Biodiversity Net Gain May 2026: Small Sites 0.2 Hectare Exemption & Brownfield Consultation Explained

Published: May 2026 | UK Planning & Ecology News

England's mandatory BNG regime has already reshaped how thousands of planning applications are assessed — yet the rules keep evolving. Following a major government consultation in April 2026, a package of targeted reforms has been confirmed that will directly affect small developers, custom-build homeowners, NSIP promoters and ecological surveyors alike. The Biodiversity Net Gain May 2026 small sites 0.2 hectare exemption brownfield consultation represents the most significant set of BNG amendments since mandatory requirements came into force, and understanding the detail now could save considerable time and cost on live projects.

Key Takeaways 🌿

• A new area-based exemption for development sites up to 0.2 hectares is expected by end of July 2026, replacing the current self-build/custom-build exemption.
• Temporary planning permissions of up to five years will be exempt from mandatory BNG.
• For minor development, offsite biodiversity gains will be given equal preference to onsite habitat creation in the gain hierarchy.
• BNG becomes mandatory for NSIPs from 2 November 2026 — NSIP promoters must prepare now.
• A live brownfield residential exemption consultation closes 10 June 2026 — respond before the deadline.

Table of Contents

1. What Changed After the April 2026 BNG Consultation?
2. The New 0.2 Hectare Small Sites Exemption
3. Temporary Permissions and the Revised Gain Hierarchy
4. BNG for NSIPs: The 2 November 2026 Deadline
5. The Live Brownfield Residential Exemption Consultation
6. What This Means in Practice for Developers and Planners
7. What This Means for Ecologists and BNG Assessors
8. FAQ
9. Conclusion

1. What Changed After the April 2026 BNG Consultation? {#april-2026}

The government's April 2026 consultation sought views on strengthening and streamlining the BNG framework across the planning system in England. The published response confirmed several concrete changes, covering exemptions, the biodiversity gain hierarchy and the extension of mandatory BNG to nationally significant infrastructure.

These updates sit alongside the existing mandatory 10% net gain requirement under Schedule 7A of the Town and Country Planning Act 1990, as inserted by the Environment Act 2021. They do not reduce the 10% target — rather, they clarify who must comply, how gains can be delivered, and which routes to compliance are available.

For a solid grounding in how the regime works, the Biodiversity Net Gain Explained guide remains a useful starting point.

2. The New 0.2 Hectare Small Sites Exemption {#small-sites}

Replacing the Self-Build Exemption

One of the most headline-grabbing changes from the Biodiversity Net Gain May 2026 small sites 0.2 hectare exemption brownfield consultation is the introduction of a straightforward area-based threshold. Sites up to 0.2 hectares will be exempt from mandatory BNG requirements, with this change expected to be legislated by the end of July 2026.

This replaces the existing exemption that applied specifically to small-scale self-build and custom-build housing. The shift to an area-based test is significant for several reasons:

• ✅ Simpler to apply — no need to demonstrate self-build status
• ✅ Broader coverage — small infill plots, garage conversions with curtilage works, and minor commercial extensions may now qualify
• ✅ Greater certainty at pre-application stage

💡 "An area-based threshold removes ambiguity. Developers and their agents can assess eligibility from a site plan rather than navigating occupancy conditions."

Important caveat: The exemption applies to the development site area, not the gross internal floor area. Developers should confirm the precise boundary measurement with their local planning authority (LPA) before assuming exemption applies. Always consult a chartered ecologist to assess whether a voluntary BNG commitment may still be appropriate or expected by the LPA.

For a broader look at which projects are currently exempt, see the Exempt Projects page.

3. Temporary Permissions and the Revised Gain Hierarchy {#temporary}

Temporary Planning Permissions

Temporary planning permissions granted for a maximum of five years will also be exempt from mandatory BNG. This is a pragmatic change that acknowledges the short-term, reversible nature of such consents — for example, construction compounds, meanwhile uses and short-term event infrastructure.

Levelling the Playing Field for Offsite Gains

Perhaps the most strategically important change for minor development is the amendment to the biodiversity gain hierarchy. Currently, the hierarchy strongly favours onsite habitat creation, with offsite gains treated as a secondary option. Under the confirmed reforms:

For minor development, offsite biodiversity gains will be given the same preference as onsite habitat creation or enhancement.

This is a meaningful shift. Many small urban sites simply cannot deliver meaningful habitat onsite — a 0.3-hectare brownfield plot surrounded by hardstanding has limited ecological potential. Allowing equal weight to offsite gains means developers can more readily purchase biodiversity units from habitat banks without first having to demonstrate that onsite delivery is impractical.

For a detailed comparison of delivery routes, the article on Biodiversity Net Gain: Off-site or On-site Delivery? sets out the key considerations clearly.

4. BNG for NSIPs: The 2 November 2026 Deadline {#nsip}

Nationally Significant Infrastructure Projects — covering major energy, transport, water and waste schemes — have until now operated outside the standard BNG framework. That changes on 2 November 2026.

From that date, all NSIP applications submitted on or after 2 November 2026 must comply with mandatory BNG requirements. NSIP promoters should note:

Given the scale and complexity of most NSIP schemes, baseline surveys alone can take multiple field seasons to complete. Promoters who delay risk either missing the November deadline or submitting incomplete biodiversity data. Engaging a chartered ecologist at the earliest opportunity is strongly advised.

5. The Live Brownfield Residential Exemption Consultation {#brownfield}

Alongside the confirmed changes, the government has launched a separate live consultation on a targeted exemption for brownfield residential development. This consultation closes on 10 June 2026.

The proposed exemption is designed to support the government's 'brownfield first' planning policy approach, recognising that previously developed land often presents particular challenges for BNG delivery — including low baseline biodiversity values, contamination constraints and limited space for habitat creation.

What the Brownfield Consultation Covers

• The scope of a potential exemption (which brownfield sites would qualify)
• Whether the exemption should apply to all residential development on brownfield land, or only specific scales or types
• Safeguards to prevent misuse of the exemption
• How the exemption interacts with existing BNG requirements and local plan policies

Developers, planners and ecologists with an interest in brownfield residential schemes should respond before 10 June 2026. The outcome of this consultation will shape policy for years to come and could significantly affect viability assessments for urban regeneration projects.

The Top 5 Takeaways from the Government's BNG Consultation article provides useful context on how previous consultations have translated into policy change.

6. What This Means in Practice for Developers and Planners {#practice}

Small Developers and Custom-Build Homeowners

• Check site area first. If the development footprint is under 0.2 ha, the new exemption — once legislated — may remove the BNG obligation entirely. Until the legislation is confirmed (expected by end of July 2026), the existing rules still apply.
• Do not assume exemption means no ecology work. Protected species surveys, habitat regulations assessments and local plan requirements may still apply independently of BNG.
• Engage the LPA early. Some LPAs have local BNG policies that go beyond the statutory minimum. Pre-application advice is essential.

For a practical overview of BNG obligations on smaller schemes, BNG for Small Development Projects is a recommended read.

NSIP Promoters

• The 2 November 2026 deadline is firm. Applications submitted on or after that date must include a biodiversity gain plan.
• Begin pre-application engagement with Natural England and the relevant examining authority now.
• Factor BNG costs — including habitat bank purchases and long-term monitoring — into project budgets at the earliest stage.

7. What This Means for Ecologists and BNG Assessors {#ecologists}

The reforms create both new workload and new complexity for ecological surveyors and BNG assessors:

🔬 Baseline surveys: The NSIP deadline will drive significant demand for Phase 1 habitat surveys, Phase 2 surveys and Biodiversity Metric assessments on large infrastructure sites. Survey season constraints mean forward planning is critical.

📋 BNG reports and assessments: Understanding what is in a Biodiversity Net Gain Assessment is increasingly important as assessors must advise clients on which exemptions apply and what documentation is required where BNG is not exempt.

📝 Section 106 and conservation covenants: The equal weighting of offsite gains for minor development will increase the volume of offsite BNG agreements. Ecologists advising on habitat banking versus land banking decisions will need to stay current on available habitat bank supply and unit pricing.

📊 Habitat bank purchase decisions: With offsite gains now on equal footing for minor development, demand for privately traded biodiversity units is likely to increase. Assessors should ensure clients understand the difference between statutory credits and private habitat bank units.

FAQ {#faq}

Q1: When will the 0.2 hectare small sites exemption come into force?
The government has indicated the new area-based exemption is expected to be introduced by the end of July 2026. Until that legislation is confirmed, current BNG rules remain in effect. Check with your LPA and a chartered ecologist for the latest position.

Q2: Does the brownfield consultation exemption already apply?
No. The brownfield residential exemption is still at consultation stage, closing 10 June 2026. It does not apply until the government formally introduces it through legislation following the consultation outcome.

Q3: If my site is under 0.2 ha, do I still need any ecology surveys?
Potentially yes. BNG exemption does not remove obligations under the Habitats Regulations, the Wildlife and Countryside Act 1981, or any local plan ecology policies. Always seek advice from a chartered ecologist.

Q4: What is the biodiversity gain hierarchy and why does the change matter?
The gain hierarchy sets the order in which BNG must be delivered: onsite first, then offsite, then statutory credits as a last resort. For minor development, the confirmed change means offsite gains are now treated equally to onsite delivery — removing a barrier for small urban sites where onsite habitat creation is impractical.

Q5: How should NSIP promoters prepare for the 2 November 2026 deadline?
Commission baseline ecological surveys immediately, engage a chartered ecologist to develop a BNG strategy, identify offsite habitat bank options, and begin drafting biodiversity gain plan documentation well ahead of the submission date.

Q6: Where can I respond to the brownfield consultation?
Responses to the brownfield residential exemption consultation should be submitted via the official government consultation portal before 10 June 2026. Check GOV.UK for the direct link and guidance notes.

Conclusion {#conclusion}

The Biodiversity Net Gain May 2026 small sites 0.2 hectare exemption brownfield consultation package marks a genuine maturation of England's BNG framework. The area-based small sites exemption brings welcome clarity for small developers and custom-build homeowners. The equal weighting of offsite gains for minor development removes a practical barrier that has complicated many urban schemes. And the mandatory extension to NSIPs from 2 November 2026 signals that BNG is now firmly embedded across the entire planning system.

Actionable Next Steps ✅

1. Measure your site. If it is close to the 0.2 ha threshold, get a precise boundary survey and monitor the July 2026 legislation.
2. Respond to the brownfield consultation before 10 June 2026 if you have an interest in previously developed land.
3. NSIP promoters: commission baseline surveys now — do not wait until autumn.
4. Ecologists and assessors: update your offsite gain advice to reflect the amended hierarchy for minor development.
5. Always consult a chartered ecologist and your local planning authority before assuming any exemption applies to your specific project.

For further guidance on navigating BNG requirements, explore the Biodiversity Net Gain resources or contact a specialist directly.

References

• Department for Environment, Food & Rural Affairs (DEFRA) / Ministry of Housing, Communities & Local Government (MHCLG). Biodiversity Net Gain: consultation on amendments to the BNG framework. GOV.UK, April 2026.
• Environment Act 2021, Schedule 7A (Town and Country Planning Act 1990, as amended).
• Natural England. Biodiversity Metric 4.0 User Guide. Natural England, 2023.
• MHCLG. Consultation on a brownfield residential development exemption from mandatory BNG. GOV.UK, May 2026. (Consultation closes 10 June 2026.)
• Planning and Infrastructure Act (in progress). NSIP BNG provisions. UK Parliament, 2025–2026.