A guide for developers
What is biodiversity net gain?
A plain guide to the 10% rule, the difference between on-site and off-site units, and how buying units discharges your planning condition. If you already know what you need, go straight to buying BNG units in Essex.
The 10% requirement
Biodiversity net gain, or BNG, is a legal requirement for most new development in England under the Environment Act 2021. It applied to major developments from 12 February 2024 and to small sites from 2 April 2024.
Your development must leave at least 10% more biodiversity value than the site had before work started. Value is measured in biodiversity units, using the statutory biodiversity metric. An ecologist surveys the habitats on your site and calculates their value before and after development.
BNG is a condition of your planning permission. Before you can start work, your local planning authority has to approve your biodiversity gain plan, which shows how you will reach the 10% gain. Habitat created for BNG must be secured and managed for at least 30 years.
Which developments are exempt?
Some developments do not have to deliver BNG, including householder applications. From 6 August 2026, new planning applications for sites under 0.2 hectares are also exempt, unless they affect priority habitat on the site. Applications made before that date stay under the earlier rules. Your ecologist or planning authority can confirm whether your site is exempt.
On-site and off-site units
The rules set an order of preference, called the biodiversity gain hierarchy.
- On-site units. You create or improve habitat within your development's red line boundary.
- Off-site units. You buy units from a habitat bank: land elsewhere where habitat is being created or improved and secured for 30 years. Off-site gains must be recorded on Natural England's biodiversity gain site register.
- Statutory credits. A last resort, sold by the government and priced to discourage their use.
Since 6 August 2026, minor developments that are not exempt can go straight to off-site units.
Location matters. Under the metric, units from a habitat bank in the same local planning authority area or National Character Area as your development count in full. Units from a neighbouring area count for three quarters, and units from further away count for half. Buying locally usually means buying fewer units. Read more about how Essex planning authorities treat off-site units.
The metric also sets trading rules. In general, you must replace lost habitat with the same type of habitat or a more valuable one.
How units discharge your planning condition
- Your ecologist completes the statutory biodiversity metric and works out how many units your development needs to reach a 10% gain.
- You agree to buy off-site units from a habitat bank.
- The units are allocated to your development, and the allocation is recorded on the biodiversity gain site register.
- You send your biodiversity gain plan, with evidence of the allocation, to your local planning authority.
- Once the authority approves the plan, the condition is met and you can start work.
We offer units from two habitat banks in Essex. See the Essex BNG schemes at Priors Farm and James Farm, or check the indicative prices for Essex units.
Not sure how many units you need?
Send us your metric, or tell us about your site and planning authority. We will explain your options in plain terms.
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