Last updated: August 23, 2026
Quick Answer: Four targeted amendments to England's Biodiversity Net Gain framework took effect on 6 August 2026, following DEFRA's July 2026 announcement. The changes introduce a new 0.2-hectare small-site exemption, a temporary development exemption, greater flexibility in the mitigation hierarchy, and the removal of the self-build/custom-build exemption. Critically, these changes are not retrospective, planning applications received before 6 August 2026 continue under the previous BNG rules. [1]
Key Takeaways
- The 0.2-hectare small-site exemption applies only where no onsite priority habitat is present or affected, it is not a blanket exemption for all small sites.
- Temporary developments lasting five years or less are now exempt, provided they do not impact priority habitat.
- The self-build and custom-build exemption has been removed; those projects must now meet the standard 10% BNG requirement.
- The mitigation hierarchy for minor developments has been updated to allow onsite habitat creation and offsite biodiversity unit purchases to be considered simultaneously.
- Applications received before 6 August 2026 are governed by the previous rules, the changes are not retrospective.
- DEFRA estimates that roughly half of all residential planning applications may fall within the new small-site exemption, reducing administrative burden significantly.
- Nationally Significant Infrastructure Projects (NSIPs) are set to come under mandatory BNG from 2 November 2026.
- Chartered ecological surveyors will need to update their assessment workflows immediately for applications submitted from 6 August 2026 onwards.
What Is Biodiversity Net Gain and Why Does It Matter?
Biodiversity Net Gain (BNG) is a mandatory 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 applications must demonstrate a minimum 10% net gain in biodiversity units, calculated using DEFRA's statutory biodiversity metric. [2]
BNG matters because England has lost an estimated significant proportion of its wildlife-rich habitats over the past century. The policy forces development to account for its ecological footprint rather than simply mitigating harm. For developers, it means every planning application in scope must be accompanied by a biodiversity metric calculation and, where necessary, a biodiversity gain plan. For a full primer, see our biodiversity net gain explained guide.
What Exactly Changed on 6 August 2026 for Biodiversity Net Gain?
Four specific amendments to the BNG framework came into force on 6 August 2026, as confirmed by DEFRA's blog post published on 14 July 2026. [1] These are not wholesale changes to the system, the core 10% net gain duty remains intact, but they meaningfully alter who must comply and how compliance is achieved.
The Four Changes at a Glance
| Change | What It Does | Key Condition |
|---|---|---|
| New 0.2-hectare small-site exemption | Exempts developments under 0.2 ha from BNG | No onsite priority habitat affected |
| Temporary development exemption | Exempts time-limited projects of 5 years or less | No priority habitat impacted |
| Updated mitigation hierarchy | Allows onsite creation and offsite units at the same stage | Applies to minor developments |
| Removal of self-build/custom-build exemption | Self-builders must now meet 10% BNG | No exemption remains for this category |
How Will the August 2026 BNG Changes Affect Your Development Project?
The answer depends on your project's size, duration, and whether priority habitat is present on site. For many small developers and self-builders, the changes cut in opposite directions, some gain relief, others lose it.
If your site is under 0.2 hectares and has no priority habitat, you are now exempt from BNG requirements for applications submitted on or after 6 August 2026. This is a meaningful reduction in cost and process for small housebuilders and infill developers. DEFRA's July 2026 announcement indicated this change could exempt approximately half of all residential planning applications from the full BNG process. [1]
If you are a self-builder or custom-builder, the August 2026 BNG changes remove the exemption you previously relied on. From 6 August 2026, your project must demonstrate a 10% biodiversity net gain, just like any other in-scope development. This is a significant shift for the self-build sector, which had previously been carved out of the mandatory requirement. [5]
If your project is temporary (consented for five years or fewer) and does not affect priority habitat, you are now exempt. This is particularly relevant for construction compounds, temporary event sites, and short-term infrastructure works. [1]
For a broader look at how to structure your approach, see our guide on achieving biodiversity net gain without the risk.
Biodiversity Net Gain Requirements Before vs After 6 August 2026
The core 10% net gain requirement has not changed. What has changed is the list of exempt development categories and the sequencing rules within the mitigation hierarchy for minor developments. [4]
Before 6 August 2026:
- Self-build and custom-build developments were exempt.
- Small sites below a certain threshold were exempt, but the 0.2-hectare rule was not in place in its current form.
- The mitigation hierarchy required developers to exhaust onsite options before considering offsite biodiversity units.
From 6 August 2026:
- Self-build and custom-build developments are no longer exempt.
- The 0.2-hectare small-site exemption applies, but only where no priority habitat is present or affected.
- Temporary developments (five years or less, no priority habitat impact) are exempt.
- For minor developments, onsite habitat creation and offsite biodiversity unit purchases can be considered at the same stage of the hierarchy, giving developers greater flexibility in how they structure their BNG strategy. [3]
This last point is practically significant. Previously, developers had to demonstrate that onsite options were exhausted before purchasing offsite units. The updated hierarchy removes that sequential constraint for minor developments, which should speed up planning negotiations and reduce the risk of abortive work. For more detail on the onsite versus offsite decision, see our article on biodiversity net gain off-site or on-site delivery.
Who Needs to Comply With the New Biodiversity Net Gain Rules?
Any planning application for development in England that is not explicitly exempt must still meet the 10% BNG requirement. The August 2026 BNG changes expand the exempt category but do not change the fundamental scope of the duty.
Exempt from BNG (as of 6 August 2026): [10]
- Developments with a site area under 0.2 hectares where no onsite priority habitat is present or affected.
- Temporary developments lasting five years or fewer that do not impact priority habitat.
- Householder applications (pre-existing exemption, unchanged).
- Permitted development (pre-existing exemption, unchanged).
- Developments impacting fewer than 25 square metres of habitat (pre-existing de minimis threshold, unchanged).
No longer exempt:
- Self-build and custom-build developments.
Coming into scope later in 2026:
- Nationally Significant Infrastructure Projects (NSIPs) fall under mandatory BNG from 2 November 2026.
How Do I Calculate Biodiversity Net Gain Under the New 2026 Standards?
The calculation method itself, DEFRA's statutory biodiversity metric, has not changed. Developers and ecologists still use the metric to assign unit values to habitats before and after development, then demonstrate that the post-development value is at least 10% higher than the pre-development baseline. [2]
What has changed is the point at which offsite units can be factored in. For minor developments, the updated mitigation hierarchy allows onsite creation and offsite unit purchases to be weighed simultaneously. In practice, this means:
- Conduct a baseline habitat survey using the statutory metric.
- Assess the impact of the proposed development on existing habitats.
- Design onsite habitat enhancements, then calculate the residual shortfall.
- For any shortfall, consider onsite creation and offsite unit purchases concurrently (for minor developments).
- As a last resort, purchase statutory biodiversity credits from DEFRA.
For a detailed walkthrough of the assessment process, see what is in a biodiversity net gain assessment. For guidance on the cost of offsite units, our article on the cost of biodiversity units and statutory credits provides current benchmarks.
Biodiversity Net Gain Exemptions: Who Doesn't Have to Comply?
The exemptions framework as of 6 August 2026 is more nuanced than it first appears. The 0.2-hectare threshold is the headline figure, but the priority habitat condition is the critical qualifier.
The priority habitat condition explained: If any part of your site contains or is adjacent to priority habitat, such as ancient woodland, lowland meadow, or coastal and floodplain grazing marsh, the small-site exemption does not apply, regardless of site size. Developers must commission a Phase 1 habitat survey (or equivalent) to confirm the absence of priority habitat before relying on this exemption. [1]
Common mistake: Assuming the 0.2-hectare exemption is automatic. It is not. Without a habitat survey confirming no priority habitat is present or affected, a local planning authority can challenge the exemption claim. This is an area where cutting corners early creates significant risk later in the planning process.
For a full breakdown of exempt development categories, see the top 12 questions planners ask about biodiversity net gain.
What Does This Mean for Chartered Ecological Surveyors?
The August 2026 BNG changes have direct implications for ecological consultants and chartered surveyors conducting biodiversity assessments. The expanded exemptions mean that more projects will require a preliminary habitat assessment to confirm exemption eligibility, particularly for sites near or below the 0.2-hectare threshold. Ecologists will increasingly be asked to provide concise, defensible written confirmation that no priority habitat is present, rather than a full biodiversity metric calculation. This shifts some workload from metric computation to rapid site appraisal and exemption verification. At the same time, the removal of the self-build exemption brings a new client group into the BNG process who may be unfamiliar with ecological survey requirements, timelines, and costs. Ecological consultancies should update their client-facing materials and fee schedules to reflect these changes, and ensure their survey workflows distinguish clearly between pre- and post-6 August 2026 applications given the non-retrospective transitional arrangements. [6]
What Happens If You Don't Meet Biodiversity Net Gain Targets?
Failure to comply with BNG requirements can result in a planning condition not being discharged, effectively stalling or blocking development. Local planning authorities are required to refuse to grant planning permission for in-scope development where a biodiversity gain plan has not been approved. [4]
Beyond planning refusal, developers who submit inaccurate biodiversity metric calculations or misrepresent exemption eligibility face the risk of enforcement action and reputational damage. The statutory biodiversity credits route, purchasing credits directly from DEFRA, exists as a last resort but carries a significant cost premium over private offsite units, making it a poor substitute for early ecological planning.
How Much Does Biodiversity Net Gain Compliance Cost?
Costs vary considerably by site size, existing habitat quality, and the route chosen to achieve the 10% gain. There is no single industry-wide figure, but the main cost components are:
- Ecological survey and metric calculation: Typically ranges from a few hundred pounds for a simple site to several thousand for complex habitats.
- Onsite habitat creation: Costs depend on the type and scale of habitat; green roofs, wildflower meadows, and tree planting carry very different price points.
- Offsite biodiversity units: Private market prices vary by habitat type and location. For current pricing context, see our guide to biodiversity credits for developers.
- Statutory biodiversity credits: DEFRA's credits are available as a last resort and are priced to encourage private market solutions first.
For small sites now exempt under the 0.2-hectare rule, the removal of the metric calculation requirement alone can save meaningful time and professional fees.
Timeline for Implementing the Biodiversity Net Gain Changes 2026
- April 2026: DEFRA published a blog post signalling the forthcoming amendments and their rationale. [5]
- 14 July 2026: DEFRA formally published the amendments and transitional arrangements. [1]
- 6 August 2026: All four changes took effect for new planning applications.
- 2 November 2026: Mandatory BNG is scheduled to extend to Nationally Significant Infrastructure Projects.
- Ongoing: Applications received before 6 August 2026 continue to be assessed under the previous BNG rules, regardless of when they are determined.
The non-retrospective nature of the changes is important for developers with live applications. If your application was validated before 6 August 2026, the previous rules apply in full, including the self-build exemption if you previously relied on it, and the sequential mitigation hierarchy. [1]
Frequently Asked Questions
Does the 0.2-hectare exemption apply automatically to all small sites?
No. The exemption only applies where no onsite priority habitat is present or affected by the development. A habitat survey is needed to confirm eligibility. Sites with priority habitat must still meet the 10% BNG requirement regardless of size. [1]
My application was submitted before 6 August 2026. Do the new rules apply to me?
No. The August 2026 BNG changes are not retrospective. Applications received before 6 August 2026 are assessed under the rules that were in force at the time of submission. [1]
I am building my own home. Am I now required to comply with BNG?
Yes. The self-build and custom-build exemption was removed on 6 August 2026. Self-build and custom-build projects submitted from that date must meet the standard 10% biodiversity net gain requirement unless another exemption applies (for example, the 0.2-hectare rule where no priority habitat is affected).
What counts as a temporary development for the new exemption?
A temporary development is one where the planning permission is granted for a period of five years or fewer and the development does not impact priority habitat. Construction compounds, temporary event structures, and short-term infrastructure works are typical examples. [10]
Has the way biodiversity units are calculated changed?
The statutory biodiversity metric itself has not changed. What has changed for minor developments is the sequencing within the mitigation hierarchy, onsite creation and offsite unit purchases can now be considered at the same stage rather than sequentially. [3]
When do Nationally Significant Infrastructure Projects need to comply with BNG?
NSIPs are scheduled to come under mandatory BNG from 2 November 2026, a separate but related change to the framework.
Where can I buy or sell biodiversity units under the new rules?
The private biodiversity unit market continues to operate as before. See our pages on how to buy biodiversity units and how to sell biodiversity units for current guidance.
Conclusion
The Biodiversity Net Gain changes of 6 August 2026 represent a targeted recalibration of England's BNG framework rather than a fundamental overhaul. The new 0.2-hectare small-site exemption will reduce the administrative burden for a large proportion of minor residential applications, but only where priority habitat is absent, making early ecological appraisal more important than ever. The removal of the self-build exemption closes a gap that had created an uneven playing field, while the updated mitigation hierarchy gives minor developers genuine flexibility in how they structure their BNG strategy.
Actionable next steps for developers and ecologists:
- Confirm whether your application was received before or after 6 August 2026, as the transitional rules are strict.
- Commission a habitat survey before assuming the 0.2-hectare exemption applies, priority habitat presence is the critical variable.
- If you are a self-builder, factor BNG costs and survey timelines into your project programme now.
- Review your BNG strategy for minor developments in light of the updated mitigation hierarchy, which may allow a more cost-effective mix of onsite and offsite measures.
- Monitor DEFRA guidance for any further updates ahead of the NSIP extension on 2 November 2026.
For a comprehensive overview of the full BNG process, visit our biodiversity net gain service page.
References
[1] Biodiversity Net Gain Amendments And Transitional Arrangements Published – defraenvironment.blog.gov.uk
[2] Understanding Biodiversity Net Gain – gov.uk
[3] Biodiversity Net Gain Rules 2026 – vailwilliams.com
[4] Biodiversity Net Gain – gov.uk
[5] Biodiversity Net Gain Whats Changing And What It Means For You – defraenvironment.blog.gov.uk
[6] Biodiversity Net Gain Procedural Updates – aspect-ecology.com
[10] Biodiversity Net Gain Exempt Developments – gov.uk