What is Biodiversity Net Gain?
Biodiversity Net Gain (BNG) is a legal requirement in the UK under the Environment Act 2021. It means that most new developments must leave habitats in a better condition for wildlife than they were before development.
In most cases, developers must achieve at least a 10% increase in biodiversity. BNG became a legal requirement for most developments in February 2024.
How does BNG work?
Before development starts, an ecologist carries out a baseline survey of the site. This records and measures the habitats that already exist, such as:
- Grassland
- Trees and woodland
- Ponds and other water bodies
- Hedgerows
For developments that are subject to BNG (some developments are exempt), the existing habitats are entered into a government-designed biodiversity metric spreadsheet.
The proposed habitats after development are also entered into the spreadsheet. This includes areas such as buildings, roads, gardens and other landscaped areas.
The spreadsheet uses formulas to calculate the type, area and quality of the habitats that will be lost, retained, enhanced or created. These are measured in habitat units.
How is the 10% gain achieved?
Any biodiversity lost as a result of development must be replaced. The developer must then provide an additional 10% biodiversity gain.
In simple terms, the completed development should provide more biodiversity than the site provided before development began.
New habitats can be created or existing habitats can be improved:
- On the development site (on-site)
- Elsewhere within the local planning authority (LPA) area (off-site)
- Outside the local planning authority area
The preferred approach is to provide the biodiversity gain on-site, or off-site within the same LPA area.
What are habitat banks?
Off-site areas where habitats are created or improved are often referred to as habitat banks or gain sites.
If a developer cannot achieve the required biodiversity gain on the development site, they can purchase habitat units from an off-site habitat bank.
The location of the habitat matters. If the habitat bank is outside the development site's local planning authority area, the developer generally has to provide more habitat units than if the gain were delivered on-site or within the LPA.
The developer is responsible for paying for all habitat creation and enhancement, whether it takes place on-site or elsewhere.
How long must the habitats be protected?
BNG habitats must be secured for at least 30 years.
They must also be monitored and managed throughout this period to make sure they reach and maintain the condition they are supposed to achieve.
BNG reporting
Every local planning authority must publish information about developments within its area that are subject to BNG.
The reporting covers the previous five years of relevant development.
Because BNG was introduced in February 2024, the first reporting period is shorter, covering developments from February 2024 to January 2026.
The first report for Stevenage Borough Council can be found here.