England’s Biodiversity Net Gain rules changed on 6 August 2026. Here is what the new 0.2-hectare exemption, self-build reform and offsite flexibility mean for planning applications.

1. Mandatory BNG still requires at least a 10% increase where it applies.
2. The householder exemption remains.
3. Protected species, designated sites and planning policy still matter.
4. Government statutory biodiversity credits remain the last resort.

Unless an exemption or transitional provision applies, planning permission is subject to the statutory biodiversity gain condition. Development must deliver at least a 10% increase in biodiversity value compared with the pre-development value of the onsite habitat. The statutory biodiversity metric is used to calculate the baseline, the post-development habitat value and any registered offsite gains.

The detailed Biodiversity Gain Plan is normally submitted after permission but must be approved before development begins. Significant onsite gains and registered offsite gains are secured and managed for at least 30 years. BNG is therefore a design, planning, delivery and long-term management issue – not simply a calculation to complete after consent.

For applications made on or after 6 August 2026, development is exempt from mandatory BNG where the entire site inside the red-line boundary is no larger than 0.2 hectares. That is 2,000 square metres, or just under half an acre.

The exemption is area-based, not impact-based. The application must explain why the biodiversity gain condition does not apply, and the location plan provides the initial evidence of site area.

There is an important ecological safeguard: the exemption does not apply where the development decreases the biodiversity value of onsite priority habitat. A site can therefore be below the numerical threshold and still require mandatory BNG. Where the habitat status or likely effects are uncertain, an early ecological review remains sensible.

A new exemption also applies to applications made on or after 6 August 2026 where the whole development is temporary and permission is limited to five years or less. The permission must require buildings or works to be removed, the authorised use to cease and the land to be reinstated within that period. The development must not decrease the biodiversity value of onsite priority habitat.

The five-year limit is cumulative. If earlier permissions for the same temporary development, combined with the new permission, would take it beyond five years, the exemption will not apply. This is particularly relevant to repeat permissions for temporary compounds, car parks and similar uses.

For non-major development that remains subject to BNG, the statutory Biodiversity Gain Hierarchy changed for applications made on or after 6 August 2026. Onsite habitat enhancement, onsite habitat creation and registered offsite biodiversity gains now sit at the same level of preference. A non-major scheme no longer has to demonstrate that onsite delivery was considered first before choosing registered offsite units.

That flexibility is not a licence to ignore ecological design. Adverse effects on onsite habitats of medium, high or very high distinctiveness must still be avoided and, where avoidance is not possible, mitigated. Government statutory biodiversity credits remain the final option. Separately, the National Planning Policy Framework mitigation hierarchy continues to apply where development would cause significant harm to biodiversity.

For architects, this can reduce pressure to force small and potentially unsuitable habitat features into constrained layouts. For planning consultants, it should reduce arguments about whether every onsite option has been exhausted. The selected solution must nevertheless be credible, deliverable and properly secured.

For new applications made on or after 6 August 2026, self-build or custom-build status no longer provides a standalone exemption from mandatory BNG.

This does not mean every self-build now requires BNG. Many single-dwelling projects will fall within the new 0.2-hectare area-based exemption, provided no onsite priority habitat is negatively affected. A self-build site over 0.2 hectares will need to meet mandatory BNG unless another exemption applies.

APPLICATIONS MADE ON OR AFTER 6 AUGUST 2026

The new exemptions and hierarchy apply, subject to their detailed conditions. Self-build or custom-build status alone no longer creates an exemption.

Reserved matters approvals are not themselves a new grant of planning permission for BNG purposes, so the position is governed by the underlying outline permission. Project teams should audit the consent history rather than treating the latest submission in isolation.

The existing exemption for a genuine householder application remains. This commonly covers works such as extensions, conservatories and loft conversions to an existing home.

It should not be confused with an application made by a householder or landowner for a new dwelling. A new house is not householder development simply because the applicant intends to live in it.

An exemption removes the statutory biodiversity gain condition; it does not remove other environmental legislation or planning policy. Protected species, designated sites, priority habitats, trees, hedgerows and wider ecological networks may still need to be assessed. Planning decisions must still apply the mitigation hierarchy, and proportionate biodiversity enhancements may still be appropriate.

Planning Practice Guidance indicates that local plans should not reapply the statutory BNG framework to exempt categories. That is different from applying justified local biodiversity policy, seeking mitigation for identified effects or asking for proportionate evidence to understand a site’s ecological constraints.

1. Confirm the application route and submission date. Record why the scheme is in scope, out of scope or exempt.
2. Check the full red-line area early. Include access, visibility splays, drainage and any other land needed for the development.
3. Screen for priority habitat and wider ecological constraints. An area calculation alone is not enough to rely safely on the new exemptions.
4. Coordinate the architect, planner, landscape professional and ecologist before the layout hardens.
5. Support an exemption statement with proportionate evidence. A clear plan and concise ecological reasoning can prevent validation queries.
6. Treat section 73, outline, reserved-matters and phased schemes as specialist cases. Review their consent history before advising.

The August 2026 amendments make BNG more proportionate for the smallest sites and more flexible for non-major development. They also create a sharper need for early, accurate triage. A simple area threshold can be checked quickly, but the correct answer still depends on application type, application date, red-line boundary, habitat status and consent history.

The best response is not to leave BNG until after the design is fixed. Establish the project’s BNG status at the outset, document the reasoning and integrate the right level of ecological input into the programme. That is the most reliable way to avoid unnecessary work while protecting planning certainty.

Frequently asked questions

Does BNG apply to a site under 0.2 hectares?

A new application made on or after 6 August 2026 may be exempt where the whole red-line site is no larger than 0.2 hectares and the development will not decrease the biodiversity value of onsite priority habitat. Wider ecology requirements can still apply.

Do self-build homes need Biodiversity Net Gain?

Self-build status no longer provides its own exemption for new applications. Many small self-build sites may qualify under the 0.2-hectare exemption, but sites above the threshold will require BNG unless another exemption applies.

Does BNG apply to a house extension?

A genuine householder application, such as an extension or loft conversion to an existing home, remains exempt. A planning application for a new dwelling is not householder development.

Do I still need an ecology survey if a development is exempt from BNG?

Possibly. The BNG exemption does not remove requirements relating to protected species, designated sites, priority habitats, trees, hedgerows or relevant national and local planning policy.

Official sources

1. Defra Environment Blog
2. Planning Practice Guidance
3. BNG exempt developments
4. Understanding Biodiversity Net Gain
5. 2026 Regulations

This article applies to planning applications in England under the Town and Country Planning Act regime. It is general guidance, not legal advice. Check the current legislation and guidance for a particular application.