What is Biodiversity Net Gain (BNG)

Fig 1: Habitat creation or enhancement via landscaping or green infrastructure

 

Biodiversity net gain is a legal requirement for planning permission introduced on 12^th February 2024 that requires developments (unless exempt) to leave the natural environment in a measurably better condition by insisting that all sites give back a 10% biodiversity uplift.  

Fig 2: Biodiversity Net Gain or Net Loss

 

All applications are required to either provide detailed information proving there will be a biodiversity increase; or explain why the requirement does not apply to the development. This will then allow agreement on the measures taken to ensure the gain, and that they are monitored during development and the life of the project.

 

For an application to be exempt from biodiversity net gain requirement, the application must provide reason(s) why and may also need to supply evidence (especially where the application is eligible for the ‘de minimis’ exemption). 

 

Possible reasons where biodiversity net gain does not apply: 


•      Self-build and custom build development 
•      Development subject to the de minimis exemption 
•      Development of a biodiversity gain site 
•      High Speed Railway development 
•      Retrospective planning permission 

 

Self Build and Custom build developments 

Homes built under these conditions are exempt from BNG requirements. 

 

To be exempt under self-build/custom build;

•      The client must have full control over the design, layout, and flow of the space. 
•      The person must also plan to build and live in the house.
•      The building must not be for sale or rental purposes.
•      The number of buildings must be 9 or less.
•      The buildings must be carried out on a site which has an area no larger than 0.5 hectares

Fig 3: Greenland and Hedgerows

 

According to The Biodiversity Gain Requirements (Exemptions) Regulations 2024:

 

Self-build and custom build applications.

(1) The biodiversity gain planning condition does not apply in relation to planning permission for development which—

1. consists of no more than 9 dwellings.
2. is carried out on a site which has an area no larger than 0.5 hectares; and
3. consists exclusively of dwellings which are self-build or custom housebuilding as defined in section 1(A1) of      the Self-build and Custom Housebuilding Act 2015(1).

 

[F1(A1) In this Act “self-build and custom housebuilding” means the building or completion by—

1. individuals,
2. associations of individuals, or
3. persons working with or for individuals or associations of individuals, of houses to be occupied as homes by those individuals.

 

De minimis exemption

The de minimis exemption is a rule that exempts very small developments from the Biodiversity Net Gain (BNG) requirement. It’s intended to apply to minor developments of 25m² as well as for things like street furniture; such as benches and disability ramps. 

 

Development subject to the de minimis exemption are developments below the 25sqm threshold. If the total area taken for development is greater than 25sqm, then BNG is triggered. Care should be taken if trees are impacted/affected e.g. the removal of one small tree is normally enough to disqualify a development from the de minimis exemption. 


 

When the de minimis exemption apply

 

•      The development impacts less than 25 square meters of non-priority habitat 
•      The development impacts less than 5 meters of non-priority linear habitats 
•      The development does not impact a priority habitat 

 

How to claim the de minimis exemption 

 

•      State your claim in your planning application form 
•      Provide reasons and evidence to support your claim 

 Include: 

•      A description of the development 
•      Existing and proposed site plans 
•      The size of the development in square meters




Planning applications are required to provide evidence that the site meets the de minimis criteria. As part of the justification, applications are encouraged to be supported with:

1. a completed metric for the pre-development and post-development value of the onsite habitat; and
2. clear habitat plans (i.e. maps) for the pre-development and post-development habitat.

 

Biodiversity gain site

Developments undertaken mainly for the purpose of fulfilling the BNG planning condition for another development are exempt.

 

Fig 4: Greenland, forest and watercourses

 

High speed rail transport network

An exemption applies to any development forming part of, or ancillary to, the high-speed railway transport network, comprising connections between all or any of the places or parts of the transport network specified in section 1(2) of the High Speed Rail (Preparation) Act 2013.

 

Retrospective planning permissions

Retrospective planning permissions, where the original application was made or granted before February 12, 2024, are generally exempt from the mandatory Biodiversity Net Gain (BNG) requirements.

 

Other exemptions

The following are exempt by the Environment Act 2021:

•      urgent crown developments
•     developments that are granted planning permission by a development order (including permitted development rights)
•      variations to existing planning permissions

 

What the biodiversity metric is 

 

Calculation of net gain will be by way of the statutory biodiversity metric. The statutory (official) biodiversity metric is the way of measuring biodiversity value for the purposes of BNG. It measures all types of habitats, including: 

•      grassland 
•      hedgerows 
•      lakes  
•      woodland 
•      watercourses such as rivers and streams 

 

 

 

For BNG, biodiversity is measured in standardised biodiversity units. The statutory biodiversity metric measures the biodiversity value of habitats by calculating the number of biodiversity units. It calculates: 

•      how many units a habitat contains before development takes place 
•      how many units are needed to replace the units of habitat lost and to achieve 10% BNG, through the creation or enhancement of habitat.  

 

In other words, it is the calculation of the baseline biodiversity unit value of a piece of land prior to planning application, less calculation of the post-intervention biodiversity unit value. The difference between the two calculations is biodiversity gain or loss. The objective of BNG is to achieve a minimum of 10% gain of biodiversity post development.

 

Fig 5: Biodiversity Net Gain

 

What is a biodiversity unit?

 

Biodiversity units are a proxy to describe biodiversity such as; area units, hedgerow units, and watercourse units.

 

Mechanisms for delivery of BNG

 

On-site (units)	Off-site (units)	Statutory Credits
Potentially in full or combination		Only if units not available
Habitat creation or enhancement; landscaping or green infrastructure	New habitat creation or enhancement on land holdings or via habitat banks	Landscape-scale strategic habitat creation delivering nature-based solutions

 

If it is not possible to achieve a net gain on the development site, then the net gain can be achieved elsewhere, through the purchase of biodiversity units/credits.

 

Statutory biodiversity credit prices

Biodiversity credit prices are based on the cost to create, maintain and monitor different habitat types. It is possible to buy fractions of a credit, if it is rounded to 2 decimal places. For example, 0.5 credits, or 3.76 credits. 

 

Area habitats are categories into; Low distinctiveness habitats; Medium distinctiveness habitats; and High distinctiveness habitats. The prices of the area habitats are based on the Tier the habitat belongs to. Visit https://www.gov.uk/guidance/statutory-biodiversity-credit-prices for a comprehensive list of types of habitat and their associated tiers and prices. Table 1 below gives a short summary of the prices.

 

Table 1: Area Habitats Tiers and Prices

Tier A1	Grassland, Heathland and shrub, cropland, urban, & Individual trees	£42,000
Tier A2	Woodland and forest	£48,000
Tier A3	Intertidal sediment	£66,000
Tier A4	Ponds, lagoons Rocky Shore, Coastal Saltmarsh	£125,000
Tier A5	Lakes	£650,000
Tier H	For Hedgerow, which is at – £44,000
Tier W	While All Watercourses, at – £230,000

 

 

 

Resources

Applicants can use the free online tool to determine if their application is exempt and to produce detailed reasons

 

Applications can utilise the Joe’s Blooms digital tool to create a completed metric sheet and habitat plans (maps) for your site.

 

Statutory biodiversity credit prices https://www.gov.uk/guidance/statutory-biodiversity-credit-prices

 

Environment Act 2021 https://www.legislation.gov.uk/ukpga/2021/30/contents