Biodiversity net gain

Introduction to BNG

Biodiversity Net Gain (BNG) is the process by which any major development that goes through the planning application process must deliver at least 10% net gain on the biodiversity baseline pre-development.

This can be delivered with a hierarchy of 1) onsite, 2) mix of on-site and off-site with a private landowner or on their own off-site land, 3) off-site statutory credits from the Government as a last resort.

This became statutory for major developments from Monday 12 February 2024 and minor developments from Tuesday 2 April 2024, therefore, relevant applications that are submitted on or after these dates will be required to follow the BNG process.

The amount of biodiversity needed to reach 10% net gain is calculated using a metric developed by Department for Environment, Food and Rural Affairs (DEFRA). 

A baseline ecological survey will be undertaken at the development site to assess the ‘before’ condition and, when input into the Statutory Metric, the baseline units can be calculated. The number of these baseline units that will be lost during development must be replaced +10% of the baseline amount. This applies for off-site and on-site.

For example: if a site has a baseline of 10 units and six are lost during development, you will need to put a total of seven units back on-site (the six that you lost + one as 10% of the baseline 10). Alternatively, you could put those seven units off-site where the uplift of that land due to the Habitat Management and Monitoring Plan (HMMP) results in a seven-unit enhancement, or a mixture of both approaches, as long as you achieve an overall unit total of 11.

Where BNG must be delivered off-site, an ecological assessment will be conducted on the proposed off-site land to calculate its baseline condition and to determine the uplift required to achieve those units.

The biodiversity enhancements must be monitored, maintained, and legally secured for 30 years under a S106 or a Conservation Covenant (CC). A CC is a private, voluntary agreements (between a landowner/leaseholder and a responsible body (e.g. LPA or conservation body/organisation) to conserve the natural or heritage features of the land, in this case to ensure specific land management processes and outcomes.

Our role as the Local Planning Authority (LPA)

Whether a developer achieves their BNG on-site (within the red line boundary), off-site on land that they own (within the blue line boundary or another site) or with a private landowner within the borough, the land will need to be secured with RBWM.

On-site significant habitats will be secured with a S106. On-site non-significant enhancements or creation will be secured via a condition. Any off-site habitat enhancement and creation works will be secured by S106 or CC with the LPA that land sits in.

We will be required to monitor this agreement for 30 years by requesting ecological progress assessments at given intervals (e.g. years 1, 2, 5, 10, 15, 20, 25, 30) depending on the habitats being created/enhanced.

The council will levy a fee to monitor the net gain as required by law, in addition to any financial penalties raised in the event of a breach or unsuccessful habitat enhancement. 

BNG monitoring fee structure

Base fee £5,139.70 

Additional fees

Small sites: 
£103 per dwelling after the first

Major residential applications:
£257.50 per apartment dwelling
£515 per house dwelling

Major non-residential applications:
£515 per hectare after the first

These figures will be increased annually in line with inflation on the 6 April each year.

A major development includes:

Residential:

1. Where the number of dwellings being proposed is ten (10) or more
2. If the specific number of dwellings to be provided is not known, a site area exceeding 0.5 hectares.

 Non-residential:

1. The provision of a building or buildings where the allocated floor space being created because of the development is 1,000 square metres or more
2. Where the development has an area of 1 hectare or more
3. Change of use applications over 1,000 square metres or more
4. All full applications concerning mineral extraction and waste development

A minor development, or small site, includes:

1. Residential development where the number of dwellings is between 1 and 9 on a site of an area 1 hectare or less, or if the number of dwellings is unknown, the site area is less than 0.5 hectares.
2. Commercial development where floor space created is less than 1,000 square metres or total site area is less than 1 hectare.
3. Development that is not the winning and working of minerals or the use of land for mineral-working deposits.
4. Development that is not waste development.

Exemptions

1. Development below a de minimis threshold
2. Householder developments
3. Small Scale Self-Build and Custom Housebuilding
4. HS2
5. Biodiversity gain sites

More information on exemptions.

For self-build, custom build and di minimis applications, we kindly request that you submit a baseline BNG metric so that we can accurately assess your exemption and be confident of no net-loss of biodiversity in line with the NPPF. In both of these cases a Small Sites Metric should be sufficient, given the size of the development is under the minor application threshold and there is no priority habitat on-site, and therefore does not have to be completed by an ecologist.

If your units are satisfied on-site, you must manage the land enhancements to the standard set out in your Habitat Management and Monitoring Plan (HMMP) or 30 years, submitting habitat progress assessments in the years set out in your S106. 

If your units are off-site, you (if using off-site land that you own) or the land manager (if using a private habitat bank) must manage the land enhancements to the standard set out in your HMMP for 30 years, submitting habitat progress assessments in the years set out in your S106. You must also register your biodiversity net gain site and any allocations of off-site gains on the National Register. You do not need to register on-site gains or statutory biodiversity credits.

Mandatory BNG and Local Planning Policy 

If your development is exempt from mandatory BNG (major or minor submitted after mandatory dates) but falls under local policy that requires a net gain (e.g. NR2), it will remain exempt as per the national exemption guidelines above.

Non-Mandatory BNG and Local Planning Policy

If your development does not fall under mandatory BNG (majors submitted before Monday 12 February 2024 and minors before Tuesday 2 April 2024) but is captured by another net gain policy (e.g. NR2), it will be required to satisfy any biodiversity net gain requirements regardless of its pre-mandatory status.

Biodiversity Net Gain is a dynamic area of planning policy, therefore this guidance may be updated over time.

(Prices updated April 2025)