BNG (Biodiversity Net Gain)

How is it measured?

BNG is calculated using a biodiversity metric, which measures the biodiversity value of habitats in ‘biodiversity units’ as a proxy for nature.

The metric can be used to calculate how a development might change the biodiversity value of a site. It can help you to design, plan and make land management decisions that better support biodiversity.

It uses changes in the extent, distinctiveness and condition of habitats, and compares the biodiversity value of habitats found on a site before and after development to determine if there is a loss or gain in biodiversity.

There are 4 key factors that underpin this comparison:

habitat size
condition
distinctiveness
location

Exemptions from Biodiversity Net Gain

The development types that are exempt from BNG are as follows:

householder development – this covers alterations and extensions to a single dwelling, including works within the boundary
development granted planning permission by a development order under section 59 - this refers to applications that do not require a planning application and includes permitted development rights
development subject to the de minimis exemption - development that does not impact a priority habitat and impacts less than 25 square metres (e.g. 5m by 5m) of onsite habitat, or 5 metres of linear habitats such as hedgerows
self-build and custom build development - development which:
- consists of no more than 9 dwellings, and
- is carried out on a site which has an 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

For applications exempt from BNG, it must be clearly stated within the Application Form which exemption (from the above list) the proposed development benefits from. For more information, please refer to the government guidance on biodiversity net gain.

Biodiversity net gain also does not apply to:

retrospective planning permissions made under section 73A
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

Providing documentation with your application

All planning applications not exempt from Biodiversity Net Gain will need to submit the following additional documents (as a minimum) in order to validate the application:

A completed relevant Biodiversity Metric Calculations Sheet - this spreadsheet will calculate how the proposed development will impact the existing baseline level of biodiversity and how the required minimum of 10% net gain in biodiversity will be achieved

Major developments should always use the Statutory Biodiversity Metric tool.

Non-major developments can use the Statutory Biodiversity Metric tool or can choose to use a simpler version of the metric tool, called the Small Sites Metric (SSM). This cannot however be used on sites where any of the following are present:
- priority habitats (excluding some hedgerows and arable field margins)
- protected sites
- European protected species
Plan(s), drawn to an identified scale and showing the direction of North, showing onsite habitat existing on the date of application (or earlier proposed date), including any irreplaceable habitat (if applicable).

The other information required for validation purposes will usually be covered by your answers within the BNG section on the Planning application form, though additional statements may sometimes be required.

Submission of the Biodiversity Gain Plan (after approval)

After Planning Permission is granted, a Biodiversity Gain Plan must be submitted and approved by the planning authority to discharge the biodiversity gain condition, prior to the commencement of development.

The Biodiversity Gain Plan sets out how the biodiversity gain objective of at least a 10% gain will be met for the development granted planning permission.

Mitigation hierarchy

Gains in biodiversity should be achieved on-site (within the proposed development site) and this should be a key consideration when designing development proposals.

This falls in line with the principle of the mitigation hierarchy that is embedded in national planning policy, where the impact on biodiversity must first be:

avoided, then
minimised, then
compensated for on-site

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

Offsetting biodiversity losses

Biodiversity offsets are conservation activities that produce a measurable increase in biodiversity value at a site and are designed to compensate for any remaining losses in biodiversity caused by a proposed development. These are in addition to any avoidance and mitigation measures that have already been implemented to reduce biodiversity loss.

Biodiversity offsets should be used as a last resort. In certain cases, they are not appropriate and should not be used.

They are only available for developments that have rigorously applied the mitigation hierarchy and must follow national government BNG principles and rules including being as local to the site of impact as possible.

They should also be located somewhere of strategic significance to ecology, for example where they help wildlife to move through the landscape by providing a connective corridor or buffering an existing wildlife site.