From February 2024, mandatory Biodiversity Net Gain (BNG) became a legal requirement for most planning applications under the Environment Act 2021. While the general rule is that all major developments must deliver at least a 10% net gain in biodiversity, there are defined exemptions and carve-outs that may apply in certain cases. Understanding whether your development site is exempt is critical for developers, planners, and landowners navigating the evolving landscape of biodiversity net gain regulations.
This article outlines a structured checklist based on the latest BNG legislation, statutory guidance, and planning practice guidance, enabling you to determine whether your site is likely to qualify for an exemption from BNG requirements.
1. Does Your Development Fall into a Statutory Exempt Category?
BNG applies to most planning permissions granted under the Town and Country Planning Act 1990, but specific exemptions are set out in regulation and clarified by DEFRA’s guidance.
Check if your proposal meets any of the following criteria:
- Householder development: Applications made by householders, including extensions, conservatories, loft conversions, and similar works to an existing dwelling. These are defined under article 2(1) of the Town and Country Planning (Development Management Procedure) (England) Order 2015.
- Permitted development: Developments granted planning permission by a development order (such as certain agricultural buildings or changes of use) without the need for a formal application.
- Development solely to enhance biodiversity: If the proposed development is carried out mainly to fulfil the BNG requirement for another development (i.e., the creation of a biodiversity gain site), it is exempt.
- High-speed rail transport network: Exemptions apply to works forming part of or ancillary to the network defined in the High Speed Rail (Preparation) Act 2013.
- Urgent Crown development: These are exempt under provisions of the Environment Act 2021.
- Irreplaceable habitats: Sites containing irreplaceable habitats (e.g., ancient woodland, lowland fens) are treated differently. BNG is not required, but these habitats trigger their own mitigation obligations under the biodiversity gain hierarchy.
2. Is the Site Below the De Minimis Threshold?
A de minimis exemption applies where the development site:
- Impacts less than 25 square metres (5m x 5m) of on-site non-priority habitat, and
- Impacts less than 5 metres of linear habitat (such as a hedgerow), and
- Does not impact any priority habitat.
3. Was Planning Permission Granted Before the Relevant Date?
BNG only applies to planning permissions granted after 12 February 2024 for major developments and after 2 April 2024 for small sites. Therefore, you may be exempt from BNG if:
- Your planning application was submitted and approved before the relevant cut-off date;
- A phased development or outline permission was granted with reserved matters before the deadline;
- The development is authorised under a local development order or neighbourhood development order adopted before BNG came into force.
This includes variations to existing permissions that remain under transitional arrangements. In these cases, biodiversity gain plans and statutory biodiversity metric calculations are not required.
4. Is Your Project a Custom or Self-Build?
Small-scale self-build and custom housebuilding developments may qualify for BNG relief. According to the regulations and DEFRA guidance, such sites are exempt if they:
- Consist of no more than 9 dwellings;
- Are on a site of no more than 0.5 hectares;
- Consist exclusively of dwellings that meet the legal definition of self-build or custom housebuilding under section 1(A1) of the Self-build and Custom Housebuilding Act 2015.
Where these conditions are satisfied, developers are not required to submit a biodiversity gain plan or demonstrate uplift using the biodiversity metric.
5. Does the Site Support Existing High-Value Habitats?
While not an exemption, the presence of irreplaceable habitat or onsite priority habitat affects how BNG rules are applied. Developments impacting such features:
- Follow the mitigation hierarchy, avoiding harm where possible;
- Demonstrate significant enhancement or compensation where unavoidable;
- Consult with the local planning authority or relevant oversight body.
These habitats are not covered by the statutory biodiversity metric in the same way as other habitats, and bespoke ecological input will be required.
6. Are You Delivering BNG On Another Site You Own?
Some developers seek to deliver their own BNG offsite on land they own or control. This does not exempt you from BNG rules, but additional requirements apply:
- You must register the land as a biodiversity gain site with Natural England.
- Submit a legally binding agreement (via Section 106 or Conservation Covenant);
- Prepare a compliant biodiversity gain plan showing how you meet the biodiversity gain objective.
Note: Civity does not support developer-led offsite habitat banks. We only supply pre-registered BNG units from landowner sites through our landbank.
7. Are You Only Enhancing Biodiversity Without Other Development?
If your project’s sole purpose is to enhance the natural environment, for example, through habitat creation, restoration, or biodiversity enhancements, and it does not include any infrastructure or buildings, it may be exempt from mandatory BNG. However:
- Planning authorities may still require submission of clear site plans.
- You may need to provide details of post-development management and funding ,
- Ongoing management obligations may still apply via legal agreements.
This exemption is not always straightforward and depends on your proposed site plans and planning context.
8. Does the Site Comprise Only Hardstanding or Low-Value Habitat?
Developments on previously developed land, such as existing car parks, yards or buildings, can have low or zero pre-development biodiversity value. While this doesn’t automatically exempt the development, it may:
- Reduce your required uplift target under the biodiversity gain condition;
- Simplify your biodiversity gain plan and metric assessment.
In some cases, sites with zero pre-development onsite habitat may have lower obligations but will still need to use the statutory biodiversity metric to confirm the baseline.
A Practical Exemption Checklist
Use the following to assess if your site may be exempt from BNG:
- Is the proposal:
- A householder development?
- Permitted development?
- Solely for biodiversity enhancements?
- Covered by a development order?
- Part of the high-speed rail network?
- An urgent Crown development?
- Does the site:
- Impact less than 25 m² of non-priority habitat?
- Affect under 5m of linear habitat?
- Contain priority habitat or irreplaceable habitat?
- Has planning permission already been granted before?
- 12 February 2024 (major development)?
- 2 April 2024 (small sites)?
- Is it a:
- Self-build or custom-build development of 9 or fewer dwellings?
- On less than 0.5 ha?
- Are you planning to:
- Enhance biodiversity only (with no buildings)?
- Develop a site of low pre-development biodiversity?
- Offset on land you already own?
Answering ‘yes’ to any of the above may indicate exemption from BNG, but always check the latest further guidance from DEFRA and your local planning authority.
At Civity…
We assist with the relevant sections of the biodiversity gain plan and provide the associated legal mechanisms (e.g., Section 106 or Conservation Covenant) to meet the biodiversity gain objective via offsetting onto our habitat banks.
We do not calculate the pre-development or post-development value of the development site; that remains the responsibility of your ecologist. Nor do we support DIY offsite delivery projects. Our role is to provide ready-to-use biodiversity units that comply with all BNG rules.
Looking Ahead
As biodiversity net gain becomes embedded into the UK planning system, understanding exemptions is just as important as understanding obligations. By using the checklist above, you can identify whether your development site qualifies for an exemption, and if not, you’ll be better prepared to meet the requirements through a transparent, compliant approach.
For developers seeking offsite units or landowners interested in registering a site, Civity provides trusted, expert support aligned with the latest BNG regulations and national planning policy.
