Biodiversity Net Gain Durham: County Planning Rules

A planning application in County Durham can be delayed or rejected at validation if its biodiversity information is missing. The site may look ordinary, yet its habitat condition can still affect whether the council accepts the application.

If you’re searching for biodiversity net gain Durham requirements, the headline rule is clear: most in-scope development must deliver at least a 10% increase in biodiversity. That gain must be measured, planned and secured for the long term.

The details matter because Durham has its own submission requirements alongside the national legal framework.

What biodiversity net gain Durham applications must show

Biodiversity Net Gain, usually called BNG, is a planning requirement created through the Environment Act 2021. It operates through Schedule 7A of the Town and Country Planning Act 1990. For qualifying developments, the applicant must achieve a minimum 10% improvement against the site’s pre-development biodiversity value.

County Durham Council applies a local validation requirement. Unless a project is exempt, applicants should submit BNG information with the planning application itself. This applies to both full and outline applications, according to the council’s Biodiversity Supplementary Planning Document.

The submission should include a BNG Strategy and proposed Habitat Plan. It should also explain the site’s existing habitats, the proposed changes and how the gain will be maintained.

The national start dates still matter. BNG generally doesn’t apply to major applications made before 12 February 2024, or small and minor applications made before 2 April 2024. However, the exemption rules changed on 6 August 2026, including a 0.2-hectare-or-smaller red-line site threshold for certain developments.

A scheme’s size alone doesn’t settle the issue. Check the latest exemption test against the application type, submission date and red-line boundary. A useful local explanation of the national requirement is available in Durham Dales Ecology’s BNG guide.

The documents Durham expects at submission

A credible BNG submission gives the planning officer enough information to test the proposal. A short statement saying that new planting will improve wildlife won’t normally be enough.

The core documents usually include:

• A habitat baseline plan showing the habitats present before development.
• A completed Statutory Biodiversity Metric.
• A proposed Habitat Plan showing the location and type of new or enhanced habitats.
• A draft Biodiversity Gain Plan.
• A draft Habitat Management and Monitoring Plan.

Start with a defensible habitat baseline

The baseline assessment should record habitat type, condition and extent. It should also identify hedgerows, watercourses and other features covered by the metric.

The ecologist should check whether the site contains irreplaceable habitat, priority habitat or protected species. Nationally or internationally designated sites near the proposal may also affect the design and assessment.

That information needs to be gathered before the application is lodged. If the baseline is weak, the council may ask for further surveys or clarification. Delays at this stage can affect the whole planning timetable.

The County Durham BNG planning guidance provides a further local reference for applicants considering assessments and habitat plans.

Match the metric to the proposed design

The Statutory Biodiversity Metric compares the site’s existing biodiversity units with the units expected after development. It assesses factors such as habitat type, area, condition, location and the quality of proposed management.

The calculation should cover the relevant habitat categories. These can include area habitats, hedgerows and watercourses. The final percentage must be supported by the plan, not separated from it.

A draft plan at application stage isn’t the same as the final approval. Once planning permission is granted, the final Biodiversity Gain Plan must satisfy the statutory process before development starts.

How the 10% biodiversity target is calculated

The 10% target is measured against the site’s baseline biodiversity value. It doesn’t mean that 10% of the site must become a wildlife area.

A small site with valuable existing habitat can create a larger BNG challenge than a bigger site covered mainly by poor-quality hardstanding.

For example, removing a mature hedgerow or species-rich grassland may create a significant loss, even if the development footprint is limited. The applicant may then need more habitat creation or enhancement to reach the required percentage.

The metric also considers whether proposed habitats can realistically reach their predicted condition. A newly planted area won’t automatically count as high-quality habitat. Its condition, distinctiveness and management prospects affect the calculation.

Durham’s policy follows the mitigation hierarchy. Applicants should first avoid habitat loss, then reduce impacts and retain or enhance habitat on the site. Off-site compensation should only be considered after on-site options have been assessed.

That order matters when a proposal removes trees, hedgerows, ponds or grassland. A plan that relies on buying units without showing why on-site measures aren’t possible may face questions during determination.

Where on-site and registered off-site measures cannot meet the requirement, statutory biodiversity credits may be available as a last resort. They are not a shortcut around site design, evidence or the mitigation hierarchy.

For biodiversity net gain Durham applications, the strongest approach is to design the layout around existing ecological features before finalising the metric.

Off-site biodiversity net gain in County Durham

Some developments cannot deliver the full gain within their red-line boundary. An applicant may then use eligible off-site biodiversity units, provided the units are properly registered and secured.

County Durham Council requires off-site habitat to be protected for at least 30 years. That protection normally uses either a Section 106 agreement with the council or a Conservation Covenant with an approved Responsible Body.

The landowner or promoter must have legal control of the off-site land for the full period. If the promoter doesn’t own the land, the landowner must be willing to enter the required legal agreement.

Before units can be placed on Natural England’s Biodiversity Gain Site Register and sold, the legal agreement must be completed. An informal promise to manage the land won’t provide the same protection.

The off-site proposal must also include:

• A habitat survey and condition assessment that establishes a reliable baseline.
• Evidence that the site can deliver a realistic uplift under the Statutory Biodiversity Metric.
• A Habitat Management and Monitoring Plan.
• Arrangements allowing the council or its representative to inspect the site and receive monitoring reports.
• Confirmation that another scheme, grant, agreement or restoration project won’t claim the same habitat benefit.

Durham also checks practical constraints. Soil nutrients, hydrology, landscape character, mineral and waste safeguarding, public rights of way, historic interests and archaeological issues can all affect delivery.

Sites must avoid damaging irreplaceable, protected or priority habitats and designated sites. The council’s off-site BNG requirements set out the legal and monitoring expectations for landowners and developers.

What residents should check in a live planning case

Durham County Council is the unitary authority responsible for planning decisions across the county. Residents who want to understand its responsibilities can read this guide to how Durham County Council is organised.

To find a local proposal, use the County Durham planning applications map. Search by postcode, street or application reference, then open the supporting documents.

When reviewing a case, look for:

• The habitat baseline and condition assessment.
• The Statutory Biodiversity Metric and claimed percentage gain.
• The proposed Habitat Plan and site layout.
• Evidence that the applicant considered avoidance and on-site mitigation.
• Details of off-site units, legal agreements and long-term monitoring.

Residents can raise material planning concerns through the council’s consultation process. Useful comments identify a missing survey, an unexplained habitat loss, a calculation that doesn’t match the drawings or a management promise with no clear funding or legal control.

Planning representations should focus on evidence and policy. Reform UK’s official policy and campaign site sets out its wider position on reducing unnecessary regulation and strengthening local accountability, but the council must assess each BNG case against the statutory planning rules.

Common mistakes that cause delay

Several errors appear repeatedly in BNG submissions.

1. Starting the ecology work too late. A rushed survey can miss seasonal features or leave no time to redesign the layout.
2. Assuming a small scheme is automatically exempt. The current exemption rules depend on the development type, site area and other conditions.
3. Treating landscaping as biodiversity gain. Ornamental planting may have limited ecological value and may not deliver the metric outcome claimed.
4. Relying on off-site units without legal control. The land must be available, suitable and secured for at least 30 years.
5. Ignoring double counting. The same habitat improvement can’t be claimed for two separate schemes, funding programmes or legal obligations.
6. Overlooking protected or irreplaceable habitat. These features need more careful treatment than an ordinary metric calculation.

A clear baseline, a consistent metric and a deliverable management plan reduce these risks before the application reaches the council.

Conclusion

County Durham’s BNG process involves more than adding a 10% figure to a planning statement. Applicants must provide the baseline evidence, metric, habitat design and management arrangements at the right stage.

The most reliable route is to identify ecological constraints early, protect valuable habitats where possible and prove that every promised gain can be maintained for 30 years. For residents, the same documents provide a practical way to test whether a proposal’s claimed biodiversity improvement is realistic.