Green banner of a blurred background with purple thistles with text reading "BNG Trading Rules Part 1 – Navigating BNG for Developers" overlaid on a photo of flowering thistles in a wild grassland habitat. — An introduction to the BNG trading rules every developer needs to understand. Part 1 focuses on how habitat type and location influence biodiversity unit eligibility.

Biodiversity Net Gain (BNG) is now a mandatory part of the planning process, and the trading rules are one of the most common areas where projects encounter delays.

Understanding how these rules apply early can help avoid incorrect assumptions about habitat replacement, unit availability and compliance.

This article simplifies the BNG trading rules outlined in the Statutory Biodiversity Metric, focusing on the fundamentals developers need to get right.

For a full overview of how the rules apply in practice, read our BNG Trading Rules Explained: A Developer’s Guide

What are BNG Trading Rules?

BNG trading rules form part of the Statutory Biodiversity Metric and determine how habitat losses must be compensated.

They are designed to ensure that biodiversity loss is replaced with habitats of equal or greater ecological value, contributing to the required minimum 10% biodiversity net gain ensuring “no net loss”.

In practice, this means developers cannot assume that any biodiversity unit will satisfy their requirement. Replacement habitats must follow specific rules relating to type, distinctiveness and module.

Key Points of BNG Trading Rules

Like-for-like or Like-for-better: The rules prioritise replacing lost habitats with similar ones (same type and distinctiveness) or with habitats of higher distinctiveness. For example, a loss of medium distinctiveness woodland should be compensated for by creating a new medium distinctiveness woodland or a higher distinctiveness habitat with the same module.

Trading within habitat modules: There are three habitat modules: Area, Hedgerow and Watercourse. Biodiversity units within each of these groups can only be replaced with units within the same group. For instance, lost hedgerow units can be compensated for with similar hedgerows or higher distinctiveness hedgerows, but not area habitat units or watercourse units of any kind.

Watercourse compensation: Watercourses must be replaced with habitats that reflect similar ecological function. Replacing a headwater stream with a lowland river wouldn’t be acceptable, for example.

Woodland considerations: Woodland creation shouldn’t come at the expense of existing woodlands. While woodland creation is encouraged, enhancement of existing woodlands can also be used for compensation. For felled woodlands, specific rules apply regarding the baseline habitat and target condition.

Why this matters for developers

The trading rules are one of the main reasons Biodiversity Gain Plans are delayed or rejected.

Common issues include:

assuming suitable habitats will be available
misunderstanding module restrictions
leaving unit sourcing to late
overlooking distinctiveness requirements

Understanding these constraints early makes it easier to build a realistic and deliverable BNG strategy.

What if Standard Rules Don’t Apply?

In exceptional circumstances, developers can apply “Rule 4”. This allows for deviations from standard trading rules if the project involves:

Restoring a historically important habitat with optimal conditions
Highly complex landscape changes like creating heathland mosaics
Large-scale river restoration projects

Read Part 2: Rule 4 explained to understand why this may apply.

The Importance of Expert Guidance

While the principles of the trading rules are straightforward, applying them to real sites can be complex. Habitat availability, location constraints and planning requirements all influence what is achievable. Early input from ecologists and BNG specialists can help avoid delays and reduce risk later in the process.

Frequently Asked Questions About BNG Trading Rules

What are BNG trading rules?
BNG trading rules determine how developers offset biodiversity loss, ensuring that like-for-like or like-for-better habitat compensation is applied when biodiversity units are secured off-site.

Can a developer purchase any biodiversity units?
No. Biodiversity units must follow trading rules - matching the type and distinctiveness of habitats impacted by development.

How do I know how many BNG units I need?
You must work with an ecologist to assess your site’s biodiversity baseline and calculate the required units using the Statutory Biodiversity Metric.

What happens if I can’t meet BNG requirements on-site?
If on-site solutions aren’t viable, you can purchase off-site biodiversity units from a registered Gain Site. Explore our Sites Directory to find units in your development area.

Need help securing off-site biodiversity units? Complete our enquiry form and send us your metric and we’ll provide a quote!

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