What BNG means for developers
Since February 2024, all major developments in England (10+ units or sites over 1 hectare) must deliver a minimum 10% Biodiversity Net Gain. Since April 2024, this extends to small sites too. This is a mandatory planning condition — you cannot discharge pre-commencement conditions without an approved BNG plan.
In practical terms, this means every development must leave the site's biodiversity in a measurably better state than before development. The gain is measured using the DEFRA Biodiversity Metric, and the created habitats must be maintained for 30 years.
How BNG works
- Baseline assessment: An ecologist surveys the site before development and calculates its current biodiversity value using the DEFRA metric. This must be done before any site clearance.
- Post-development plan: You design your development to include habitat creation that delivers 10% more biodiversity units than the baseline.
- Hierarchy of delivery: On-site habitat creation is preferred. If you can't achieve 10% on-site, you can buy off-site BNG units from a registered habitat bank, or as a last resort purchase statutory credits from the government.
- Habitat management plan: A 30-year plan for maintaining the created habitats must be submitted and secured (usually via planning condition or Section 106 agreement).
Costs to budget for
- Ecological survey: £2,000–£5,000 for the baseline biodiversity assessment
- BNG metric calculation: £1,500–£3,000 (usually done by the ecologist)
- On-site habitat creation: £10,000–£50,000+ depending on the site, area available, and habitat types required
- Off-site BNG credits: £25,000–£50,000+ per biodiversity unit if on-site delivery isn't feasible
- Statutory credits: ~£42,000 per unit (last resort, most expensive option)
- 30-year management plan: £3,000–£8,000 for preparation, plus ongoing management costs
On a typical 10-unit residential scheme, BNG costs are approximately £15,000–£40,000 if delivered on-site. This should be included in your development appraisal as a line item.
Impact on development finance
BNG affects your development finance application in several ways:
- Cost schedule: Include BNG costs as a separate line item. Lenders now expect to see this, and omitting it suggests you haven't properly scoped the project.
- Programme: Ecological surveys must be done before site clearance, and some surveys are seasonal (bat surveys: May–September). Factor this into your programme — a missed survey window can delay the entire project by months.
- Pre-commencement conditions: The BNG plan must be approved by the local authority before construction starts. Lenders want to see this condition discharged before first drawdown.
- Site design: BNG may require dedicating part of the site to habitat creation, reducing the developable area. This affects unit count, GDV, and therefore the financial appraisal.
Presenting BNG in your application
When you upload your documents to Assesr, include the ecological survey and BNG costs in your cost schedule. The AI credit paper presents BNG compliance as part of the planning assessment, showing lenders you've properly accounted for this requirement. This is increasingly a differentiator — developers who've properly planned for BNG demonstrate competence and thoroughness.