Biodiversity Net Gain explained, and what changed in August 2026.

Biodiversity Net Gain is one of the biggest recent shifts in the English planning system, and one of the most misunderstood. For some projects it is a high cost and a long-term commitment; for many others, particularly after the changes in August 2026, it does not apply at all. Knowing which camp your scheme falls into early saves a great deal of time and money. This is a plain-English guide to what BNG is, what recently changed, and the options for delivering it. It reflects the rules as they stand in August 2026, and because BNG is evolving quickly, you should always check the current position.

What is Biodiversity Net Gain?

Biodiversity Net Gain, or BNG, is a legal requirement for most new development in England to leave nature in a measurably better state than it was before. In practice, that means delivering a 10% net gain in biodiversity, measured in standardised biodiversity units using the government's statutory metric. It became mandatory for major development on 12 February 2024, and for smaller sites shortly after, under Schedule 7A of the Town and Country Planning Act 1990, introduced by the Environment Act 2021. It applies to most planning permissions and must be resolved before an application can be determined.

The 10% and the 30 years

Two numbers matter. The first is the 10% uplift in biodiversity value your scheme has to achieve. The second, and the one people underestimate, is 30: any habitat you create or enhance to meet BNG must be secured and maintained for at least 30 years, usually through a planning obligation (a section 106 agreement) or a conservation covenant. BNG is not a one-off box ticked at application stage. It is a long-term management commitment that runs with the land.

How the gain is delivered: the hierarchy

There is a set order for delivering your 10%. First, on-site: creating or enhancing habitat within the red line of your development. Where a scheme cannot achieve all of its gain on-site, the shortfall is met off-site by securing biodiversity units from land elsewhere, often called a habitat bank. Only as a last resort can you buy statutory biodiversity credits from the government, and these are deliberately priced to be the least attractive option. For most constrained sites, off-site units are the practical way to close the gap.

What changed on 6 August 2026

BNG has just been significantly relaxed for smaller developments. From 6 August 2026, it no longer applies to planning applications where the site area within the red line is 0.2 hectares (about 2,000 square metres) or less, provided no on-site priority habitat is affected. Short-term temporary developments, permitted for five years or less, were also exempted, and small developments can now go straight to off-site delivery without first exhausting on-site options. One catch: the previous self-build and custom-build exemption was removed on the same date, so those schemes now rely on the new 0.2 hectare rule instead. For many individual homes, extensions, and small plots, the practical effect is that BNG no longer bites.

Is your project exempt?

The main exemptions, as they stand, are: householder applications, such as extensions, loft conversions and conservatories; developments of 0.2 hectares or less within the red line; genuinely small impacts under the de minimis threshold, meaning less than 25 square metres of habitat or 5 metres of hedgerow; and short-term temporary permissions. Two important caveats apply to the area-based and de minimis exemptions: both fall away if on-site priority habitat is affected, so a small site with valuable habitat can still be caught. If you are unsure which side of the line your project sits, it is well worth checking before you design around an assumption. Whether priority habitat is present is a question for an ecological survey, and those surveys are season-dependent, so it is worth checking the timing early with our ecology survey calendar. Trees and hedgerows on a site carry their own separate protections, which we cover in our trees, TPOs and tree surveys.

BNG is specialist work, and where we come in

BNG assessments, and the metric calculations behind them, are specialist ecological work that we do not carry out ourselves. We work with several ecologists who provide that advice, and we bring the right one in as part of your planning strategy so it is handled properly. Where we can help directly is sourcing off-site units. Where a scheme needs biodiversity units it cannot deliver on-site, off-site units are usually better value than statutory government credits, and we can help developers source them. We are also working with landowners bringing units forward. So whether you own land that could generate units, or you are a developer who needs them, we would be glad to connect the two. To be clear, this is about sourcing units, not calculating your BNG requirement, which is a job for your ecologist.

Common questions

Does BNG apply to a single house or an extension?

Often not, especially since 6 August 2026. Householder works such as extensions are exempt, and a new house on a plot of 0.2 hectares or less is now generally outside BNG too, unless on-site priority habitat is affected. Larger plots and most major schemes remain subject to BNG.

What is the 0.2 hectare exemption?

From 6 August 2026, BNG does not apply where the site area inside the red line boundary is 0.2 hectares (around 2,000 square metres) or less. It is a straightforward area test, but it does not apply if on-site priority habitat would be impacted.

How long does Biodiversity Net Gain have to be maintained?

At least 30 years. Habitat created or enhanced to meet BNG is secured through a section 106 agreement or a conservation covenant, and must be managed and monitored for the full period.

Do you calculate BNG or provide the metric?

No. The BNG assessment and metric calculation are specialist ecological work, and we work with ecologists who provide that. We can help directly by sourcing off-site biodiversity units, as an alternative to statutory government credits, for schemes that need them.