Last updated: August 26, 2026
Quick Answer: On 6 August 2026, the government amended England's Biodiversity Net Gain (BNG) regulations, replacing the previous 25 m² de minimis threshold with a new 0.2 hectare (2,000 m²) small site exemption. Developments with a footprint at or below this threshold are now exempt from mandatory BNG requirements, provided the site does not contain or affect priority habitats. Additional changes include a new exemption for time-limited planning permissions of five years or less, and the removal of the self-build and custom-build exemption for new applications submitted from that date.
Key Takeaways
- The Biodiversity Net Gain changes 6 August 2026 small site exemption raises the exemption threshold from 25 m² to 0.2 ha (2,000 m²), freeing many small residential and commercial schemes from mandatory BNG.
- Developments affecting priority habitats do not qualify for the small site exemption, regardless of size.
- A new exemption covers planning permissions that are time-limited to five years or fewer.
- The self-build and custom-build exemption has been removed for applications submitted on or after 6 August 2026.
- Minor developments now have greater flexibility to combine onsite and offsite biodiversity gains.
- BNG will extend to Nationally Significant Infrastructure Projects (NSIPs) from November 2026.
- Exempt sites are still subject to NPPF biodiversity policies and local planning authority requirements.
- Developers should reassess current and pipeline projects against the new thresholds immediately.
What Is Biodiversity Net Gain and Why Does It Matter?
Biodiversity Net Gain is a planning requirement in England that obliges developers to leave biodiversity in a measurably better state than before development. Under the Environment Act 2021, most planning permissions must deliver at least a 10% net gain in biodiversity value, assessed using the Defra biodiversity metric. [5]
BNG matters because England has lost significant proportions of its wildlife habitats over recent decades. The policy shifts the cost of habitat loss onto developers and landowners, requiring them to either create or enhance habitats onsite, purchase biodiversity units from registered offsite providers, or buy statutory biodiversity credits from the government as a last resort. [7]
What Changed on 6 August 2026 for BNG Requirements?
Four significant changes took effect on 6 August 2026, reshaping how BNG applies to smaller and time-limited developments across England. [1]
1. New 0.2 ha small site exemption
The previous de minimis threshold of 25 m² was widely criticised as too low to offer meaningful relief to small developers. The new threshold of 0.2 ha (2,000 m²) exempts a far broader range of minor developments. [3]
2. New time-limited planning permission exemption
Developments granted planning permission for five years or fewer are now exempt from mandatory BNG. This covers temporary structures, meanwhile uses, and short-term commercial operations. [4]
3. Removal of the self-build and custom-build exemption
Applications submitted on or after 6 August 2026 can no longer rely on the self-build or custom-build exemption. Those schemes must now comply with full BNG requirements. [1]
4. Greater flexibility for minor developments
Minor developments can now combine onsite habitat creation with offsite biodiversity units more freely, reducing the pressure to deliver all gains within the site boundary. [8]
What Counts as a Small Site Under the New BNG Rules?
A small site under the Biodiversity Net Gain changes 6 August 2026 small site exemption is any development with a total footprint at or below 0.2 hectares (2,000 m²). The measurement applies to the area of land directly affected by the development, not the total site area. [4]
Critical caveat: The exemption does not apply if the development affects a priority habitat, such as ancient woodland, species-rich grassland, or lowland heath. In those cases, full BNG compliance is required regardless of the site's size. [4]
Developers should check the Natural England Priority Habitats Inventory before assuming exemption applies. Local planning authorities retain the right to refuse applications on biodiversity grounds even where the statutory BNG exemption is met.
Is My Development Eligible for the Small Site Exemption?
Use this decision framework to assess eligibility:
| Criterion | Exempt? |
|---|---|
| Development footprint is 0.2 ha or less | Potentially yes |
| Site contains or affects priority habitat | No |
| Planning permission is time-limited to 5 years or fewer | Yes (separate exemption) |
| Self-build or custom-build application (post-6 Aug 2026) | No |
| Householder application within existing curtilage | Check LPA guidance |
| Development affecting a SSSI | No |
Edge case: A development with a footprint of 0.18 ha that sits adjacent to a priority habitat corridor may still face BNG scrutiny from the LPA under NPPF biodiversity policies, even if it technically qualifies for the statutory exemption. [9]
What's the Difference Between Old and New BNG Rules?
The table below summarises the most significant shifts.
| Rule | Before 6 August 2026 | From 6 August 2026 |
|---|---|---|
| Small site threshold | 25 m² de minimis | 0.2 ha (2,000 m²) |
| Time-limited permissions | No specific exemption | Exempt if 5 years or fewer |
| Self-build/custom-build | Exempt | No longer exempt |
| Onsite/offsite flexibility | More restricted for minor sites | Greater flexibility confirmed |
| NSIP coverage | Not yet in scope | Extension due November 2026 |
The shift from 25 m² to 2,000 m² is a fortyfold increase in the exemption area, meaning a large number of small infill plots, garden developments, and minor commercial extensions will no longer require a Biodiversity Net Gain Statement or metric calculation. [3]
Do Residential Developments Need Biodiversity Net Gain?
Yes, most residential developments in England still require BNG compliance, but the new small site exemption removes the requirement for smaller schemes. A single dwelling on a plot of 0.2 ha or less, with no priority habitat present, is now exempt from mandatory BNG. Larger residential schemes, estate developments, and any project affecting priority habitats must still deliver a minimum 10% net gain. [5]
Self-build and custom-build projects are no longer exempt from 6 August 2026 onwards. Developers pursuing those routes must factor BNG costs and habitat management plans into their project budgets. [1]
How Do I Calculate Biodiversity Net Gain for My Project?
BNG is calculated using the Defra Biodiversity Metric (currently version 4.0). The process involves:
- Baseline survey: A suitably qualified ecologist surveys existing habitats on the site and assigns biodiversity units using the metric.
- Post-development assessment: The ecologist models the habitats that will exist after development and any onsite enhancements.
- Gap analysis: If the post-development score is less than 110% of the baseline (the 10% net gain target), additional offsite units or statutory credits must be purchased.
- Biodiversity Gain Plan: Submitted to the LPA before development commences, detailing how and where the 10% gain will be delivered and maintained for at least 30 years. [7]
Common mistake: Developers sometimes commission ecological surveys too late in the design process, after planning has been submitted. This limits the ability to redesign the scheme to maximise onsite gains and reduces cost efficiency.
How Much Does Biodiversity Net Gain Cost for Developers?
Costs vary significantly depending on site conditions and the gap between baseline and target biodiversity units. Rough benchmarks based on industry data:
- Ecological baseline survey: from approximately £1,500 to £5,000+ depending on site size and complexity.
- Offsite biodiversity units: market prices vary by habitat type and location; units have been trading in a wide range depending on habitat quality and geography.
- Statutory biodiversity credits (government last resort): priced by Defra and generally more expensive than the open market, by design.
The new 0.2 ha exemption removes these costs entirely for qualifying small sites, which is a material saving for small developers and self-builders who previously had to commission metric assessments for minor schemes. [6]
Which Projects Are Exempt from Biodiversity Net Gain?
Under the updated rules, the following categories are exempt from mandatory BNG in England:
- Developments with a footprint of 0.2 ha or less (no priority habitats affected)
- Planning permissions time-limited to five years or fewer
- Householder applications (in most cases, subject to LPA policy)
- Permitted development rights (where no full planning application is required)
- Emergency development
- Development with no impact on habitats (for example, change of use of a building with no external works)
Projects that are not exempt include self-build and custom-build applications (from 6 August 2026), any development affecting priority habitats, and Nationally Significant Infrastructure Projects from November 2026 onwards. [4]
What Happens if I Don't Meet Biodiversity Net Gain Targets?
Failure to submit an approved Biodiversity Gain Plan before commencing development is a breach of planning condition. Consequences include:
- Planning enforcement action by the LPA, including stop notices.
- Inability to lawfully commence development.
- Potential requirement to retrospectively purchase offsite units or statutory credits at higher cost.
- Reputational and legal risk for developers and contractors.
LPAs are required to monitor BNG delivery and can take enforcement action where habitat management obligations under legal agreements are not met over the 30-year management period. [5]
How Long Do Biodiversity Net Gain Improvements Need to Last?
BNG habitat enhancements must be maintained and monitored for a minimum of 30 years from the date the Biodiversity Gain Plan is approved. This applies to both onsite and offsite gains. The obligation is secured through a planning condition, legal agreement, or conservation covenant. [7]
The new five-year time-limited exemption is specifically for temporary permissions where the development itself will be removed within that period. It does not reduce the 30-year management requirement for non-exempt sites.
What About the November 2026 Extension to NSIPs?
BNG will extend to Nationally Significant Infrastructure Projects from November 2026. NSIPs include major energy, transport, water, and waste infrastructure that is consented through the Development Consent Order process rather than the standard planning system. [1]
This extension means promoters of large infrastructure schemes must begin factoring BNG into their environmental impact assessments and project costings now. The scale of habitat impact associated with NSIPs means the biodiversity unit requirements and associated costs will be substantially larger than for typical planning applications.
Where Can I Find Biodiversity Net Gain Guidance for England?
The primary sources of statutory and policy guidance are:
- gov.uk BNG guidance hub: Covers the full BNG framework, metric, exemptions, and Biodiversity Gain Plan requirements. [5]
- Defra environment blog: Published updates on the August 2026 changes and the government's rationale. [1]
- gov.uk exempt developments page: Definitive list of exempt development categories under the updated rules. [4]
- Local planning authority pre-application services: Many LPAs offer pre-application advice on BNG requirements specific to their area.
What Developers Must Do Now: Action Checklist
Review every live and pipeline project against the new 0.2 ha threshold and priority habitat data before assuming exemption applies.
- Confirm whether each project's footprint falls at or below 0.2 ha (2,000 m²).
- Check the Natural England Priority Habitats Inventory for each site.
- For time-limited permissions, confirm the permission duration is five years or fewer to qualify for the new exemption.
- Remove any reliance on the self-build or custom-build exemption for applications not yet submitted.
- Engage a suitably qualified ecologist at the earliest design stage for non-exempt sites.
- Submit a Biodiversity Gain Plan to the LPA before commencing any non-exempt development.
- For NSIP promoters: begin BNG assessment and habitat baseline work ahead of the November 2026 extension.
- Review legal agreements and planning conditions on recently consented schemes to confirm BNG obligations are correctly documented.
- Check LPA-specific policies, as some authorities impose requirements beyond the statutory minimum. [9]
Common Mistakes Developers Make with BNG
Assuming exemption without checking priority habitats. The 0.2 ha threshold does not override the priority habitat caveat. A small site on species-rich grassland is not exempt.
Late ecological surveys. Commissioning surveys after planning submission limits design flexibility and increases costs.
Confusing the footprint with the site area. The exemption threshold applies to the area of land directly affected by development, not the total landholding.
Ignoring NPPF biodiversity policies on exempt sites. Statutory BNG exemption does not remove the LPA's ability to apply NPPF policies requiring biodiversity protection and enhancement. [9]
Overlooking the 30-year management obligation. Developers sometimes secure planning without adequately budgeting for long-term habitat management costs.
Frequently Asked Questions
Q: Does the 0.2 ha small site exemption apply automatically, or does it need to be claimed?
A: The exemption applies by operation of law to qualifying developments, but developers should clearly state in their planning application that the exemption is being relied upon and provide evidence that the footprint is at or below 0.2 ha and that no priority habitats are affected. [4]
Q: Can a development be split into smaller phases to fall under the 0.2 ha threshold?
A: No. Artificial phasing to circumvent BNG thresholds is likely to be treated as a single development by the LPA. Developers should not rely on this approach.
Q: What happens to applications submitted before 6 August 2026 that relied on the self-build exemption?
A: Transitional provisions protect applications submitted before 6 August 2026. The removal of the self-build exemption applies only to new applications submitted on or after that date. [1]
Q: Are permitted development rights affected by the August 2026 changes?
A: Permitted development rights that do not require a full planning application remain outside the mandatory BNG regime. The August 2026 changes affect applications made under the Town and Country Planning Act framework. [4]
Q: Does the five-year time-limited exemption apply to temporary agricultural buildings?
A: The exemption covers planning permissions time-limited to five years or fewer. Whether a specific agricultural building qualifies depends on the terms of the permission and whether it falls within a broader exempt category. LPA pre-application advice is recommended.
Q: When does BNG apply to NSIPs?
A: The government has confirmed BNG will extend to Nationally Significant Infrastructure Projects from November 2026. NSIP promoters should begin habitat baseline assessments and BNG planning now. [1]
Conclusion
The Biodiversity Net Gain changes 6 August 2026 small site exemption represent the most significant recalibration of BNG policy since mandatory requirements came into force. The fortyfold increase in the exemption threshold removes a genuine compliance burden from small developers, while the removal of the self-build exemption closes a route that had been widely used. The upcoming NSIP extension signals that BNG is maturing into a permanent, system-wide requirement across all major development in England.
Developers, planning consultants, and landowners should act now: audit current and pipeline projects against the new thresholds, engage ecologists early, and prepare for the NSIP extension if relevant to their portfolios. Those who treat BNG as a compliance box to tick at the last moment will continue to face cost and programme risk. Those who integrate it into early design will find it increasingly manageable.
References
[1] Biodiversity Net Gain: What's Changing And What It Means For You – defraenvironment.blog.gov.uk
[3] Biodiversity Net Gain Changes August 2026 – gaiacompany.io
[4] Biodiversity Net Gain Exempt Developments – gov.uk
[5] Biodiversity Net Gain – gov.uk
[6] Key Changes Confirmed To Biodiversity Net Gain – cla.org.uk
[7] Understanding Biodiversity Net Gain – gov.uk
[8] Biodiversity Net Gain BNG Changes From 6 August 2026 What You Need To Know – union4.co.uk
[9] planninggeek.co.uk – planninggeek.co.uk
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