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Biodiversity Net Gain (BNG) now mandatory on small development sites

View profile for Louise Clifton
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Biodiversity Net Gain (BNG) was introduced by the Environment Act 2021 which provided for a minimum of 10% BNG requirement to ensure that developments deliver a positive benefit for nature and to mitigate the impact of the development.

Developers are therefore required to assess the type of habitat affected by the proposed development and its condition before submission of the planning application to the local planning authority. Please click here if you want to read my earlier blog which provides more background information on BNG.

What are the changes to BNG for small sites from 2 April 2024?
From 2 April 2024, the minimum ten percent BNG requirement is now mandatory on “small developments” defined as being:

  • residential development where the number of dwellings is between 1 and 9 on a site area of 1 hectare or less, or if the number of dwellings is unknown the site area is less than 0.5 hectares; or
  • commercial development where floor space created is less than 1,000 square metres or total site area is less than 1 hectare: or
  • development that is not the winning and working of minerals or the use of land for mineral-working deposits; or
  • development that is not waste development.

When carrying out an assessment of a small development site, the developer can use either the Small Sites Metric (“SSM”) in their calculation or the Statutory Biodiversity Metric (“SBM”), but a combination of both is not allowed. Be careful when making this decision as the SSM only allows for the creation or enhancement of very low, low, and medium distinctiveness habitats and cannot be used for priority habitats or European protected species or on protected sites. If you want to create or enhance to habitats of higher distinctiveness bands in order to provide biodiversity units post development the SBM must be used. It may be beneficial in this planning stage to employ the services of an ecologist who will be able to assist and can save time and money in the long run.

What are the differences between SBM and SSM in BNG calculations?
SBM – calculation tool

  • The range of distinctiveness of habitats covers from very low to very high.
  • The statutory biodiversity metric condition assessments (which is carried out by an ecologist) is determined by the habitat condition.
  • An ecologist will inform the appropriate habitat interventions.
  • Off-site sections are available.

SSM – calculation tool

  • The range of distinctiveness of habitats ranges from very low to medium (no high or very high distinctiveness habitats are included).
  • Existing and enhanced habitat’s condition is automated.
  • Specific habitat interventions are available for each habitat type.
  • The SSM does not have an off-site section, however if your small site requires any off-site units, you can still use the SSM calculation tool to calculate any on-site gains ready for submission to the local planning authority when required.

For further help and guidance please click on the following links for the SSM and SBM User Guides published by the published by the Department for Environment Food & Rural Affairs. SSM User Guide or SBM User guide.

The preference by the local planning authority is firstly to provide BNG on the development site where the impact is most great and then, if this is not possible, to find a site where the developer can provide the requisite BNG within the administrative boundary of the local planning authority. Please see my earlier blog for more details on this “mitigation hierarchy”.

Are there any exemptions to BNG?
There are still some exemptions to BNG, and these include:

  • Planning applications made before 12 February 2024, when mandatory BNG came into effect.
  • There are transitional arrangements for variations to existing planning permissions, for further information please see the planning practice guidance.
  • A development that does not impact a priority habitat and impacts less than 25sqm of on-site habitat or 5 metres of on-site linear habitats e.g. hedgerows.
  • Householder applications as defined under article 2(1) of the Town and Country Planning (Development Management Procedure) (England) Order 2015.
  • Self-build and custom build application which must consist exclusively of no more than 9 dwellings which are either self-build or custom housebuilding and the site area is no larger than 0.5 hectares.
  • Developments which are mainly to fulfil a BNG planning condition on another development, a development which is granted permission under a development order, and those developments which are carried out under permitted development rights.

It is planned that from November 2025 BNG will also be applicable to nationally significant infrastructure projects.

Since 12 February 2024, BNG has come to the forefront of the minds of landowners and developers and, as a firm, we are receiving an increasing number of enquiries in relation to both the allocation of units to be registered on the Biodiversity Gain Site Register and section 106 agreements obliging developers to provide the 10% gain. With the advent of small developments now also being required to provide a 10% gain, we expect this area to continue to grow.

Please contact one of the team if you wish to discuss any issues pertaining to the BNG process and the regulations surrounding these.