BNG Monitoring Survey for Architects: UK Guide
Biodiversity Net Gain (BNG) is now mandatory for most developments in England — requiring at least 10% net gain in biodiversity value maintained for 30 years. Here is what architects need to know.
Key Requirements for Architects
| Aspect | Requirement | | --- | --- | | Trigger | 10% biodiversity net gain mandatory since Feb 2024 (major sites) and April 2024 (small sites) | | Who calculates | Statutory Metric: Ecologist or Landscape Architect; Small Sites Metric: Architect can calculate | | Duration | 30-year management and monitoring via s106 or conservation covenant | | Submission | Biodiversity Gain Plan required before planning approval |
Trigger Levels and Exemptions
| Development Type | BNG Required? | | --- | --- | | Residential 1–9 dwellings on <1 hectare | Yes | | Non-residential <1,000m² or <1 hectare | Yes | | Householder applications | Exempt | | Pre-Feb 2024 planning submissions | Exempt | | De minimis (<25m² habitat impact) | Exempt |
Note: Small Sites Metric cannot be used if statutory protected sites are within 500m of site boundary — requires full Statutory Biodiversity Metric.
Habitat Management and Monitoring Plan (HMMP)
The HMMP is the core 30-year compliance document:
| Component | Details | | --- | --- | | Purpose | Shows how habitats will be managed, maintained, and monitored for 30 years | | Who prepares | Competent professional ecologist (not architect) | | When submitted | Draft with Biodiversity Gain Plan at planning stage; finalized after approval | | Monitoring frequency | Years: 2, 5, 10, 15, 20, 25, 30 | | Adaptive management | Trigger levels for remedial action if habitat condition falls |
2025 Costs
| Service | Cost (ex VAT) | | --- | --- | | BNG assessment (small sites) | From £950 | | LPA BNG monitoring fee (minor apps) | £2,610 | | LPA BNG monitoring fee (major apps) | £4,180 | | HMMP preparation | Variable by complexity |
Frequently Asked Questions
Q: Can architects calculate BNG using the Small Sites Metric?
Yes — for qualifying small sites. Full Statutory Metric requires an ecologist.
Q: Who prepares the HMMP?
A competent professional ecologist — not the architect.
Q: What happens if habitat condition falls below target?
The HMMP must include trigger levels and adaptive management procedures.