Unlocking Biodiversity Net Gain: What Architects & Planners Must Know
The Basics: What Is Biodiversity Net Gain & Why It’s Now Essential for Planning
Biodiversity Net Gain (BNG) isn’t just another box-ticking exercise—it’s a game-changer in planning and development. If you don’t factor it in from the start, your planning application could be dead on arrival.
BNG is a requirement that ensures new developments leave the natural environment in a measurably better state than before. The goal is simple: enhance habitats, support wildlife, and make sure that urban growth doesn’t come at the cost of biodiversity.
From November 2023, under the UK’s Environment Act 2021, most planning applications must deliver a minimum of 10% net gain in biodiversity. That means your project must improve natural habitats either onsite, offsite, or through biodiversity credits. Ignore it, and you’ll face planning rejections, costly redesigns, and delays that could derail your timeline.
For architects and planning consultants, this isn’t just about compliance—it’s about creating developments that are future-proof, sustainable, and more likely to get approval without endless back-and-forths.
The 10% Rule: Understanding the Minimum Biodiversity Increase Requirement
The 10% rule is the headline requirement of BNG. But what does that actually mean in practice?
Simply put, the biodiversity value of your site must be at least 10% higher after development than it was before. This is measured using Natural England’s Biodiversity Metric, which assesses habitats based on their size, type, and condition.
Here’s how it works:
- Baseline Biodiversity Assessment – Before you submit a planning application, an ecologist will survey the site to establish its existing biodiversity value.
- Post-Development Biodiversity Plan – You’ll need to demonstrate how your project will deliver a 10% uplift, whether through on-site habitat improvements, offsite compensation, or buying biodiversity credits.
- Long-Term Maintenance – BNG isn’t a quick fix. Approved projects must maintain biodiversity improvements for at least 30 years.
The challenge? If your site has low biodiversity to begin with, achieving a 10% uplift might be straightforward. But if your site is already rich in wildlife, hitting that target can be much harder. That’s where smart planning and early integration become essential.
Key Legislation & Policy: How Biodiversity Net Gain Affects Your Planning Application
BNG isn’t optional—it’s now a legal requirement for most developments in England. The key piece of legislation driving this change is the Environment Act 2021, which made BNG mandatory for planning permissions under the Town and Country Planning Act 1990.
Here’s what you need to know:
- From November 2023, all major developments must deliver at least 10% net gain in biodiversity.
- From April 2024, this requirement extends to smaller developments.
- BNG must be secured through planning conditions or legal agreements, ensuring long-term maintenance.
- Local Planning Authorities (LPAs) may require higher BNG targets, particularly in areas with strict environmental policies.
Failing to meet BNG requirements can lead to planning refusals, redesign costs, and prolonged approval processes. Some councils are already rejecting applications that don’t adequately address biodiversity from the outset.
For architects and planning consultants, this means BNG needs to be embedded into the design process from day one. Waiting until the last minute will only lead to expensive delays and revisions.
BNG isn’t just a compliance issue—it’s a strategic advantage. Projects that successfully incorporate biodiversity enhancements are more likely to gain community support, meet sustainability targets, and secure planning approval faster.
How to Integrate Biodiversity Net Gain Without Blowing Your Budget or Timeline
Smart Site Selection: Choosing Locations That Naturally Support Biodiversity Net Gain
You wouldn’t build a house on a floodplain without expecting problems, right? The same logic applies to biodiversity net gain (BNG). Some sites give you a head start, while others make meeting the 10% uplift a headache. Site selection is everything.
Greenfield sites might seem like an easy win—blank slates with fewer constraints. But they often have higher baseline biodiversity, meaning you need to deliver more uplift. Brownfield sites, on the other hand, often start with low biodiversity value, making the 10% increase easier to achieve.
Look for sites with degraded habitats or low-value landscapes. A former industrial site or intensively farmed land is a great candidate. If biodiversity is already minimal, even small interventions—wildflower meadows, green roofs, or hedgerows—can deliver a big percentage gain.
Avoid sites with existing high-value habitats. If your chosen plot already houses priority species, ancient woodland, or protected wetlands, your BNG obligations become more complex. You may have to compensate for habitat loss elsewhere, adding cost and complexity.
Early ecological assessments are crucial. A Preliminary Ecological Appraisal (PEA) will give you a snapshot of the site’s current biodiversity, helping you gauge how much uplift is required. Skipping this step could mean committing to a site that’s a nightmare for BNG compliance.
Cost-Effective Enhancements: Practical Ways to Boost Biodiversity Without Major Redesigns
You don’t need to throw money at biodiversity net gain to get results. Small, strategic changes can boost biodiversity without eating into your budget or requiring a full redesign.
Start with landscaping. Native plant species support local wildlife better than ornamental ones. Swapping generic grass lawns for native wildflowers improves biodiversity while reducing maintenance costs.
Hedgerows are a win-win. They provide habitat corridors for wildlife, improve aesthetics, and can even double as sustainable drainage features. Replacing fences with hedgerows is a simple, low-cost way to deliver net gain.
Green roofs and living walls aren’t just trendy—they’re biodiversity boosters. They provide additional habitat, help with drainage, and improve air quality. In urban developments, they can be an easy way to meet BNG targets without sacrificing valuable space.
Water features offer huge biodiversity potential. Even small ponds or swales can attract amphibians, insects, and birds. They also help with Sustainable Drainage Systems (SuDS), reducing flood risk while ticking the BNG box.
Think beyond plants. Bird and bat boxes are low-cost, easy to install, and instantly improve biodiversity value. Choose species-specific designs to maximise impact.
If possible, retain and enhance existing habitats. Mature trees, scrubland, and natural watercourses already support biodiversity. Preserving and improving them often costs less than creating new habitats from scratch.
Timing Matters: Aligning Surveys & Implementation to Avoid Costly Delays
Timing can make or break your biodiversity net gain strategy. Get it wrong, and you risk expensive delays, missed planning deadlines, and last-minute redesigns.
Ecological surveys are seasonal. Many species can only be surveyed at specific times of the year. Great crested newts, for example, require surveys between March and June. Bat activity surveys run from May to September. If you miss these windows, you wait—sometimes for months.
Plan surveys early. A Preliminary Ecological Appraisal (PEA) should be one of your first steps. If protected species are found, further surveys may be needed, and these have strict seasonal windows. Delaying this process can push your entire project back.
Factor in habitat creation timelines. Some biodiversity enhancements take time to establish. Newly planted hedgerows won’t provide full habitat value immediately. If your strategy relies on newly created habitats, allow time for them to mature before they’re assessed.
Construction timing matters too. Avoid site clearance during bird nesting season (March to August) to prevent delays. If clearance is unavoidable, pre-emptive surveys and mitigation measures can help keep your project on track.
Align biodiversity net gain implementation with other project milestones. Integrating biodiversity enhancements into early-stage planning avoids costly retrofits later. Retrofitting SuDS, for example, is far more expensive than designing them in from the start.
Work with ecologists early. A well-planned BNG strategy ensures compliance without disrupting your timeline. If you need expert input, collaborating at the design stage prevents last-minute hurdles that could derail your planning application.
For more guidance on ensuring your project meets biodiversity net gain requirements, visit Comprehensive Ecology Surveys for Planning.
The No-Nonsense Guide to Passing Biodiversity Net Gain Assessments First Time
The Biodiversity Metric Explained: How Your Project’s Score Is Calculated
Biodiversity Net Gain (BNG) is not just another box-ticking exercise—it’s a measurable standard that determines whether your development enhances biodiversity by at least 10%. The key to passing your Biodiversity Net Gain assessment is understanding how the score is calculated.
At the core of the assessment is the Biodiversity Metric, a tool that quantifies biodiversity before and after development. It evaluates habitat type, size, condition, and strategic significance. The formula is simple in theory:
(Post-Development Biodiversity Value – Pre-Development Biodiversity Value) ÷ Pre-Development Biodiversity Value × 100 = % Net Gain
But in practice, small miscalculations can derail your application. For example, if your project reduces high-value habitats without adequate compensation, your score plummets. If you’re redeveloping brownfield land, you may start with a lower biodiversity value, making it easier to achieve a net gain.
Local planning authorities scrutinise these numbers. If your calculations are off or lack supporting evidence, you’ll be asked to revise your plans—delaying approval. Understanding the metric upfront helps you design with biodiversity in mind rather than scrambling to fix issues later.
Common Pitfalls & How to Avoid Them: What Causes Applications to Fail?
BNG assessments fail for one of three reasons: poor planning, inaccurate surveys, or weak mitigation strategies. Avoid these, and you’ll save time, money, and frustration.
1. Ignoring Baseline Assessments
Your pre-development habitat value sets the foundation for your net gain target. If you don’t accurately assess it, everything else collapses. A rushed Preliminary Ecological Appraisal (PEA) or Phase 1 Habitat Survey can lead to incorrect data. If the local authority disputes your baseline, expect delays.
2. Overlooking Habitat Condition Scores
Not all habitats are equal. A mature woodland holds more biodiversity value than a manicured lawn. The Biodiversity Metric assigns condition scores, and failing to account for this can skew your results. If you underestimate the condition of existing habitats, your net gain projections won’t hold up to scrutiny.
3. Relying Too Heavily on Off-Site Compensation
BNG prioritises on-site enhancements. If your strategy leans too much on offsetting biodiversity loss elsewhere, planners may push back. Many councils prefer developments that integrate green roofs, wildlife corridors, and native planting rather than relying on external biodiversity banks.
4. Failing to Align with Local Biodiversity Policies
National BNG requirements set the baseline, but local planning authorities often have stricter policies. Some councils demand higher than 10% net gain. Others have specific habitat priorities. If your proposal doesn’t align with local biodiversity strategies, it could face rejection.
5. Underestimating Long-Term Management Requirements
BNG isn’t a one-off action. The law requires a 30-year commitment to maintaining biodiversity improvements. If your plan doesn’t include a clear, enforceable management strategy, it raises red flags. Planners need confidence that your net gain won’t deteriorate over time.
Expert Collaboration: When & How to Work with Ecologists for Seamless Approval
Working with an ecologist isn’t just about ticking a compliance box—it’s about designing a project that passes assessment the first time. Many architects and planning consultants wait too long to involve ecological experts, which leads to costly redesigns and missed planning deadlines. The right approach is to integrate ecological input from the start.
When Should You Bring in an Ecologist?
Engage an ecologist before site selection if possible. A high-risk site with protected species or priority habitats will make achieving Biodiversity Net Gain harder. If you’re already committed to a location, involve an ecologist during the earliest design stages to avoid last-minute surprises.
How Can an Ecologist Help?
1. Accurate Baseline Surveys – A professional ecological consultant ensures your starting biodiversity value is correctly assessed, preventing disputes with planning authorities.
2. Optimised Design Strategies – They recommend biodiversity enhancements that align with your project goals—whether that’s green infrastructure, habitat creation, or strategic planting.
3. Biodiversity Metric Calculations – An ecologist ensures your calculations meet regulatory standards, reducing the risk of rejection.
4. Planning Application Support – They supply the necessary reports to satisfy local authorities, helping you avoid unnecessary back-and-forth.
5. Long-Term Biodiversity Management Plans – Authorities require proof that biodiversity improvements will last for at least 30 years. An ecologist structures this plan so it meets compliance standards.
The best way to ensure a smooth planning approval is to treat biodiversity as an integral design element, not an afterthought. If you wait until late-stage planning to factor in biodiversity, the fixes will be more expensive and disruptive. Smart collaboration with ecologists streamlines the process, helping you meet Biodiversity Net Gain requirements without unnecessary setbacks.
If you want expert guidance on Biodiversity Net Gain assessments and seamless planning approval, our ecological consultancy can help. Visit Biodiversity Net Gain Consultancy to get personalised advice tailored to your project.
Here is a video Matt did with Sean Tofts of The Small Sites Alliance on the very topic of BNG!