Biodiversity Net Gain Changes 2026: What Developers, Landowners and Planners Must Know

England's mandatory Biodiversity Net Gain framework has already reshaped how planning applications are assessed — but 2026 brings the most significant wave of amendments since the policy launched in February 2024. From a new small-site exemption to BNG becoming compulsory for the UK's largest infrastructure projects, the Biodiversity Net Gain changes 2026 will affect virtually every corner of the development sector. Here is a clear, accurate guide to what is changing, when, and what action is required.

Key Takeaways 🌿

• 31 July 2026: A new exemption for sites of 0.2 hectares or below replaces the previous self/custom-build exemption.
• 2 November 2026: Mandatory BNG extends to Nationally Significant Infrastructure Projects (NSIPs).
• A planned exemption for temporary developments of five years or less is in the pipeline.
• Defra's brownfield residential consultation (closing 10 June 2026) proposes exempting sites up to 2.5 hectares.
• The core 10% net gain requirement remains unchanged for all non-exempt developments.

Table of Contents

1. What Is Biodiversity Net Gain and the 10% Rule?
2. Overview of the Biodiversity Net Gain Changes 2026
3. New Small-Site Exemption: 0.2 Hectares or Below (31 July 2026)
4. BNG Mandatory for NSIPs (2 November 2026)
5. Planned Exemption for Temporary Developments
6. Defra's Brownfield Residential Consultation
7. What Developers and Landowners Should Do Now
8. FAQ
9. Conclusion

What Is Biodiversity Net Gain and the 10% Rule? {#what-is-bng}

Biodiversity Net Gain is a planning requirement under Schedule 7A of the Environment Act 2021. It mandates that new development must leave biodiversity in a measurably better state than before construction began. The headline figure is a minimum 10% net gain in biodiversity value, calculated using the statutory Biodiversity Metric.

In practice, this means:

• A baseline habitat survey is conducted before development.
• The metric calculates the post-development biodiversity value.
• Any shortfall must be addressed through on-site habitat creation, off-site habitat delivery, or the purchase of statutory biodiversity credits from the government as a last resort.
• A Biodiversity Gain Plan must be submitted and approved before development commences.

For a fuller breakdown of how the framework operates, the Biodiversity Net Gain explained guide covers the mechanics in detail.

💡 Pull quote: "The 10% net gain threshold is a floor, not a ceiling — local planning authorities can and do set higher requirements."

Overview of the Biodiversity Net Gain Changes 2026 {#overview-2026}

The table below summarises the confirmed and proposed Biodiversity Net Gain changes 2026 at a glance:

Each of these is explored in detail below.

New Small-Site Exemption: 0.2 Hectares or Below (31 July 2026) {#small-site-exemption}

From 31 July 2026, developments on sites of 0.2 hectares or below will be exempt from mandatory BNG. This replaces the previous self-build and custom-build exemption, which was widely regarded as too narrow to provide meaningful relief to small developers.

What this means in practice

• Any planning application for a site with a total area of 0.2 ha or less — roughly half an acre — will no longer need to submit a Biodiversity Gain Plan.
• The exemption applies regardless of the type of development, provided the site area threshold is met.
• The previous self/custom-build exemption is removed and superseded by this broader, area-based rule.

🏗️ Who benefits most? Small housebuilders, infill developers, and urban regeneration projects on tight plots are the primary beneficiaries. For context on how BNG has applied to smaller schemes, see this guide to BNG for small development projects.

Important caveats

Developers should not assume that being below the 0.2 ha threshold automatically removes all ecological obligations. Local planning authorities may still request ecological surveys, and permitted development rights carry separate conditions. Always confirm the position with the relevant local authority before assuming full exemption.

For a comprehensive list of current and upcoming exempt categories, the exempt projects page provides up-to-date guidance.

BNG Mandatory for NSIPs (2 November 2026) {#nsips}

The most significant expansion of mandatory BNG in 2026 is its extension to Nationally Significant Infrastructure Projects from 2 November 2026.

NSIPs include:

• Major road and rail schemes
• Airports and harbour developments
• Offshore and onshore energy infrastructure (power stations, wind farms)
• Water and wastewater treatment works above certain thresholds

These projects are consented through the Development Consent Order (DCO) process, overseen by the Planning Inspectorate rather than local planning authorities. From November 2026, applicants will need to demonstrate a minimum 10% biodiversity net gain as part of their DCO application.

Why this matters

NSIPs are, by definition, large-scale. The biodiversity units required to offset the impact of a major motorway junction or a new reservoir will be substantial. This creates significant demand for off-site biodiversity units and habitat bank agreements, opening a major commercial opportunity for landowners willing to create and sell units.

Landowners with suitable land — particularly those with degraded agricultural fields or riparian corridors — should explore the potential to sell biodiversity units into this expanding market well before November 2026.

Planned Exemption for Temporary Developments {#temporary}

The government has signalled a planned exemption for temporary developments lasting five years or less. While the precise legislative mechanism and commencement date have not yet been confirmed, the policy intent is clear: short-term developments — such as construction compounds, temporary event infrastructure, or meanwhile uses — should not face the same BNG obligations as permanent schemes.

Developers relying on this exemption should monitor Defra and DLUHC announcements closely, as secondary legislation will be required to bring it into force.

Defra's Brownfield Residential Consultation {#brownfield}

Defra launched a targeted consultation on a proposed brownfield residential exemption for sites of up to 2.5 hectares. The consultation closed on 10 June 2026.

The proposal in brief

• Residential developments on previously developed (brownfield) land up to 2.5 ha in area would be exempt from mandatory BNG.
• The rationale is to reduce barriers to brownfield housing delivery, a key government priority under its 1.5 million homes target.
• The exemption would sit alongside — not replace — the new 0.2 ha area-based exemption.

Points of debate

Critics argue that brownfield land, while often low in biodiversity value, can still support notable species such as invertebrates, reptiles, and certain plant communities. A blanket exemption risks removing incentives to deliver even modest ecological enhancements on these sites.

Supporters counter that the viability challenges on brownfield land are real, and that mandatory BNG costs can tip marginal schemes into non-viability.

The outcome of this consultation will shape BNG policy significantly. Developers and landowners with brownfield interests should review the top takeaways from government BNG consultations to understand how previous consultations have translated into policy.

What Developers and Landowners Should Do Now {#action}

The Biodiversity Net Gain changes 2026 require proactive planning rather than reactive compliance. Here are the priority actions:

For developers 🏢

1. Audit your pipeline — identify which sites fall below 0.2 ha and may qualify for the July 2026 exemption.
2. Review NSIP applications — if any projects are going through the DCO process, begin biodiversity baseline surveys and metric calculations now.
3. Monitor the brownfield consultation outcome — if you hold brownfield sites between 0.2 and 2.5 ha, the Defra decision will directly affect your compliance obligations.
4. Engage a qualified ecologist early — understanding your biodiversity net gain assessment requirements at the pre-application stage avoids costly delays.
5. Explore on-site and off-site delivery options — achieving biodiversity net gain without unnecessary risk requires a clear strategy from day one.

For landowners 🌾

1. Assess land suitability for habitat creation — the NSIP mandate will drive significant demand for off-site units.
2. Understand the habitat banking market — explore the difference between land banking and habitat banking before entering agreements.
3. Seek specialist advice on long-term management obligations, which run for a minimum of 30 years under current rules.

For planning professionals 📋

• Update pre-application advice templates to reflect the July 2026 exemption threshold.
• Ensure local validation checklists are revised before the 31 July commencement date.
• Familiarise teams with the DCO BNG process ahead of November 2026.

FAQ {#faq}

Q: Does the 0.2 ha exemption apply to the net developable area or the total site area?
A: The exemption applies to the total site area of the development, not just the built footprint or net developable area.

Q: Will NSIPs need to use the same statutory Biodiversity Metric as standard planning applications?
A: Yes. NSIPs will use the same statutory metric framework, though the Planning Inspectorate will issue specific guidance on how the Biodiversity Gain Plan should be presented within DCO documentation.

Q: Can a developer still voluntarily deliver BNG on an exempt site?
A: Absolutely. Exemption means the requirement is not mandatory — developers can still choose to deliver net gain, which may support planning applications and demonstrate environmental credentials.

Q: What happens if the brownfield exemption is confirmed — will sites already in the planning system benefit?
A: This will depend on the transitional provisions set out in the secondary legislation. Developers with live applications should seek legal advice on whether retrospective exemption applies.

Q: Where can developers buy biodiversity units if on-site delivery is not possible?
A: Units can be sourced from registered habitat bank operators or, as a last resort, through government statutory credits. See the guidance on how to buy biodiversity units for options.

Q: Are there still developments that were always exempt from BNG?
A: Yes. Householder applications, permitted development, and certain other categories remain exempt. The exempt projects page provides the current full list.

Conclusion {#conclusion}

The Biodiversity Net Gain changes 2026 represent the most consequential evolution of England's BNG framework to date. The new 0.2 ha small-site exemption from 31 July offers genuine relief to small developers, while the extension to NSIPs from 2 November dramatically expands the policy's reach into major infrastructure. The proposed brownfield and temporary development exemptions, if confirmed, will further reshape compliance obligations across the sector.

Actionable next steps:

• ✅ Review your development pipeline against the 0.2 ha threshold before 31 July 2026.
• ✅ Begin NSIP biodiversity baseline work immediately if DCO applications are planned.
• ✅ Track the outcome of Defra's brownfield consultation.
• ✅ Engage a specialist ecologist early — BNG compliance is far simpler when built into project design from the outset.

The 10% net gain requirement is not going away. For all non-exempt developments, robust ecological assessment and a clear delivery strategy remain essential. The sooner developers, landowners, and planning professionals embed BNG into their workflows, the better placed they will be to navigate both the current rules and whatever changes come next.

References

• HM Government. (2021). Environment Act 2021. legislation.gov.uk
• Department for Environment, Food & Rural Affairs (Defra). (2024). Biodiversity Net Gain: General guidance for developers. gov.uk
• Planning Inspectorate. (2024). Nationally Significant Infrastructure Projects: Overview. gov.uk
• Defra. (2026). Targeted brownfield residential exemption: Consultation. gov.uk