes such as proxy habitats and a potential new medium-distinctiveness urban habitat category. These updates are expected later in 2026.

Separately, there is now a live consultation on a possible targeted exemption for brownfield residential development, published on 15 April 2026. That consultation asks whether an exemption should be introduced, what size thresholds should apply, and how brownfield residential development should be defined. The consultation closes on 10 June 2026.

For now, though, this remains a proposal under consultation rather than a live exemption. That means brownfield residential developers should not assume that a new carve-out already exists. The current BNG requirement still applies unless an existing exemption is available.

Will the metric process become easier?

Government’s April 2026 response also points toward a more streamlined metric process, but here the timing is important. It says the statutory metric user guides and tools will be updated and republished later in 2026, subject to parliamentary scheduling. It also says there will be a digital metric service in future, but the timetable for that may not align with the next changes to the current tools, which may initially still be progressed through the Excel-based tools.

So while the direction of travel is clearly towards simplification, applicants should not yet assume a fully digitised process this summer. For live applications, the safer assumption is that the current toolset and current guidance still need to be worked with unless and until updated versions are formally published.

What does this mean in practice for small-site applicants?

The key issue is timing. For schemes being submitted now, the existing regime still applies. For schemes expected to be submitted after the summer, there may be value in checking whether the proposed 0.2 hectare exemption, the revised hierarchy for minor development, or the removal of the self-build exemption could alter the route through the system.

That does not mean every applicant should simply wait. The better approach is to test the scheme against both positions: first, whether it works under the current rules; and second, whether an announced reform is likely to change the strategy if the application timing moves into the second half of 2026. For some sites, that may affect whether BNG work is commissioned now, whether an off-site solution is built into viability, or whether a scheme is accelerated to avoid uncertainty.

Conclusion

Biodiversity Net Gain for small sites in 2026 is now a moving target. The current regime remains in force, but the April 2026 reform package points to a more flexible system for smaller developments, especially through the proposed 0.2 hectare exemption and the revised approach to off-site delivery for minor schemes. The question is not whether BNG still matters for small sites. It does. The more useful question is whether the scheme is being prepared under the rules that apply today, or the ones likely to apply after summer 2026.

The April 2026 government response sets out a package of reforms intended to make BNG easier to operate for minor, medium and brownfield development.