Biodiversity Net Gain

Biodiversity Net Gain is an approach to development that leaves habitats measurably better than they were before. The gain is calculated using a statutory metric that scores habitats by type, condition, distinctiveness and location.

The work has two halves: establishing an accurate baseline, and designing a post-development scheme that delivers the required uplift.

The statutory thresholds, exemptions and required percentage change from time to time, so this page describes how the process works rather than quoting figures. For the position that applies to a specific site, ask.

The baseline is a UK Habitat Classification survey of the site, with each parcel assessed for condition against published criteria. Everything downstream depends on this being right.

An inflated baseline creates an uplift requirement that cannot be met on site. An under-recorded one gets challenged by the authority. The value of the survey is in its accuracy.

Habitat parcels are entered into the statutory metric to produce the pre-development baseline score, and the proposed post-development habitats are modelled against it.

Where the scheme falls short, options are tested: enhancement of retained habitat, creation of new habitat on site, or off-site units. The aim is to find the version that works for the site and the programme rather than defaulting to the most expensive route.

• A UKHab baseline survey and habitat condition assessment
• Completed statutory metric calculations
• A biodiversity net gain assessment report
• A net gain strategy setting out how the required uplift is delivered
• A Habitat Management and Monitoring Plan where the scheme requires one

Habitat condition assessment relies on being able to identify what is growing. Surveys carried out outside the main growing season carry caveats, and grassland in particular is difficult to assess accurately in winter.

Where a winter baseline is unavoidable, it can be done with clearly stated limitations and revisited — but a spring or summer survey produces a stronger, less contestable baseline.