Mandatory biodiversity net gain (BNG) changed again on 6 August 2026. The changes are important because they alter which smaller schemes fall within the statutory BNG regime, and they remove an exemption that some self-build and custom-build projects had been relying on.
The practical point is simple: a project team should now check the application date, the red-line site area and whether priority habitat is affected before assuming that BNG applies — or that it does not.
What changed on 6 August 2026?
The most significant new exemption applies to planning applications where the development site is no larger than 0.2 hectares. For applications made on or after 6 August 2026, mandatory BNG does not apply where the site area within the red-line boundary is 0.2 hectares or below, provided the development does not impact on-site priority habitat.
This is a site-area test, not a dwelling-number test. The red-line boundary submitted with the planning application is therefore an important starting point when deciding whether the exemption is available.
A second exemption now applies to development that is wholly temporary and permitted for five years or less, again provided that priority habitat is not affected. The government guidance also makes clear that the temporary-development exemption cannot be used to string together successive permissions so that the same temporary development effectively continues beyond five years.
Self-build and custom-build projects need particular care
The former self-build and custom-build BNG exemption no longer applies to new planning applications made on or after 6 August 2026. That change is easy to miss because projects already in the system can be treated differently.
If a qualifying self-build or custom-build application was made before 6 August 2026, the previous exemption can still be relevant. The government guidance also sets out transitional treatment for some later variations of permissions that were already exempt. It is therefore worth checking the history of the permission rather than applying the new rules to an older project without qualification.
The 0.2-hectare exemption is not the same as the de minimis exemption
There are now two different small-scale concepts in the BNG rules and they should not be confused.
The new 0.2-hectare exemption looks at the area of the development site within the red-line boundary. The separate de minimis exemption looks at the amount of habitat affected: less than 25 square metres of on-site habitat and less than 5 metres of on-site linear habitat, with priority-habitat safeguards applying.
A project may be small in one sense but not the other. That is why a quick review of the planning boundary and ecological context is more reliable than relying on a general description such as “small site”.
Priority habitat remains a key qualification
The new 0.2-hectare and temporary-development exemptions do not apply where the development impacts on-site priority habitat. The de minimis exemption also carries a priority-habitat safeguard.
For developers, this means that the size threshold should not become a reason to skip early ecological consideration. A small red-line area can still contain or affect habitat that changes the BNG position, and that is best identified before the planning strategy is fixed.
What should developers check now?
For planning applications being prepared now, we would check four things at the outset:
- Application date: the new exemptions apply to relevant applications made on or after 6 August 2026.
- Red-line area: confirm the actual site area rather than relying on an approximate development footprint.
- Priority habitat: establish whether any on-site priority habitat could be affected.
- Permission history: section 73 applications and older permissions can have transitional treatment, so the original consent matters.
If BNG still applies, the statutory biodiversity metric remains the mechanism for calculating pre-development and post-development biodiversity value. Early use of the metric can help test different layouts and habitat strategies before design decisions become expensive to change.
Why this matters at planning stage
The 2026 changes remove mandatory BNG from a meaningful number of genuinely small developments, but they do not remove the need to understand the site’s ecological constraints. Local planning policy, protected species, designated sites, priority habitats and other ecological requirements continue to sit outside the narrow question of whether the statutory BNG condition applies.
For that reason, we would treat the exemption as a scope decision rather than as a substitute for ecological due diligence.
If you are preparing a planning application and are unsure whether BNG applies, EnviroSolution can review the site and planning context alongside the wider ecology requirements. Project details and plans can also be sent through the structured enquiry builder.
Major infrastructure enters mandatory BNG from 2 November 2026
The 2026 changes are not limited to small planning applications. From 2 November 2026, biodiversity net gain becomes mandatory for nationally significant infrastructure projects (NSIPs) in England where the development consent order application is made on or after that date.
Those projects will need to deliver at least 10% biodiversity net gain and follow the biodiversity gain statement relevant to the project type. The August 2026 developer guidance also explains how on-site and off-site gains, temporary impacts, the statutory metric and biodiversity gain plans fit into the NSIP process.
For infrastructure promoters, the practical implication is that ecological baseline work and the biodiversity strategy need to be integrated into DCO preparation early enough to influence design rather than being treated as a late-stage compliance exercise.