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Biodiversity Net Gain (BNG)

Overview including exemptions

This website provides only a general summary regarding BNG. There is a range of national policy, guidance, requirements and further information on BNG, see for example the Government’s guidance:

BNG collection including guidance for developers 
Calculate biodiversity value with the statutory biodiversity metric
Statutory biodiversity metric tools and guides 

And, for example, see the Merseyside Environmental Advisory Service website

Biodiversity net gain (BNG) is a new requirement introduced by the Government to make sure new development delivers a net positive impact on the natural environment – a net gain for biodiversity. The 2021 Environment Act makes 10% biodiversity net gain (BNG) mandatory for almost all development:

• For major development – for applications submitted from 15th January 2024
• For minor development – for applications submitted from 2nd April 2024

There are special rules for development affecting irreplaceable habitats such as coastal sand dunes, ancient woodland and lowland fen.

Major development includes proposals for 10 or more homes or on a site of 0.5 hectares or more when the number of homes is unknown, non-residential development and changes of use with a floorspace of 1,000 sq. m or more, development on sites of 1 hectare or more and waste and minerals development. Proposals for major development must use the Statutory Biodiversity Metric.

Minor development is development that is not major development. Many minor development proposals can use the Small Sites Metric. However, restrictions on use apply where protected species or priority habitat and designated sites are present; applicants should make sure that it is appropriate to use the Small Sites Metric.

There are a number of exemptions to 10% mandatory BNG (you should check the details on the Government’s website). Broadly the exemptions include:

• Householder development (house extensions)
• Development granted planning permission by a development order (including permitted development)
• Development subject to the ‘de minimis ‘exemption: Development that does not impact a priority habitat and impacts less than 25 square metres (for example 5 metres by 5 metres) of onsite habitat or 5 metres of linear habitats such as hedgerows.
• Self-build and custom build development of 9 or less dwellings which is on a site which has an area no larger than 0.5 hectares, and consists exclusively of dwellings which meet the legal definition of self-build or custom housebuilding
• Development of biodiversity net gain sites
• Applications for discharge, removal or variation of a condition of a planning application which was not subject to the 10% BNG requirements.

There are specific requirements for 10% BNG, for each of:

• Habitats on the site (area habitat units)
• Hedgerows if there are already hedges on the site (hedgerow units)
• Watercourses if the site contains or is next to a watercourse (watercourse units).

A minimum of 10% BNG must be achieved for each of these which are relevant to the site – gains from habitats, hedgerows and watercourses cannot be averaged out. The gains must be specific and measurable, and either the Government’s Statutory Biodiversity Metric or Small Sites Metric must be used to show this, depending on circumstances. The type of habitats to be created or enhanced to provide 10% BNG depend mainly on the type and distinctiveness (value) of habitats already on the site.

New developments are still required to be designed and planned in ways that minimise any loss and damage to existing habitats and compensate and off-set any damage caused. They must still follow the mitigation hierarchy and Biodiversity Net Gain hierarchy. That is, impacts on biodiversity must first be:

• Avoided, then
• Minimised, then
• Compensated for on- site, then
• Only as a last resort, if compensating for losses on-site is not possible, then biodiversity losses should be offset by gains off-site.

The new BNG requirements do not change existing levels of species protection and does not replace the processes linked to protected species regimes. Ecological surveys will still be required and mitigation and enhancements for protected and notable species, such as provision of bat, bird and hedgehog boxes will still be required and will be dealt with separately from BNG provision.

The preference is for 10% BNG to be achieved within the development site. Where this cannot be achieved, off-site provision can be made, as close to the development site as possible. Off-site BNG must meet rigorous government procedural and other requirements. This on-site and off-site BNG must also be managed and maintained in line with the approved ‘gain plan’ for at least 30 years, and this will be secured through condition or legal agreement. If on-site or off-site net gain cannot be provided, the applicant must purchase national credits to achieve 10% BNG. Only habitats created outside of residential curtilage can contribute towards BNG. Any habitats provided within gardens must be assigned the ‘vegetated garden’ habitat category within the Metric.

The BNG process – what information needs to be submitted and when

Submission stage / submission of the planning application
You must meet the national validation checklist requirements and submit as part of your planning application. All of the following a) - d) are needed:

a) A statement setting out whether you think mandatory BNG applies, or whether your think that your application is exempt and why this is the case

b) A correctly completed Statutory Biodiversity Metric or Small Sites Metric (whichever applies), in excel format, and accompanying information setting out the pre-development biodiversity value of your development site.

Usually this will be the current biodiversity value, but if the site has been degraded (for example removal of trees and vegetation) this must be prior to degradation, or 30th January 2020, whichever is earliest. Where the site has been degraded as part of a previous planning permission if this was undertaken after 25 August 2023 the pre-degradation baseline should be used.

The Statutory Biodiversity Metric must be completed by a competent person, as set out nationally. There are additional competency requirements regarding watercourses.

c) A plan drawn to an identified scale, also showing the direction of North, showing onsite habitat at this date (including any irreplaceable habitat). Accompanying GIS information in MapInfo or ArcInfo shape file format would be helpful too.

d) A description of any irreplaceable habitat.

Although we have not yet updated our Validation Checklist to include updated Local Validation Requirements for BNG, we would strongly encourage applicants also to submit:

e) A draft Gain Plan, or statement about how you intend to achieve 10% BNG (type, whether on-site or off-site etc).

f) An indication of whether you will provide BNG on-site, off-site or via national credits. For off-site provision, whether you have a site or provider in mind.

Pre-commencement stage and later stages

The Council cannot approve the Biodiversity Gain Plan as part of the initial decision on the planning application. Instead, this will be subject to a ’pre-commencement condition’. This means that development cannot commence (begin) until the final Gain Plan has been submitted and approved by the Council. For on-site and off-site habitat this includes approval of information about the maintenance of (for example for on-site significant habitat) for at least 30 years, and provision of monitoring reports at time intervals as agreed.

The final Gain Plan cannot be submitted until (at the earliest) the day after planning permission has been granted. We recommend you use the Government’s Gain Plan template.

More information about the overall process can be found in Government guidance. See for example:

BNG collection including guidance for developers.
Calculate biodiversity value with the statutory biodiversity metric
Statutory biodiversity metric tools and guides 

More information about the Small Sites Metric

Government guidance specific to the Small Sites Metric includes:

Small Sites Metric (Statutory Biodiversity Metric) User Guide (Feb 2024) 
Small Sites Metric (Feb 2024) 

The habitat survey and Small Sites Metric calculation must be completed by a ‘competent person’, not necessarily a suitably qualified ecologist. The competency is aligned with the British Standard ‘Process for designing and implementing biodiversity net gain: BS 8683:2021’. They should also be competent in identifying the following and should submit evidence of their competence with the Small Sites Metric:

  • Habitats present on site (pre-development)
  • Management requirements for habitats to be created or enhanced within the landscape design (post-development).

The Small Sites Metric requires a site walkover and photos as supporting evidence, together with information such as the number of vascular plant species per sq m. A detailed condition assessment is not required. However, you will need to provide evidence of how any proposed habitats will meet the pre-set habitat condition assigned by the Small Sites Metric. Habitats proposed within gardens, including trees or hedgerows cannot be inputted as BNG.


Last Updated on Wednesday, May 15, 2024

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