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Biodiversity Net Gain..... what you need to know.

Under the Environment Act 2021, starting in November 2023, developers in England will be required to deliver at least 10% “Biodiversity Net Gain” (BNG) when building new housing, industrial units or commercial developments to ensure delivery of a positive benefit to nature. BNG will be measured using Defra’s biodiversity metric and habitats will need to be secured for at least 30 years. There will also be a legal duty for public bodies to protect and enhance biodiversity. New biodiversity reporting will be required by local authorities and spatial strategies named: Local Nature Recovery Strategies, will be made mandatory for new developments.


There are exemptions for certain developments, including: permitted development, certain householder applications, development of specific types of ownership that may be disproportionately impacted by the requirement (such as residential self-build), and brownfield sites that meet specific criteria.


To meet the added 10% requirement, the BNG Metric will be required to calculate the biodiversity value of the site. BNG can be achieved through On-site, Off-site and, as a last resort, Statutory (Biodiversity) Credits.




All developments:


Must try to avoid loss of habitat if this cannot be done, habitat must be created either on-site or off-site.

On-site means on the land the development work is on. Off-site is either owned land away from the development site, or units that have been bought from a land manager.

If on-site or off-site land cannot be used, statutory credits must be bought from the government. Evidence must be provided for using this option. This must be a last resort. The government will invest in habitat creation elsewhere in England.

All 3 options may be combined to make up the BNG. This must be discussed with an ecologist, as proof will be required as to why one option alone cannot be used. Approval will be required from the local planning authority before building can commence.



Large scale developments:


Large sites will be subject to BNG legislation from the start of November 2023.

BNG metric will be used to calculate the net gain of biodiversity from the project, with an addition of 10% being required (110% biodiversity from initial values prior to start of development).

Small scale or individual developments:


Small sites will be subject to a longer transition period, with BNG legislation not mandatory until April 2024.

Exemptions have been made for developments such as self-build homes to ensure the new legislation is targeted at larger developers that would cause the most biodiversity loss.

Small sites are also subject to an alternative metric for calculating BNG.




The Local Planning Authorities will have to approve a Biodiversity Net Gain plan for development work before it can start.

The biodiversity metric is a habitat-based approach used to assess an area’s value to wildlife. The metric uses habitat features to calculate a biodiversity value. It can be used to calculate how a development, or a change in land management, will change the biodiversity value of a site. For example, building houses, planting a woodland or sowing a wildflower meadow.

It can also be used to assess the biodiversity unit value of an area of land, demonstrate biodiversity net gains or losses in a consistent way, measure and account for direct impacts on biodiversity and compare proposals for a site - such as creating or enhancing habitat on-site or off-site.

The metric calculates the values as ‘biodiversity units’. Biodiversity units are calculated using the size of the habitat, its quality and location. Habitats can encompass both land and intertidal areas. Existing habitats and planned new habitats created during development or land changed will both be assessed.


The metric should be used with ecological advice.


If you need advice on a project that needs Biodiversity Net Gain calculations please get in touch with enims today, we are more than happy to talk you through what you may need to consider and how we can support you on delivering Biodiversity Net Gain to your project.






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