Biodiversity Net Gain
Clear, informed guidance to help deliver meaningful gains for nature.
Biodiversity Net Gain doesn’t need to be complex or reactive. With clear ecological evidence and considered advice, it can be planned for from the outset, supporting lasting, measurable benefits for nature. Get in touch to find out more about our assessments and consultancy.
What is Biodiversity Net Gain?
Biodiversity Net Gain (BNG) is a planning requirement designed to ensure that developments leave biodiversity in a measurably better state than before.
In practice, this means assessing the habitats present on a site before development and demonstrating how proposals will deliver a minimum 10% net gain in biodiversity value.
BNG assessment encourages thoughtful design, early consideration of habitats and long-term outcomes for nature. Gains can be delivered through habitat retention, enhancement or creation, and must be secured and managed for at least 30 years.
Josh Brown is a qualified River Condition Assessment (RCA) Surveyor approved on 5th August 2025 by the Cartographer RCA Team and RGS for Continuing Professional Development.
When approached early, alongside an experienced ecological consultant, BNG becomes a practical part of responsible development rather than an obstacle to planning.
When is Biodiversity Net Gain required?
Biodiversity Net Gain is now a requirement for most planning applications in England and applies to both major and minor developments, with a few exemptions.
It became mandatory on 12th February 2024 for major developments and in April 2024 for minor developments, under Schedule 7A of the Town and Country Planning Act 1990.
At aLyne Ecology, we’ve been carrying out BNG Assessments since the Defra Biodiversity Metric was introduced and can advise on how to achieve Biodiversity Net Gain through the biodiversity gain hierarchy.
Biodiversity Net Gain is typically required where:
- A planning application is submitted for new residential, commercial or mixed-use development.
- Development will result in loss, degradation or change of habitats within the redline boundary.
- A local planning authority applies BNG requirements as part of validation or determination.
- Planning conditions require submission of a Biodiversity Gain Plan.
Understanding whether the legislation applies, and how it should be addressed, is an important early step in avoiding delay or redesign later in the planning process. For guidance, contact our team or read more about exemptions here.
Survey seasonality
The optimal survey season for Biodiversity Net Gain surveys is between April and September, allowing for any required species or habitat surveys.
Optimal Survey Season
Sub-Optimal Survey Season
Survey Not Possible
Biodiversity Net Gain
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
Biodiversity Net Gain & other ecological surveys
Biodiversity Net Gain should be considered as part of the wider ecological picture, conducted alongside the following surveys:
- Preliminary Ecological Appraisal (PEA): A PEA is required ahead of the BNG process to identify habitats, ecological constraints and opportunities across a site.
- Habitat Condition Assessment: A Habitat Condition Assessment is required to establish the baseline quality and value of existing habitats.
- Landscape Plan: A detailed and scaled Landscape Plan is then used to understand how habitats will be retained, enhanced or created as part of the proposed development.
Together, this information feeds into the BNG Calculations, allowing biodiversity units to be calculated before and after development.
Our Biodiversity Net Gain process
Our approach is designed to build clarity at each stage and reduce uncertainty within the planning process. The process focuses on understanding your site, your proposals and the options available.
01
Early review & scoping
The site and proposed development are reviewed to confirm whether BNG applies and how it should be addressed in a proportionate way.
02
Baseline habitat assessment
Existing habitats are assessed and their condition recorded to establish an accurate baseline for BNG calculations. This is achieved through PEAs, Habitat Condition Assessments and Landscape Plans.
03
BNG metric calculation
The statutory biodiversity metric is used to calculate pre- and post-development biodiversity value, based on the proposals and ecological evidence.
04
Options appraisal
On-site retention, enhancement and creation options are explored first, with off-site solutions considered only where necessary.
05
BNG planning & reporting
Findings and recommendations are brought together in a clear Biodiversity Gain Plan to support planning submission and decision-making.
01
Early review & scoping
The site and proposed development are reviewed to confirm whether BNG applies and how it should be addressed in a proportionate way.
02
Baseline habitat assessment
Existing habitats are assessed and their condition recorded to establish an accurate baseline for BNG calculations. This is achieved through PEAs, Habitat Condition Assessments and Landscape Plans.
03
BNG metric calculation
The statutory biodiversity metric is used to calculate pre- and post-development biodiversity value, based on the proposals and ecological evidence.
04
Options appraisal
On-site retention, enhancement and creation options are explored first, with off-site solutions considered only where necessary.
05
BNG planning & reporting
Findings and recommendations are brought together in a clear Biodiversity Gain Plan to support planning submission and decision-making.
Project outcomes for Biodiversity Net Gain
A Biodiversity Net Gain assessment provides the clarity and evidence needed to move your project forward while meeting planning and ecological responsibilities.
A completed BNG assessment will typically deliver:
- A clear biodiversity unit position, based on a robust baseline and post-development assessment.
- Early identification of constraints and opportunities, informing design decisions.
- A defined delivery pathway, setting out how biodiversity gains will be achieved and secured.
- Reduced risk of late-stage redesign or delay, through proportionate, upfront advice.
- Clear next steps, including habitat delivery, management or off-site options where required.
- Planning-ready evidence, suitable for submission to the local planning authority.
Please note: Any further species surveys required will be specified and quoted for separately.
Why choose aLyne Ecology for your BNG Assessment?
We deliver efficient, high-quality ecological surveys through a well-organised and thorough approach. With over 20 years’ experience, you’ll receive clear, expert ecological advice from an independent team that truly cares about your success, as well as responsible outcomes for nature.
Efficient service
Our experienced, easily mobilised team can provide a quick turnaround on considered ecological advice and planning-ready reports.
Highly qualified
Our senior team includes a Qualified River Condition Assessment (RCA) Surveyor and FISC Level 3 ecologist for specialist advice.
Fully compliant reports
All reports are prepared in line with CIEEM guidance and BS 42020, ensuring robust planning application support.
Expert, friendly team
Our ecologists combine technical expertise with a practical, friendly approach to help your project move forward.
Discuss your Biodiversity Net Gain requirements
A clear understanding of your site and proposals, as early in the process as possible, makes it far easier to address BNG successfully.
Contact our friendly, experienced ecologists today to discuss your project and understand what’s required, when it’s needed and how it can be delivered responsibly.
Contact details
info@alyneecology.co.ukDiscuss your Biodiversity Net Gain requirements
A clear understanding of your site and proposals, as early in the process as possible, makes it far easier to address BNG successfully.
Contact our friendly, experienced ecologists today to discuss your project and understand what’s required, when it’s needed and how it can be delivered responsibly.