What Developments are Exempt from BNG?

In the UK, Biodiversity Net Gain (BNG) regulations require most new developments to achieve at least a 10% improvement in biodiversity value, maintained for a minimum of 30 years. 

This mandate, introduced under the Environment Act 2021, applies to both major and small-scale projects as of 2024. 

However, there are specific BNG exemptions carved out to keep the policy practical and proportionate. The government has kept these exceptions limited in scope, in order to keep the list of exemptions “narrow and focused” and maintain ambition while easing burdens on very small or special cases.

In line with our mission, this guide clarifies which types of development are exempt from the mandatory BNG requirement, helping you determine if your project qualifies for an exemption. 

BNG policy is new and sometimes confusing. By clearly explaining the exemptions below, we hope to equip you with the knowledge to plan confidently and avoid missteps.

BNG Exemptions at a Glance

The main categories of development that are exempt from the mandatory BNG rules include:

• The BNG De Minimis Threshold – extremely small developments with trivial habitat impacts (below a defined area/length threshold).
  
  
• Householder Applications – home improvement projects by individual householders (e.g. extensions or loft conversions).
  
  
• Small Sites – minor developments below the “major” site threshold (typically small-scale residential or commercial projects).
  
  
• Temporary Permissions – projects granted on a short-term (temporary) planning permission.
  
  
• Biodiversity Gain Site Enhancements – developments undertaken solely to create biodiversity gains for another project.
  
  
• Self-Build and Custom Housebuilding – small-scale housing developments (up to 9 homes) built or commissioned by individuals.
  
  

The BNG De Minimis Threshold

This exemption covers extremely small-scale proposals. If a project will disturb less than 25 square metres of non-priority habitat (about a 5m × 5m area) and under 5 metres of hedgerow or other linear habitat, and it does not impact any priority habitat, then it does not need to deliver a 10% net gain. 

These strict criteria ensure trivial works (like installing a bench or a ramp on existing hardstanding) aren’t burdened with BNG requirements. 

All conditions must be met; if even one threshold is exceeded or if any priority habitat (e.g. an ancient woodland) is affected, the de minimis exemption cannot be claimed. 

Developers are advised to check available habitat data (for example, priority habitat inventories) to confirm their site qualifies.

Householder Applications

Householder applications, essentially improvements to an individual private dwelling, are generally exempt from BNG. 

This category includes modest projects within the curtilage of an existing house, such as home extensions, conservatories or loft conversions. 

If your planning application is submitted by a homeowner for works on their own property, it will not be subject to the 10% net gain requirement. 

However, this exemption does not cover proposals that change the use of a house or increase the number of dwellings on the site (for example, converting a single house into flats would not be exempt).

Small Sites

‘Small sites’ refers to developments below the threshold of a major project. 

For example, residential sites with up to 9 dwellings on under 1 hectare of land (or under 0.5 ha if the number of homes isn’t specified), and non-residential projects under 1 hectare or 1,000 m² floorspace. 

Small sites were initially given a later start date for BNG: the 10% net gain rule did not apply to them until April 2024, two months after it began for larger developments.

Now that this grace period has passed, small sites are no longer exempt and they must achieve net gain just like major projects. 

However, recognising their scale, regulators have provided a simplified biodiversity metric for small developments to use. 

If your project qualifies as a “small site” by the above criteria, it’s important to follow the proper process and tools designed for these smaller-scale BNG assessments.

Temporary Permissions

Temporary planning permissions (time-limited developments) do not enjoy any automatic exemption under the BNG rules. 

In practice, if a temporary project has minimal habitat impact it might qualify as de minimis; otherwise, it is treated like any permanent development in needing a BNG plan. 

(During the initial BNG roll-out, small developments with temporary permissions were not required to comply until April 2024, but beyond that date a temporary status alone is not a free pass.)

Biodiversity Gain Site Enhancements

This exemption applies when a project’s sole purpose is to create or improve habitat in order to fulfill the BNG requirement of another development. 

In other words, if you are undertaking a scheme purely to deliver biodiversity enhancements as an off-site gain for a separate project’s planning condition, that scheme itself is not required to achieve an additional 10% net gain. 

Without this carve-out, an off-site habitat creation project intended to compensate for another development would paradoxically need its own BNG, leading to a never-ending cycle of habitat creation. 

To prevent that, developments which solely enhance biodiversity to meet another project’s BNG obligation (and related efforts such as making the site publicly accessible for recreation or education without charge) are exempt from the net gain mandate.

Self-Build and Custom Housebuilding

Small-scale self-build or custom housebuilding developments are exempt from BNG requirements, provided they meet specific size criteria. The project must consist of no more than 9 dwellings and occupy a site of 0.5 hectares or less. 

Crucially, all the homes must qualify as “self-build or custom housebuilding” under the legal definition – meaning individual owner-builders (or groups of individuals) have primary input into designing and building the houses for their own residence. 

If a self-build project stays within the 9-unit/0.5 ha limit, it does not need to deliver a 10% net gain. However, if it exceeds those thresholds or is part of a larger development, then BNG requirements apply as normal.

The Importance of Data and Expert Guidance

Knowing about these exemptions is only the first step. In practice, even if your development seems exempt, it’s vital to verify and document that status carefully – misinterpretation of the rules can lead to costly delays or non-compliance. Having precise ecological data and expert guidance is crucial for:

Avoiding regulatory pitfalls. BNG exemptions are meant to be the exception, not the rule. Yet more than 75% of planning applications initially claimed an exemption when BNG came into effect, indicating widespread attempts to use these narrow criteria. 

Misusing an exemption (or wrongly assuming one applies) can backfire, if later scrutiny shows the project didn’t truly qualify, you run the risk of your  application being refused or among other unexpected conditions. 

By understanding the limits and using accurate data up front, you can steer clear of these problems.

Making a compelling case to local planning authorities. If you plan to claim an exemption, you’ll need solid evidence to satisfy the council. 

Many local planning authorities have limited capacity to independently verify biodiversity details, so providing a robust, data-backed justification is essential. 

High-quality habitat surveys, biodiversity metrics, and clear documentation can demonstrate to planners that your project meets the exemption criteria, helping avoid protracted negotiations or compliance issues.

Confirming a development’s eligibility for an exemption. It’s one thing to assume your site is under 25 m² of impact or has no priority habitat, it’s another to prove it. Reliable baseline data is key to confirming eligibility. 

For example, consulting up-to-date habitat maps and records will reveal if any priority habitat is present on your site. 

Precise measurements of the affected area, along with biodiversity metric calculations, allow you to definitively show that your development falls below the de minimis threshold or meets the self-build criteria, as applicable. This level of certainty can save time and prevent disputes later on.

Our online platform delivers AI-powered habitat assessments with high accuracy and detail, equipping you with the facts needed to navigate BNG regulations confidently. 

With Gentian as a trusted partner, offering both cutting-edge data and visionary expertise, you can ensure no aspect is overlooked, whether you are confirming an exemption or optimising a full BNG plan.

Beyond BNG Compliance

Even if your development is legally exempt from delivering net gain, there are still strong reasons to embrace nature-positive practices. 

Voluntarily integrating biodiversity enhancements can improve a site’s resilience and long-term value, enhance community appeal, and contribute to broader sustainability goals.

For further reading or support, explore our resources and services on Biodiversity Net Gain Assessments. Take the next step towards streamlined, successful BNG compliance and get in touch with a member of our team via the form below: