Biodiversity Net Gain Rules Changed in August 2026: What Developers Need to Know
28th August 2026
Biodiversity Net Gain Rules Changed in August 2026: What Developers Need to Know
Changes to England’s Biodiversity Net Gain rules came into force on 6 August 2026, affecting which developments are exempt and giving some smaller developments more flexibility over how they deliver their required biodiversity gain.
For developers, landowners and planning teams, the changes are worth understanding before submitting a new planning application. The rules do not simply remove BNG requirements for small development. Instead, they introduce new exemptions in some circumstances while removing others.
Here is what has changed.
A new exemption for developments of 0.2 hectares or less
Planning applications made on or after 6 August 2026 can be exempt from mandatory Biodiversity Net Gain where the development site is 0.2 hectares or smaller.
The site area is based on the land within the red line planning application boundary.
There is an important exception. The exemption does not apply where the development would impact an on-site priority habitat. In those circumstances, mandatory BNG may still apply even where the overall site is 0.2 hectares or less.
For small development sites, this is one of the most significant changes to the BNG framework since the requirements were introduced.
The self-build and custom-build exemption has been removed
Previously, qualifying self-build and custom-build housing could be exempt from mandatory BNG.
For new planning applications made on or after 6 August 2026, that exemption no longer applies.
This means a self-build or custom-build scheme may now need to deliver the required Biodiversity Net Gain unless another exemption applies, such as the new 0.2-hectare site exemption.
Applications submitted before 6 August are subject to the previous arrangements, and transitional provisions also apply to certain variations of existing permissions.
New exemption for short-term temporary development
A new exemption has also been introduced for some temporary developments.
For planning applications made from 6 August 2026, mandatory BNG does not apply where:
- the whole development is temporary
- planning permission is granted for no more than five years
- the development does not impact an on-site priority habitat
The exemption is therefore aimed at genuinely short-term development rather than permanent development operating under a temporary arrangement.
Minor developments have more flexibility over off-site BNG
The Biodiversity Gain Hierarchy has also changed for non-major, or minor, development.
For new applications made from 6 August 2026, qualifying minor developments no longer have to prioritise creating or enhancing habitat on the development site before considering registered off-site biodiversity gains.
On-site habitat creation, on-site enhancement and registered off-site gains are now treated at the same level within this part of the hierarchy.
In practical terms, this can allow a small developer to choose an appropriate off-site solution without first having to demonstrate why the necessary BNG cannot be delivered on site.
Government statutory biodiversity credits remain the final option where suitable on-site or off-site delivery cannot be achieved.
The Biodiversity Gain Plan template was also updated on 6 August to reflect this change. Minor developments that are not otherwise exempt do not need to justify why they are using off-site biodiversity units.
What has not changed?
The central requirement remains the same for developments that are within scope.
Most qualifying developments in England must still deliver at least 10% Biodiversity Net Gain, calculated using the statutory biodiversity metric.
Where significant habitat is created or enhanced to deliver BNG, it will generally need to be secured and managed for at least 30 years.
The existing de minimis exemption also remains. Development may be exempt where it affects less than 25m² of on-site habitat and less than 5 metres of linear habitat such as hedgerow, provided priority habitat is not affected.
Do the new rules apply to existing planning applications?
Generally, no.
The August changes were introduced with transitional arrangements and apply primarily to new planning applications submitted from 6 August 2026.
Applications and permissions already progressing under the earlier framework generally remain subject to the previous BNG rules. There are also specific arrangements for Section 73 applications and variations of permissions, so the history of an individual application can matter.
Developers should therefore check which version of the rules applies rather than assuming the latest exemptions automatically apply to an existing project.
What do the changes mean for developers?
For some smaller schemes, the new rules should reduce the amount of BNG work required at planning stage.
The 0.2-hectare exemption removes many very small sites from mandatory BNG altogether, while the revised hierarchy gives other minor developments more freedom to use registered off-site BNG units where that is the most practical solution.
At the same time, the removal of the self-build exemption means some projects that previously fell outside the BNG regime may now need to address it.
Early assessment remains useful. Establishing whether an exemption applies, understanding the site's existing habitats and calculating any likely unit requirement can reduce uncertainty later in the planning process.
Further BNG changes are coming
The Government has confirmed that further reforms are planned, although these have not yet come into force.
Proposals include:
- an exemption for development whose main purpose is conserving or enhancing biodiversity
- a targeted exemption for certain improvements to parks, playing fields and public gardens
- changes to the statutory biodiversity metric, including how spatial risk is assessed
- further changes concerning brownfield and Open Mosaic Habitat
The timetable for these measures has not yet been confirmed.
Separately, mandatory Biodiversity Net Gain will be extended to nationally significant infrastructure projects from 2 November 2026. New NSIP applications submitted from that date will generally need to deliver at least 10% BNG under a separate framework.
Need off-site BNG units?
Where a development remains subject to BNG and the requirement cannot or does not need to be delivered entirely on site, registered off-site biodiversity units can form part of the solution.
Biodiversity & Habitat Solutions provides off-site BNG units from Chalksole Farm in Kent, with options available for developments requiring registered biodiversity gains.