What is biodiversity net gain?
Biodiversity net gain (BNG) is defined as an approach to development and/or land management that delivers measurable improvements for biodiversity by creating or enhancing habitats, leaving nature in a better state than beforehand.
The word ‘biodiversity’ comes from the term ‘biological diversity’. It refers to the variety of all living organisms, including animals, insects, plants, bacteria and fungi. A habitat is the area and resources used by a living organism or group of animals and plants.
BNG can be achieved on-site, off-site or through a combination of on-site and off-site measures.
Natural England has produced a biodiversity net gain blog, which provides an overview of BNG and its benefits.
Under the Environment Act 2021, all planning permissions in England (with a few exemptions) will have to deliver at least 10% biodiversity net gain. For major developments this applied from 12 February 2024 and for small sites from 2 April 2024.
Local Plan
Policy EE2 of the Local Plan requires all new development to provide a net gain in biodiversity. This means improving biodiversity by creating or enhancing habitats, leaving nature in a better state that it was before.
Biodiversity net gain guidance
Our Biodiversity Net Gain guidance (PDF) sets out how the value of biodiversity should be assessed and what evidence should be provided alongside planning applications to demonstrate an improvement in biodiversity.
The Biodiversity Metric 3.0 was launched by DEFRA in July 2021 and provides ecologists, developers, planners and other interested parties with a means of assessing changes in biodiversity value (losses or gains) brought about by development or changes in land management. The metric is a habitat-based approach to determining a proxy biodiversity value.
The Biodiversity Metric ‘rewards’ landowners who undertake work early, creating or enhancing habitats in advance, allowing them to generate more biodiversity units from their land. It also ensures all habitats are recorded, scored and valued for their importance for wildlife. If a site is cleared prior to submission of a planning application, then the baseline for such a calculation would be taken from the precleared state.
We expect planning applicants to assess BNG using the Biodiversity Metric 3.0 (or the most up to date version). The use of the Biodiversity Metric and the provision of BNG are in addition to legal obligations and should properly assess and mitigate/compensate impacts on protected and/or priority species through the development management process. It is also separate from other considerations such as open space standards and green infrastructure, although there may be inherent linkages.
The metric calculations and associated evidence must be prepared by a professional or suitably qualified/experienced ecologist.
Applicants will be expected to assess BNG in accordance with the Biodiversity Net Gain guidance, to ensure a consistent approach is taken to the consideration of information and decision making. If this guidance is not followed, and the Biodiversity Metric is not
used, we will still require all planning applications to demonstrate how they are achieving net gain in a measurable way, in accordance with the NPPF and Policy EE2 of the adopted Local Plan. However, the use of an alternative methodology may lead to significant time delays as the Council may be required to request further evidence that a net gain in biodiversity is being achieved.
Current exempt developments
The following types of development are currently exempt from the statutory BNG requirements:
- local development orders
- Simplified Planning Zones
- neighbourhood development orders
- successful enforcement appeals; and
- deemed planning permission
- permission in principle (but the subsequent technical details consent would be subject to BNG
- householder development
- development granted planning permission by a development order under Section 59
- development subject to the de minimis exemption – Development that does not impact a priority habitat and impacts less than 25 square metres of onsite habitat, or 5 metres of linear habitats such as hedgerows
- self-build and custom build development which:
- consists of no more than 9 dwellings, and
- is on a site area no larger than 0.5 hectares, and
- consists exclusively of dwellings which are self-build or custom housebuilding as defined in section 1 (A1) of the Self-build and Custom Housebuilding Act 2015
- urgent Crown development granted permission under section 293A of the Town and Country Planning Act 1990
- development of a biodiversity gain site. Development which is undertaken solely or mainly for the purpose of fulfilling, in whole or in part, the biodiversity gain condition which applies in relation to another development
- development related to the high speed railway transport network. Development forming part of, or ancillary to, the high speed railway transport network comprising connections between all or any of the places or parts of the transport network specified in section 1(2) of the High Speed Rail (Preparation) Act 2013
The government website contains further information on exemptions and what development the de minimis exemption applies to.
How is the biodiversity net gain objective of 10% calculated?
The biodiversity gain objective of at least a 10% gain is measured against the pre-development biodiversity value of the onsite habitat for the development. The objective is met if the post-development biodiversity value is exceeded by at least 10%. This 10% gain is calculated in reference to the:
- projected biodiversity value of the onsite habitat at the time the development is completed (“the post development biodiversity value of the onsite habitat”)
- biodiversity value in relation to the development of any registered offsite biodiversity gain allocated to the development; and
- biodiversity value of any biodiversity credits purchased for the development
The statutory biodiversity metric is used to calculate the pre-development and post-development biodiversity value of the development’s onsite habitat, as well as the biodiversity value for offsite biodiversity gains and biodiversity credits. It uses habitat information to generate “biodiversity units”, a proxy measure for biodiversity value. The statutory biodiversity metric data value inputs include habitat type, size, distinctiveness, condition, and its location in the local area.
The statutory biodiversity metric calculation tools must be submitted as part of the Biodiversity Gain Plan to demonstrate the statutory biodiversity metric formula has been accurately applied.
The Department for Environment, Food and Rural Affairs (DEFRA) has published guidance on the statutory biodiversity metric, including information on how it is used.