Biodiversity net gain (BNG)

Use this page to understand the ideas behind BNG, who it affects, how we are involved as your Local Planning Authority, and how you can meet the requirements when submitting your planning application.

Understanding BNG

Biodiversity net gain (BNG) is a new process designed for the planning system to make sure new development delivers a net positive impact on the natural environment. It requires new developments to be designed and planned in ways that minimise any loss and damage to existing habitats, and then to compensate and off-set any damage caused.

See the section on how to deliver the BNG requirement, below, for more detailed information and guidance.

What is meant by biodiversity net gain?

Biodiversity net gain is defined as the achievement of measurable gains for biodiversity through new development i.e., biodiversity is left in a measurably better state than before development commenced.

Select a topic below to read more about how the policy has evolved.

National Policy

The delivery of BNG is a mandatory requirement of the planning system. It directly affects people who need to secure planning permission for new projects above a certain size. It is unlawful to issue a planning approval for any qualifying project that does not secure 10% BNG, with 30-year management and monitoring.

This will apply to small sites from 2 April 2024, and implementation for Nationally Significant Infrastructure Projects is planned for 2025.

Read the government guidance for mandatory biodiversity net gain

The National Planning Policy Framework (2019) sets out that planning policies and decisions ‘should contribute to and enhance the natural and local environment, by minimising impact on and providing net gains for biodiversity…’

The Environment Act (2021) contains a BNG condition for planning permissions. Secondary legislation provides practical measures that enable the law to be enforced and operate in daily life. These comprise of one commencement order and six regulations, which work together to deliver the BNG framework.

B&NES Policy

In July 2020, we declared an Ecological Emergency, recognising the severity of the degradation of the natural environment and loss of wildlife, and the urgent need to act to restore nature.

Read more about what we are doing to address the Ecological Emergency

We committed to bringing forward the requirement to deliver BNG for local planning applications through our Local Plan Partial Update (LPPU). Policy NE3a (Biodiversity Net Gain) gained full statutory weight when we adopted the LPPU on 19 January 2023.

What BNG means for your planning application

Qualifying developments will 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.

Select a topic below, to understand in more detail what this may mean for your application.

Exemptions

The exemptions for mandatory BNG are the same for local BNG policy.

Householder applications and permitted development are exempt from mandatory BNG requirements and policy NE3a, but are encouraged to deliver habitat and species enhancements in accordance with policy D5e (Building Design). These could include simple additions, such as the provision of integrated bird and bat boxes, or the use of native and nectar-rich species within landscaping schemes, for example.

Self-build and custom build developments 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 are also exempt.

From 1 October 2025, any application for a self or custom build home must be accompanied by a Section 106 agreement or Section 106 unilateral undertaking. This legal requirement ensures all proposed properties meet the definition set out in the Self Build and Custom Housing Act 2015 (as amended). The S106 agreement acts as a safeguard, confirming that each development genuinely qualifies as a self or custom build project.

To assist applicants, a unilateral undertaking template is available to download. Local authorities will use this mechanism to maintain compliance, uphold standards, and prevent misuse under the relevant legislation.

The development of biodiversity gain sites for the purpose of fulfilling the BNG planning condition for another development are exempt.

For all other developments where priority habitat is not impacted, BNG will not be applicable where the impact of the habitat is less than 25 square metres of 5m length of a linear habitat such as a hedgerow.

Major applications

Major planning applications will be expected to deliver a minimum of 10% biodiversity gains, with habitat management and monitoring secured for at least 30 years. The gains must be calculated using the statutory (official) biodiversity metric.

Minor applications

Minor planning applications are expected to demonstrate no net loss, and appropriate net gain. After the 2 April 2024 a 10% gain will be required. The gains must be calculated using the statutory (official) biodiversity metric, however, if your development qualifies as a small site, you can use a simpler version, called the small sites metric.

Delivering BNG

All planning projects subject to BNG requirements should consider BNG from the very outset, prior to site design, and ideally at site selection stage to help minimise the need for providing replacement habitats.

We have produced guidance to support the implementation of Local Plan Partial Update (LPPU) policy.

The Mitigation Hierarchy

The mitigation hierarchy is a concept designed to help minimise the impacts of development and is a critical element of the BNG process. It can be used to help minimise the habitat off-setting and gains required.

The concept requires site planning and design to consider biodiversity from the outset. Harm to biodiversity must always first be avoided and then minimised. Where avoidance of harm is not possible, mitigation approaches should be used, and as a last resort, compensation, and off-setting.

On-site BNG provision

Biodiversity gains can often be achieved within a development site and can be linked to the provision of green spaces (such as community orchards and landscaped areas). These gains are usually referred to as on-site gains and will often be the preferred solution. These can help to achieve good placemaking, providing better places to live and work, and ensuring communities have good access to nature-rich sites.

Off-site BNG provision

There will be some circumstances when the full BNG requirement cannot be met on-site within the application site boundary. In these circumstances off-site BNG habitat will be required.

We recognise that we have an important role to play and are exploring ways that off-site habitat gains can be successfully achieved and delivered, including the role council land could play.

For more information about our BNG off-site provision projects, please email us at Nature_Recovery@bathnes.gov.uk