Biodiversity Net Gain extended to small sites

Following the introduction of biodiversity net gain for major developments on 12 February 2024, the framework was extended to small sites from 2 April 2024.

'Small sites' are defined as ‘not major developments’, which means:

• Residential development where the number of dwellings is between 1 and 9 on a site of an area 1 hectare or less, or if the number of dwellings is unknown, the site area is less than 0.5 hectares
• Commercial development where floor space created is less than 1,000 square metres or total site area is less than 1 hectare
• Development that is not the winning and working of minerals or the use of land for mineral-working deposits
• Development that is not waste development   

Members are reminded householder applications are exempt from mandatory BNG.

To help smaller developers, the small sites biodiversity metric tool has been developed by the Government to allow the calculation of biodiversity value for small developments. This tool functions similarly to the biodiversity metric used for major developments.

As with larger sites, the small sites biodiversity metric tool must be completed by a competent person with the knowledge and skills to perform specified tasks and to complete and review SSM calculations.

Developers of smaller sites are faced with the same options when meeting the 10% uplift demanded by BNG:

• Create habitats within the boundary of the development
• Create habitats both on-site and off-site
• Off-site may mean additional land owned by the developer or land owned by a third party which the developed invests in
• Purchasing biodiversity credits from the government

The reduced area for development is likely to challenge smaller developers adopting BNG on their sites; it cannot be assumed that a small site will necessarily have a low ecological value pre-development. Fortunately, there are no generic minimum areas for onsite BNG. Local planning authorities will assess this on a case-by-case depending on the habitat.  Local authorities are also committed to developing policies to help guide small developers.

Analysis by Defra during the consultation stage of BNG suggests costs associated with delivering net gain are likely to be lower than the cost of building and land. Estimated costs for residential brownfield land are between 0.1% and 0.8% and slightly higher for greenfield land – between 0.1% and 3.9%.

Defra acknowledges the costs associated with BNG are most likely to be felt by developers in the Midlands and the North, who will experience the highest potential costs as a percentage of build costs.   

Further reading
Defra: The small site's metric