Biodiversity Net Gain Changes, August 2026

Biodiversity Net Gain Changes: new exemptions reshape planning requirements for small sites.

England’s statutory Biodiversity Net Gain regime changes came into force on 6 August 2026. They remove the mandatory requirement from many developments on sites of 0.2 hectares or less, while bringing new self build and custom build applications into the regime.

For developers, architects and planning advisers, the changes should make some small applications more straightforward. However, the exemptions depend on the application date, site boundary and presence of priority habitat. They should therefore be checked before ecology work and project budgets are finalised.

What changed on 6 August?

The Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026 introduce four principal changes.

1. Development on a site no larger than 0.2 hectares, equivalent to 2,000 square metres, is now exempt from mandatory Biodiversity Net Gain. The exemption applies to planning applications made on or after 6 August 2026. It does not apply where the development would affect priority habitat within the site. The site area is measured using the red line boundary, rather than simply the footprint of the proposed building or works.
2. Wholly temporary developments can be exempt where planning permission requires the use, buildings or works to be removed and the land reinstated within five years. Again, the exemption is unavailable if priority habitat would be affected. Successive temporary permissions cannot be used to extend the total period beyond five years while retaining the exemption.
3. The previous exemption for qualifying self build and custom build housing has been removed. New applications made from 6 August must now meet Biodiversity Net Gain requirements unless another exemption applies, such as the new 0.2 hectare threshold.
4. The Biodiversity Gain Hierarchy has been adjusted for non-major development. Habitat creation and enhancement onsite, and the use of registered offsite gains, now sit at the same level of preference. This gives smaller developments greater freedom to use offsite units where fitting the required gain within a constrained site would undermine the scheme.

The purchase of statutory biodiversity credits remains the final option. Avoiding or mitigating damage to habitats of medium, high or very high distinctiveness also remains the first consideration. The revised hierarchy should not be interpreted as permission to disregard existing ecological value. The changes and their transitional arrangements are summarised in updated government planning guidance and Defra’s implementation announcement.

Why the application date matters

The new rules are controlled by the date on which the planning application was made, not the date on which it is determined. Applications submitted before 6 August continue under the earlier arrangements. This is particularly important for self build and custom build schemes. An eligible application made before the change can retain the former exemption, whereas a comparable application submitted from 6 August may be subject to the statutory condition.

For non-major applications that remain within the regime, the original Biodiversity Gain Hierarchy also continues to apply where the application was made before 6 August. Project teams should therefore record the relevant submission date and avoid assuming that every undetermined application has moved onto the new rules.

A narrower requirement, not an end to ecological design

Mandatory Biodiversity Net Gain normally requires applicable development to deliver at least a 10 per cent increase in biodiversity value. Unless exempt, a Biodiversity Gain Plan must be approved before development begins. The government expects the area based exemption to remove more than half of the smallest applications currently delivering mandatory Biodiversity Net Gain from the regime. Its stated intention is to concentrate limited developer and local authority resources on proposals with greater ecological impacts. This estimate is set out in the government response to the 2025 consultation.

An exemption from the statutory condition does not, however, remove every ecological consideration. Protected species, protected sites, trees, local planning policies and the wider mitigation hierarchy may still be relevant. Defra also says that exempt development should continue to incorporate nature friendly features where practicable. This leaves room for proportionate measures such as retaining mature vegetation, integrating planting into drainage strategies and providing habitat features that support the character and long term resilience of a place.

Practical points for project teams

Project sponsors and advisers should now:

• confirm the planning application date before deciding which rules apply;
• calculate the full area inside the red line boundary, rather than relying on the building footprint;
• check for priority habitat before claiming the 0.2 hectare or temporary development exemption;
• review self build and custom build projects that were budgeted on the assumption of an automatic exemption;
• state clearly within the application why an exemption is considered to apply;
• retain suitable plans and ecological evidence where the exemption is not immediately apparent;
• test onsite and offsite delivery options early for non-major schemes that remain subject to the 10 per cent requirement.

Government guidance confirms that the application’s location plan can provide the starting point for assessing compliance with the 0.2 hectare threshold. Where habitat status is uncertain, early ecological advice may still prevent validation questions, redesign and delay. The Defra exemptions guidance provides the detailed qualifying conditions.

A more proportionate regime, with important boundaries

The August Biodiversity Net Gain changes should simplify planning for many genuinely small or short term projects. At the same time, the removal of the self build exemption means that some schemes face new work and cost.

The practical lesson is that site size alone is not enough. Application timing, the red line boundary and existing habitat all determine the correct route. Teams that establish those facts at project outset will be better placed to commission proportionate ecology work, protect programme certainty and avoid unexpected requirements at validation or before commencement.