Biodiversity net gain just changed twice in a fortnight

§1What happened

Mandatory biodiversity net gain — the requirement to deliver a 10% uplift — has been part of the system since 2024, and it has been the single most complained-about addition to small-scheme planning in years. The complaint was proportionality: the assessment cost roughly the same whether you were building four hundred homes or one, and on the smallest sites it could exceed the value of the land it was measuring.

The Government has now acted on that. From 31 July 2026, non-major development on sites of 0.2 hectares or smaller is exempt, provided the development doesn't affect priority habitat.

The estimate attached to the change is that around half of residential planning applications fall out of the regime.

§2The exemption that disappeared on the same day

Less widely noticed, and more likely to hurt someone: the self-build and custom-build exemption has been removed, with effect from the same date.

The logic is presumably that the new 0.2 hectare threshold catches most self-build plots anyway, and for most it will. But not all. A self-build on a generous rural plot, or one where the red line takes in more land than the house needs, can be over 0.2 hectares — and that scheme has just moved from exempt to caught.

If you were relying on the self-build exemption, your position needs re-checking. Not eventually. Before you submit.

§3And a third change, five days later

From 6 August 2026, the on-site-first hierarchy applies only to major development.

Previously, a scheme had to demonstrate that on-site biodiversity enhancement wasn't achievable before it could meet its obligation with off-site units. For non-major development that requirement has gone — off-site units can be used without evidencing that on-site was impossible.

That is a small but useful simplification. The "prove you tried" step was a meaningful cost on small schemes, and it produced a lot of documents that nobody was ever going to rely on.

§4What exempt does not mean

This is where people will overreach, so it's worth being blunt.

Exempt from BNG is not the same as unconstrained. The National Planning Policy Framework still applies. Protected species law still applies, entirely separately, and it has nothing to do with these thresholds. Trees, hedgerows and watercourses are all still protected by their own regimes.

And an application that causes significant harm to biodiversity which can't be avoided, mitigated or compensated is still refusable — exemption or not.

The change removes a metric and a paperwork exercise from small schemes. It does not remove ecology from planning.

§5Priority habitat is the condition everyone will skip

The exemption is conditional on the development not affecting priority habitat. That condition will be the thing that catches people, because it isn't visible from a site visit and it isn't intuitive.

Priority habitats include things that don't look like habitat to a non-specialist — certain grasslands, hedgerows, orchards, ponds. A scrubby corner of a paddock can be one. If there's any prospect of priority habitat on or adjacent to the site, the exemption needs checking rather than assuming.

§6What to do now

If you're about to submit: check whether you're under 0.2 hectares and whether priority habitat is engaged. If both answers are favourable, you have just saved an assessment.

If you were relying on the self-build exemption: re-check immediately. The route you were on has closed.

If you're mid-application: transitional arrangements matter and they're detailed. Where a scheme is caught between regimes, that's worth an hour of proper advice rather than a guess.

If your site is over 0.2 hectares: nothing has changed for you except the hierarchy, and only if you're non-major.