Phased Development in Biodiversity Net Gain

BNG in Phased Developments

Under the statutory framework established by the Environment Act 2021, mandatory BNG requirements insist that developments leave nature in a measurably better state than before works started.

While single-stage development projects achieve ecological targets in one go, multi-stage schemes operate under different statutory requirements.

Spreading works across different phases is the standard way to manage construction logistics, funding and shifting market conditions across a large-scale project, including in both commercial and residential developments.

Based on the national planning policy framework (NPPF) and all of the guidance published by the Department for Environment, Food and Rural Affairs (DEFRA), developers need to deliver at least 10% net gain above the site baseline on an identified scale.

Whenever outline permission is granted subject to a pre-commencement planning obligation or as a result of meeting standard planning conditions, the planning process requires a clear roadmap showing how the proposed development meets its ecological obligations.

Once you see planning permission granted, knowing how your ecological accounting splits across reserved matters applications is essential before any development work can start.

What is Phased Development?

In planning terms, phased development refers to any scheme where the full build programme is divided into distinct parcels delivered over a long period of time.

Rather than applying for full and detailed permission across a large site in one go, an applicant can secure outline planning permission for the whole boundary before submitting separate applications for individual parcels of land.

By doing this, developers can see housing layouts, infrastructure routes and landscaping details become refined over several years while the initial ground works get underway.

For BNG purposes, when a permission identifies clear phases, it won’t be possible to calculate final post-development value figures for plots of land that may not be built for five or ten years.

Instead, the relevant local planning authority assesses the entire red line boundary at the planning application stage to establish the pre-development biodiversity value.

The baseline calculation records all existing habitats at the relevant date. By establishing the baseline at the date immediately before works or an agreed earlier date (backed by the formal publication date of official ecological maps), local authorities make sure that all subsequent work delivers genuine site biodiversity improvements across the entire development site.

For sites with existing permissions granted before the rules changed, specific exemptions and formal transitional arrangements clarify whether or not the mandate applies.

Two-Tier Approval Process

To manage net gain across multi-year build programmes without locking developers into unworkable early designs, the UK government established a structured two-stage submission framework:

1. The Overall Plan

Before any physical development can begin on any part of the site, the applicant must submit an overall biodiversity gain plan to the local council.

The overarching document sets the baseline pre-development value across the masterplan, projects the overall strategy for habitat creation, and outlines the proposed balance of biodiversity units allocated for each parcel.

2. The Phase Plan

Prior to commencement of each specific phase, the applicant submits a detailed phase biodiversity gain plan.

The document offers full details of on-site enhancements, calculates the exact post-development biodiversity value for each parcel, and confirms the individual phase’s contribution towards the site-wide target.

The local planning authority will evaluate each submission before issuing its formal planning decisions based on whether the phase can proceed.

No parcel of land can discharge its biodiversity gain condition until the local council grants formal LPA approval for the phase-specific BNG plan, ensuring that the development meets national standards before ground is broken.

Phased Development Methodology

As a way of avoiding bottlenecks, ecological mitigation needs a coordinated approach across complex development schemes.

Whenever developers map out planning projects that span across several years and involve tens of thousands of square metres of infrastructure, calculating ecological balances in isolation has the potential to create viability issues.

Developers need to follow the biodiversity gain hierarchy of avoiding adverse effects on wildlife corridors first, mitigating on-site where possible, and delivering significant on-site enhancements before considering off-site alternatives.

To streamline the process, developers must calculate all impacts using the statutory biodiversity metric from Natural England. The tool measures baseline figures against proposed post-development plans, generating a completed biodiversity ledger that proves the project will achieve biodiversity net gain.

When it comes to managing a phased delivery project, early pre-application engagement with planning officers and ecological consultants is strongly encouraged.

With it, you can establish firm proposals ahead of time, clarify any potential requirements regarding irreplaceable habitat, and ensure that building regulations and local nature recovery strategies (LNRSs) are addressed from day one.

Choosing the Right Phased Development Approach

Every masterplan handles spatial constraints differently.

Selecting an appropriate phased approach early determines whether or not your planning project runs smoothly or hits resistance:

• Self-Contained Phases: Each parcel delivers its own 10% BNG entirely within its own boundary. It works best when every phase contains generous open space and native planting.
• Centralised Green Infrastructure: Common in a major development, the first phase or an early dedicated parcel like an ecological park or wetland delivers substantial open space. The upfront gain generates surplus units that offset losses in dense and built-up later phases.
• Staged Off-Site Allocation: Wherever physical site constraints prevent full delivery on-site, developers schedule the purchase of registered off-site units across different parcels to align with build stages and cash flow.

Managing the Metric Across Multiple Phases

A common risk in multi-phase delivery is front-loading habitat destruction while back-loading habitat creation.

If earlier phases clear extensive scrub or woodland to build spine roads, drainage attenuation and site compounds, the planning project incurs an immediate ecological deficit.

To prevent later parcels from becoming unviable, the overall plan needs to maintain a running balance sheet of units. When it comes to submitting each phase plan, the person submitting the document has to provide evidence of the running ledger and outline the specific steps taken to safeguard existing green corridors.

The data tracks the cumulative balance across subsequent phases, accounts for temporary works like haul roads active for as much as three years, and offers the additional information needed to confirm progress towards the overall biodiversity gain objective.

Legal Agreements and Long-Term Commitments

Any significant on-site habitat enhancements or off-site land relied upon to satisfy BNG conditions must be legally secured for at least 30 years to create a lasting positive impact.

For phased schemes, coordinating the legal obligations involves careful structuring:

• Commitments: Local authorities confirm 30-year commitments via a section 106 agreement or statutory conservation covenants.
• Management and Monitoring: The person completing the application needs a habitat management and monitoring plan (HMMP) as a way of scheduling habitat assessments, reporting milestones, and ensuring that management actions are submitted to the local council at regular intervals.
• Habitat Protection: Newly created habitats delivered at an early stage need to be physically protected from dust, soil compaction and heavy plant activity while contractors work on an adjacent parcel of land.

Contingency Plans

Even the best masterplans may need to change.

Shifts in economic viability, design adjustments between reserved matters and unforeseen ground conditions can alter a phase’s projected unit yield.

To ensure that permitting development continues without interruption, developers should establish suitable contingency plans:

• Reallocating Internal Surpluses: If one phase delivers a higher percentage gain than anticipated, the surplus units can be formally transferred to balance a shortfall in another parcel.
• Sourcing Off-Site Units: If on-site layout changes reduce the available green infrastructure, you can source off-site units as registered off-site biodiversity gain from a habitat bank listed on the national biodiversity gain site register.
• The Safety Net of Statutory Credits: If sufficient local off-site units are genuinely unavailable, developers can use statutory biodiversity credits purchased directly from the government as a last resort to satisfy the condition requiring net gain.

Guidance on Working BNG into Your Plans

In order to manage biodiversity net gain (BNG) across multi-stage schemes, what’s needed is ecological expertise, meticulous metric calculation, and practical commercial insight.

At Arbtech, we work with developers, land agents, architects, planning consultants and more to deal with any friction in the local authority’s decision-making process.

Our team can coordinate the entire ecological workflow for your multi-stage project. Elements of this include calculating the biodiversity value using the statutory biodiversity metric, creating your biodiversity net gain plan, producing biodiversity enhancements on your site, and delivering measurable net gains to ensure that your development is compliant.

Get a Quote for Our Services

Keep your phased build moving forward without planning delays by speaking to our team directly.

If you want a free quote for the services we provide, give us information about your site and project, including your location, formal outline planning decision notice, boundary plans, and any available supporting evidence relating to your scheme.

All you need to do is fill out our online quote form with your name and address, project details and site plans, or you can call us or email us instead. Our team will then review the further information relating to your requirements, ask for any further details we need, and work out what you need to satisfy your biodiversity net gain requirements.

Even if you just want further guidance on what to do next, get in touch with Arbtech today, and our team will happily assist you.