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Biodiversity Net Gain Explained
Master the legal requirement for 10% Biodiversity Net Gain, including calculation methods, on-site delivery, and off-site options.
Legal Requirement Since February 2024
Biodiversity Net Gain (BNG) is now a legal requirement for most planning applications in England. Developments must deliver a minimum 10% net gain in biodiversity.
Applies to: Major developments (from February 2024) and small sites (from April 2024)
What is Biodiversity Net Gain?
Biodiversity Net Gain (BNG) is an approach to development that leaves biodiversity in a measurably better state than before development. It requires developers to ensure habitats for wildlife are enhanced and left in a better state than they were pre-development.
The 10% Requirement
Developments must achieve a minimum 10% net gain in biodiversity value compared to the pre-development baseline, measured using the statutory biodiversity metric.
Key Principles
Mitigation Hierarchy
- Avoid impacts
- Minimize impacts
- Restore on-site
- Offset off-site
Additionality
BNG must be additional to what would have happened anyway, not double-count existing commitments.
30-Year Commitment
BNG habitats must be secured and maintained for at least 30 years through legal agreements.
When Does BNG Apply?
Developments That Require BNG
- Major developments (10+ homes or 1,000m²+ commercial)
- Small sites (1-9 homes or under 1,000m² commercial)
- Developments requiring Environmental Impact Assessment
- Any development that impacts priority habitats
Exemptions
- Householder applications (extensions, outbuildings)
- Brownfield sites with biodiversity value below de minimis threshold
- Permitted Development rights
- Nationally Significant Infrastructure Projects (separate regime)
- Emergency works
The Biodiversity Metric
The statutory biodiversity metric is a habitat-based approach that calculates biodiversity value in 'biodiversity units'. It considers habitat type, condition, strategic significance, and connectivity.
How the Metric Works
Biodiversity Units Calculation
Biodiversity Units = Habitat Area × Habitat Distinctiveness × Habitat Condition × Strategic Significance × ConnectivityHabitat Distinctiveness
Habitat Condition
Professional Assessment Required
The biodiversity metric requires specialist ecological knowledge to complete accurately. Most developers engage qualified ecologists to undertake the assessment.
Delivery Options
On-Site Delivery
Creating or enhancing habitats within the development site boundary.
- Full control over delivery and management
- Can enhance development's green credentials
- Often most cost-effective option
- Provides immediate local benefits
Off-Site Delivery
Creating or enhancing habitats on land outside the development site.
- Must be in same Local Planning Authority area (or adjoining)
- Should be same National Character Area where possible
- Requires legal agreement for 30-year management
- Must demonstrate additionality
Statutory Biodiversity Credits
Government-issued credits as a last resort when on-site or off-site delivery isn't possible.
- Significantly more expensive than other options
- Must demonstrate why other options aren't feasible
- Credits purchased from government at set prices
- Should be avoided where possible
Implementation Process
Baseline Assessment
Conduct ecological survey to establish pre-development biodiversity value using the statutory metric.
Timeline: 4-8 weeks depending on site size and complexity
Design Integration
Integrate BNG requirements into development design, following mitigation hierarchy.
Key Consideration: Early integration reduces costs and improves outcomes
Post-Development Assessment
Calculate post-development biodiversity value and demonstrate 10% net gain.
Requirement: Must show minimum 10% increase in biodiversity units
Legal Agreements
Secure 30-year management and monitoring through planning obligations or conservation covenants.
Options: Section 106 agreements, planning conditions, or conservation covenants
Monitoring and Management
Implement 30-year habitat management plan with regular monitoring and reporting.
Frequency: Annual monitoring for first 5 years, then every 3-5 years
Cost Considerations
| Delivery Method | Typical Cost per Unit | Additional Costs |
|---|---|---|
| On-site creation | £15,000 - £25,000 | 30-year management |
| Off-site provision | £20,000 - £35,000 | Land acquisition, legal fees |
| Statutory credits | £42,000 - £48,000 | None (all-inclusive) |
Cost Planning Tips
- Budget 2-5% of total development cost for BNG
- Early ecological assessment reduces uncertainty
- On-site delivery usually most cost-effective
- Consider BNG in land acquisition decisions
- Factor in 30-year management costs