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Last updated: September 19, 2026
Half of all new residential planning permissions in England are about to fall outside mandatory biodiversity rules entirely. That is not a leak or a rumour, it is the practical effect of a threshold DEFRA has now confirmed. This September 2026 analysis sets out exactly what the UK Biodiversity Net Gain November 2026 infrastructure duty and 0.2ha exemption mean for anyone building, surveying, or advising on land in England right now.
Quick Answer
The UK government has confirmed two major Biodiversity Net Gain (BNG) changes for 2026: a 0.2 hectare exemption for small sites, in force from before 31 July 2026, and a new 10% biodiversity net gain duty for Nationally Significant Infrastructure Projects (NSIPs) starting 2 November 2026. Alongside these, the self-build/custom-build exemption has been removed, and the biodiversity gain hierarchy for minor development now treats offsite gains as equal in priority to onsite habitat creation [1][5][10].
Key Takeaways
- The 0.2 hectare exemption removes mandatory BNG for roughly half of residential planning permissions, mainly small infill and minor sites [7][3].
- The exemption does not apply where a site contains, or is within a set distance of, irreplaceable habitat or certain priority habitats [4][8].
- The small self-build and custom-build BNG exemption has been withdrawn, meaning individual self-builders on qualifying land must now assess BNG duties [5][6].
- From 2 November 2026, Nationally Significant Infrastructure Projects, major roads, railways, and energy schemes, face a mandatory 10% net gain duty [10][1].
- For minor development, offsite biodiversity gains now rank equally with onsite habitat creation in the biodiversity gain hierarchy, giving developers more flexibility [3][6].
- Legal commentators, including analysis referenced by Freeths and Pinsent Masons, describe the changes as a rebalancing exercise: easing pressure on small builders while tightening the net around large-scale schemes.
- Ecological consultants should expect more due diligence work on threshold assessments and less routine metric work on the smallest sites.
What is UK Biodiversity Net Gain in 2026?
Biodiversity Net Gain is the legal requirement, introduced under the Environment Act 2021, that most new development in England must leave biodiversity in a measurably better state than before construction started, typically by delivering at least a 10% net gain in habitat value [2][9].
Developers demonstrate this using the statutory biodiversity metric, which scores habitats before and after development based on type, condition, size, and strategic significance. The resulting gain can be delivered onsite, offsite through habitat banks or land management agreements, or through statutory biodiversity credits bought from DEFRA as a last resort [9][2]. By 2026, BNG has moved from a new requirement bedding in since 2024 to a mature planning condition that most local planning authorities apply routinely, with two major carve-outs now reshaping who actually needs to comply.
What's changing with the UK Biodiversity Net Gain November 2026 infrastructure duty and 0.2ha exemption?
Two structural changes define the 2026 BNG reforms: a new small-sites exemption based on a 0.2 hectare area threshold, and a new mandatory 10% net gain duty extending BNG to national infrastructure from 2 November 2026 [1][10]. Together they mark the biggest shift in BNG scope since the regime launched.
The 0.2 hectare exemption
The 0.2 hectare exemption removes the statutory BNG requirement for developments on sites below that area threshold, confirmed to take effect before 31 July 2026 under secondary legislation [7][6]. DEFRA and industry analysis estimate this exempts around half of residential planning permissions granted in England, because so many housing schemes, infill plots, small backland sites, minor extensions to existing settlements, fall under 0.2 hectares [7][3].
The exemption is measured against the total site area of the application, not just the developed footprint, and applies at the point permission is determined [4][8]. It does not apply automatically, however, where the site contains a priority habitat, an irreplaceable habitat such as ancient woodland, or falls within a protected buffer zone, in those cases, full BNG assessment is still required regardless of size [4][8].
Removal of the self-build and custom-build exemption
The previous exemption that shielded small-scale self-build and custom-build homes from BNG duties has been withdrawn as part of the same reform package [5][6]. Individual self-builders on sites above 0.2 hectares, or on sites containing priority habitat, must now comply with the same biodiversity gain requirements as commercial developers. DEFRA's rationale is consistency: allowing area-based exemptions to do the work of protecting small projects, rather than exemptions tied to who is building rather than what is being built [1][5].
The November 2026 NSIP infrastructure duty
From 2 November 2026, BNG becomes a statutory duty for Nationally Significant Infrastructure Projects, covering major roads, railways, and energy infrastructure consented through the NSIP regime [10][1]. These projects must now deliver a minimum 10% biodiversity net gain, aligning infrastructure consenting with the same baseline standard already applied to most town and country planning applications [10].
Who has to comply with the November 2026 infrastructure duty, and who is exempt?
Compliance now depends on project type and site size rather than a single blanket rule. Housing and minor development are judged against the 0.2 hectare threshold and priority habitat caveats, while major infrastructure is judged against the new NSIP duty [4][10].
What counts as infrastructure under BNG rules: the November 2026 duty applies specifically to projects consented under the Planning Act 2008 NSIP regime, large-scale energy generation, electricity transmission, major road schemes, and rail infrastructure that exceed the thresholds requiring national-level consent [10][1]. Smaller highway improvements and local energy schemes consented through ordinary planning permission remain subject to the standard 10% BNG rule that has applied since 2024, not the new NSIP-specific duty.
Which projects are exempt: alongside the 0.2 hectare small-sites exemption, existing de minimis exemptions continue to apply to householder applications, biodiversity-neutral changes of use, and certain permitted development rights that do not require full planning permission [4][2]. These pre-existing exemptions run alongside, not instead of, the new area-based rule.
Is my small development exempt: a development is likely exempt if its total site area is below 0.2 hectares and it contains no priority or irreplaceable habitat; it is not exempt if it sits on or near ancient woodland, veteran trees, or other protected habitat categories, regardless of size [8][4]. Applicants should always request a written confirmation from the local planning authority rather than assuming exemption.
BNG for housing vs infrastructure: what's the difference?
Housing developments below 0.2 hectares can now be exempt outright, while all NSIP infrastructure, regardless of size, must meet the 10% net gain duty from 2 November 2026 [7][10]. This creates a two-track system: small residential schemes get relief, while major infrastructure gets tighter, more formalised obligations.
| Feature | Residential/minor development | NSIP infrastructure |
|---|---|---|
| Net gain requirement | 10%, unless exempt under 0.2ha rule | 10%, mandatory from 2 Nov 2026 |
| Area-based exemption | Yes, below 0.2ha (with priority habitat caveat) | No exemption |
| Gain hierarchy | Onsite and offsite gains now ranked equally | Onsite preferred, offsite/credits as fallback |
| Consent route | Local planning authority | Planning Act 2008 (NSIP) |
For minor development specifically, the biodiversity gain hierarchy has been amended so that offsite gains, bought through habitat banks or conservation agreements, rank equally with onsite habitat creation, rather than being treated as a lesser fallback option [3][6]. This gives smaller developers more flexibility to buy into existing habitat schemes instead of redesigning site layouts around onsite planting.
How do you calculate Biodiversity Net Gain for your project?
BNG is calculated using the statutory biodiversity metric, which compares the biodiversity value of the site before development against its projected value after development and management, expressed in standardised habitat units [9][2]. A qualified ecologist first surveys the baseline habitat, scoring distinctiveness, condition, and strategic significance, then models the post-development habitat plan against the same criteria.
Practical steps for 2026 applications:
- Confirm site area against the 0.2 hectare threshold before commissioning a full metric assessment.
- Check for priority or irreplaceable habitat using DEFRA's habitat classification guidance [4].
- Commission a Preliminary Ecological Appraisal to establish baseline habitat units.
- Model onsite habitat creation, then offsite options where onsite gain is limited by site constraints.
- Submit the completed biodiversity metric calculation with the planning application, plus a habitat management and monitoring plan.
Common mistake: treating the 0.2 hectare figure as covering only the built footprint. It applies to the whole application site boundary, so a small house on a large garden plot can still fall outside the exemption [7][8].
What happens if you don't meet BNG targets, and can you pay into a fund instead?
Failing to meet the required net gain means planning permission cannot be lawfully granted or implemented, since BNG delivery is now a condition attached to most permissions under the Environment Act 2021 [2][9]. Non-compliance after implementation can trigger enforcement action and breach of planning condition proceedings.
Where onsite and offsite habitat delivery genuinely cannot meet the required 10%, developers can purchase statutory biodiversity credits from DEFRA as a last-resort mechanism, though these are priced to be more expensive than direct habitat delivery and are intended as a backstop, not a routine option [9][2]. Choose statutory credits only after exhausting realistic onsite and offsite habitat options, since planning authorities expect evidence that credits were genuinely a last resort.
How much does Biodiversity Net Gain cost, and what mistakes should you avoid?
BNG costs vary widely by site size, habitat baseline, and delivery route, and no single verified figure applies across all projects, so developers should budget based on a site-specific metric assessment rather than industry averages. Costs typically include ecological survey fees, metric assessment, habitat creation or offsite unit purchase, and a 30-year monitoring and management commitment [9][2].
Common compliance mistakes seen across 2026 applications include:
- Assuming exemption without checking for priority habitat on or near the site [4][8].
- Leaving metric calculations until after outline permission, when habitat options are already constrained by layout.
- Underestimating the 30-year management and monitoring obligation attached to onsite habitat delivery.
- Self-builders assuming the old custom-build exemption still applies after its withdrawal [5][6].
How long do BNG requirements last after completion?
Habitat delivered to meet a BNG obligation must be secured and managed for a minimum of 30 years from the point habitat creation or enhancement begins, regardless of whether the gain is delivered onsite or offsite [9][2]. This obligation is typically secured through a conservation covenant, a planning condition, or a Section 106 agreement, and it survives changes of site ownership.
What to do next for developers, surveyors, and ecological consultants
Professionals working across planning, surveying, and ecology should treat September 2026 as the point to re-check every live pipeline against the new rules, not wait for the November commencement date.
Developers:
- Audit current and pipeline sites against the 0.2 hectare threshold and priority habitat criteria before assuming exemption.
- Reassess self-build or custom-build schemes previously relying on the withdrawn exemption.
- Budget infrastructure schemes for the 10% NSIP duty ahead of 2 November 2026.
Surveyors and ecological consultants:
- Expect increased demand for threshold and habitat-screening assessments on small sites rather than full metric surveys.
- Build offsite habitat bank relationships now, since offsite gains rank equally with onsite delivery under the revised hierarchy.
- Track DEFRA guidance updates closely, since transitional arrangements affect which applications the new rules apply to [1][6].
Planning teams and legal advisers:
- Review permissions granted near the 31 July 2026 commencement date for transitional eligibility.
- Prepare NSIP-related environmental statements to include the 10% net gain duty from November 2026 onward.
Frequently Asked Questions
Does the 0.2 hectare exemption apply automatically to all small sites?
No. It applies to sites under 0.2 hectares total area, but not where the site contains or is near priority or irreplaceable habitat, in which case full BNG assessment is still required [4][8].
When did the 0.2ha exemption come into force?
DEFRA confirmed the exemption takes effect before 31 July 2026, under secondary legislation amending the BNG regime [7][6].
What is the November 2026 infrastructure duty?
From 2 November 2026, Nationally Significant Infrastructure Projects, major roads, railways, and energy schemes, must deliver a mandatory 10% biodiversity net gain [10][1].
Can self-builders still claim a small-scale BNG exemption?
No. The dedicated self-build and custom-build exemption has been removed; self-builders now follow the same area-based and habitat-based rules as other developers [5][6].
Are offsite biodiversity gains as good as onsite gains for minor development?
Under the amended biodiversity gain hierarchy, offsite gains now rank equally with onsite habitat creation for minor development, giving developers more delivery flexibility [3][6].
How long must delivered habitat be maintained?
A minimum of 30 years, secured through a conservation covenant, planning condition, or Section 106 agreement [9][2].
Conclusion
The UK Biodiversity Net Gain November 2026 infrastructure duty and 0.2ha exemption mark a genuine turning point in how BNG applies across England: smaller housing schemes gain welcome relief, while national infrastructure faces its first hard-edged biodiversity obligation. Developers should audit site areas and habitat status now, ecological consultants should pivot capacity toward threshold screening and offsite habitat partnerships, and infrastructure promoters should build the 10% duty into cost and design planning well before 2 November 2026. Acting before the transitional window closes will avoid costly redesigns and enforcement risk later.
References
[1] Biodiversity Net Gain Whats Changing And What It Means For You – defraenvironment.blog.gov.uk
[2] Understanding Biodiversity Net Gain – gov.uk
[3] Bng Changes 2026 Exemptions Metric Updates – landbng.uk
[4] Biodiversity Net Gain Exempt Developments – gov.uk
[5] Key Changes Confirmed To Biodiversity Net Gain – cla.org.uk
[6] Biodiversity Net Gain Changes August 2026 – gaiacompany.io
[7] Bng 0 2 Hectare Exemption In Force 31 July 2026 Small Sites Biodiversity Net Gain What Changes Today – Bng 0 2 hectare exemption in force 31 july 2026 small sites biodiversity net gain what changes today
[8] Biodiversity Net Gain Changes 2026 – biodiverseconsulting.co.uk
[9] Biodiversity Net Gain – gov.uk
[10] Biodiversity Net Gain For Major Infrastructure Projects New Guidance – defraenvironment.blog.gov.uk