News & Media

Mandatory Biodiversity Net Gain for Small Sites
Biodiversity Net Gain (BNG) became mandatory for small sites on April 2, 2024. Previously exempt from BNG, this alteration means it is now a legal requirement for small sites to deliver BNG the same way as any other development. Any damage or loss of habitat must be fully compensated, and an additional 10% of new or better-quality habitat must be created. It should be noted that permitted developments such as extensions and roof alterations are still exempt.

‘Small sites’, defined by the Biodiversity Metric, are sites not classed as significant developments under the Town and Country Planning (Development Management Procedure) (England) Order 2015. This includes:
• Residential developments of 1-9 dwellings on a site smaller than 1ha or, if the number of homes is unknown, smaller than 0.5ha
• Commercial developments where floor space is under 1,000m2, or the total site area is under 1ha
Even if these meet the criteria, some projects are still classified as significant developments regardless of size. For example, mineral works such as mining or waste development such as landfills and processing plants cannot be classed as small sites under BNG. A site's natural resources may also change how it is assessed for BNG. Sites with priority habitats, statutory sites, or European protected species cannot be evaluated as small, regardless of size.

All developments require the assessment of a site’s biodiversity value through the use of a metric. For most sites, the Statutory Metric is used to calculate biodiversity units, but for sites that meet the above criteria, the Small Sites Metric (SSM) can be used instead. The SSM is a simplified version of the Statutory Metric, which makes calculating biodiversity units of small sites more efficient. The SSM can calculate biodiversity units of area, linear and watercourse habitats in the same way as the statutory metric. However, some more complex habitats are not included and can only be assessed using the statutory metric. The SSM can calculate a baseline biodiversity unit value for a site or unit uplift of on-site habitat creation and enhancement. The SSM cannot calculate off-site gains, which must be handled separately.
Delivery of BNG on small sites can be challenging. By definition, small sites need more space to create habitats on-site. To achieve BNG on-site, an empathetic landscape design must carefully slot high-quality habitat around the proposed development to compensate for habitat loss. On-site development is impossible for small sites where most of the footprint is to be developed.

If on-site habitat creation is not possible, developers must seek off-site compensation, which can be challenging for minor unit shortfalls. To achieve BNG off-site, developers can purchase units from other gain sites or habitat banks. Due to the associated fees, many vendors do not consider small unit trades profitable. Therefore, many developers wish to use other areas of land they own for off-site unit generation. Although the same landowner owns these sites and may be adjacent to the development site, they are still classified as off-site enhancements as they fall outside the red-line boundary. As such, they must be registered and their units formally allocated to the site like any other gain site. However, as the SSM does not include off-site measures, the calculation is often carried out using the statutory metrics of the provider from which you are buying units. Developers must provide evidence of their off-site gains in a biodiversity gain plan, as they are not included in the SSM. Delivery for small sites can substantially burden developers due to the limited space and associated costs of buying units.

To mitigate some of these issues, developers should be mindful of BNG delivery for small sites from the very start of the project. Staying aware of the legal requirements ensures that measures can be taken early to ensure possible BNG delivery. You may consider extending the red line boundary of the development site to make space for habitat creation or enhancement. This is a logical approach to meeting BNG on-site, but extending the site boundary may drive costs up in other areas, and the site may no longer qualify as a small site. Reducing impacts on existing habitat is also an excellent way to reduce the amount you have to offset. You can minimise the units you need to generate by minimising your impacts. This could mean you can achieve BNG on-site where the impacts were too significant. You could reduce your impact on existing habitats by developing on brownfield sites. Thinking outside the box is beneficial when it comes to compact habitat design and features like green roofs can be hugely helpful in maximising the space available to you.

For more info on BNG, check out our website dedicated to this service: https://www.biodiversity-net-gain.co.uk/home.html