BREAKING NEWS: Major Biodiversity Net Gain (BNG) Exemptions Announced for Small Sites (0.2ha)
The landscape of mandatory Biodiversity Net Gain (BNG) has just shifted significantly.
In a major announcement on December 16, 2025, as part of broader planning reforms aimed at boosting housebuilding, the UK government confirmed critical changes to BNG regulations. These changes are designed to reduce the regulatory burden on small developers and SME builders.
If you are involved in land development, planning, or architecture, understanding these new BNG exemptions is vital for your upcoming projects. Here is a breakdown of the government’s latest announcement and what it means for your compliance obligations.
The Headline Change: The New 0.2 Hectare Exemption
The most significant aspect of the Written Ministerial Statement is the confirmation of a new, blanket exemption threshold.
The Housing Secretary has confirmed that the government will exempt smaller developments of up to 0.2 hectares from mandatory Biodiversity Net Gain.
Up until now, many small sites—unless qualifying for specific "de minimis" or self-build exemptions—faced the same 10% net gain requirement as larger developments, often requiring complex ecological surveys and the use of the Small Sites Metric (SSM).
This new 0.2ha BNG rule is intended to streamline the planning process for the smallest housing projects, removing a significant cost and time barrier for SME developers working on minor sites.
Beyond 0.2ha: Proposed Brownfield Exemptions
The reforms do not stop at the smallest sites. The announcement also revealed that the Department for Environment, Food and Rural Affairs (Defra) will "consult rapidly" on further targeted exemptions.
The government is proposing an additional BNG exemption for residential brownfield development. They are currently testing the definitions and proposing a site size threshold of up to 2.5 hectares for this exemption.
Note: Unlike the 0.2ha rule, the brownfield exemption is currently just a proposal subject to consultation. It is not yet confirmed policy.
Simplified Requirements for Medium Sites
For sites that do not fall under the new 0.2ha exemption, the government has also signalled its intention to introduce a suite of "simplified requirements" to improve BNG implementation on remaining small and medium sites.
While details are scarce, this likely points to future reforms of the Small Sites Metric and potentially reduced monitoring periods for developments that are just above the new exemption threshold.
Clarification: The New Rule vs. The "Self-Build" Exemption
It is crucial for developers not to confuse this new announcement with existing rules.
The current Self-Build and Custom Housebuilding exemption (in force since early 2024) remains separate. That applies to sites under 0.5 hectares with no more than 9 dwellings, provided they are exclusively for self-build.
The new announcement is a broader, area-based exemption for any development under 0.2 hectares, regardless of whether it is self-build or speculative housing.
When Do the New BNG Rules Come into Force?
This is the most critical question for developers with current pipeline projects.
While the 0.2ha exemption is now confirmed government policy, it is not yet law.
Mandatory BNG is enshrined in the Environment Act 2021. To implement this new exemption, the government must pass secondary legislation.
The government has stated that the full implementation timeline and consultation responses will be published "in the New Year" (early 2026).
Therefore, as of today, existing BNG rules still strictly apply to planning applications. Developers should watch closely for the legislative updates in early 2026 that will officially enact this change.
