ECOLOGY · EVIDENCE · BETTER DESIGN DECISIONS
BNG assessment for planning and development
Understand your site’s biodiversity value, test your proposals and find a practical route to Biodiversity Net Gain.
ACP Consultants brings together UKHab baseline evidence, habitat condition assessment and biodiversity metric calculations. We help developers, architects and planning teams make informed decisions before the design becomes difficult to change.
Discuss your BNG assessment
A CLEAR STARTING POINT
What is a BNG assessment?
A Biodiversity Net Gain (BNG) assessment compares the biodiversity value of existing habitats with the proposed development. It uses habitat evidence and the appropriate biodiversity metric to identify losses, gains and any shortfall.
However, the result is more than a percentage. A useful assessment explains what the numbers mean for your layout, habitat proposals and planning submission. It also identifies assumptions that need further evidence.
Start while the design is still flexible. For example, retaining a valuable habitat may avoid a difficult replacement requirement later.
ESTABLISH THE RIGHT SCOPE
Does your development need an assessment?
First, check the planning route, application date, site boundary and habitats affected. Non-exempt development in England normally needs to demonstrate at least 10% BNG. Local policy may require more.
From 6 August 2026, an exemption applies to applications for sites of 0.2 hectares or less. However, it does not apply where the development impacts on-site priority habitat. Other exemptions and transitional rules may also matter.
A small site is not automatically suitable for the Small Sites Metric. We check both the exemption position and the appropriate assessment method.
FROM EVIDENCE TO A WORKABLE STRATEGY
How a BNG assessment works
We agree the scope around your site and planning stage. Then we connect the baseline, design and calculations so that each recommendation has a clear evidence trail.
- 01
Understand the site
Review your boundary, proposals, existing ecology information and planning requirements. Identify gaps before fieldwork starts.
- 02
Establish the baseline
Map habitats and gather condition evidence where required. Keep the survey, photographs and parcel references consistent.
- 03
Test the proposals
Calculate baseline and proposed biodiversity units. Check losses, retention, enhancement and habitat creation against the relevant metric rules.
- 04
Refine the strategy
Explain the results, test agreed design changes and identify any remaining shortfall or further evidence needed.
Assessment is iterative. If the layout changes, the habitat plans and metric may need updating too.
RELIABLE INPUTS MATTER
UKHab baseline and habitat condition evidence
For many terrestrial sites, UK Habitat Classification (UKHab) provides the starting point for habitat mapping. The assessment connects each mapped habitat parcel with the evidence needed for the metric.
Habitat type and habitat condition answer different questions. Type identifies the habitat; condition describes its quality against the relevant criteria. Neither should come from an unsupported assumption.
We also check that areas, lengths and parcel references agree across the survey, plans and workbook. This helps your project team understand how the calculation relates to the site.
Read more about habitat condition assessment and BNG habitat mapping.
A traceable baseline
- Mapped habitat
- A clear location, boundary and parcel reference.
- Field evidence
- Survey findings, relevant photographs and condition records.
- Metric entry
- Inputs that match the mapped habitat and supporting evidence.
- Design response
- A clear explanation of retention, loss, enhancement or creation.
Rivers and ditches need the appropriate specialist evidence. Explore river and ditch condition assessments where relevant.
MAKE THE ASSESSMENT USEFUL
Turn biodiversity calculations into design decisions
A proposed planting area does not automatically replace every habitat loss. The assessment needs to consider habitat type, realistic target condition and the metric’s rules.
We explain the constraints to your design team. Together, we can test practical options such as adjusting a footprint, retaining a boundary feature or refining the landscape proposals.
Where a shortfall remains, we identify the relevant off-site biodiversity unit requirements. Non-exempt minor developments can consider on-site and off-site delivery together under the rules introduced in August 2026.
For the workbook and calculation method, see our Statutory Biodiversity Metric service.
ILLUSTRATIVE DESIGN EXAMPLE
One layout change can alter the assessment
A development layout removes a boundary hedgerow and replaces it with amenity planting elsewhere.
Does the proposal address hedgerow units and the relevant trading rules? An overall habitat percentage alone cannot answer this.
Test whether the boundary can be retained, then calculate any remaining loss and the appropriate compensation.
This is an explanatory scenario, not an ACP case study or a prediction of units, cost or planning approval.
A CLEAR, AGREED PACKAGE
What you receive from your BNG assessment
Your quotation should explain the outputs, assumptions and number of design iterations included. Depending on your agreed scope and planning stage, the package may include:
| Output | What it helps you understand |
|---|---|
| Baseline habitat evidence | The habitats present, mapped parcels and supporting condition evidence where required. |
| Biodiversity metric workbook | Baseline and proposed units, separate unit types, gains, shortfalls and relevant rule checks. |
| Habitat plans | How the existing site and proposed habitat measures connect to the calculation. |
| Assessment findings | The design implications, assumptions, limitations and recommended next steps. |
| Agreed design review | How a revised layout or habitat proposal changes the assessment outcome. |
A BNG report presents the assessment evidence. A Biodiversity Gain Plan is a separate planning-stage document. Confirm which documents your commission includes.
Unsure what the council needs?
Send the request and your latest plans. We can help identify the assessment scope and avoid commissioning the wrong package.
PLAN THE WORK WITH CONFIDENCE
BNG assessment cost and timing
The cost depends on the work your site needs. Site size matters, but habitat complexity, survey evidence and design revisions can be equally important.
We scope the assessment before quoting. This makes it clearer what the fee includes and what would be a separate instruction.
Timing also depends on access, suitable survey conditions and the availability of up-to-date plans. Where evidence is missing, we explain what can progress now and what needs to follow.
Agree the programme early, particularly if your application deadline is approaching. A rushed workbook cannot resolve missing field evidence.
What affects the quotation?
- Baseline evidence: whether suitable recent survey information is already available.
- Habitat complexity: the range of habitats and any specialist watercourse work.
- Design stage: how developed the proposals are and how many options need testing.
- Submission scope: the reports, plans and follow-up support required.
- Delivery strategy: whether the assessment needs to consider off-site provision.
Survey fees, assessment fees, off-site unit purchases and long-term habitat management are different costs. Ask what is included before comparing quotations.
WORKING WITH ACP
Clear advice, with your project and the environment in view
We explain what the evidence supports, where uncertainty remains and what your team needs to do next. If a proposal creates an ecological problem, we raise it and help explore a practical response.
Advice you can act on
Understand the implications for your plans, rather than receiving a calculation without context.
Joined-up discussion
Connect ecological findings with the work of your architect, landscape designer and planning adviser.
Honest assessment
Make decisions using clear assumptions and evidence. Planning approval remains with the relevant authority.
COMMON QUESTIONS
BNG assessment questions
When should I commission a BNG assessment?
Start before fixing the layout or submitting the planning application. Early assessment gives your team more scope to avoid habitat losses and test alternatives. If you already have permission, send the conditions and approved plans so we can review the next stage.
Can you use an existing ecology survey?
Possibly. We first check its age, coverage, habitat information and suitability for the current proposal. A previous report may provide useful evidence, but it may not include everything needed for a biodiversity metric calculation. We explain any additional work before agreeing the scope.
Is a BNG assessment the same as a protected-species survey?
No. BNG assessment focuses on habitats and biodiversity units. Protected-species work answers different ecological and legal questions. A project may need both; the BNG result does not replace species surveys, mitigation or licensing requirements.
Can a Small Sites Metric assessment avoid a condition survey?
The Small Sites Metric uses fixed condition values, so it does not require the same condition assessment as the full metric. However, you must first check eligibility and identify the habitats correctly. Our Small Sites Metric guidance explains the appropriate route.
What happens if my design does not achieve the required gain?
We identify the shortfall and the affected unit types. Then we consider agreed design changes and the appropriate delivery options. Where off-site units are needed, the assessment should identify the relevant requirements. Different unit types are not interchangeable.
Does reaching 10% guarantee planning approval?
No. The percentage is only one part of the assessment. Metric rules, habitat proposals, supporting evidence and other planning requirements still matter. The planning authority decides whether the submission is acceptable.
What should I send for a quotation?
Send the site location, red-line boundary, latest layout and any existing ecology reports. Include the planning reference or council request where available. Tell us your intended submission date and whether you need an initial assessment, design review or further planning-stage documents.
YOUR NEXT STEP
Let’s scope your BNG assessment
Send your site location, red-line boundary and latest plans. Tell us your planning stage and what you need help with.
We will review the information and explain the appropriate next steps.
0330 236 7329
hello@acp-consultants.com
Existing ecology reports or a council request are useful too. You can email documents when discussing the scope.
Useful references
These official sources explain the framework behind the assessment. Requirements depend on the site, planning route and application date.
- GOV.UK — developments exempt from mandatory BNG
- GOV.UK — understanding Biodiversity Net Gain
- GOV.UK — using the Statutory Biodiversity Metric
- Defra — current metric tools and user guides
For the wider planning context, explore our BNG legislation and guidance.
Disclaimer date: October 2026
Biodiversity Net Gain requirements depend on the development, planning route, application date and habitats affected. Exemptions and metric requirements should therefore be considered on a project-specific basis.
ACP Consultants can provide ecological surveys, habitat assessment, biodiversity metric calculations and BNG advice. Acceptance of BNG information and approval of planning submissions remain matters for the relevant planning authority or other decision-maker.
Statutory guidance, metric tools and BNG requirements may change. This page provides general information and does not replace advice on your particular development. The disclaimer date is not a technical review date.