On-Site vs Off-Site BNG Monitoring: What's the Difference?
When planning your BNG biodiversity net gain requirement, you must decide whether to deliver gains on your development site (on-site) or on land elsewhere (off-site). This guide explains the differences, when to use each, and what it means for monitoring.
Key Differences
| Aspect | On-Site BNG | Off-Site BNG | | --- | --- | --- | | Location | Within your development red line | Outside your site boundary | | What it involves | Green spaces, ponds, wildflower meadows, green roofs, woodland | Habitat banks, large-scale habitat restoration | | When to use | First priority — when space allows | When on-site is insufficient or not feasible | | 30-year monitoring | Managed by landowner/developer | Managed by habitat bank or third party | | Proximity principle | N/A — on-site | Same LPA/NCA preferred; spatial multipliers apply |
The BNG Hierarchy
Follow the mitigation hierarchy before choosing your BNG delivery approach:
- Avoid habitat loss where possible
- Mitigate effects that cannot be avoided
- Enhance on-site habitat (on-site BNG)
- Create on-site habitat
- Use registered off-site biodiversity gain (off-site BNG units)
- Purchase statutory biodiversity credits (last resort only)
You must demonstrate efforts to deliver maximum on-site BNG before using off-site options.
When to Use On-Site BNG
On-site BNG is always the first choice:
| Suitable For | Examples | | --- | --- | | Sites with landscaped areas | Residential gardens, communal green space | | Green roofs / brown roofs | Flat roof extensions, roof terraces | | Sustainable drainage | Swales, detention basins, wildlife ponds | | Enhanced boundary planting | Hedgerows, tree planting, wildflower verges | | Urban greening | Living walls, climbing plants, street trees |
On-site BNG demonstrates sustainability commitment and enhances property value.
When to Use Off-Site BNG
Off-site BNG is used when:
| Situation | Reason | | --- | --- | | Urban sites with no green space | On-site delivery not physically possible | | Listed buildings | No scope for external habitat creation | | Conservation areas | Planning restrictions on landscape alterations | | When on-site cannot achieve 10% | Spatial constraints | | Speed of delivery | Habitat bank units immediately available |
Off-site BNG uses registered biodiversity gain sites — typically large-scale habitat restoration projects managed by specialist operators.
Off-Site BNG Costs (2025)
| Habitat Type | Starting Price | | --- | --- | | General guide | From £19,000 per unit | | Woodland | £34,000–£36,000 per unit | | Lakes / Ponds | £58,000–£80,000 per unit | | Watercourse | £125,000–£145,000 per unit |
Spatial risk multipliers affect pricing:
| Location | Multiplier | | --- | --- | | Same LPA / National Character Area | 1:1 | | Neighbouring LPA / NCA | 1.33:1 | | Further away | Up to 2:1 |
Regional differences are significant. Prices in South England are typically 15–25% higher than North England for equivalent habitats.
Statutory Biodiversity Credits (Last Resort)
If neither on-site nor off-site BNG is achievable:
| Habitat Type | Price per Credit | | --- | --- | | Low distinctiveness (improved grassland) | £42,000 per credit | | Standard habitats | Higher |
Statutory credits from Natural England are the last resort — use only when off-site units are unavailable.
Legal Securing
| BNG Type | Securing Mechanism | | --- | --- | | On-site BNG | Section 106 agreement or conservation covenant | | Off-site BNG | Conservation covenant with habitat bank operator | | Statutory credits | Purchase from Natural England |
Both on-site and off-site BNG must be legally secured for a minimum of 30 years.
30-Year Monitoring Implications
| BNG Type | Who Monitors | Who Pays | | --- | --- | --- | | On-site | Developer / landowner (or appointed ecologist) | Developer / landowner | | Off-site | Habitat bank operator | Included in unit price | | Statutory credits | Natural England | Included in credit price |
For off-site BNG, monitoring is managed by the habitat bank operator as part of their habitat management obligation. This is included in the unit price.
Frequently Asked Questions
Q: Can I split BNG between on-site and off-site?
Yes — many developments use a combination. Maximum on-site BNG is delivered first, with off-site units making up the balance to reach 10%.
Q: Does off-site BNG require a site visit to the habitat bank?
No — the habitat bank operator manages the off-site site. You do not need to visit the receptor site unless you wish to verify the habitat creation.
Q: What happens if the habitat bank fails to deliver BNG?
Conservation covenants include performance bonds and insurance. If the habitat bank fails, the LPA can call on these protections to ensure the BNG commitment is fulfilled.
Q: Is off-site BNG less valuable than on-site BNG?
Both count equally towards the 10% net gain requirement. The proximity principle (same LPA preferred) and spatial multipliers reflect the ecological value of proximity, but legally both satisfy BNG requirements.
Q: Can I sell off-site BNG units I create?
If you create habitat on your land beyond your BNG requirement, you could register as a habitat bank and sell surplus units. This requires formal registration and compliance with the biodiversity gain site register.
Q: Does on-site BNG increase my maintenance burden?
Yes — on-site BNG means you (or your management company) are responsible for 30-year habitat management. Off-site BNG transfers this burden to the habitat bank operator.
Q: What is a spatial risk multiplier?
A spatial risk multiplier increases the number of biodiversity units required when the off-site habitat is located further from the development. This reflects the reduced ecological connectivity of distant sites. Multipliers range from 1:1 (same LPA) to 2:1 (remote locations).