There are a few exemptions which can be found here https://www.gov.uk/guidance/biodiversity-net-gain-exempt-developments
The type, condition, and area of habitats on site are determined prior to the development. Then, each habitat included in the proposed development is calculated, with each habitat assessed on its condition, size and location.
This habitat data, along with information on local biodiversity action plans (Nature Recovery Strategies), are input into the Biodiversity Metric (versions are currently being updated regularly, but the statutory metric is the main one), which results in the calculation of Biodiversity Units. The difference between the baseline and proposed development biodiversity units provide a percentage – this is the Biodiversity Net Gain.
With a minimum of 10% biodiversity net gain needed for a development to be approved in both habitat and linear units, we then recommend the best ways in which to achieve this.
For example, on a recent project, the biodiversity net gain was calculated for the proposed development where a +8.96% net gain was achieved. Therefore, to meet the minimum 10% net gain, a further +1.04% was needed.
We recommended using a species-rich grass seed mix, such as WFT-Species-Rich-26, for the proposed amenity grassland. We calculated that enhancing 0.8 Ha of the proposed amenity grassland would meet the minimum 10% net gain. Another option was to include patches of mixed scrub, totalling at least 0.1 Ha, which would also meet the 10% net gain requirement.
An emerging BNG unit market is being created by the private sector, whereby sites that can’t make the loss or 10% on site and buy units off-site, these normally need to be in the county and landscape character area e.g. if modified grassland is required you have to replace that with modified grassland in the same or better condition.
A Biodiversity Net Gain calculation and subsequent report can be carried out any time of the year.
Following the grant of planning and if the 10% is possible on site it is likely that a Habitat Management and Monitoring Plan (HMMP) will be required in order to allow the management of habitats for a 30yr period, these are substantial documents and require both ecological knowledge and habitat management knowledge.
If you are buying units, the habitat bank will have already had an ecologist undertake this work.
The final piece of paperwork is called a BNG Gain Plan, this is a fairy straight forward document that brings all the info into one place, this is usually a condition of the planning permission.
