Biodiversity net gain (BNG) requires many new developments in England to leave nature in a measurably better state than before, usually by at least 10%. It's worked out with an official metric and has to be secured for 30 years. For a small project it can add real cost and complication, so it's important to know whether it applies.
Projects that don't need BNG
- Householder applications: extensions, loft conversions, conservatories and outbuildings
- Small sites: from 6 August 2026, development on a site of 0.2 hectares or less (about half an acre), unless it's major development
- "De minimis" developments: those affecting less than 25 square metres of habitat, or less than 5 metres of hedgerow
- Permitted development, including Class Q prior approvals
- Temporary permissions of five years or less (from 6 August 2026)
The small sites, de minimis and temporary exemptions don't apply if the work would affect a priority habitat.
Self-build homes
The separate self-build exemption ended on 6 August 2026 for new applications. In practice, most self-build plots are under 0.2 hectares, so they're covered by the new small sites exemption instead.
Projects that usually do need BNG
- new homes on sites larger than 0.2 hectares
- major development: 10 or more homes, or larger commercial schemes
- larger commercial, agricultural or equestrian buildings on bigger sites
What if it applies?
You'll need an ecologist to assess the habitat before and after, using the metric, and a plan to deliver the gain: on site, through off-site units, or as a last resort through statutory credits. Since August 2026, smaller (non-major) schemes can use off-site units without first proving that on-site gain isn't possible.
Wildlife still matters either way
Even where BNG doesn't apply, protected species such as bats, newts and nesting birds are still protected by law, and the council will still apply its own policies on trees, hedgerows and habitats. A roof alteration or barn conversion may still need a bat survey.
How we can help
We check whether BNG applies when we first look at your project, arrange an ecologist where it's needed, and design to keep the requirement as simple as possible.
Book a free home visit
Ben will visit your site, tell you which surveys and reports your project actually needs, and give you a fixed quote.
Every site is different. This guide is general information, not advice on your project. For a straight answer about your property, book a free home visit: Ben will come and look, with no obligation.
Who'll handle your project: Benjamin Plunkett, our Managing Director and Planning & Heritage Consultant, is your point of contact from the first site visit to the decision. Charlie Plunkett MCIAT produces the drawings.
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