Biodiversity Net Gain rules have changed: what smaller development sites need to know
- TP Editorial Team
- 3 hours ago
- 3 min read
Changes to England’s Biodiversity Net Gain requirements took effect on 6 August 2026. They should simplify matters for some smaller developments, but they also remove an exemption previously available to self-build and custom-build schemes.
Biodiversity Net Gain, usually referred to as BNG, generally requires qualifying development to achieve at least a 10% increase in biodiversity value. Although the detailed Biodiversity Gain Plan is normally dealt with after permission has been granted, BNG should be considered from the beginning because it can affect site layout, landscaping, viability and the amount of developable land.
The new 0.2-hectare exemption
Planning applications made on or after 6 August 2026 may be exempt from mandatory BNG where the application site is no larger than 0.2 hectares and the development does not affect priority habitat.
This is based on the total area inside the application’s red-line boundary, rather than simply the footprint of the proposed buildings. Care is therefore needed when drawing the application boundary, particularly where access, landscaping or drainage land is required.
The exemption does not remove the wider need to consider ecology. Protected species, trees, hedgerows and local planning policies may still require surveys, mitigation or biodiversity enhancements.
A change for self-build and custom-build projects
The previous BNG exemption for qualifying self-build and custom-build schemes of up to nine dwellings on sites no larger than 0.5 hectares has been removed for applications made from 6 August.
A self-build scheme may still benefit from the new exemption if its entire application site is no larger than 0.2 hectares and no priority habitat is affected. Schemes above that threshold will generally need to address BNG in the same way as other residential development.
This makes early site assessment particularly important for custom-build plots and small groups of bespoke homes.
Greater flexibility for minor development
The BNG hierarchy has also been amended for non-major development. Onsite habitat enhancement, onsite habitat creation and registered offsite biodiversity gains now sit at the same level of preference.
This should give smaller schemes more flexibility where trying to provide all the required habitat within the development would produce a cramped layout, compromise good design or result in habitat that is difficult to maintain.
Statutory biodiversity credits remain the final option. The changes also do not remove the need to avoid or mitigate harm to important habitats.
Temporary development
Development granted wholly on a temporary basis for no more than five years may also be exempt, provided it does not affect priority habitat and the permission requires the development to be removed and the land reinstated.
What applicants should do
For smaller developments, four early questions are now particularly useful:
Is the entire red-line site no larger than 0.2 hectares?
Could any priority habitat be affected?
Is the proposal genuinely exempt, and can that be demonstrated?
If BNG applies, should it be delivered onsite, offsite or through a combination?
An exemption should not simply be assumed. Applicants who consider that BNG does not apply must explain the relevant exemption in their planning submission.
The changes may reduce cost and complexity for some small sites, while creating a new requirement for certain self-build schemes. Establishing the position before the layout is fixed will help avoid redesign, additional surveys and unexpected viability issues later.
Tyler Parkes advises on planning strategy, architecture and site design for residential and commercial development throughout the Midlands. Bringing these disciplines together at an early stage can help ensure that ecological requirements, good design and development value are considered as part of the same process.
The detailed requirements are set out in the updated government BNG planning guidance. The Planning Advisory Service also provides a useful summary of the changes effective from 6 August 2026.
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