New Biodiversity Net Gain Exemptions: Everything Developers Need to Know from August 2026

Important changes to England’s mandatory biodiversity net gain requirements came into force on 6 August 2026. The changes introduce new exemptions for smaller sites and temporary developments, remove the previous exemption for self-build and custom-build schemes, and provide greater flexibility for non-major developments that remain subject to BNG.

For developers, landowners and planning professionals, the key question is now whether a development qualifies for one of the new exemptions and whether sufficient evidence is available to support that position.

At a Glance

• New applications on sites of 0.2ha or below are exempt unless onsite priority habitat is impacted.
• Qualifying temporary developments of no more than five years are exempt.
• The standalone self-build and custom-build exemption has been removed.
• Non-major developments that remain subject to BNG no longer need to prioritise onsite BNG delivery over purchasing offsite biodiversity units.
• Applications submitted before 6 August 2026 remain subject to the previous rules.

What Changed on 6 August 2026?

The principal changes are:

• Planning applications for development on sites of 0.2 hectares or below are exempt where the application was made on or after 6 August 2026 and no onsite priority habitat is negatively impacted.
• Qualifying temporary developments permitted for five years or less may be exempt.
• The previous self-build and custom-build exemption has been removed for new applications.
• The Biodiversity Gain Hierarchy has been amended for non-major developments, providing greater flexibility to use registered offsite biodiversity gains.

The new exemptions generally apply only to planning applications submitted on or after 6 August 2026. Applications already submitted before that date continue to be assessed under the BNG rules that applied when the application was made.

The New 0.2-Hectare Exemption

The most significant change is the introduction of an area-based exemption for development sites measuring 0.2 hectares or below. This is equivalent to 2,000 square metres or approximately 0.494 acres. A site measuring exactly 0.2 hectares is included within the exemption.

The exemption applies across different development types, rather than being restricted to residential schemes or particular forms of minor development. A qualifying residential, commercial, agricultural or mixed-use development could therefore benefit from the exemption.

Importantly, the threshold relates to the total site area within the planning application’s red-line boundary. It is not based on the size of the proposed building, the development footprint or the amount of habitat being removed.

For example, a building with a footprint of 500 square metres on a red-line site measuring 0.3 hectares would not qualify for the new area-based exemption ‘Developments of 0.2 hectares or below’. Conversely, a development footprint occupying most of a 0.19-hectare site could potentially qualify.

Where the exemption applies, the development should not be required to deliver the statutory minimum 10% biodiversity net gain or submit a Biodiversity Gain Plan under the mandatory BNG regime.

However, there is one particularly important qualification: the exemption does not apply where the development negatively impacts an onsite priority habitat.

The Priority Habitat Exception

Priority habitats are habitats identified as being of particular importance for biodiversity under section 41 of the Natural Environment and Rural Communities Act 2006. They include a range of grassland, woodland, wetland, coastal and other more common habitat types such as hedgerows.

The presence of priority habitat within a red-line boundary does not necessarily prevent the exemption from applying. The relevant issue is whether the development will negatively impact that habitat.

An impact can include the loss or degradation of a habitat where this reduces its biodiversity value. Consequently, a development may be able to avoid an impact through its design, appropriate protection measures or by retaining the habitat unaffected.

Nevertheless, some priority habitats are not immediately apparent without appropriate ecological assessment. A site should not be assumed to be exempt simply because it falls below the 0.2-hectare threshold.

Where the priority habitat position is uncertain, an early ecological review can establish whether priority habitat is present, whether it would be affected and what supporting information should accompany the application.

The New Temporary Development Exemption

A separate exemption has been introduced for certain temporary developments permitted for no more than five years.

To qualify:

• The whole development must be solely temporary.
• Planning permission must be granted for a period of five years or less.
• The permission must require the authorised buildings or works to be removed, the use to cease and the land to be reinstated within that period.
• The development must not negatively impact onsite priority habitat.
• The application must have been submitted on or after 6 August 2026.

The exemption may be relevant to developments such as temporary car parks, construction compounds and other short-term uses. However, describing a development as temporary will not, by itself, make it exempt.

Successive planning permissions cannot be used to extend the same temporary development beyond five years while retaining the exemption. For example, if temporary permission is granted for four years, a subsequent permission for another three years would take the combined period above five years and would not qualify for this exemption.

The Self-Build and Custom-Build Exemption Has Been Removed

Before 6 August 2026, an exemption was available for qualifying self-build and custom-build developments.

This standalone exemption has now been removed for new applications on or after 6 August 2026.

Self-build and custom-build developments are not necessarily subject to BNG, however, because another exemption may apply. In particular, many smaller self-build sites may fall within the new 0.2-hectare exemption.

A single self-build dwelling proposed on a 0.16 hectare site, for example, should be exempt if no priority habitat is negatively impacted. A similar proposal on a 0.21 hectare vegetated site would no longer be automatically exempt and would need to be assessed against the remaining exemptions.

Qualifying self-build applications made before 6 August 2026 retain the previous exemption. The application date is therefore critical when establishing the relevant requirements.

What Happens to Applications Already in the Planning System?

The new area-based and temporary-development exemptions are not retrospective.

An application submitted before 6 August 2026 does not become exempt because the site is below 0.2 hectares, even where the application remains undetermined. It continues under the BNG rules in place at the time when it was submitted.

Similarly, the changes do not remove BNG requirements from existing planning permissions. Where mandatory BNG applied when an application was submitted and permission was granted, the associated requirements must still be delivered.

This may include an approved Biodiversity Gain Plan, Habitat Management and Monitoring Plan, planning conditions, Section 106 obligations and long-term 30-year habitat management commitments for significant biodiversity gains.

Particular care is also needed with Section 73 applications to vary or remove planning conditions attached to an existing planning permission. The new 0.2 hectare and temporary development exemptions do not apply to a Section 73 permission where the original permission was applied for or granted before 6 August 2026. A Section 73 application cannot be used simply to remove the statutory biodiversity gain condition from an existing permission.

The De Minimis Exemption Remains Available

The existing de minimis exemption has not been replaced by the new area-based exemption.

It can apply where a development:

• Does not negatively impact onsite priority habitat.
• Impacts less than 25 square metres of onsite habitat with a biodiversity value greater than zero.
• Impacts less than five metres of onsite linear habitat, such as a hedgerow.

The distinction is that the 0.2 hectare exemption is based on the size of the red-line site boundary, while the de minimis exemption is based on the amount of habitat being impacted.

The de minimis exemption can therefore remain relevant to sites larger than 0.2 hectares. Examples could include changes of use, development on sealed surfaces, work within existing building footprints or proposals resulting in only a very small loss of vegetated habitat such as grass.

Applicants relying on the de minimis exemption should provide sufficient evidence to demonstrate that the thresholds will not be exceeded. Multiple small areas of habitat impact must be considered cumulatively.

Other Exemptions Remain

Other established exemptions including householder applications, permitted development rights and development undertaken solely or mainly to create an offsite biodiversity gain also remain in place.

Greater Flexibility to Use Offsite Biodiversity Gains

The same regulatory changes also modified the Biodiversity Gain Hierarchy for non-major developments that remain subject to BNG.

Previously, the hierarchy prioritised on site habitat enhancement and creation first, ahead of using registered offsite biodiversity gains (such as habitat banks), once on-site opportunities were exhausted. For relevant non-major applications submitted on or after 6 August 2026, onsite enhancement, onsite creation and registered offsite biodiversity gains are now treated at the same level of preference.

This gives smaller developments greater flexibility to use offsite biodiversity units where onsite delivery of habitats would be impractical, disproportionately expensive or incompatible with the intended use of the site.

Statutory biodiversity credits remain the final option. The requirement to avoid and mitigate impacts to habitats of medium, high and very high distinctiveness also continues to apply. The modified BNG hierarchy should not be confused with the wider ecological mitigation hierarchy, which requires ecological harm to be avoided, mitigated and only compensated for as a last resort.

Does an Exemption Mean No Ecology Work is Required?

Being exempt from mandatory BNG does not remove other ecological and planning requirements.

An exempt development may still need to address:

• Protected species such as bats, great crested newts, badgers and nesting birds.
• Impacts on designated sites and local wildlife sites.
• Priority habitats.
• National and local planning policies relating to biodiversity.
• The ecological mitigation hierarchy.
• Appropriate biodiversity protection and enhancement measures.

The relevant planning authority may therefore still require ecological information, even where a statutory BNG metric and Biodiversity Gain Plan are not required.

What Should Applicants Do Now?

Before relying on an exemption, applicants or their agents should:

1. Confirm when the planning application will be (or was) submitted.
2. Measure the complete site within the red-line boundary.
3. Identify the specific exemption being relied upon, if any.
4. Establish whether priority habitat is present and whether it will be impacted (this may require habitat assessment, potentially undertaken as part of a Preliminary Ecological Appraisal).
5. Consider whether protected species or other ecological constraints are relevant.
6. Provide a statement with the application explaining why the biodiversity gain condition does not apply, with reference to which exemptions or transitional arrangements you believe apply.
7. Include supporting plans or ecological evidence where the position is not self-evident.

Proportionate ecological input may still be advisable to confirm the ‘priority habitat’ position and reduce the risk of validation queries or delays.

Further Changes Are Expected

The August amendments represent the first phase of changes to BNG announced following the government’s consultation.

Further proposals include exemptions for development whose primary objective is to conserve or enhance biodiversity, and exemptions for certain developments enhancing parks, playing fields and public gardens. Further changes to the statutory biodiversity metric and a separate government response concerning residential brownfield development are also expected.

These proposals should not yet be treated as current exemptions.

How We Can Help

The new exemptions should reduce the BNG burden for many smaller developments, but the correct position depends on the site boundary, application history, habitats present and proposed impacts.

Elton Ecology can review your red-line boundary and development proposals, establish whether an exemption is likely to apply and identify the proportionate ecological information needed for a robust planning submission.

If you are preparing an application and are unsure whether BNG applies, send us your red-line plan and a brief description of the proposals for an initial review.

The new BNG rules are set out in the GOV.UK guidance on exempt developments, the updated Planning Practice Guidance on BNG and the 2026 Regulations.

This article relates to development requiring planning permission under the Town and Country Planning Act 1990 in England. Information correct as at August 2026.