Biodiversity Net Gain
UK Planning Requirement for 10% Biodiversity Net Gain
BNG Implementation Timeline
February 2024
Major developments (TCPA 1990)
April 2024
Small sites (1-9 homes, under 1 ha)
November 2025
Nationally Significant Infrastructure Projects
What is Biodiversity Net Gain?
Biodiversity Net Gain (BNG) is a mandatory planning requirement where developers must ensure development projects deliver at least 10% net gain in biodiversity value compared to the pre-development baseline. It's measured using the Defra Biodiversity Metric.
10% Minimum
Mandatory 10% biodiversity net gain for most developments
Metric-Based
Calculated using official Defra Biodiversity Metric 4.0
30-Year Minimum
BNG habitat management secured for at least 30 years
BNG Requirements & Scope
Developments Requiring BNG
- Most planning applications requiring planning permission
- Small sites (1-9 homes or under 1 hectare) from April 2024
- Permitted development rights with prior approval
- Nationally Significant Infrastructure Projects (from November 2025)
- Marine developments affecting intertidal habitats
Exemptions
- Developments on sites with baseline biodiversity value below 2 units per hectare
- Householder applications (extensions, outbuildings)
- Self-build and custom housebuilding
- Brownfield sites in certain circumstances
- Development with alternative environmental assessment (e.g., EIA)
BNG Calculation Process
Baseline Assessment
Survey and map existing habitats on site using UK Habitat Classification system
- Comprehensive ecological survey by qualified ecologist
- Map all habitat types and their condition
- Calculate baseline biodiversity units using Defra Metric 4.0
- Consider habitat distinctiveness, condition, and strategic significance
Post-Development Assessment
Calculate biodiversity value after development using the same methodology
- Map proposed habitat creation, retention, and enhancement
- Apply condition scores for new and retained habitats
- Include time-to-target multipliers for habitat establishment
- Account for spatial risk factors and difficulty of creation
Net Gain Calculation
Compare post-development to baseline to determine net gain percentage
- Calculate: ((Post-development units - Baseline units) / Baseline units) × 100
- Must achieve minimum 10% net gain
- Habitat trading rules apply (like-for-like or higher value)
- Rivers and linear features calculated separately
Mitigation Hierarchy
Apply avoid, mitigate, compensate hierarchy before considering offsite units
- Avoid: Minimize impact on highest value habitats
- Mitigate: Reduce impacts through design modifications
- Compensate: On-site habitat creation and enhancement
- Offset: Purchase off-site biodiversity credits if needed
BNG Delivery Options
On-site Provision
Create, restore, or enhance habitats within the development site boundary
- • Preferred option in mitigation hierarchy
- • Integrated landscape design
- • Green infrastructure creation
- • Habitat corridors and connectivity
Best for: Sites with space and suitable conditions
Off-site Provision
Deliver BNG on land outside the development site but within the local area
- • Local planning authority area preferred
- • Neighbouring authority if justified
- • Must be additional to existing commitments
- • 30-year management requirement
Best for: Constrained sites with local land available
Biodiversity Credits
Purchase statutory biodiversity credits from government as last resort
- • Available when on/off-site not possible
- • Significantly more expensive option
- • Credits fund habitat creation elsewhere
- • Immediate payment required
Cost: £42,000-48,000 per biodiversity unit
BNG Implementation Costs
Survey & Assessment
Habitat Creation
Management Costs (30 years)
Biodiversity Credits (Last Resort)
£42,000
Grassland unit
£48,000
Woodland/scrubland unit
£48,000
Wetland unit
BNG Planning Application Process
Pre-Application
- Commission baseline habitat survey
- Complete Biodiversity Metric calculation
- Design development to minimize biodiversity loss
- Identify on-site and off-site BNG opportunities
- Consult with Local Planning Authority
With Application
- Biodiversity Net Gain Statement
- Biodiversity Metric 4.0 calculation
- Habitat Management and Monitoring Plan
- Legal agreements for off-site provision
- Financial security arrangements
Common BNG Challenges & Solutions
Challenges
Limited off-site land availability
Suitable land for habitat creation is scarce near development sites
High biodiversity credit costs
Government credits cost £42,000-48,000 per unit
Complex metric calculations
Biodiversity Metric 4.0 requires specialist ecological expertise
30-year management commitment
Long-term habitat management and monitoring obligations
Solutions
Early engagement with habitat banks
Partner with habitat banking providers for guaranteed off-site units
Maximize on-site provision
Integrate green infrastructure and biodiversity into design
Specialist ecological consultancy
Engage qualified ecologists early in design process
Conservation covenants
Use legal mechanisms to secure long-term habitat management
Habitat Banking Market
Market Development
A growing market of habitat banks and environmental consultancies is emerging to provide off-site biodiversity units, offering an alternative to expensive government credits.
- • Habitat banking operators create and manage sites
- • Advance habitat creation before selling units
- • Competitive pricing vs government credits
- • Focus on high-value habitat creation
Investment Opportunity
Habitat banking represents a significant investment opportunity with strong returns and positive environmental impact, backed by guaranteed regulatory demand.
- • Estimated £1.35bn annual market by 2030
- • Typical unit costs: £15,000-25,000
- • Government credits: £42,000-48,000
- • Strong returns with social impact
BNG Integration with Other Requirements
Environmental Impact Assessment
BNG requirements apply alongside EIA for major developments
- • Coordinate biodiversity assessments
- • Align mitigation measures
- • Integrate monitoring requirements
Protected Species Licensing
BNG delivery can support mitigation for protected species
- • Great crested newt district licencing
- • Bat mitigation and compensation
- • Habitat creation for multiple species
Corporate Biodiversity Reporting
BNG delivery supports biodiversity reporting commitments
- • Demonstrate nature positive impact
- • TNFD disclosure alignment
- • Support biodiversity duty compliance
Biodiversity Net Gain FAQs
What happens if I can't achieve 10% net gain on-site?
How long do BNG obligations last?
Can BNG be delivered on the same site as carbon offsets?
What about developments on brownfield sites?
How does BNG relate to other biodiversity requirements?
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