How to Integrate Biodiversity Net Gain into Site Plans

Since 12 February 2024, Biodiversity Net Gain (BNG) has become a mandatory consideration for most major developments. The requirement extends to small sites, meaning biodiversity net gain is now a central part of all planning applications across England.

For developers, the key challenge is not simply understanding the legislation, but integrating biodiversity into site plans early enough to avoid redesign, delay or additional cost.

This guide explains how to integrate BNG effectively and pragmatically into development site layouts.

The statutory BNG requirement requires most developments to deliver at least a 10% uplift in biodiversity value compared to the pre-development baseline. This uplift must be calculated using the statutory biodiversity metric and formally submitted to the local planning authority as part of a Biodiversity Gain Plan.

Importantly, biodiversity enhancements must be:

• Secured through planning
• Maintained for at least 30 years
• Legally binding

This is typically achieved through a Section 106 agreement or conservation covenant, depending on whether measures are delivered on-site or off-site.

The emphasis is no longer simply on mitigation. It is about achieving biodiversity net gain in a measurable and legally secure way.

Successful site BNG integration begins with understanding existing site habitats. A clear ecological baseline allows you to design with biodiversity in mind rather than retrofitting solutions later.

This typically involves:

• A habitat survey
• Assessment of ecological constraints
• Metric calculations to determine biodiversity units
• Identification of high-value features

Understanding the starting point is critical to integrating biodiversity in a way that works spatially and financially.

Before adding new habitat creation areas, the mitigation hierarchy should guide decision-making.

This means:

1. Avoid impacts where possible
2. Minimise unavoidable harm
3. Restore habitats on site
4. Compensate only as a last resort

Planning authorities and Natural England expect developers to demonstrate that they have followed this approach. Simply offsetting losses off-site without considering on-site solutions is unlikely to be supported.

When biodiversity is considered early in the design process, layout changes can often preserve higher-value habitats while still achieving development objectives.

The most effective way to enhance biodiversity is to integrate it directly into the development site layout.

This may include:

• Retaining and buffering existing habitats
• Creating species-rich grassland
• Introducing native planting schemes
• Designing sustainable drainage features as habitat
• Incorporating green roofs or living walls

These measures should be embedded into the site masterplan rather than treated as peripheral features.

Working collaboratively with ecologists, landscape architects and land managers at the concept stage allows biodiversity enhancements to complement placemaking rather than compete with developable area.

There are circumstances where achieving biodiversity net gain entirely within the red line boundary is not feasible, often due to space constraints, competing layout demands or viability considerations. In these cases, developers may need to consider a combination of on-site and off-site solutions to meet the BNG requirement in a compliant and deliverable way.

Off-site delivery can take several forms, including the purchase of biodiversity units from an established habitat bank, entering into conservation covenants to secure long-term habitat management, securing land through a Section 106 agreement, or working directly with land managers to deliver habitat creation or enhancement elsewhere. In more limited situations, statutory biodiversity credits from the government may be used, although this approach is intended as a last resort where alternative options are not reasonably available.

Planning authorities will expect clear justification for any off-site provision, alongside robust evidence that on-site opportunities have been fully explored in accordance with the mitigation hierarchy before compensatory measures are relied upon.

Delivering biodiversity uplift is only part of the process. Measures must also be secured and managed long-term.

All biodiversity enhancements must be maintained for at least 30 years. This requires clear management and monitoring plans that demonstrate how habitats will establish and mature over time.

The Biodiversity Gain Plan, submitted to the local planning authority, must set out:

• The baseline habitat value
• The post-development habitat design
• How the uplift will be achieved
• How it will be monitored and reported

This legal and monitoring framework is now a standard part of planning applications.

The most effective way to integrate biodiversity net gain into site plans is to treat it as a core design constraint rather than a compliance exercise.

Developers should:

• Engage ecological input at the feasibility stage
• Undertake early metric calculations
• Align BNG strategy with planning
• Consider long-term management responsibilities
• Factor legal agreements into timelines

When integrated early, BNG can enhance site value, improve placemaking quality and support positive engagement with planning authorities.

When did Biodiversity Net Gain become mandatory?

Mandatory biodiversity net gain came into force for major development on 12 February 2024 and was extended to small sites from April 2024 in England.

Does every development need to deliver BNG?

Most developments require at least a 10% net gain, although certain exemptions apply. The requirement applies to the majority of planning applications unless specifically excluded.

Can biodiversity net gain be delivered entirely off-site?

Yes, but only where on-site opportunities have been fully explored first. Off-site delivery must be secured through legal mechanisms such as conservation covenants or Section 106 agreements and maintained for at least 30 years.

How long must biodiversity enhancements be managed?

All BNG habitat creation and enhancement must be maintained for a minimum of 30 years under legally binding agreements.

At Collington Winter Environmental, we support developers in integrating biodiversity net gain into site plans from concept through to discharge of planning conditions.

Our team provides early-stage metric assessments, strategic advice on achieving biodiversity net gain, and clear guidance on whether on-site or off-site solutions are most appropriate. We work collaboratively with design teams to ensure biodiversity is integrated efficiently, proportionately and in line with planning authority expectations.

If you are preparing planning applications and need advice on meeting the BNG requirement, contact Collington Winter Environmental today via info@collingtonwinter.co.uk or by filling in our contact form below for pragmatic, development-focused guidance.