Biodiversity Net Gain Changes 6 August 2026: What Developers Must Know Now

Last updated: August 24, 2026

Quick Answer: On 6 August 2026, the Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026 came into force, introducing a new 0.2-hectare site exemption, a temporary development exemption, and the removal of the self-build exemption. The core 10% net gain requirement remains unchanged. Developers, ecologists, and planning consultants must reassess their project portfolios immediately to determine which schemes are newly in scope and which qualify for the new exemptions.

Key Takeaways

• A new exemption applies to development sites of no more than 0.2 hectares where no onsite priority habitat is affected.
• Temporary developments where land is fully reinstated within five years are now exempt, unless priority habitat is negatively impacted.
• The self-build and custom-build exemption has been removed; schemes above the 0.2ha threshold now fall within mandatory BNG for the first time.
• For minor developments that remain in scope, offsite biodiversity gains now carry equal priority to onsite creation or enhancement in the biodiversity gain hierarchy.
• The 10% mandatory net gain requirement is unchanged for all developments still within scope.
• From 2 November 2026, BNG becomes mandatory for Nationally Significant Infrastructure Projects (NSIPs).
• Developers with live applications should urgently review whether their scheme's exemption status has changed.

What Is Biodiversity Net Gain and Why Does It Matter for Developers

Biodiversity Net Gain (BNG) is a planning requirement in England that obliges developers to leave biodiversity in a measurably better state than before development took place. Under the Environment Act 2021, most new developments must deliver at least a 10% net gain in biodiversity units, calculated using Natural England's Biodiversity Metric.

For developers, BNG is not optional. It is a pre-commencement condition on planning permissions, meaning work cannot legally start until a compliant Biodiversity Gain Plan has been approved by the local planning authority (LPA). Failure to comply can halt a project entirely. The regime has applied to major developments since February 2024 and to minor developments since April 2024, making it one of the most significant planning policy shifts in a generation.

Biodiversity Net Gain Changes August 2026: What's New

The Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026, which came into force on 6 August 2026, introduced four substantive changes to the existing BNG framework. These are the most significant amendments to the regime since its rollout began.

Summary of the four key changes:

Change	Detail
New 0.2ha site exemption	Sites of no more than 0.2ha with no onsite priority habitat affected are exempt
Temporary development exemption	Land reinstated within 5 years is exempt, unless priority habitat is impacted
Self-build exemption removed	Self-build/custom-build schemes above 0.2ha now fall within mandatory BNG
Amended biodiversity gain hierarchy	For minor in-scope developments, offsite gains now equal onsite gains in priority

The 10% net gain target itself has not changed. Developers whose projects remain in scope must still meet this threshold.

Biodiversity Net Gain Exemptions and Thresholds August 2026

Two new exemptions came into force on 6 August 2026, and one existing exemption was removed.

New 0.2-hectare site exemption

Development on a site of no more than 0.2 hectares is now exempt from mandatory BNG, provided that no onsite priority habitat is present or affected. This is a meaningful threshold for small infill plots, garden developments, and minor residential schemes. Developers must confirm both conditions are met: the site area must not exceed 0.2ha, and the development must not negatively affect any priority habitat on that land.

New temporary development exemption

Developments where the land will be fully reinstated to its prior condition within five years are now exempt. This covers uses such as temporary construction compounds, short-term event infrastructure, and certain utilities works. The exemption does not apply where priority habitat would be negatively impacted during the temporary period, even if the land is later reinstated.

Removal of the self-build exemption

Previously, self-build and custom-build housing schemes were exempt from mandatory BNG. From 6 August 2026, that exemption no longer exists for schemes above the 0.2ha threshold. Any self-build or custom-build project on a site larger than 0.2ha must now comply with mandatory BNG in full, including the 10% net gain requirement and submission of a Biodiversity Gain Plan. This is a significant change for self-build developers who may not have factored BNG costs into their project appraisals.

How Will the August 2026 BNG Changes Affect My Development Project

The impact depends on the type, scale, and site characteristics of your development.

• Small sites under 0.2ha with no priority habitat: Likely newly exempt. Confirm site area and commission a habitat survey to verify no priority habitat is present.
• Temporary developments: Review whether your project meets the five-year reinstatement test and whether any priority habitat is at risk during the temporary phase.
• Self-build schemes above 0.2ha: Now in scope for the first time. A Biodiversity Metric assessment and Biodiversity Gain Plan will be required before commencement.
• Minor developments already in scope: The amended gain hierarchy means offsite options are now equally valid as onsite measures, which may open up more cost-effective routes to compliance.
• Major developments: No change to the core framework. The 10% requirement and existing hierarchy apply as before.

Planning consultants at firms including Tozers and Savills have advised clients to review all live applications and pre-application inquiries in light of the August 2026 changes, particularly where self-build or small-site exemptions were previously assumed.

Biodiversity Net Gain Requirements for Developers in 2026

For developments that remain in scope after the August 2026 amendments, the core requirements are unchanged. Developers must:

1. Commission a baseline habitat survey using Natural England's Biodiversity Metric (currently version 4.0).
2. Calculate the pre-development biodiversity unit value of the site.
3. Design the development to achieve at least 10% more biodiversity units than the baseline.
4. Submit a Biodiversity Gain Plan to the LPA as a pre-commencement condition.
5. Secure a Biodiversity Gain Site agreement or statutory biodiversity credits if offsite or credit-based delivery is required.
6. Ensure any habitat management and monitoring obligations are secured for a minimum of 30 years.

Wealden District Council, among other LPAs, has published updated guidance for applicants following the August 2026 regulatory changes, clarifying how the new exemptions will be assessed at the local level.

How the Amended Biodiversity Gain Hierarchy Affects Minor Developments

For minor developments that are not exempt, the biodiversity gain hierarchy has been amended so that offsite biodiversity gains carry equal priority to onsite creation and enhancement. Previously, the hierarchy required developers to maximise onsite gains first, then look to offsite measures, and only use statutory biodiversity credits as a last resort.

Under the revised hierarchy for minor developments:

• Onsite creation and enhancement
• Offsite biodiversity gains (now at equal priority to onsite)
• Statutory biodiversity credits (last resort, as before)

This change gives minor developers greater flexibility. Where onsite habitat creation is impractical due to site constraints, offsite gains through a registered Biodiversity Gain Site are now a fully equivalent option rather than a secondary fallback. This is particularly relevant for urban infill sites and brownfield developments where meaningful onsite habitat creation is difficult.

How to Calculate Biodiversity Net Gain for Your Site

Biodiversity Net Gain is calculated using Natural England's Biodiversity Metric, which assigns unit values to habitats based on their type, condition, and size. The calculation compares pre-development and post-development habitat values to determine whether a 10% net gain is achieved.

Key steps in the calculation:

1. Map and classify all habitats on the site using the UK Habitat Classification.
2. Assess the condition of each habitat (poor, moderate, or good).
3. Apply the metric to calculate pre-development biodiversity units.
4. Model the post-development habitat scenario, including any onsite or offsite enhancements.
5. Confirm the post-development total is at least 10% higher than the pre-development baseline.
6. Account for spatial risk multipliers if offsite habitats are used.

Ecologists and planning consultants should use the most current version of the metric. Defra and Natural England publish updates to the metric tool on GOV.UK, and LPAs will typically specify which version is acceptable for submissions.

Biodiversity Net Gain Offsetting Options for Developers

Where onsite gains are insufficient or impractical, developers have two main routes to offset the shortfall.

Registered Biodiversity Gain Sites: Private landowners can register land as a Biodiversity Gain Site and sell biodiversity units to developers. Following the August 2026 amendments, this route is now equally prioritised alongside onsite measures for minor developments. The off-site habitat must be secured through a conservation covenant or planning obligation for at least 30 years.

Statutory biodiversity credits: Defra operates a statutory credit scheme as a last resort. Credits are purchased directly from government and are priced to incentivise onsite and offsite delivery first. Credit prices are set by Defra and are publicly available on GOV.UK.

Savills and other land agents have noted growing demand for registered Biodiversity Gain Sites as the BNG market matures, with unit prices varying considerably by habitat type and geographic location.

How Much Will Biodiversity Net Gain Cost My Development

BNG costs vary widely depending on site size, baseline habitat quality, and the delivery route chosen. No single verified benchmark applies across all development types, but the following cost drivers are well established:

• Ecological survey costs: Typically a few thousand pounds for a small site; more for complex or larger sites.
• Onsite habitat creation: Costs depend on the type of habitat, landscaping requirements, and long-term management obligations.
• Offsite unit purchase: Market prices for biodiversity units from registered Biodiversity Gain Sites vary by habitat type and region. Prices are set by the market and can range from hundreds to thousands of pounds per unit.
• Statutory credits: Defra's credit prices are published on GOV.UK and are intentionally set above market rates to encourage non-credit delivery.

For self-build developers newly brought into scope by the August 2026 changes, early engagement with an ecologist is strongly recommended to understand likely BNG costs before finalising site acquisition or project budgets.

Upcoming Milestone: BNG for Nationally Significant Infrastructure Projects

From 2 November 2026, BNG becomes mandatory for Nationally Significant Infrastructure Projects (NSIPs) in England. NSIPs include major energy, transport, water, and waste infrastructure consented under the Planning Act 2008. This is a separate and significant expansion of the BNG regime, and NSIP promoters should already be integrating BNG requirements into their Development Consent Order applications and environmental impact assessments.

Local Government Lawyer has highlighted that the NSIP expansion will require close coordination between the Planning Inspectorate, Defra, and Natural England to ensure consistent application of the biodiversity gain hierarchy at the national infrastructure scale.

Common Mistakes Developers Make with Biodiversity Net Gain

Awareness of common errors can prevent costly delays at the planning stage.

• Assuming exemption without verification: The new 0.2ha exemption requires confirmation that no priority habitat is present. Developers who assume exemption without a habitat survey risk enforcement action.
• Overlooking the removal of the self-build exemption: Self-build developers who began pre-application discussions before August 2026 may not have been advised of the change. All self-build schemes above 0.2ha must now be reassessed.
• Leaving BNG too late: BNG is a pre-commencement condition. Leaving the Biodiversity Gain Plan to the final stages of pre-construction can cause significant delays.
• Using outdated metric versions: LPAs may reject submissions based on superseded versions of the Biodiversity Metric.
• Underestimating 30-year management costs: Long-term habitat management obligations are a real cost and must be factored into project viability assessments.

What Developers Must Do Now

The August 2026 changes require immediate action across several project types.

For all developers with live applications or projects in pre-application:

1. Review your site area. If it is at or near 0.2ha, commission a habitat survey to confirm whether the new exemption applies.
2. If your project involves temporary development, assess whether the five-year reinstatement test is met and whether priority habitat is at risk.
3. If you are a self-build developer with a site above 0.2ha, engage an ecologist immediately to begin the BNG assessment process.
4. For minor developments in scope, explore offsite biodiversity gain options as an equal alternative to onsite measures.
5. Confirm your Biodiversity Metric version with your LPA before submission.
6. If you are an NSIP promoter, begin integrating mandatory BNG requirements ahead of the 2 November 2026 deadline.

Planning law firms including Tozers have advised that developers who act early will be better placed to secure cost-effective biodiversity unit prices and avoid pre-commencement delays.

Biodiversity Net Gain vs Environmental Impact Assessment: Key Differences

BNG and Environmental Impact Assessment (EIA) are related but distinct requirements.

• EIA assesses the likely significant effects of a development on the environment, including biodiversity. It is a process of assessment and mitigation, not a mandatory outcome target.
• BNG requires a measurable, positive outcome: at least 10% more biodiversity units post-development than pre-development. It is a condition of planning permission, not just an assessment.

The two processes interact: EIA ecological chapters will inform the baseline habitat data used in BNG calculations, and mitigation measures identified through EIA may contribute to BNG delivery. However, a positive EIA outcome does not automatically mean BNG compliance, and vice versa.

FAQ

Q: Do the August 2026 BNG changes apply to all of England?
Yes. The Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026 apply across England. BNG is not devolved to Wales, Scotland, or Northern Ireland under the same framework.

Q: My self-build site is exactly 0.2ha with no priority habitat. Am I exempt?
Yes, provided the site is no more than 0.2ha and no onsite priority habitat is affected. You should obtain a habitat survey to confirm no priority habitat is present before relying on this exemption.

Q: Does the 10% net gain requirement change under the August 2026 regulations?
No. The core 10% net gain requirement remains unchanged for all developments that remain within scope of mandatory BNG.

Q: What counts as a "temporary development" for the new exemption?
The exemption applies where the land will be fully reinstated to its prior condition within five years of the development commencing. It does not apply where priority habitat would be negatively impacted during the temporary period, even if reinstatement is planned.

Q: When does BNG become mandatory for NSIPs?
BNG becomes mandatory for Nationally Significant Infrastructure Projects from 2 November 2026.

Q: Can a minor developer now use offsite biodiversity units without exhausting onsite options first?
Yes. Under the amended biodiversity gain hierarchy for minor developments, offsite biodiversity gains now carry equal priority to onsite creation and enhancement. Developers are no longer required to maximise onsite gains before turning to offsite options.

Q: Where can developers buy biodiversity credits or offsets?
Registered Biodiversity Gain Sites can be found through the Natural England biodiversity gain site register on GOV.UK. Statutory biodiversity credits are purchased directly from Defra. Private brokers and land agents such as Savills also facilitate unit transactions in the emerging biodiversity unit market.

Conclusion

The Biodiversity Net Gain changes of 6 August 2026 represent a meaningful recalibration of the BNG regime in England. The new 0.2ha site exemption and temporary development exemption will reduce the compliance burden for genuinely small or short-term projects. But the removal of the self-build exemption brings a new cohort of developers into mandatory BNG for the first time, and the amended gain hierarchy for minor developments opens up more flexible compliance routes.

The 10% net gain requirement is not going away. With the NSIP expansion arriving on 2 November 2026, the scope of mandatory BNG will only grow. Developers, ecologists, and planning consultants who act now, reviewing live projects, commissioning habitat surveys, and engaging with LPAs early, will be best placed to manage costs, avoid delays, and deliver compliant, viable schemes.

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