Construction & Property

Meet biodiversity net gain requirements for development

How to comply with mandatory 10% biodiversity net gain (BNG) requirements when developing land in England. Covers the statutory biodiversity metric, delivery options, habitat management plans, and protected species obligations.

UK-wide
Guide summary

You must increase the wildlife value of your development site by at least 10%. This is called biodiversity net gain (BNG). You need a qualified ecologist to measure your site's current wildlife value and create a plan showing how you will achieve the 10% increase. Your planning application will be rejected without this plan.

  • Achieve minimum 10% biodiversity increase
  • Maintain biodiversity gain for 30 years
  • Apply to most planning applications in England
  • Major developments apply from 12 February 2024
  • Small sites apply from 2 April 2024
  • Use Statutory Biodiversity Metric 4.0 for calculation
  • Brownfield sites are not exempt
  • Householder applications and self-build are exempt
  • De minimis exemption under 25 sqm habitat impact
  • Hire qualified ecologist for habitat assessment
On this page
UK-wide

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If you're developing land in England, you must now deliver a measurable 10% increase in biodiversity value compared to the pre-development state of your site. This is biodiversity net gain (BNG) - and it's not optional.

BNG fundamentally changes how development works. You cannot simply pay a fee to avoid it. Your planning application will be invalid without a biodiversity gain plan showing how you'll achieve the 10% uplift and maintain it for 30 years.

This guide explains what you need to do, when it applies, and how to comply. Getting BNG right early in your project saves time and money - leaving it until planning submission often causes delays and unexpected costs.

When does BNG apply to your development?

BNG is now mandatory for most planning applications in England. The requirement was phased in during 2024, with different start dates depending on development size.

Does your project require BNG?

Use this quick check to determine if BNG applies:

  • Are you submitting a planning application in England? → BNG likely applies
  • Is your site entirely hard standing with zero vegetation? → BNG still applies (your baseline is zero, so any habitat creation achieves gain)
  • Are you building a single self-build dwelling? → Exempt
  • Is it a householder application (extension to your home)? → Exempt
  • Will your development impact less than 25 sqm of habitat AND less than 5 m of linear feature, with no onsite priority habitat affected? → Exempt (de minimis)

Important: Brownfield sites are NOT exempt. The assumption that previously developed land doesn't need BNG is incorrect - brownfield sites often have significant biodiversity value from colonising vegetation, and you must still achieve 10% net gain from that baseline.

Understanding the biodiversity metric

BNG is measured using the statutory biodiversity metric - an official calculation tool that converts habitat area, type, and condition into standardised "biodiversity units". Your development must result in 10% more biodiversity units than the baseline.

You'll need a qualified ecologist to complete the metric calculation. While the spreadsheet is free to download, the underlying habitat survey requires specialist knowledge of UK habitat classification and condition assessment.

What affects your biodiversity score

The metric isn't just about area - a 1-hectare car park has different biodiversity value to a 1-hectare meadow. Key factors include:

  • Habitat type: Ancient woodland scores much higher than amenity grassland. Losing high-value habitats requires much more compensation.
  • Condition: A species-rich meadow in good condition scores higher than a degraded one. You can gain units by improving condition, not just creating new habitat.
  • Strategic location: Habitat within Local Nature Recovery Strategy priority areas scores higher than habitat elsewhere.
  • Irreplaceability: Some habitats (ancient woodland, irreplaceable grasslands) cannot be traded - you must avoid impacting them entirely.

Timing matters: Your baseline survey must be completed within 2 years of your planning application. Surveys are season-dependent - you may need to survey in spring/summer for certain habitats. Plan ahead.

How to deliver your 10% net gain

You have three options for achieving BNG, but they're not equal choices. You must follow a hierarchy - demonstrating why you cannot deliver on-site before moving to off-site, and why off-site is impossible before using statutory credits.

Option 1: On-site delivery (preferred)

Creating or enhancing habitats on your development site is usually the most cost-effective approach and is strongly preferred by planning authorities. Examples include:

  • Green roofs and living walls
  • Wildlife-friendly landscaping with native species
  • Wildflower meadows instead of amenity grass
  • Retention ponds and sustainable drainage features
  • Hedgerow planting along boundaries
  • Enhancing existing habitats (e.g., improving grassland condition through management)

Design tip: Integrate BNG into your scheme design from the start. Retrofitting biodiversity features costs more and delivers less than designing them in.

Option 2: Off-site delivery

If you cannot achieve 10% on-site (common for constrained urban sites), you can deliver BNG off-site by:

  • Purchasing biodiversity units from a registered habitat bank - third-party land managers create and maintain habitat, selling units to developers
  • Creating habitat on other land you control - this must be registered on the national BNG register before you can use the units

Location rules: Off-site gains should be within the same Local Nature Recovery Strategy area as your development where possible. Cross-boundary delivery is permitted but may face scrutiny from planning authorities.

Cost indication: Habitat bank unit prices vary by location, habitat type, and market demand. As of 2024, expect to pay £15,000-£50,000 per biodiversity unit for off-site delivery in most areas. This is still cheaper than statutory credits.

Option 3: Statutory credits (last resort)

Statutory biodiversity credits from Natural England are the option of last resort. You can only use them if you can demonstrate that on-site and off-site delivery are not possible.

Why credits are expensive: The government deliberately prices credits high to incentivise on-site and off-site delivery. Current prices range from £48,000 to £650,000 per biodiversity unit depending on habitat type.

Even a small development might need several units, making credits uneconomic for most projects. Credits should be a genuine last resort, not a convenient way to avoid proper biodiversity planning.

The biodiversity gain plan

Every planning application subject to BNG must include a biodiversity gain plan. This is a formal document that:

  • Shows the pre-development baseline biodiversity value (from your metric calculation)
  • Shows the post-development biodiversity value (with your proposed habitats)
  • Demonstrates how you'll achieve the 10% net gain
  • Explains your delivery approach (on-site, off-site, or credits)
  • Includes or references your habitat management and monitoring plan

Your planning application will be invalid without a biodiversity gain plan. The local planning authority will assess it as part of determining your application.

30-year maintenance requirement

BNG isn't just about creating habitat - you must maintain it for at least 30 years. This is a legal obligation secured through planning conditions, Section 106 agreements, or conservation covenants.

Budgeting for 30-year maintenance

Many developers underestimate the long-term cost of BNG. You need to factor in:

  • Habitat establishment (years 1-5): Higher management intensity - watering, replacing failed planting, weed control. Budget £500-£1,000+ per hectare per year.
  • Ongoing management (years 6-30): Regular maintenance - mowing, grazing, coppicing, monitoring. Budget £200-£500 per hectare per year.
  • Monitoring surveys: Professional ecological surveys at years 2, 5, 10, 15, 20, 30 minimum. Budget £500-£2,000 per survey depending on site size.
  • Contingency: If habitats fail to reach target condition, you'll need remedial action. Build in 10-20% contingency.

Who's responsible? You can transfer maintenance responsibility to a management company, but you'll typically need to provide an endowment fund to cover 30 years of costs upfront. This might be £5,000-£20,000+ per hectare depending on habitat type.

Protected species and Section 41 habitats

BNG doesn't replace your existing obligations to protect wildlife. If your site has protected species (bats, great crested newts, badgers, nesting birds) or priority habitats, you need additional surveys and may need licences from Natural England.

When you need a protected species licence

If your development will disturb protected species or damage their habitats, you must obtain a licence from Natural England before starting work. Common scenarios include:

  • Bats: Demolishing or renovating buildings, felling mature trees
  • Great crested newts: Developing near ponds or wetlands
  • Badgers: Developing near badger setts
  • Nesting birds: Clearing vegetation during breeding season (March-August)

Licence timeline: Natural England aims to determine licence applications within 30 working days, but complex cases take longer. Factor this into your programme.

Common mistakes to avoid

BNG is new and many developers are making avoidable errors. Learn from others' mistakes:

  • Leaving BNG until planning submission: Baseline surveys are season-dependent and take time. Metric calculations reveal whether your scheme is viable. Start BNG assessment at feasibility stage.
  • Assuming brownfield sites are exempt: They're not. Colonising vegetation, scrub, and grassland all have biodiversity value that must be replaced plus 10%.
  • Clearing sites before baseline survey: Your baseline is the state of the site at survey, not after clearance. Deliberately degrading a site before survey is potentially unlawful and will be investigated.
  • Underestimating irreplaceable habitats: Ancient woodland, veteran trees, and irreplaceable grasslands cannot be offset. If your site has these, redesign to avoid impact.
  • Forgetting linear features: Hedgerows and watercourses are measured separately in the metric. Losing a hedge requires creating substantial new hedgerow to compensate.
  • Ignoring the 30-year obligation: The habitat you create must be maintained for 30 years. Budget for this from day one.

Step-by-step: Achieving BNG compliance

Follow this process to ensure your development meets BNG requirements:

  1. 1

    Commission an ecological baseline survey

    Engage a qualified ecologist to survey your site and classify habitats using UK Habitat Classification (UKHab). The survey must be completed within 2 years of your planning application. Some habitats require surveys at specific times of year, so start early. The ecologist will produce a baseline habitat map and condition assessment.

  2. 2

    Calculate your baseline biodiversity value

    Your ecologist uses the statutory biodiversity metric to calculate your site's current biodiversity value in 'biodiversity units'. This is your baseline. The calculation accounts for habitat type, condition, strategic significance, and area/length. Keep this metric spreadsheet - you'll submit it with your planning application.

  3. 3

    Check for protected species and priority habitats

    Review the Section 41 list of priority habitats and species. If any are present, you may need additional surveys (e.g., bat activity surveys, great crested newt presence/absence) and potentially licences from Natural England. Protected species issues can delay projects significantly if discovered late.

  4. 4

    Design your development to minimise habitat loss

    Work with your design team to retain valuable habitats where possible. The BNG hierarchy prefers avoidance over compensation. Keeping mature trees, hedgerows, or water features reduces the net gain you need to create elsewhere. It's often cheaper to design around existing habitats than replace them.

  5. 5

    Design on-site habitat creation and enhancement

    Plan what new or enhanced habitats you'll create on-site. Consider green roofs, wildlife-friendly landscaping, wildflower areas, ponds, and hedgerows. Your ecologist can advise which habitats deliver the most biodiversity units for your site. Remember maintenance requirements - don't propose habitats you can't maintain for 30 years.

  6. 6

    Calculate your post-development biodiversity value

    Use the metric to calculate the biodiversity value after development, including your proposed habitat creation. The post-development value must be at least 10% higher than baseline. If you can't achieve this on-site, you'll need off-site delivery or credits.

  7. 7

    Secure off-site delivery if needed

    If on-site delivery falls short, identify off-site options. Contact local habitat banks to purchase biodiversity units, or register your own off-site land on the national BNG register. Off-site gains must be legally secured before you can rely on them.

  8. 8

    Prepare your habitat management and monitoring plan

    Draft an HMMP covering 30 years of habitat management. Include management prescriptions (what will be done), monitoring schedule (when you'll check), success criteria (target habitat conditions), and remedial measures (what happens if targets aren't met). This forms part of your biodiversity gain plan.

  9. 9

    Compile your biodiversity gain plan

    Assemble all elements into a formal biodiversity gain plan: baseline assessment, post-development calculations, delivery strategy (on-site, off-site, credits), HMMP, and relevant supporting documents. This is submitted with your planning application.

  10. 10

    Submit with your planning application

    Include your biodiversity gain plan and metric spreadsheet with your planning application. The local planning authority will review it as part of determination. Be prepared to answer questions or provide additional information if requested.

  11. 11

    Secure gains through legal agreement

    Before or at planning decision, secure your BNG commitment through appropriate legal mechanisms - typically a planning condition, Section 106 obligation, or conservation covenant. Off-site gains must be registered on the national register before the planning condition can be discharged.

  12. 12

    Implement and maintain for 30 years

    After permission is granted and development begins, implement your habitat creation as planned. Maintain and monitor for the full 30-year period, reporting to the local planning authority as required by your HMMP. If habitats fail to establish, take remedial action.

Construction & Property Requirement

Construction sector: BNG applies to almost all development

If you're a developer, housebuilder, or contractor undertaking work that requires planning permission in England, BNG affects you. This includes:

  • Residential developments (10+ units from Feb 2024, 1-9 units from April 2024)
  • Commercial and industrial developments
  • Mixed-use schemes
  • Infrastructure projects (roads, utilities, etc.)
  • Nationally Significant Infrastructure Projects (for applications submitted on or after 2 November 2026)

Key actions for construction businesses:

  • Build BNG assessment into your land acquisition due diligence
  • Commission baseline surveys early in the development cycle
  • Factor 30-year maintenance costs into scheme viability
  • Train project teams on BNG requirements
  • Develop relationships with habitat banks for off-site delivery
GOV.UK BNG guidance for developers (opens in a new tab)

Enforcement and penalties

BNG is enforced through the planning system. Non-compliance has serious consequences:

  • Invalid application: Planning applications without a biodiversity gain plan are invalid and will not be determined
  • Condition breach: Failing to deliver promised BNG is a breach of planning condition, triggering enforcement action
  • Stop notices: Local planning authorities can issue stop notices halting development
  • Prosecution: Serious or persistent breaches can result in prosecution

For wildlife offences (harming protected species, destroying habitats without licence), penalties are severe:

Costs and budgeting

BNG adds costs to development, but these are manageable with proper planning. Typical cost elements:

  • Ecological surveys: £1,000-£5,000+ depending on site size and complexity
  • Metric calculation: £500-£2,000 (often included with survey)
  • On-site habitat creation: £5,000-£50,000+ per hectare depending on habitat type
  • Off-site biodiversity units: £15,000-£50,000 per unit from habitat banks
  • Statutory credits: £48,000-£650,000 per unit (avoid if possible)
  • 30-year management endowment: £5,000-£20,000+ per hectare
  • Legal agreements: £2,000-£5,000 for S106 or conservation covenant

Cost-saving strategies:

  • Start BNG assessment early - design changes cost more later
  • Retain existing habitats where possible - avoiding loss is cheaper than compensation
  • Maximise on-site delivery - usually cheaper than off-site or credits
  • Choose habitats that deliver high biodiversity units with lower maintenance costs
  • Consider community or strategic landholding for off-site delivery at scale

Resources and support

Getting BNG right requires expertise. Consider engaging:

  • Ecological consultants: For baseline surveys, metric calculations, and HMMP preparation. Use CIEEM-registered ecologists.
  • Landscape architects: To design habitat creation that integrates with your development
  • Planning consultants: To navigate the planning process and negotiate conditions
  • Habitat banks: To secure off-site delivery if needed