This case study relates to a development in Chippenham, Wiltshire and is a small site where a dwelling is being replaced with a larger dwelling. This project exemplifies how we help clients navigate mandatory biodiversity requirements while ensuring compliance with the Environment Act 2021 and the National Planning Policy Framework (NPPF).
The goal? To quantify the site’s existing biodiversity value, assess the impact of the proposed development, and recommend actionable steps to achieve a minimum 10% net gain in biodiversity – a legal requirement under Schedule 7A of the Town and Country Planning Act 1990.
The Challenge
The site, a residential property with a garden, presented a mix of habitats including sealed surfaces (the dwelling, drive, parking, paths, and patio), a vegetated garden (lawn, shrubs, and small trees), and two medium-sized trees.
Using the Defra Statutory Metric – the standard tool for measuring biodiversity change in England – we needed to determine whether the post-development habitat value would meet the mandatory 10% net gain target, and if not, identify the shortfall and propose a solution.
Our Approach
Our process began with a detailed habitat survey conducted in December 2024 by our expert ecologist, Miguel Canovas CEnv, alongside an ecological appraisal. This was complemented by an Arboricultural Report, ensuring a comprehensive baseline of the site’s pre-development conditions.
We categorised the habitats as follows:
- Sealed surfaces: 1860 m2, contributing 0 biodiversity units.
- Vegetated garden: 680 m2, delivering 0.37 units.
- Two medium trees: 326 m2, assessed as moderate condition, contributing 0.26 units.
Total pre-development biodiversity value: 0.63 units.
Next, we evaluated the post-development scenario, which included:
- Sealed surfaces: Increased to 1950 m2 (0 units).
- Vegetated garden: Reduced to 600 m2 (0.38 units).
- Trees: Removed from the site, reducing their contribution to zero.
Total post-development biodiversity value: 0.38 units.
The result? A net loss of 40.8% – below the required 10% gain (0.70 units), leaving a deficit of 0.32 units.
The Solution
Our analysis confirmed that on-site measures alone wouldn’t achieve the mandatory 10% net gain. To bridge the gap, we recommended the purchase of 0.32 off-site biodiversity units. This pragmatic solution leverages the flexibility of current legislation, which allows units to be purchased after planning approval.
We provided clear guidance to the client, referencing official resources such as the UK Government’s Biodiversity Net Gain guidance, ensuring they understood the next steps and timelines for compliance.
Outcome
This project demonstrates the power of precise ecological assessment and strategic planning. By combining fieldwork, the Defra Statutory Metric, and expert recommendations, we enabled our client to move forward confidently with their development plans while meeting legal biodiversity obligations. The purchase of off-site units not only offsets the on-site loss but contributes to broader conservation efforts – a win for both the project and the environment.
Why It Matters
Under the Environment Act 2021, Biodiversity Net Gain is no longer optional – it’s a cornerstone of sustainable development in England.
For more information on how we can support your project with BNG assessments, contact us today!