What is Biodiversity Net Gain?

What is Biodiversity Net Gain?

Biodiversity net gain (BNG) is a development approach that requires projects to deliver a measurable improvement in biodiversity compared to the pre-development baseline. Rather than merely minimizing ecological damage, BNG mandates that the residual biodiversity value after development—including on-site retention, on-site enhancement, and off-site compensation—exceeds the original value by a specified percentage. England's Environment Act 2021 made a minimum 10% BNG mandatory for most planning permissions from February 2024.

Why It Matters

BNG represents a paradigm shift in how development interacts with nature. The traditional approach—avoid, minimize, and compensate for biodiversity loss—aimed to prevent net loss but rarely achieved it. Studies of biodiversity offsets under older frameworks found that the majority failed to deliver equivalent biodiversity outcomes. BNG raises the bar by requiring demonstrated improvement, not just mitigation.

The mandatory 10% BNG requirement in England affects virtually all development requiring planning permission—housing, commercial, infrastructure, and energy projects. Developers must submit a biodiversity metric calculation demonstrating how they will achieve the required gain, and the commitment is secured through a 30-year management and monitoring plan. This has created a new market for biodiversity units and habitat banking.

The financial implications are significant. Developers who cannot achieve BNG on-site must purchase statutory biodiversity credits at prices set by the government—currently £42,000 per unit for most habitat types. This creates a strong incentive to deliver BNG through good design and on-site habitat creation rather than purchasing expensive credits. The market for off-site habitat banking, where landowners create or enhance habitats and sell the resulting biodiversity units, is growing rapidly.

Other jurisdictions are watching England's implementation closely. Scotland, Wales, and several Australian states are developing similar frameworks. The EU's Nature Restoration Law requires member states to restore degraded ecosystems, which may evolve toward BNG-style requirements for development. The concept is likely to become a global standard for reconciling development with nature conservation.

How It Works / Key Components

BNG is measured using the statutory biodiversity metric (currently Metric 4.0 in England), a habitat-based calculator that assigns biodiversity units to land parcels based on habitat type, condition, and strategic significance. The metric is designed to be applied by ecologists at the pre-development stage, producing a baseline biodiversity value against which post-development outcomes are measured.

The mitigation hierarchy remains central: avoid impacts where possible, minimize unavoidable impacts, and compensate for residual losses. BNG adds a fourth step—enhancement—requiring the final outcome to exceed the baseline by at least 10%. Developers must demonstrate that they have followed the hierarchy rather than jumping directly to off-site compensation.

On-site measures include retaining existing high-value habitats, enhancing degraded habitats, creating new habitats as part of landscaping and green infrastructure, and incorporating biodiversity features into building design (green roofs, swift bricks, bat boxes). Off-site measures involve creating or enhancing habitats on land outside the development boundary, secured through conservation covenants or planning obligations.

Habitat management and monitoring plans ensure that created or enhanced habitats achieve their target condition. Plans must cover a minimum 30-year management period, with regular monitoring and reporting. If habitats fail to reach target condition, remedial action is required. This long-term commitment distinguishes BNG from historical mitigation approaches that often lacked follow-through.

Council Fire's Approach

Council Fire integrates biodiversity net gain into development planning from the earliest stages, ensuring BNG requirements enhance rather than constrain project outcomes. We conduct baseline assessments, optimize site designs to maximize on-site BNG delivery, evaluate off-site options where needed, and structure long-term management plans that satisfy regulatory requirements.

Frequently Asked Questions

Does BNG apply to all developments?

In England, mandatory BNG applies to most developments requiring planning permission, with exemptions for householder applications, small sites (phased introduction), and nationally significant infrastructure projects (which have separate requirements). The scope is expanding as implementation matures.

How much does BNG add to development costs?

Studies estimate BNG adds 0.5-1.5% to total development costs for typical residential projects when addressed early in design. Costs are higher when developers rely on off-site credits due to poor on-site design. Early ecological input during masterplanning significantly reduces costs.

What is a biodiversity unit?

A biodiversity unit is the currency of BNG measurement—a composite score reflecting habitat area, type, condition, and strategic significance. One unit does not equal one hectare; high-quality habitats in strategic locations generate more units per hectare than degraded habitats in non-strategic locations.