Beyond BNG Compliance: What Your Technical Drawings Must Show for Biodiversity Net Gain Approval
According to the Home Builders Federation's 2025 report, 98% of small and medium-sized builders find implementing Biodiversity Net Gain (BNG) a major challenge. The primary difficulties cited aren't philosophical objections to environmental enhancement—they're practical problems with technical complexity, local authority capacity gaps, and confusion about exactly what documentation planning authorities require.
Since 12 February 2024 (for major development) and 2 April 2024 (for small sites), the Environment Act 2021 has required virtually all planning applications to demonstrate a mandatory 10% Biodiversity Net Gain (GOV.UK). This isn't a design aspiration or a nice-to-have environmental gesture—it's a statutory requirement with specific technical documentation standards. Get the submission wrong, and your application will be invalidated before it's even assessed.
The confusion is understandable. BNG involves multiple components: ecological surveys using standardised habitat classification, metric calculations using government-mandated software, habitat management planning covering 30 years, and crucially, technical drawings that spatially represent the baseline condition and proposed changes. It's this final component—the technical drawings—that trips up many applicants.
Local Planning Authorities need to verify that your metric calculations match the actual site, that proposed habitat creation is spatially feasible, and that the 10% net gain can actually be delivered. Without accurate technical drawings linking the numbers to the ground, your BNG submission lacks credibility. Let's examine exactly what technical drawings must show for BNG approval.
Understanding the BNG Framework
Before exploring technical drawing requirements, it's worth understanding the regulatory framework these drawings must satisfy.
The Legal Requirement
The Environment Act 2021 established biodiversity net gain as a condition of planning permission. The statutory basis is clear: most planning applications must achieve a minimum 10% gain in biodiversity value compared to the pre-development baseline (GOV.UK Understanding Biodiversity Net Gain). This gain must be measured using the Statutory Biodiversity Metric—a government-provided Excel tool that calculates biodiversity units based on habitat area, type, condition, and strategic significance.
The 10% applies separately to three habitat categories: area habitats (grassland, woodland, scrub), hedgerows (linear features), and watercourses (rivers and streams). Each must achieve 10% individually—you cannot offset hedgerow loss with grassland creation.
Who It Applies To
BNG applies to all major planning applications (10+ dwellings or 0.5+ hectares) and most minor applications. Limited exemptions exist for small house extensions, householder applications, and certain self-build projects, but essentially, if you're building houses, BNG applies.
According to the Local Government Association's PAS BNG FAQs (Local Government Association), authorities are still developing their assessment procedures, creating uncertainty for applicants about exactly what will be accepted.
Baseline Assessment: What Must Be Mapped
BNG starts with establishing the baseline—the ecological value of the site in its pre-development state. This baseline sets the benchmark against which the 10% gain is measured. Accuracy is critical: overstate the baseline and you'll struggle to achieve 10% gain; understate it and you'll over-deliver habitat creation, wasting developable land.
Pre-Development Habitat Survey
The baseline habitat survey must use the UK Habitat Classification (UKHab) system—a standardised taxonomy that aligns with the Statutory Biodiversity Metric. Ecologists survey the site, identify habitat types (e.g., modified grassland, dense scrub, introduced shrub, buildings), assess condition (poor, moderate, good based on specific criteria), and map spatial extent.
CIRIA's BNG Good Practice Principles (CIEEM) emphasise that habitat surveys must be recent (typically within 12 months), conducted during appropriate seasons (growing season for vegetation identification), and undertaken by competent ecologists.
Technical Drawing Requirements for Baseline
The baseline habitat plan must translate the ecological survey into a spatially accurate technical drawing. South Oxfordshire District Council's BNG Technical Note and Wyre Council's BNG Guidance for Applicants 2025 (Wyre Council) both specify minimum technical standards.
Scale: Baseline plans are typically prepared at 1:500 for small sites (under 1 hectare) or 1:1250 for larger sites. The scale must be adequate to accurately show habitat parcel boundaries.
Base mapping: Plans must use current Ordnance Survey mapping with appropriate licensing. Traced or copied OS mapping without licensing is legally problematic and undermines submission credibility.
Habitat parcel mapping: Each distinct habitat type and condition must be shown as a separate colour-coded parcel. Parcels are numbered (e.g., Habitat 1, Habitat 2) and linked to the metric spreadsheet where area, type, condition, and strategic significance are recorded.
Reference numbers and labels: Each habitat parcel requires clear labelling showing the habitat reference number, UKHab classification code, condition, and area. For example: "Habitat 3: Modified grassland – other neutral (g3c), Moderate condition, 0.42 ha".
Site boundary: The development site boundary (typically the red line from planning application drawings) must be clearly shown so the LPA can verify which habitats are within the application area.
What LPAs Scrutinise
Local Planning Authority ecologists examine baseline plans for consistency with the metric spreadsheet, accuracy of habitat classification and condition assessment, and credibility of spatial representation. Common rejection reasons include habitat areas on the plan not matching metric entries, habitat classifications that don't align with photograph evidence, condition assessments that appear optimistic without supporting justification, and poor-quality plans with indistinct boundaries or missing reference numbers.
Post-Development Proposals: The Creation & Enhancement Plan
If the baseline plan shows what exists, the post-development plan shows what will be created. This is where BNG moves from assessment to design—demonstrating how habitat creation and enhancement will deliver the mandatory 10% gain.
What Must Be Shown
The post-development habitat plan maps proposed habitat creation areas with habitat types, condition targets, and spatial extent. Enhancement zones show where retained habitats will be improved from poor to moderate condition, or moderate to good. New hedgerow planting and linear feature creation demonstrate how hedgerow unit gains will be achieved.
The challenge is integrating ecological requirements with development viability. Achieving 10% net gain typically requires dedicating 15-30% of site area to habitat creation and enhancement—land that cannot be built on.
CIRIA's BNG Good Practice Principles (CIEEM) emphasise that habitat creation must be ecologically credible—proposing to create woodland on shallow chalk soils, or wetland on free-draining sands, won't be accepted.
Technical Drawing Requirements
Post-development plans must use the same scale and base mapping as baseline plans. Each proposed habitat creation or enhancement area must be colour-coded distinctly from baseline habitats. Habitat reference numbers continue from the baseline.
Management zones and responsibility boundaries must be shown if different areas will be managed by different parties. Integration with landscape and drainage plans is essential—the habitat creation plan must align with the landscape architect's planting scheme and the civil engineer's drainage strategy.
Citing a recent example, Wyre Council's 2025 BNG Guidance (Wyre Council) emphasises that post-development plans must demonstrate practical deliverability—habitat creation must fit within the development layout, not be an afterthought.
The Delivery Reality
Achieving 10% net gain on-site is straightforward on brownfield sites with low baseline value. The challenge comes with greenfield sites that already have moderate or good condition habitats. Small sites particularly struggle—limited space for meaningful habitat creation after accommodating dwellings, gardens, and access.
The alternative is off-site provision: purchasing biodiversity units from habitat banks or buying statutory credits from the government, with statutory credits starting around £42,000 and increasing substantially depending on habitat type (2024 pricing). For a development requiring 3 biodiversity units to achieve 10% gain, costs could exceed £126,000.
The Statutory Metric & Technical Submission Package
The Statutory Biodiversity Metric (GOV.UK) is a complex Excel tool that calculates biodiversity units. The metric version must be current—using superseded versions invalidates the submission.
Required Documentation Package
BNG submissions comprise multiple documents that must be internally consistent:
Completed Statutory Biodiversity Metric (Excel file) containing all habitat data and calculations
Baseline habitat plan (technical drawing) spatially representing pre-development habitat
Post-development habitat plan (technical drawing) showing proposed creation and enhancement
BNG Assessment Report (written document) providing narrative explanation
Habitat Management and Monitoring Plan covering 30 years
Evidence of off-site provision or statutory credits if 10% cannot be achieved on-site
South Oxfordshire's BNG Technical Note and the Local Government Association's PAS BNG FAQs emphasise that submission quality directly affects validation speed.
Technical Quality Standards
Metric calculations must be completed by competent persons—typically professional ecologists with BNG metric training. Competent person declarations are often required.
Data tables within the metric must link directly to habitat reference numbers on drawings. If Habitat 3 in the metric is "Modified grassland, Moderate condition, 0.42 ha", then Habitat 3 on the baseline plan must show this exact area, type, and condition.
Common Pitfalls & How to Avoid Them
Pitfall 1: Survey Timing Issues - Conducting habitat surveys outside appropriate seasons undermines baseline accuracy. The solution is commissioning Preliminary Ecological Appraisal in advance, ideally 12-18 months before planned submission.
Pitfall 2: Metric-Drawing Mismatches - When habitat areas in the metric don't match areas on drawings, LPAs cannot validate the submission. The solution is systematic cross-checking before submission.
Pitfall 3: Unrealistic Habitat Creation - Proposing habitat types that don't match site conditions invites rejection. The solution is ecologists and landscape architects working collaboratively.
Pitfall 4: Inadequate Management Plans - Thirty-year management plans often lack detail. The solution is professional habitat management planning prepared by ecologists with management experience.
Pitfall 5: Neglecting Trading Rules - The metric includes trading rules preventing off-setting high distinctiveness habitat with low distinctiveness creation. The solution is understanding trading rules before finalising site layouts.
Beyond Compliance: Strategic BNG Integration
Best practice views BNG as an opportunity, not merely a compliance hurdle. Well-designed BNG delivers multiple benefits: ecological enhancement contributing to local biodiversity priorities, green infrastructure providing resident amenity, climate resilience through tree planting, and marketing differentiation for developments with strong environmental credentials.
The Sovatech Approach: Coordinating BNG Technical Documentation
At Sovatech Consulting, we work alongside ecologists and landscape architects to prepare technical drawings that satisfy BNG submission requirements. Our role is ensuring baseline and post-development habitat plans are spatially accurate, link clearly to metric calculations, integrate with landscape and drainage designs, and meet Local Planning Authority technical standards.
We understand that BNG has added substantial complexity to planning submissions, particularly for SME developers working with multiple consultants. Technical drawing coordination—ensuring consistency between the ecologist's metric, the landscape architect's planting plan, and the civil engineer's drainage design—prevents the mismatches that trigger validation refusal.
If your development requires BNG compliance and you need technical drawing coordination to ensure your submission meets Local Planning Authority standards, contact Sovatech Consulting. We'll work with your ecologists and landscape architects to prepare accurate, metric-compliant habitat plans that support first-time validation and demonstrate your commitment to environmental enhancement.
