Mandatory 10% biodiversity net gain does not apply to every application — and the exemption list is about to change in a big way: from 6 August 2026, developments on sites of 0.2 hectares or less are exempt, alongside new rules for temporary permissions. This checker applies the current GOV.UK list, including the switch-over.
Check your exemption
The checker needs JavaScript. The official list is on GOV.UK.
The exemptions, plainly
- Householder applications — extensions, lofts, outbuildings: exempt.
- De minimis — less than 25 m² of on-site habitat affected and under 5 m of hedgerow: exempt (evidence the areas).
- Permitted development — outside mandatory BNG entirely.
- Self-build and custom build — up to 9 dwellings on up to 0.5 ha: exempt for applications before 6 August 2026.
- From 6 August 2026 — sites with a red-line area of 0.2 ha or less are exempt, and wholly temporary developments (permission for 5 years or less) join the list.
What the August 2026 change really means
For small developers the timing now matters. A 0.15 ha scheme submitted in July 2026 carries full BNG obligations; the same scheme submitted after 6 August is exempt. Conversely, self-builders on sites between 0.2 and 0.5 ha lose their route and should apply before the switch. Check both dates against your programme — and remember exemption from the mandatory scheme does not stop a local plan policy asking for proportionate biodiversity enhancements.
If BNG applies after all
You will need the statutory metric, a habitat plan secured for 30 years, and evidence you followed the hierarchy — on-site first, off-site units second, statutory credits (from £42,000 per credit, doubled by the multiplier) last. See what failure costs in the credit cost calculator and the full 2026 price analysis.
How Fortress Associates can help
Our automated sustainability statement is free and ready in minutes — covering the 10% BNG requirement, water efficiency (110 l/p/d), urban greening and BREEAM where required, for every UK local authority. Pair it with the document checklist generator, or ask us about a tricky site.
Sources & further reading
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