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Biodiversity Net Gain (BNG)

What is BNG?

Simply put biodiversity net gain (BNG) is a way of creating and improving natural habitats. BNG makes sure development has a measurably positive impact (‘net gain’) on biodiversity, compared to what was there before development.

This objective is for development to deliver at least a 10% increase in biodiversity value relative to the pre-development biodiversity value of the onsite habitat. This increase can be achieved through onsite biodiversity gains, registered offsite biodiversity gains or statutory biodiversity credits.

Important Dates

Currently only major developments are required to comply with this requirement (as of 12th February 2024), with a number of exemptions. Including small projects which will come into play as of 2nd April 2024

Depending on the planning authority they may also have specific policy requirements relating to BNG, so you should check before moving forward with a development.


How is the biodiversity gain objective of 10% gain calculated? 

The biodiversity gain objective of at least a 10% gain is measured against the pre-development biodiversity value of the onsite habitat for the development. The objective is met if the post-development biodiversity value is exceeded by at least 10%. This 10% gain is calculated in reference to:

  • the projected biodiversity value of the onsite habitat at the time the development is completed (“the post development biodiversity value of the onsite habitat”);

  • the biodiversity value in relation to the development of any registered offsite biodiversity gain allocated to the development; and

  • the biodiversity value of any biodiversity credits purchased for the development.

The statutory biodiversity metric is used to calculate the pre-development and post-development biodiversity value of the development’s onsite habitat, as well as the biodiversity value for offsite biodiversity gains and biodiversity credits. It uses habitat information to generate “biodiversity units”, a proxy measure for biodiversity value. The statutory biodiversity metric data value inputs include habitat type, size, distinctiveness, condition, and its location in the local area.

The statutory biodiversity metric calculation tools must be submitted as part of the Biodiversity Gain Plan to demonstrate the statutory biodiversity metric formula has been accurately applied



1. Small developments (exempt until 2 April 2024)

A small development 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 

2. Developments below the threshold

A development that does not impact a priority habitat and impacts less than:   

  • 25 square metres (5m by 5m) of on-site habitat   

  • 5 metres of on-site linear habitats such as hedgerows


3. Householder applications

It includes, for example, small projects like home extensions, conservatories or loft conversions.


4. Existing planning applications 

If a planning application for a development was made before day one of mandatory BNG on 12 February 2024, the development is exempt from BNG.


5. Variations of planning permission

If the S73 application relates to a scheme that was either granted before 12 February 2024 or the application for the original permission was made before 12 February 2024


6. Self-build and custom build* applications

Self-builds :   

  • consists of no more than 9 dwellings 

  • on a site that has an area no larger than 0.5 hectares    

  • consists exclusively of dwellings that are self-build or custom housebuilding


* Definitions of self-build and custom build means the building or completion by—

(a) individuals,

(b)associations of individuals, or

(c) persons working with or for individuals or associations of individuals, of houses to be occupied as homes by those individuals.

But it does not include the building of a house on a plot acquired from a person who builds the house wholly or mainly to plans or specifications decided or offered by that person


If you want to discuss a project or require further information about BNG and how it affects your development please give us a call on 0115 8700454


Information was correct as of 10th March 2024.


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