Biodiversity Net Gain Requirements: Guidance for Developers

Biodiversity Net Gain (BNG) represents an approach to development and land use in England and Wales, aiming to ensure that new developments leave the natural environment in a measurably better state than before.

Developers can achieve net gain by mitigating biodiversity loss, using habitat creation techniques, retaining various species and habitat types and protecting ecological features.

Due to relevant national legislation, biodiversity net gain is now mandatory in all parts of England and Wales in 2024. Most local planning authorities are now requesting a biodiversity net gain report to be submitted with the planning application for planning permission.

If you are looking to have planning permission granted on a proposed development, it is now essential to stay up to date with biodiversity net gain requirements.

Biodiversity net gain requirements

BNG has now been made a mandatory planning policy under the Town and Country Planning Act 1990 (as inserted by schedule 14 of the Environment Act 2021). This policy mandates that all new developments must now deliver at least 10% biodiversity net gain at a minimum.

The BNG approach involves a structured assessment of the biodiversity value of a site before development, followed by the design and implementation of measures to increase this value post-development.

This can be achieved through on-site enhancements, off-site biodiversity projects, or a combination of both. Importantly, the net gain must be maintained for at least 30 years, ensuring long-term benefits for wildlife and ecosystems. If the required BNG levels are not met initially, a mitigation hierarchy should be followed until the project reaches the required standard.

Biodiversity net gain is especially significant for protected or important nature conservation sites and sites of special scientific interest. BNG is already commonly used for local nature recovery strategies and National Planning Policy Framework.

What types of developments will BNG apply to?

As of the 12 February 2024, all major developments must now meet the Town and Country Planning Act 1990 requirements. Major developments include residential developments with 10 or more dwellings or if the site area is greater than 0.5 hectares. Any planning applications made before this date are considered exempt from biodiversity net gain.

Biodiversity net gain was also made mandatory for small sites from 2 April 2024 onwards. Small sites include residential developments where the number of dwellings is between 1 or 9 or if the site area is less than 0.5 hectares. Small sites also include commercial developments where floor space created is less than 1,000 square metres or the overall site area is less than 1 hectare.

Biodiversity net gain principles

According to the Chartered Institute of Ecology and Environmental Management (CIEEM), there are 10 crucial good practice principles of biodiversity net gain. These should help to achieve BNG if they are followed accordingly. The mandatory biodiversity net gain principles include the following:

• Utilise the mitigation hierarchy to minimise the impact on biodiversity
• Eliminate any negative impacts on biodiversity
• Communicate each BNG outcome with complete transparency
• Cover all areas of sustainability, including societal and economic factors
• Involve any pre-development and post-development stakeholders in creating mandatory net gain solutions
• Focus on producing long-term environmental benefits from BNG
• Understand the variable factors and potential risks in order to achieve biodiversity and deliver net gain
• Offer nature conservation that exceeds the stated BNG requirements
• Determine a suitable method in order to secure measurable biodiversity net gains
• Ensure the best possible results from biodiversity net gain

For case studies and a practical guide on biodiversity net gain principles, visit the CIEEM website.

Our team has strong experience completing biodiversity net gain and will provide guidance throughout the planning system process, from the initial land purchase agreements to monitoring assessments.

Calculating biodiversity net gain

Metrics assign every habitat on a site a ‘biodiversity unit value’ according to its relative importance for biodiversity. This enables comparison between the existing value of a site and what will be delivered through development or management and post development. This may include an increase in natural habitats through retention and enhancement and/or creation, which goes over and above the environmental habitat originally on site.

BNG can be calculated through the DEFRA biodiversity metric 4.0, which requires a limited number of factors. These factors include:

• The type of habitat (those which exist on site and off site)

• Any locations (if they are local environment priorities)
• The size of habitat parcels in kilometres or hectares
• The condition of any habitat parcels

The government website also provides a biodiversity calculation tool which can help to determine your biodiversity unit score. This will then translate into the standards of your local planning authority.

Implementing biodiversity net gain

If you are unsure of how statutory biodiversity net gain delivery may affect your planning application, you should contact your local planning authority. If they indicate that your development could be significantly impacted, we recommend that you contact an experienced ecologist as soon as possible.

They can discuss whether your development plans meet the required standards as well as any measures you may need to take in order to meet development planning requirements.

At Collington Winter, our team has strong experience in ensuring that overall, there is a gain for biodiversity for developments and will provide guidance throughout the planning process. We can ensure that one of our experienced biodiversity ecologists visits your development site to assist with any ecological reports and a biodiversity gain plan.

Our ecologists will complete a habitat classification assessment, and the data is then used to calculate a number of biodiversity units to measure changes to the natural environment, pre and post development. This metric is currently Defra Biodiversity Metric 4.0. This data can then be used to create a habitat management and monitoring plan.

How can Collington Winter assist?

Our team of ecologists and land managers have helped numerous clients over the years, including policy guidance for BNG in England. 

We can assist with biodiversity net gain by providing: 

• BNG guidance
• Assessments
• Mitigation

Please get in touch if you would like further information about biodiversity net gain requirements. We can also develop land management plans.

Our Ecology Director, Olivia Collington, holds a Natural England license. If you would like to find out more about the services we provide, feel free to contact us using the details below.