Which developments will be subject to biodiversity net gain?

The Government is considering exempting the following types of development:

• Where impact is below a ‘de minimis’ threshold, where there would be negligible or minimal impact to low or medium distinctiveness habitats only. No gain will be required where the baseline biodiversity score is zero in any event. The consultation covers the appropriate threshold for area-based habitat and linear habitat (hedgerows, watercourses and lines of trees).
• Householder and change of use applications
• Creation of biodiversity net gain sites
• Self-build and custom housebuilding (at present the Government does not see a clear need for exemptions, but recognises the sensitivity of such schemes to costs).

After consideration, the Government is not proposing to exempt low value, brownfield sites, temporary permissions, certain sites where permitted development rights do not apply or developments within statutory designated sites for nature conservation (e.g. SSSI, SACs, SPAs and Marine Conservation Zones).

A simplified biodiversity metric is proposed for small sites (less than 10 dwellings or 0.5 hectares for other developments), unless priority or protected habitats are present. The Government is consulting upon whether a transition period of longer than 2 years should apply for minor development.

For NSIPs, the Government proposes to introduce net gain from November 2025 for sites outside the marine environment. It is consulting on specific exemptions and a ‘core’ statement for NSIPs for biodiversity net gain policy, to be integrated subsequently into National Policy Statements as they are revised.

Special rules will apply to irreplaceable habitats, defined in the NPPF as habitats which are very difficult or take a significant time to restore or replace once destroyed, taking account of their age, uniqueness, species diversity or rarity. They include ancient woodland, ancient or veteran trees, blanket bog, limestone pavement, salt marsh, sand dunes and lowland fen. In place of the 10% gain, bespoke compensation would be agreed for areas of these habitats and the BNG Plan would explain how adverse effects have been minimised. The Government proposes to list ‘irreplaceable’ habitats and provide principles to guide bespoke compensation.