Biodiversity Net Gain BNG Update September 2026: Amendments Developers Must Act On

Last updated: September 28, 2026

Quick Answer

The Biodiversity Net Gain BNG update September 2026 amendments developers need to know centre on Defra's Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026, which took effect on 6 August 2026. The headline change is a new 0.2-hectare exemption for small sites without priority habitat, the end of the automatic self-build exemption, and confirmation that nationally significant infrastructure projects (NSIPs) will face mandatory 10% BNG from 2 November 2026. The core 10% net gain requirement for everything else remains unchanged.

Key Takeaways

• From 6 August 2026, sites of 0.2 hectares or less with no priority habitat impact are exempt from mandatory BNG, but only for applications made on or after that date.
• The self-build and custom-build housing exemption ended for applications submitted from 6 August 2026 onward; these schemes now sit under the general exemption framework.
• The 10% net gain requirement has not changed for non-exempt development and remains the statutory floor.
• Minor developments can now go straight to off-site biodiversity units without first proving on-site options are exhausted.
• NSIPs become subject to mandatory BNG for Development Consent Order applications made on or after 2 November 2026.
• The statutory biodiversity metric was updated in July 2026 to reflect the new exemption and NSIP rules.
• Off-site unit prices remain volatile and vary sharply by habitat type and region.
• Local Planning Authorities are enforcing more consistently in 2026, with habitat management and monitoring plans under closer scrutiny.

What Is Biodiversity Net Gain and Who Needs to Comply

Biodiversity Net Gain is a legal requirement under the Environment Act 2021 that most development in England must leave habitats measurably better than before construction started, using a 10% biodiversity value uplift as the benchmark. It applies to development consented under the Town and Country Planning Act 1990, and from November 2026 it extends fully to nationally significant infrastructure projects.

Compliance is required from anyone submitting a qualifying planning application: housebuilders, commercial developers, landowners bringing forward sites, and infrastructure promoters. Local Planning Authorities cannot grant planning permission for a non-exempt scheme without an approved biodiversity gain plan. For a full grounding in the mechanics, see this Biodiversity Net Gain explained guide.

Biodiversity Net Gain September 2026 Changes Explained

The September 2026 position reflects amendments Defra confirmed in its July 2026 environment blog and formalised through updated Planning Practice Guidance published on 31 July 2026. These changes took legal effect from 6 August 2026 and apply to new applications, not retrospectively to schemes already in the system.

The key regulatory moves are:

• New paragraphs 003a and 004a added to the Planning Practice Guidance on BNG, clarifying how the small-site exemption and minor-development flexibility operate.
• A 0.2-hectare de minimis threshold, replacing the previous approach of exempting only specific development types like self-build housing.
• Simplified sequencing for minor development, removing the requirement to exhaust on-site habitat options before registering off-site units.
• Transitional provisions confirming that applications submitted before 6 August 2026 continue under the rules that applied when they were lodged.

Defra has framed these as proportionality fixes rather than a retreat from the policy's ambition, and further targeted exemptions covering enhancement schemes and public-realm projects are expected to be defined later in 2026.

How Do the New BNG Amendments Affect Developers

The amendments mainly reduce friction for small and minor schemes while tightening the rules around self-build. Larger developers see little change beyond confirmation that the 10% requirement and metric-based assessment process continue as before.

Practical effects include:

• Developers with red-line boundaries under 0.2 hectares can potentially skip BNG entirely, cutting survey and unit-purchase costs, provided no priority habitat is present.
• Self-build and custom-build applicants submitted from 6 August 2026 must now assess BNG obligations like any other applicant, which was not the case previously.
• Minor developers gain flexibility to combine on-site enhancement with registered off-site units simultaneously, rather than proving on-site delivery is impossible first.
• Larger schemes remain fully bound by the statutory metric, biodiversity gain plans and the 30-year habitat management commitment.

CIEEM and RTPI briefings issued after the July 2026 update both flag that developers should not assume exemption without checking site-specific conditions, since priority habitat presence overrides the area threshold regardless of site size.

Biodiversity Net Gain Exemptions and Thresholds 2026

The 0.2-hectare exemption is the most significant threshold change of 2026, but it is not automatic and several older exemptions remain in force alongside it. Developers must check both the area rule and habitat conditions before assuming a scheme falls outside mandatory BNG.

Exemption category	Condition	Applies from
Small-site (de minimis)	Site ≤ 0.2 hectares, no priority habitat impact	Applications from 6 August 2026
Self-build/custom-build	No longer a standalone exemption	Ends for applications from 6 August 2026
Temporary permissions	Planning permission of 5 years or less	Confirmed 2026, subject to local criteria
Householder applications	Minor domestic extensions/alterations	Ongoing (pre-2026 exemption retained)
Biodiversity enhancement schemes	Certain habitat-improvement-led projects	Being refined through 2026

A common mistake is assuming brownfield land automatically qualifies for the small-site exemption. If a 0.15-hectare brownfield plot still supports a patch of priority grassland or hedgerow habitat, the exemption does not apply and the 10% requirement stands. The CLA has advised landowners bringing forward small parcels to commission a habitat check before relying on the area threshold. For background on qualifying thresholds generally, see how to achieve 10% Biodiversity Net Gain.

Biodiversity Net Gain Requirements for New Projects 2026

The default requirement for any non-exempt project remains a minimum 10% net gain in biodiversity value, measured using the statutory biodiversity metric before and after development. This has not shifted since BNG became mandatory for most planning applications in February 2024, and Defra's 2026 amendments reinforce rather than dilute it.

New for 2026: NSIPs face mandatory BNG for Development Consent Order applications submitted on or after 2 November 2026, aligned to the same 10% floor used in town and country planning. Habitat value for NSIP schemes is assessed at the point the biodiversity gain plan is submitted, and developers must define a "BNG project boundary" focused on impacted and enhancement habitats rather than the full DCO boundary. Applications made before 2 November 2026 are not caught, even if the resulting DCO is later amended.

BNG Calculator Tool September 2026 Update and How to Calculate BNG for Residential Development

The statutory biodiversity metric, the official calculator behind every BNG assessment, was updated in July 2026 to build in the 0.2-hectare exemption logic and prepare for NSIP rollout on 2 November 2026. Developers and ecologists must use the current version of the tool; older metric versions are not accepted by Natural England or most Local Planning Authorities.

For residential schemes, calculating BNG involves four steps:

1. Baseline survey, a qualified ecologist records existing habitat type, condition, and area or length on-site (UKHab classification).
2. Metric input, baseline data is entered into the statutory metric alongside the post-development habitat design.
3. Gap calculation, the tool calculates the biodiversity value shortfall or surplus against the 10% target.
4. Delivery route selection, any shortfall is met through on-site creation, registered off-site units, or (as a last resort) statutory biodiversity credits bought from Defra.

Small errors in habitat condition scoring at step one are the most common cause of failed submissions, so many developers now commission an independent biodiversity net gain report before formal submission to catch discrepancies early.

Biodiversity Net Gain vs Environmental Impact Assessment

BNG and Environmental Impact Assessment (EIA) are separate legal processes that often run in parallel but serve different purposes. EIA assesses the wider environmental effects of a project, including noise, air quality, landscape and ecology, while BNG focuses narrowly on quantifying and offsetting biodiversity value using the statutory metric.

Key distinctions:

• EIA is required for larger or more environmentally significant projects screened under the EIA Regulations; BNG applies to nearly all qualifying planning applications regardless of scale.
• EIA produces a qualitative and quantitative Environmental Statement; BNG produces a numeric metric score and a legally binding biodiversity gain plan.
• A project can require both, neither, or just one. Passing EIA screening does not exempt a scheme from BNG, and vice versa.

BNG Habitat Creation: Offsite vs Onsite Requirements and Costs

On-site delivery means creating or enhancing habitat within the development's own red-line boundary, while off-site delivery means buying biodiversity units from another registered site or, as a fallback, statutory credits from Defra. Since July 2026, minor developments no longer have to prove on-site options are exhausted before choosing off-site units.

Cost is the deciding factor for most developers. Off-site unit pricing in September 2026 continues to vary widely by habitat type and region:

• Lower-distinctiveness grassland units trade at the more affordable end of the market.
• Higher-distinctiveness habitats (wetland, woodland, species-rich grassland) command significantly higher prices due to limited supply.
• Regional scarcity of registered off-site sites near London and the South East pushes prices higher than in the North and Midlands.

Developers weighing the two routes should read Biodiversity Net Gain off-site or on-site delivery and the guide to biodiversity credits for developers before committing, since switching delivery routes mid-application can delay decisions by months. Sites considering supplying units into the market can review options via sell biodiversity units.

What Are the Penalties for Not Meeting BNG Targets

Failing to secure an approved biodiversity gain plan means a Local Planning Authority cannot lawfully grant planning permission for a non-exempt scheme, effectively halting the project at source. Once permission is granted, breach of BNG conditions, such as failing to deliver or maintain habitat, can trigger enforcement action under standard planning enforcement powers.

Local Planning Authorities in 2026 are increasingly checking:

• Whether biodiversity gain plans match the metric submitted at decision stage.
• Whether habitat management and monitoring plans (covering the 30-year commitment) are being followed.
• Whether off-site units registered on the biodiversity gain site register actually correspond to the claimed allocation.

RTPI guidance issued to planning officers this year encourages condition-based enforcement, meaning non-compliance can result in breach of condition notices, and in persistent cases, enforcement notices requiring remedial habitat works.

Common Mistakes Developers Make With BNG

The most frequent error is assuming exemption without checking for priority habitat, which can invalidate a claimed 0.2-hectare exemption entirely. Other recurring mistakes include submitting outdated metric versions, underestimating habitat condition scoring, and leaving off-site unit sourcing until after permission is granted, when prices and availability may have shifted.

Architects and design teams also frequently treat BNG as an afterthought rather than a site-layout constraint from the outset. Practical guidance on avoiding this is covered in how architects can solve Biodiversity Net Gain.

Compliance Checklist for Developers, September 2026

1. Confirm your application date. Applications before 6 August 2026 follow the old rules; those on or after follow the new amendments.
2. Check red-line boundary area against the 0.2-hectare threshold and survey for priority habitat before assuming exemption.
3. If self-build or custom-build, note that the standalone exemption no longer applies from 6 August 2026.
4. Use the current version of the statutory biodiversity metric, updated July 2026.
5. Decide on-site, off-site, or blended delivery early; minor developments can now go straight to off-site units.
6. Budget for off-site unit price volatility, checking current market rates before finalising viability assessments.
7. Prepare a habitat management and monitoring plan covering the full 30-year commitment period.
8. Confirm NSIP status; if applicable, plan for mandatory BNG on any DCO application from 2 November 2026.
9. Retain evidence of baseline surveys and metric calculations for LPA audit and enforcement checks.

For a broader planning-stage view, see 8 Biodiversity Net Gain points on planning your project.

A Note for Small Developers and Landowners

Small developers benefit the most from the September 2026 amendments, but the benefit only applies cleanly to genuinely small, low-impact sites. If your site is under 0.2 hectares and free of priority habitat, exemption removes a significant cost and time burden. If it exceeds that threshold, or contains any hedgerow, grassland or wetland habitat of note, the full 10% requirement still applies, and self-build applicants in particular should not assume the old exemption still protects them.

Landowners with spare land suitable for habitat creation are seeing steadier demand from developers seeking off-site units, particularly for higher-distinctiveness habitat types. Details on getting a site registered are available via buy biodiversity units.

FAQ

Does the 10% BNG requirement still apply in September 2026?
Yes. The core 10% net gain requirement for non-exempt development is unchanged; only exemption thresholds and process flexibility have been amended.

When did the July 2026 amendments actually take legal effect?
The Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026 took effect from 6 August 2026, following guidance updates published 31 July 2026.

Can a self-build project still be exempt from BNG?
Not automatically. The standalone self-build exemption ended for applications made from 6 August 2026, though the 0.2-hectare small-site exemption may still apply if the plot qualifies.

Do NSIPs need to comply with BNG now?
Not yet. Mandatory BNG for NSIPs applies to Development Consent Order applications submitted on or after 2 November 2026, not before.

How do I know if my site qualifies for the 0.2-hectare exemption?
Check the red-line boundary area and confirm, through an ecological survey, that no priority habitat is present on-site; both conditions must be met.

What happens if a Local Planning Authority finds a breach of BNG conditions?
It can pursue standard planning enforcement, including breach of condition or enforcement notices requiring remedial habitat delivery.

Conclusion

The Biodiversity Net Gain BNG update September 2026 amendments developers are working through mark a proportionality adjustment, not a policy retreat. The 0.2-hectare exemption and simplified minor-development rules genuinely reduce burden for small, low-impact schemes, but the core 10% requirement, the statutory metric, and 30-year habitat commitments remain firmly in place for everything else. Self-build applicants and NSIP promoters face the most consequential timeline changes this year.

Next steps: confirm your application date against 6 August 2026, verify site area and priority habitat status before assuming exemption, and update to the July 2026 metric version before submitting any new gain plan. If your project sits near the exemption threshold or involves off-site unit sourcing, get an ecologist's assessment early rather than after permission is sought.