What’s changing?
From 6 August 2026, many planning applications on sites of 0.2 hectares (around half an acre) or less will be be exempt from the mandatory BNG rules. The exemption applies to the whole site within the planning application’s red-line boundary, not just the area being built on.
Does every small site qualify?
No. The exemption does not apply if the site contains priority habitat. Some projects may still need ecological advice to establish whether the exemption applies.
What does this mean for homeowners?
Most householder applications, including extensions, loft conversions and conservatories, are already exempt from BNG. The new rules are more likely to benefit:
- Replacement dwellings
- New homes
- Small residential developments
- Some rural and commercial projects
I’m building my own home. Does this affect me?
Yes, it could. The current BNG exemption for many self-build projects ends for new planning applications submitted after 6 August 2026. Some smaller self-build projects may qualify under the new 0.2-hectare exemption, while others may need to meet the full BNG requirements. It depends on:
- The size of the site
- When the application is submitted
- Whether any priority habitat is affected
Will it save me money?
Possibly. If your project qualifies for the exemption, you may need less Biodiversity Net Gain work. This could reduce professional fees and planning costs. However, ecological surveys may still be needed for bats, trees, protected species or other planning requirements.
Will planning be quicker?
It may simplify some planning applications, but it does not guarantee a faster planning decision. Planning officers will still consider issues such as design, highways, flood risk and ecology.
What if I already have planning permission?
Planning terminology can be confusing. A Section 73 application allows changes to the conditions attached to an existing planning permission. It is often used to make relatively minor amendments without submitting a completely new planning application. If you’re applying to make a minor change to an existing planning permission (known as a Section 73 application), you may not need to comply with the new Biodiversity Net Gain requirements. Where the original self-build planning permission was exempt, that exemption will normally continue to apply to the Section 73 application. If you’re unsure whether this applies to your project, it’s worth seeking advice before submitting your application.
What should I do next?
Before submitting a planning application, ask yourself:
- Is my application being submitted after 6 August 2026?
- Is my site 0.2 hectares or less?
- Does the site contain any priority habitat?
- Will I still need ecological surveys?
Getting these answers early can help avoid unnecessary costs and delays.
How O2i Design can help
Planning rules continue to evolve and our O2i Design team aims to explain the latest guidance in plain English and advise how it applies to your project. Where specialist ecological advice is needed, we work alongside experienced consultants to help you prepare a robust planning application. To read more about our residential projects and self builds take a look here.
This article provides O2i Design’s summary of the Government’s Biodiversity Net Gain guidance, based on the information available at the time of publication. It is intended as general guidance only and should not be relied upon as legal, planning or ecological advice. Every site is different, and the requirements for your project will depend on its individual circumstances. For the latest official guidance, please refer to the GOV.UK website. You can read the Government advise here: https://www.gov.uk/guidance/understanding-biodiversity-net-gain and here: https://www.gov.uk/guidance/biodiversity-net-gain-exempt-developments and here : https://www.gov.uk/guidance/biodiversity-net-gain-exempt-developments#developments-subject-to-the-de-minimis-rule
Updated: July 2026 .
