Check the application date and the whole site
The August changes apply through the 2026 amendment regulations and their transitional provisions. The area-based exemption concerns the planning application's red-line site, not merely the footprint of the proposed building. A small house on a larger application site should not automatically be treated as a site below the exemption threshold. [2] [3]
Earlier permissions and applications can retain the treatment provided by the transitional rules, including specified section 73 applications. Establish the original application date and permission history rather than applying the newest exemption wording indiscriminately to every amendment. [3]
Other exemptions remain important
Householder development and permitted development have exemptions. A separate de minimis exemption can apply where there is no impact on priority habitat and the impact falls below the specified habitat thresholds: less than 25 square metres of area habitat and less than five metres of linear habitat. These are different tests from the new site-area exemption. [2]
The removal of the self-build exemption does not mean every self-build project now needs BNG. A self-build proposal may qualify for another exemption, such as the new area-based exemption, if its conditions are satisfied. Conversely, calling a larger scheme “self-build” no longer supplies a standalone exemption for a new application. [2]
Exempt from BNG does not mean exempt from ecology
BNG is one part of the assessment. Protected species and habitats remain subject to their own requirements, and a council may need ecological evidence to understand the proposal's effects. A bat roost cannot be disregarded because an extension is a householder application. [4] [5]
Ask a competent ecology professional to advise where habitat type or priority-habitat impact is uncertain. Record the exemption relied upon and the evidence supporting it, rather than using an unexplained sentence saying that the project is too small.
What happens when BNG applies?
The statutory metric measures biodiversity value; the target is not simply a promise to landscape 10% of the site. Delivery may involve onsite habitat, off-site units or, as a last resort, statutory credits. The biodiversity gain plan must be approved before the development starts, and significant onsite gains and off-site gains normally carry at least 30 years of management commitments. [1] [6]
Give the ecologist the proposed layout early enough to assess realistic habitat retention and delivery options. Treat the ecological baseline, the metric and the eventual management obligations as connected parts of the project.
Announced further reforms
Defra's July 2026 update describes additional work on exemptions and the metric, alongside the separate brownfield consultation. Those announcements are not a general exemption for brownfield development. Use the exemptions in the current official guidance and enacted regulations, and check the commencement of any further reform. [7]