BNG Biodiversity Net Gain Developer Guide: What Developers Need to Know
Biodiversity Net Gain (BNG) is now mandatory for most planning applications in England. This developer guide covers everything you need to know — from whether BNG applies to your project, to how to deliver it, and what the 30-year obligation means.
BNG Key Requirements
| Requirement | Detail | | --- | --- | | Mandatory percentage | Minimum 10% net gain in biodiversity | | Legal basis | Schedule 7A of Town and Country Planning Act 1990 (inserted by Schedule 14 of the Environment Act 2021) | | 30-year obligation | Habitats must be secured and maintained for minimum 30 years | | When mandatory | Major developments: 12 February 2024; Small sites: April 2024; NSIPs: May 2026 | | Recording | Must be registered on Natural England's statutory BNG register |
4 Steps Every Developer Must Take
| Step | Action | | --- | --- | | 1. Find out about BNG | Check whether your development is exempt | | 2. Decide how to achieve BNG | Follow the biodiversity gain hierarchy | | 3. Measure biodiversity impact | Use the Statutory Biodiversity Metric 4.0 tool | | 4. Submit a Biodiversity Gain Plan | Must be approved by LPA before development starts |
The Biodiversity Gain Plan must be approved by your Local Planning Authority before development starts — the LPA has 8 weeks to approve.
The Biodiversity Gain Hierarchy
Always follow this order:
| Option | Description | When to Use | | --- | --- | --- | | On-site | Enhance or create habitats within your development red line | Preferred — planners encourage this | | Off-site | Buy biodiversity units from a registered habitat bank or enhance land you own elsewhere | If on-site cannot achieve 10% | | Statutory credits | Purchase from Natural England | Last resort only |
You must demonstrate that on-site delivery has been maximised before using off-site options. Statutory credits should only be purchased when no other option is available.
Is Your Development Exempt?
| Exemption | Applies To | | --- | --- | | Householder applications | Extensions, loft conversions, conservatories | | De minimis threshold | Developments impacting <25 m² of habitat AND <5 m of linear habitat (hedgerows), no priority habitat | | Small-scale self-build | Custom housebuilding below threshold | | Biodiversity gain sites | Where the application is itself for a BNG habitat creation project | | NSIPs (until May 2026) | Nationally Significant Infrastructure Projects |
What Cannot Reduce the 10% Requirement
| Misconception | Reality | | --- | --- | | Viability issues | No provision for reduction — 10% is mandatory | | Brownfield land | BNG still applies (unless de minimis) | | Small sites below threshold | May be exempt but must confirm | | Affordable housing | Does not exempt from BNG |
How BNG Is Calculated
BNG uses the Defra Statutory Biodiversity Metric 4.0:
| Factor | Description | | --- | --- | | Baseline | Pre-development biodiversity value of your site | | Post-development | Biodiversity value after development (including habitat creation) | | Net gain | (Post-dev units − baseline units) ÷ baseline units × 100 | | Minimum | Must be ≥10% |
The metric converts habitats into biodiversity units based on area, distinctiveness, condition, and strategic significance.
Delivering BNG On-Site
On-site BNG options include:
| Habitat Type | Examples | | --- | --- | | Green roofs | Biodiverse brown roofs, sedum roofs | | Landscaped areas | Wildflower meadows, native planting | | Ponds and SUDS | Wildlife ponds, swales, detention basins | | Trees and hedgerows | Native tree planting, species-rich hedgerows | | Enhanced existing habitats | Improving grassland condition from poor to moderate |
Delivering BNG Off-Site
If on-site delivery is insufficient:
| Option | Description | Starting Cost | | --- | --- | --- | | Registered habitat bank | Purchase units from a habitat bank operator | From £19,000 per unit | | Land you own elsewhere | Enhance other land you own | Variable | | Statutory credits | Purchase from Natural England | From £42,000 per credit |
Spatial risk multipliers increase the number of units needed based on distance from your site to the receptor habitat.
The 30-Year Obligation
BNG habitats must be secured for a minimum of 30 years through a legal agreement:
| Securing Mechanism | Used For | | --- | --- | | Section 106 agreement | Most common — included in planning obligation | | Conservation covenant | Can survive change of ownership | | Planning condition | Some LPAs use planning conditions |
The 30-year period starts from the date habitat creation is completed. Monitoring reports must be submitted to the LPA at defined intervals (typically years 1, 2, 5, 10, 15, 20, 25, 30).
Who Manages BNG Habitats Long-Term?
| Responsibility | Who | | --- | --- | | Securing the obligation | Developer (at planning stage) | | 30-year habitat management | Landowner or appointed management company | | Monitoring and reporting | Ecologist appointed by the responsible party | | LPA oversight | Local Planning Authority |
For off-site BNG, the habitat bank operator manages the habitat and monitoring as part of their unit price.
BNG vs Other Ecological Requirements
| Requirement | Separate From BNG? | | --- | --- | | Preliminary Ecological Appraisal (PEA) | Yes — different purpose | | Protected species surveys (bats, newts, etc.) | Yes — separate legislation | | Environmental Impact Assessment | Yes — separate process | | Nutrient neutrality (Netz A and SSSI) | Yes — separate requirements |
BNG is in addition to, not instead of, other ecological requirements.
2025 BNG Costs for Developers
| Cost Component | Typical Range (ex VAT) | | --- | --- | | BNG baseline assessment | £1,500–£7,500 | | Biodiversity Gain Plan | £800–£2,500 | | HMMP drafting | £500–£2,000 | | On-site habitat creation | Varies — landscape architect required | | Off-site biodiversity units | From £19,000 per unit | | Statutory biodiversity credits | From £42,000 per credit | | LPA monitoring fees | Varies by council | | 30-year monitoring programme | £8,000–£25,000+ |
Key Contacts
| Organisation | Role | | --- | --- | | Natural England | BNG register, statutory credits, HMMP templates | | Local Planning Authority | Approves Biodiversity Gain Plan, enforces monitoring | | Habitat bank operators | Supply off-site BNG units | | RICS-regulated ecologists | Conduct baseline surveys and monitoring |
Frequently Asked Questions
Q: Does BNG apply in Wales or Scotland?
No — BNG is an England-only requirement under the Environment Act 2021. Wales and Scotland have different biodiversity planning requirements.
Q: When must the Biodiversity Gain Plan be approved?
The Biodiversity Gain Plan must be approved by your LPA before development starts. The LPA has 8 weeks to approve once submitted.
Q: Can BNG be delivered on a roof?
Yes — biodiverse brown roofs and green roofs count towards on-site BNG. They are a useful option for urban sites with limited ground-level space.
Q: What happens if I cannot achieve 10% on or off-site?
If no on-site or off-site options are available, you must purchase statutory biodiversity credits from Natural England. This is the most expensive option and should be the last resort.
Q: Does the 30-year obligation affect my site's sale value?
The BNG obligation runs with the land, not the developer. If you sell the property, the monitoring obligation transfers to the new owner via the Section 106 agreement or conservation covenant.
Q: Can I phase BNG delivery across a large development?
Yes — phased developments can deliver BNG in stages. Each phase must achieve its proportional BNG requirement, with monitoring starting from the completion of that phase.
Q: What if my planning permission lapses before development starts?
If planning permission lapses, a new Biodiversity Gain Plan may be required. Discuss with your LPA whether your existing approval and BNG obligation remain valid.