At Civity, we work closely with landowners, developers, and local authorities to help deliver Biodiversity Net Gain (BNG) in a way that’s practical, ethical, and legally sound. One of the most common and often confusing topics we encounter is additionality—especially when it comes to stacking environmental payments and understanding what’s eligible within the planning process.
In this blog, we explain what additionality means in BNG, why it matters for compliance, and how it affects opportunities for income stacking. If you’re a land manager, developer, or involved in planning decisions, this guide is for you.
What is Additionality in BNG?
In simple terms, additionality in the context of Biodiversity Net Gain (BNG) means that the biodiversity improvements being proposed must be in addition to what would have happened anyway. You can’t claim BNG units for habitat creation or enhancement that are already legally required or are being delivered under another environmental scheme unless certain strict conditions are met.
The mandatory BNG requirement introduced through the Environment Act sets clear expectations for how developers must deliver biodiversity gains above the pre-development biodiversity value of the land. These gains must be measurable using the biodiversity metric, and crucially, they must be additional.
Why Does Additionality Matter?
The principle of additionality protects the integrity of BNG. It ensures that biodiversity units and biodiversity credits truly represent a net gain for the natural environment rather than double-counting actions already committed under other schemes.
Without clear additionality, developers might claim biodiversity benefits for work they were already obligated to do—undermining the biodiversity gain objective and weakening trust in the system.
That’s why local planning authorities and Responsible Bodies scrutinise this closely when reviewing a biodiversity gain plan or a site applying to be on the biodiversity gain site register.
If you’re new to the concept of habitat banks, our blog is What is a BNG Habitat Bank? Offers a useful introduction.
Income Stacking: What You Can and Can’t Combine with BNG
Income stacking refers to combining BNG payments with other environmental payments—such as those from carbon markets or public land management schemes. While this can help maximise land use and revenue, it introduces complexity in terms of eligibility and additionality.
Here’s a breakdown of what’s typically permitted:
Often Compatible with BNG:
- Woodland Carbon Code: Potentially stackable if clearly delivering additional biodiversity uplift on what was required by the scheme.
- Voluntary markets: e.g. for carbon or nutrient neutrality, provided gains are quantifiable and not double-counted.
- ELMs (Environmental Land Management schemes): Some actions may be stackable, especially if the habitat enhancements for BNG go beyond ELM baselines.
Usually Not Compatible:
- Same land, same outcome: You can’t claim BNG and carbon credits for the exact same parcel unless distinct outcomes are achieved.
- Legal obligations: If enhancements are already required under a planning obligation or planning permission, you can’t use them for BNG units unless an extra value is demonstrably added.
- Existing habitat maintenance: Actions to maintain another obligation or prevent deterioration of existing habitat do not qualify for BNG units.
To be eligible, the biodiversity gains must clearly exceed what’s already being delivered through other means. This includes showing a measurable uplift in biodiversity value using statutory biodiversity metric calculations.
Key Terms Around Additionality
- Double counting: Claiming biodiversity gains for actions already rewarded through another scheme.
- Same land, same outcome: A scenario where the land area and ecological benefit overlap across schemes, making it ineligible for BNG.
- Additional value: Demonstrating extra ecological benefit beyond the baseline of another funding stream.
These principles are embedded in guidance on off-site biodiversity units and the biodiversity gain hierarchy, which prioritises onsite habitat delivery before turning to off site options.
Planning Considerations for Additionality
Under the Town and Country Planning Act, the delivery of BNG is linked to the relevant planning permission. That means demonstrating additionality is crucial during the planning process, whether you’re submitting a full application or a phased development.
Local planning authorities will expect a clear biodiversity gain statement as part of your planning documents, explaining:
- The biodiversity baseline and how it was measured
- What habitat banks or off-site areas are being used (if BNG is not to be fully delivered on-site)
- How additionality is proven, particularly where other schemes are in place
On-site BNG to be delivered as part of a planning application (where the proposed habitats are considered ‘Significant’) will need to be secured via SE106 agreed with the LPA.
Offsite BNG delivery (to be delivered via a Habitat Bank) needs to be secured via a Section 106 agreement or a Conservation Covenant—both forms of legal agreement ensuring that habitat management and monitoring continue long-term.
Common Scenarios We See
Eligible:
- A landowner creates a new wetland on previously species-poor arable land, not under any existing scheme, and sells BNG units.
- A woodland planting project using the Woodland Carbon Code is expanded, and a separate biodiversity gain is quantified using biodiversity net gain unit uplift in another habitat zone.
Not Eligible:
- A developer tries to claim they can sell BNG units for habitat enhancement/management on their land. However, these units are already allocated to contribute to their 10% net gain on-site (to enable their onsite planning permission)
- A land manager signs up to multiple schemes offering payments for the same habitat enhancements on the same parcel.
Our Role at Civity
We support clients in assessing whether land meets the mandatory BNG requirement and whether it’s suitable for selling biodiversity units through establishing a habitat bank. Our work includes:
- Helping landowners navigate emerging markets and avoid double-counting
- Guiding developers through the biodiversity metric and mitigation hierarchy
- Securing compliant legal agreements to lock in habitat creation and long-term monitoring plans
Learn how we can help you sell biodiversity units through the Civity landbank.
Where questions arise—particularly in areas like ecosystem service stacking or natural or heritage features—we liaise with DEFRA or legal specialists as needed to ensure compliance.
Final Thoughts: Getting Additionality Right
Understanding and demonstrating additionality is central to the ability to deliver Biodiversity Net Gain, whether you’re creating units to sell or seeking permission for a development.
Our advice? Start early. For developers, that means mapping pre-development biodiversity conditions accurately, using the correct biodiversity metric, and focusing on meeting Biodiversity Net Gain (BNG) requirements in line with planning policy. For landowners creating habitat banks, it’s essential to consider additionality—ensuring proposed habitats deliver gains beyond what’s already legally required or funded elsewhere. Getting this right from the outset helps avoid eligibility issues, supports registration on the biodiversity gain site register, and ensures your project contributes meaningfully to nature recovery.
If you’re unsure about your project’s additionality or how to stack other environmental payments, we’re here to help. At Civity, we bring ecology and planning together to support nature-positive outcomes that work—for landowners, developers, and the environment.
Looking to sell biodiversity units and develop a BNG Habitat Bank? Get in touch with our team today.
For Natural England’s official position, see their Biodiversity Net Gain guidance on GOV.UK.
