Biodiversity Net Gain 2026: Small Sites 0.2ha Exemption, NSIP Developers & What Changes Now

Fewer than 5% of England's development sites exceed 1 hectare — yet until now, even the smallest plots have faced the full weight of mandatory Biodiversity Net Gain (BNG) compliance. That is about to change. Defra has confirmed a package of significant BNG reforms expected to take effect by around the end of July 2026 (subject to parliamentary time), reshaping how Biodiversity Net Gain 2026 small sites 0.2ha exemption NSIP developers must approach ecology obligations across England. From a new area-based exemption for micro-developments to BNG landing on Nationally Significant Infrastructure Projects (NSIPs) from November 2026, the landscape is shifting fast — and the window to prepare is narrowing.

Key Takeaways 🌿

• A new 0.2ha area-based exemption is expected by end of July 2026, removing BNG obligations for the smallest development sites.
• The self-build and custom-build exemption will be removed, meaning those projects must now comply with BNG requirements.
• Temporary planning permissions of up to five years will be exempt from mandatory BNG.
• NSIPs will be subject to BNG from November 2026, assessed on impacted habitats only — not the full red-line boundary.
• The 10% mandatory net gain requirement remains unchanged for all non-exempt developments.

Table of Contents

1. Why These 2026 BNG Changes Matter
2. The New 0.2ha Small Sites Exemption Explained
3. Self-Build Exemption Removed: Who Is Affected?
4. Temporary Planning Permissions: A New Exemption
5. Offsite Gains for Minor Development: A Level Playing Field
6. BNG for NSIP Developers from November 2026
7. Residential Brownfield: A Possible Further Exemption
8. What Developers, Landowners & Planners Must Do Now
9. FAQ
10. Conclusion

1. Why These 2026 BNG Changes Matter {#why-these-changes-matter}

Mandatory BNG has been in force for standard planning permissions since February 2024, and for small sites since April 2024. The reforms now confirmed by Defra represent the most substantial recalibration of the framework since its launch.

For ecology consultants and BNG practitioners, the changes create both complexity and opportunity. Clients will ask whether their site is exempt. Landowners selling biodiversity units need to understand new demand signals. Planners must update local validation checklists. Getting ahead of these changes — rather than reacting to them — is the only viable professional strategy in 2026.

For a solid grounding in how BNG works before diving into the changes, the Biodiversity Net Gain explained guide from Biodiversity Surveyors provides a clear starting point.

2. The New 0.2ha Small Sites Exemption Explained {#02ha-exemption}

"Defra has confirmed a new area-based exemption for developments of 0.2 hectares or below, expected by around the end of July 2026, subject to parliamentary time."

This is the headline change for small-scale developers. Currently, BNG applies to minor developments (those with fewer than 10 dwellings or under 1,000m² of commercial floorspace) unless they fall under a specific listed exemption. The new 0.2ha threshold introduces a straightforward area-based test — if the development footprint is 0.2ha or below, BNG obligations will not apply.

What Does 0.2 Hectares Look Like in Practice?

Key points for practitioners:

• The exemption is area-based, not unit-count-based — a clean, measurable threshold.
• Accurate site measurement will become critical; boundary disputes near the 0.2ha mark will require careful survey work.
• Clients should not assume exemption without a verified site area calculation.

For sites that do fall above the threshold and require compliance, understanding BNG for small development projects remains essential reading.

3. Self-Build Exemption Removed: Who Is Affected? {#self-build-exemption-removed}

The existing exemption for small-scale self-build and custom-build development is to be removed under the same legislative package. This is a significant reversal.

Previously, self-builders and custom-build developers benefited from an automatic exemption regardless of site size. Under the reformed framework, self-build projects will need to assess whether they qualify under the new 0.2ha area-based exemption. If their site exceeds 0.2ha, they will face full BNG obligations.

Practical implications:

• Self-build clients with plots over 0.2ha must now commission a Biodiversity Net Gain assessment.
• Many self-builders are unfamiliar with BNG — early client education will prevent delays at planning.
• Custom-build developers managing multiple plots should audit their pipeline now.

4. Temporary Planning Permissions: A New Exemption {#temporary-permissions}

Defra has confirmed that temporary planning permissions of up to five years will be exempt from mandatory BNG. This is a pragmatic and logical change — requiring long-term habitat creation commitments (typically 30 years) for developments that will be removed within five years has always been difficult to justify ecologically or commercially.

This exemption will be particularly relevant for:

• 🏗️ Construction compounds and temporary works areas
• 🎪 Temporary event venues and seasonal structures
• 🌾 Short-term agricultural storage or processing facilities
• 🚧 Infrastructure enabling works with defined end dates

Ecology consultants should still advise clients to document the temporary nature of the permission clearly, as local planning authorities will need to verify the five-year threshold.

5. Offsite Gains for Minor Development: A Level Playing Field {#offsite-gains}

One of the most practically significant reforms for minor development is the amendment to the biodiversity gain hierarchy. Currently, the hierarchy requires developers to prioritise onsite habitat creation before considering offsite gains or statutory credits.

Under the confirmed changes, offsite gains will rank equally with onsite gains for minor development. This removes a significant barrier for small sites where meaningful onsite habitat creation is often physically impossible.

For ecology consultants advising on minor schemes, this means:

• Offsite habitat bank units can be proposed without first exhausting onsite options.
• Biodiversity gain plans for minor development become simpler to structure.
• Demand for quality offsite habitat bank units is likely to increase.

This change aligns with the practical reality that a 0.3ha housing scheme cannot always deliver meaningful habitat onsite. For a detailed comparison of delivery routes, see Biodiversity Net Gain: Off-site or On-site Delivery?

6. BNG for NSIP Developers from November 2026 {#nsip-developers}

The extension of mandatory BNG to Nationally Significant Infrastructure Projects (NSIPs) from November 2026 is the most significant structural expansion of the framework since its launch.

NSIPs include nationally important infrastructure such as large energy projects, major road and rail schemes, airports, and large-scale water infrastructure — projects consented through the Development Consent Order (DCO) process rather than standard planning permission.

How NSIP BNG Assessment Will Work

Defra has confirmed a critical distinction in how BNG will be assessed for NSIPs:

BNG for NSIPs will be assessed only on impacted habitats — not across the full red-line boundary of the project.

This is a fundamentally different approach from standard BNG, where the entire application site is assessed. For a linear infrastructure project with a 50km red-line boundary, this distinction is enormous — it focuses obligations on areas of genuine ecological impact rather than administrative boundaries.

What NSIP developers must prepare for:

NSIP project teams should begin habitat baseline surveys now. Lead times for ecological surveys, metric calculations, and securing offsite habitat units are substantial. For NSIP developers new to the framework, the guide to biodiversity credits for developers provides useful context on compliance routes.

7. Residential Brownfield: A Possible Further Exemption {#brownfield-exemption}

Defra has also consulted on a possible exemption for residential brownfield development. This remains a proposal rather than confirmed policy, but it signals the direction of government thinking — particularly given the political priority placed on urban regeneration and housebuilding targets.

Ecology consultants should monitor this closely. If confirmed, it could significantly affect BNG demand in urban areas and the viability of certain habitat bank sites targeting urban offset demand.

8. What Developers, Landowners & Planners Must Do Now {#what-to-do-now}

The confirmed Biodiversity Net Gain 2026 small sites 0.2ha exemption and NSIP developer obligations require immediate action across the sector.

For developers:

• ✅ Audit your development pipeline against the 0.2ha threshold
• ✅ Review any self-build or custom-build projects above 0.2ha for BNG compliance gaps
• ✅ For NSIP projects, commission baseline habitat surveys without delay
• ✅ Explore offsite habitat units early — supply is not unlimited

For landowners:

• ✅ Increased demand for offsite units from minor development (following hierarchy change) and NSIPs creates new opportunities — explore selling biodiversity units
• ✅ Habitat bank agreements take time to establish; begin conversations now

For planners:

• ✅ Update validation checklists to reflect the 0.2ha exemption threshold
• ✅ Prepare for self-build applicants who previously assumed exemption
• ✅ Familiarise yourselves with NSIP BNG assessment methodology ahead of November 2026

For a comprehensive overview of obligations and exemptions, the exempt projects guidance is an essential reference.

FAQ {#faq}

Q: Does the 0.2ha exemption apply automatically, or does it need to be declared?
A: Developers will still need to declare the exemption to the local planning authority. Accurate site area measurement is essential, as the threshold is area-based.

Q: Will self-build projects on plots under 0.2ha still be exempt?
A: Yes — if the site falls within the new 0.2ha area-based exemption, BNG will not apply regardless of whether it is self-build or conventional development.

Q: Does the 10% net gain requirement change under any of these reforms?
A: No. Defra has confirmed the mandatory 10% biodiversity net gain requirement remains in place for all non-exempt developments.

Q: When exactly will BNG apply to NSIPs?
A: Defra has confirmed November 2026 as the target date for BNG to apply to Nationally Significant Infrastructure Projects.

Q: How does the offsite hierarchy change affect minor development planning?
A: For minor development, offsite gains will rank equally with onsite gains — meaning developers no longer need to demonstrate that onsite delivery is impossible before proposing offsite units.

Q: Is the residential brownfield exemption confirmed?
A: No. Defra has consulted on this possibility, but it is not yet confirmed policy. Practitioners should monitor gov.uk for updates.

Conclusion {#conclusion}

The Biodiversity Net Gain 2026 reforms — including the small sites 0.2ha exemption, the removal of the self-build carve-out, the new temporary permissions exemption, the hierarchy change for minor development, and the extension to NSIP developers — represent a genuine recalibration of England's BNG framework. The core 10% mandatory net gain obligation is not going anywhere, but the rules around who must comply, and how, are being substantially refined.

Actionable next steps:

1. Audit your pipeline now — identify which projects fall below 0.2ha and which self-build schemes need BNG compliance plans.
2. Commission baseline surveys early — particularly for NSIP projects, where lead times are long.
3. Engage with habitat bank providers — offsite unit supply will tighten as NSIP demand enters the market.
4. Stay close to gov.uk — the July 2026 legislative changes are subject to parliamentary time and may shift.
5. Brief your clients proactively — those who plan ahead will avoid costly delays.

For tailored support navigating these changes, Biodiversity Surveyors' guidance for developers provides expert, up-to-date advice for every stage of the planning process.

All policy information in this article is attributed to Defra/gov.uk announcements. Changes are subject to parliamentary time and practitioners should verify the latest position on gov.uk before advising clients.