Biodiversity Net Gain Changes from 6 August 2026 Developer Guide

Last updated: August 10, 2026

Quick Answer: Four days into the new regime, the 6 August 2026 BNG amendment package has reshaped mandatory biodiversity net gain obligations for developers across England. Key changes include a new 0.2 hectare size exemption, a temporary development exemption, removal of the self and custom-build exemption, and a revised biodiversity gain hierarchy for minor developments. Developers who have not yet reviewed their project pipelines against these changes should do so immediately.

Key Takeaways

• A new 0.2 hectare exemption applies to the smallest developments, but only where there is no negative impact on onsite priority habitat.
• A temporary development exemption now covers projects where land is fully reinstated within five years.
• The self and custom-build exemption has been removed, those projects now require full BNG compliance.
• For minor developments, onsite creation/enhancement and registered offsite gains can now be considered at the same stage in the biodiversity gain hierarchy.
• BNG will become mandatory for Nationally Significant Infrastructure Projects (NSIPs) from November 2026.
• Developers cannot rely on statutory credits as a first resort, the hierarchy still requires genuine effort to achieve gains onsite or through registered offsite units before credits are used.
• Local planning authorities (LPAs) are applying the new rules from 6 August 2026; pre-application discussions should reflect the updated framework.

What Is Biodiversity Net Gain and Why Does It Matter?

Biodiversity net gain (BNG) is a legal requirement under Schedule 7A of the Town and Country Planning Act 1990, inserted by the Environment Act 2021. It requires most new developments in England to deliver a measurable 10% improvement in biodiversity value compared to the pre-development baseline, secured for a minimum of 30 years.

BNG matters because England has lost a significant proportion of its wildlife habitats over the past century. The policy forces developers to account for ecological impact as a material planning condition, not an optional add-on. For a fuller explanation of why this policy exists, see 5 reasons why biodiversity net gain is important to UK development.

How Do the August 2026 BNG Changes Affect Developers?

The 6 August 2026 amendment package directly changes who must comply, how compliance is structured, and what routes are available for minor developments. This is the most significant update to the BNG framework since mandatory requirements were extended to small sites in April 2024.

The four core changes are:

1. 0.2 hectare exemption, Developments with a site area below 0.2 hectares are now exempt from mandatory BNG, provided the development does not result in any negative impact on priority habitat located onsite. If priority habitat is present and would be affected, the exemption does not apply.
2. Temporary development exemption, Projects where the land will be fully reinstated to its pre-development condition within five years qualify for exemption. This is particularly relevant for construction compounds, temporary access routes, and short-term infrastructure works.
3. Removal of the self and custom-build exemption, Previously, self-build and custom-build projects were exempt. From 6 August 2026, they are not. Any self or custom-build application submitted on or after this date must meet the standard 10% BNG requirement.
4. Modified biodiversity gain hierarchy for minor development, Under the previous hierarchy, developers had to demonstrate that onsite measures were exhausted before offsite options were considered. For minor developments, onsite creation/enhancement and registered offsite gains can now be assessed at the same stage, giving applicants more flexibility in how they structure their BNG strategy.

What Are the Main Differences in the New BNG Requirements?

The table below summarises the most important before-and-after changes for quick reference.

Which Projects Are Exempt from the August 2026 BNG Rules?

Several exemption categories exist under the updated framework. The 6 August 2026 changes added two new ones and removed one.

Current exemptions include:

• Developments under 0.2 hectares with no negative impact on onsite priority habitat (new from 6 August 2026)
• Temporary developments where full land reinstatement occurs within five years (new from 6 August 2026)
• Householder applications (unchanged)
• Permitted development rights where BNG is not triggered (unchanged)
• Development on brownfield land with no biodiversity value (subject to assessment)

No longer exempt:

• Self and custom-build developments

Common mistake: Assuming the 0.2 ha exemption applies automatically. It does not. If any priority habitat is present onsite and would be negatively affected, the exemption is void and full BNG compliance is required. Developers should commission a habitat survey before relying on this exemption.

Small Developments and Biodiversity Net Gain Requirements 2026

Small developments, those below 0.2 hectares, can now claim exemption under the August 2026 rules, but the priority habitat condition is a hard constraint. This is important for infill plots, small residential schemes, and urban regeneration projects where remnant habitats such as hedgerows, wildflower grassland, or veteran trees may be present.

If a small site contains no priority habitat, the developer should document this clearly in the planning application. If priority habitat is present, a full biodiversity net gain assessment is still required.

Biodiversity Net Gain Alternatives to On-Site Measures

For minor developments, the revised hierarchy means offsite registered gains are now a parallel option alongside onsite measures, not a last resort. Statutory biodiversity credits (purchased from Defra) remain the final backstop and should not be treated as a convenient shortcut.

The hierarchy for minor development from 6 August 2026:

1. Onsite habitat creation or enhancement AND registered offsite gains (considered together at this stage)
2. Statutory biodiversity credits (only where steps above are genuinely undeliverable)

For larger and major developments, the original sequential hierarchy still applies: onsite first, then registered offsite, then statutory credits. See the detailed guide on biodiversity net gain off-site or on-site delivery for further analysis of how to structure your approach.

Biodiversity Net Gain: What's Changed, Full Summary List

This section serves as a quick-reference checklist anchored to the confirmed 6 August 2026 changes.

What's changed:

• New 0.2 ha exemption introduced (with priority habitat condition)
• New temporary development exemption (5-year reinstatement requirement)
• Self and custom-build exemption removed
• Biodiversity gain hierarchy modified for minor developments (onsite and registered offsite now considered simultaneously)
• NSIPs confirmed for mandatory BNG from November 2026 (Defra guidance)
• LPAs expected to apply updated rules to all applications validated on or after 6 August 2026

What Developers Should Do Now, Practical Checklist

The following steps reflect Defra's updated developer guidance and Local Government Association advice to LPAs on applying the new framework.

Immediate actions:

• Review all live planning applications to confirm which exemption category, if any, applies under the new rules
• For sites under 0.2 ha, commission a Phase 1 habitat survey to confirm whether priority habitat is present before claiming exemption
• For temporary development projects, document the reinstatement timeline clearly in the planning submission
• Remove any reliance on the self and custom-build exemption for applications not yet validated
• For minor developments, update your BNG strategy to reflect the revised hierarchy, offsite registered gains can now be considered alongside onsite measures
• If your pipeline includes NSIPs, begin BNG assessment work now ahead of the November 2026 mandatory date
• Engage your LPA at pre-application stage to confirm how they are applying the updated guidance

For a structured approach to building your BNG strategy, the guidance for developers resource provides a practical starting framework.

How Much Does Biodiversity Net Gain Compliance Cost?

BNG compliance costs vary considerably depending on site size, baseline habitat quality, and the route chosen to achieve the 10% uplift. No single authoritative cost figure applies to all developments.

Cost drivers include:

• Ecological survey and assessment fees (Phase 1 and Phase 2 surveys where required)
• Onsite habitat creation or enhancement works
• Registered offsite biodiversity unit purchase prices (set by the market, not by government)
• Statutory biodiversity credit costs (published by Defra and updated periodically)
• Legal costs for habitat management and monitoring agreements (typically 30-year obligations)

For a breakdown of statutory credit pricing, see the guide to cost of biodiversity units and statutory credits. For offsite unit purchasing options, the guide to biodiversity credits for developers is a useful reference.

How Long Does a Biodiversity Net Gain Assessment Take?

A standard BNG assessment for a minor development typically takes between two and six weeks from initial site survey to submission-ready report, depending on survey season constraints and site complexity. Larger or ecologically sensitive sites may take longer, particularly where protected species surveys are required alongside the habitat baseline.

Key stages:

1. Phase 1 habitat survey (typically one site visit plus report)
2. Biodiversity metric calculation using the Defra statutory metric
3. BNG strategy development (onsite, offsite, or combined)
4. Biodiversity gain plan preparation for planning submission

Surveys must be carried out at the appropriate time of year for the habitats present. Leaving assessment work until after planning submission is a common and costly mistake. See how to conduct a biodiversity impact assessment for a step-by-step walkthrough.

Biodiversity Net Gain Common Mistakes Developers Make

The most frequent errors in BNG compliance fall into a small number of categories that are largely avoidable with early planning.

• Assuming exemption without checking for priority habitat. The 0.2 ha exemption is conditional. Developers who skip a habitat survey and claim exemption incorrectly risk planning refusal or enforcement action.
• Treating statutory credits as a default. Credits are a last resort. LPAs and Defra expect developers to demonstrate that onsite and offsite options have been genuinely explored.
• Late engagement with ecology. BNG assessments require survey data that cannot be retrospectively collected. Starting ecology work after design is fixed increases costs and delays.
• Misunderstanding the 30-year obligation. The biodiversity gain plan must secure habitat management for 30 years. Developers who do not factor this into land disposal or estate management strategies create legal complications later.
• Ignoring the updated hierarchy for minor developments. Some applicants are still submitting BNG strategies based on the pre-August 2026 sequential hierarchy. LPAs are now applying the revised framework.

What Happens If You Don't Meet Biodiversity Net Gain Targets?

Failure to meet BNG requirements is a statutory ground for planning refusal. BNG is a pre-commencement condition on most permissions, meaning development cannot lawfully begin until the biodiversity gain plan is approved by the LPA.

If a developer commences development without an approved biodiversity gain plan, the LPA has enforcement powers under the Town and Country Planning Act 1990. Post-completion, failure to maintain habitats in line with the approved plan can result in enforcement action and, in serious cases, criminal liability.

Who Needs to Hire a Biodiversity Consultant for BNG?

Any developer whose project is not exempt from BNG under the current rules should engage a qualified ecologist or biodiversity consultant. This includes:

• All major and minor planning applications (subject to exemptions)
• Self and custom-build applications from 6 August 2026 onwards
• NSIP promoters preparing for the November 2026 mandatory date

Consultants should hold relevant professional qualifications (such as CIEEM membership) and be familiar with the current Defra statutory biodiversity metric. See what do you need in a biodiversity net gain report for guidance on what a compliant report must contain.

Biodiversity Net Gain Monitoring and Aftercare Obligations

BNG is not a one-time compliance exercise. The biodiversity gain plan requires habitat management and monitoring for 30 years, secured by a planning condition or legal agreement. Developers must ensure that whoever will own or manage the land after completion understands and is legally bound by these obligations.

For offsite gains, the registered gain site operator carries the monitoring responsibility, but the developer must ensure the legal agreement is in place before planning permission is granted.

Can You Appeal a Biodiversity Net Gain Decision?

Yes. If an LPA refuses planning permission on BNG grounds, or imposes BNG conditions that the developer considers unreasonable, the standard planning appeal process applies. Appeals are determined by the Planning Inspectorate, which will assess whether the LPA's application of the BNG requirement was lawful and proportionate.

Developers should ensure their BNG strategy is well-documented and supported by a robust ecological assessment before appealing, as inspectors will scrutinise the technical basis of the biodiversity metric calculation.

Frequently Asked Questions

Does the 0.2 hectare exemption apply to all small sites automatically?
No. The exemption applies only where the development does not result in a negative impact on priority habitat present onsite. A habitat survey is needed to confirm eligibility.

What counts as "reinstatement" under the temporary development exemption?
Reinstatement means restoring the land to its pre-development condition within five years of the development commencing. The obligation must be secured in the planning permission or a legal agreement.

Are self-build projects now fully subject to the 10% BNG requirement?
Yes. The self and custom-build exemption was removed on 6 August 2026. Any application validated on or after that date must comply with mandatory BNG.

When does BNG become mandatory for NSIPs?
Defra has confirmed that BNG will become mandatory for Nationally Significant Infrastructure Projects from November 2026.

Can a minor development use offsite units without first exhausting onsite options?
Under the revised hierarchy from 6 August 2026, yes. For minor developments, onsite creation/enhancement and registered offsite gains are now considered at the same stage. Statutory credits remain the last resort.

What is the Defra statutory biodiversity metric?
It is the government-approved calculation tool used to measure the biodiversity value of habitats before and after development. It produces a score in "biodiversity units" that determines whether a project achieves the required 10% net gain.

Who enforces BNG compliance after planning permission is granted?
The local planning authority monitors compliance with biodiversity gain plan conditions. Natural England has a role in relation to registered offsite gain sites and statutory credits.

Conclusion

Four days into the new regime, the 6 August 2026 BNG amendment package represents a meaningful recalibration of mandatory biodiversity net gain obligations. The 0.2 hectare exemption offers genuine relief for the smallest developments, but only where priority habitat is absent, making early habitat surveys non-negotiable. The removal of the self and custom-build exemption closes a gap that had allowed a category of residential development to sidestep ecological accountability. The revised hierarchy for minor developments gives applicants more flexibility, but the underlying 10% target and 30-year commitment remain unchanged.

Actionable next steps for developers:

1. Audit your current pipeline against the four key changes before submitting any new applications.
2. Commission habitat surveys for any sub-0.2 ha site where you intend to claim exemption.
3. Update BNG strategies for minor developments to reflect the revised gain hierarchy.
4. Brief your planning and legal teams on the removal of the self and custom-build exemption.
5. If your portfolio includes NSIPs, begin BNG assessment work now, November 2026 will arrive quickly.

The LGA has advised local planning authorities to apply the updated rules to all applications validated from 6 August 2026. Developers who engage early, survey thoroughly, and plan their BNG strategy before design is fixed will be best placed to navigate the updated framework efficiently.

Interactive BNG Exemption Checker

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References

• Defra, Biodiversity Net Gain: Developer Guidance, updated August 2026. https://www.gov.uk/guidance/biodiversity-net-gain
• Defra, Biodiversity Net Gain: Exemptions Guidance, updated August 2026. https://www.gov.uk/guidance/biodiversity-net-gain-exemptions
• Local Government Association, Biodiversity Net Gain: Guidance for Local Authorities, 2024. https://www.local.gov.uk/topics/planning-and-housing/biodiversity-net-gain
• Environment Act 2021, Schedule 7A (Town and Country Planning Act 1990 as amended). https://www.legislation.gov.uk/ukpga/2021/30/schedule/14
• Natural England, Statutory Biodiversity Metric: User Guide, 2023. https://www.gov.uk/government/publications/statutory-biodiversity-metric-tools-and-guides