What Is Biodiversity Net Gain (BNG)

Biodiversity net gain (BNG) is a way of creating and improving biodiversity by requiring development to have a positive impact (‘net gain’) on biodiversity.

The Government has made it a mandatory requirement for certain development to achieve a minimum of 10% BNG through the Environment Act 2021.

BNG became mandatory for major planning applications from 12 February 2024 and for minor applications from 2 April 2024.

Qualifying developments have to demonstrate, and then deliver, measurable net gains for biodiversity which must be secured, managed, and monitored.

The exact requirements, and methods are different for different categories of application.

How Much BNG Is Required?

A minimum 10% BNG is required reflecting the requirements of the Environment Act.  

Net gains are additional to any mitigation or compensation that is required to address development impacts. Development must therefore accord with the mitigation hierarchy (explained further in the Biodiversity Guidance (October 2022)) and additionally achieve net gains for biodiversity.

How Is BNG Measured? 

BNG for major planning applications should be measured using the most recent version of the Statutory Biodiversity Metric. The Statutory Biodiversity Metric calculates a proxy biodiversity value based on the type and condition of habitats present on site prior to development and proposed through development. This allows the pre- and post-development biodiversity value to be calculated by an ecologist. 

The Small Sites Metric should be used for minor planning applications, unless the site contains priority habitat or supports European Protected Species, in which case the Statutory Metric should be used.

The Statutory Biodiversity Metric, Small Sites Metric and associated user guides can be downloaded from Statutory Biodiversity Metric tools and guides

What Type And Scale Of Development Does BNG Apply To? 

Table 1 sets out the BNG requirements for various types and scales of development and shows how this should be measured.

Table 2 sets out the national exemptions from BNG. 

BNG does not apply to any development where the on-site habitat includes irreplaceable habitats (such as ancient woodland and ancient and veteran trees), nor does it replace existing protections, for example for designated sites or protected species.

Table 1 - BNG Requirements

Type of development Scale of development Requirement  Biodiversity Metric
Residential Development Major: 
Development of 10 or more dwellings;  
OR, the number of dwellings is not known and the site area is greater than 0.5 hectares.
Minimum 10% BNG; on site opportunities maximised Statutory Biodiversity Metric
Non-residential development Major: 
Floorspace is 1,000m2 or more;  
OR, the amount of floorspace is not known and the site area is greater than 1 hectare.
Minimum 10% BNG; on site opportunities maximised Statutory Biodiversity Metric
Residential development Minor: 
Development of between 1-9 dwellings; 
OR, the number of dwellings is not known and the site area is less than 0.5 hectares.
Minimum 10% BNG; on site opportunities maximised Small Sites Metric (provided no priority habitat or European species are on site)
Non-residential development

Floorspace is less than 1,000m2;

OR, the amount of floorspace is not known and the site area is less than 1 hectare.

Minimum 10% BNG; on site opportunities maximised Small Sites Metric (provided no priority habitat or European species are on site)

Table 2 - Exemptions from 10% BNG

Type of development Requirements
  • Section 73 permissions where the original permission which the section 73 relates to was either granted before 12 February 2024 or the application for the original permission was made before 12 February 2024.
  • Householder development (to alter or enlarge a single house).
  • Permitted development and prior approvals
  • Development that does not impact priority habitat and impacts less than 25m2 (eg 5m by 5m) of habitat that has a biodiversity value greater than zero or 5m of linear habitat such as hedgerows (the impact on onsite habitat is “de minimis”).
  • Self-build and custom build development providing no more than 9 dwellings on a site no larger than 0.5ha.
  • Sites developed to provide off-site BNG.
10% BNG not required.  
Proposals are encouraged to consider application of the mitigation hierarchy and appropriate measures that support the enhancement of biodiversity, e.g. bee bricks, swifts bricks, biodiverse landscaping.

DEFRA has produced some guidance on exemptions.

Where Should BNG Be Provided?

Government guidance confirms that BNG should be achieved in a way that is consistent with the Biodiversity Gain Hierarchy. This emphasises that onsite biodiversity gains should be considered first, followed by offsite biodiversity gains on registered sites, with biodiversity credits as a last resort.  

BNG should therefore be provided on-site in the first instance and be designed appropriately for the development and local situation.

What If BNG Cannot Be Achieved On Site? 

Where it is clearly demonstrated that meaningful on-site BNG cannot be achieved, off-site opportunities should be pursued.

Land used for off-site BNG delivery should be secured for the length of the net gain agreement, either via Section 106 agreements, or a conservation covenant. Planning applicants will not need to have both in place to secure a site – just one of those two options. A conservation covenant is a private voluntary legal agreement, made in writing, between a Responsible Body and a landowner which establishes that land will be used for a conservation purpose. A Responsible Body can be a local authority, a public body or charity (where at least some of its main purposes or functions relate to conservation) or a private sector organisation (where at least some of its main activities relate to conservation).

What Is Required At Planning Application Stage 

The following mandatory information must be submitted with the planning application and will be required for validation purposes. In addition, East Staffordshire Borough Council require some additional information which should also be submitted at planning application stage:

Mandatory Validation Requirements 

  • A statement confirming whether the applicant considers BNG is applicable and the reasons why not, where relevant.

Where BNG is applicable:

  • The completed Statutory Biodiversity (major development) or Small Site (minor development) Metric showing the pre-development biodiversity value of onsite habitat on the date of application (or earlier date); Please note we can only accept these in excel format (.xls) and it must include the date of the assessment, details of the assessor and whether the applicant is requesting permission to purchase statutory biodiversity credits. The metric needs to be completed by a competent person – the level of competency is defined in the metric user guides.
  • Where an earlier date is proposed, the proposed earlier dates and the reasons for proposing that date;
  • A statement confirming whether the biodiversity value of the on-site habitat is lower on the application date due to any degradation activities;
  • A description of any irreplaceable habitat on the site; and
  • A scale plan showing onsite habitat on the date of application (or earlier date), including irreplaceable habitat.

Local Validation Requirements 

A draft Biodiversity Gain Plan which sets out the following additional information: 

  • The approach to how adverse effects have been avoided and minimised;
  • The baseline habitat conditions survey;
  • The proposed post-development biodiversity value of on-site habitat, calculated using the Statutory Biodiversity or Small Site Metric;
  • Any off-site BNG proposed and its value; and
  • A description of arrangements for habitat management and monitoring.

Where on-site BNG is proposed:

  • A scale plan showing the proposals for habitat enhancement or creation required to meet post-development value.

The Defra Biodiversity Gain Plan template illustrates how applicants could demonstrate that their development would achieve BNG.

What information must be provided if a development proposal is considered to be within the scope of the de minimis exemption?

If applicants consider that their development proposal would be within the scope of the de minimis exemption, they must state in their planning application form that they consider the proposal to be subject to the de minimis exemption and provide reasons for this. This will enable the Council to consider whether the proposal is genuinely exempt at the validation stage.

When providing reasons for the de minimis exemption, the applicant should provide sufficient evidence to support their justification. In cases where the development would be smaller than 25 square metres the following may be sufficient evidence:

  • the description of development,
  • existing and proposed site plans (supported by aerial photographs if relevant), and
  • the development’s area size (in square metres).  

Where it cannot be clearly demonstrated through site plans and descriptions whether an onsite habitat would be lost or degraded by the development, applicants are strongly encouraged to provide a completed metric for the pre-development and post-development value for the onsite habitat and clear plans identifying the nature and size of this pre-development onsite habitat and how much of it will be impacted by the development. 

Please note that planning applications which are not exempt from BNG (as defined in Table 2 above) and planning applications  considered exempt by virtue of de minimis impact on onsite habitat must be accompanied by the above information. 

Planning applications where BNG is applicable and those considered exempt due to de minimis impact which do not include the above information will be invalidated and returned.