To achieve biodiversity net gain, a project must incorporate a measurable increase in natural habitat over and above what is lost. It can be achieved on-site, off-site, or through a combination of measures.

The Chartered Institute of Ecology and Environmental Management (CIEEM) defines Biodiversity Net Gain as:

“An approach to development that leaves biodiversity in a better state than before.”

With the Environment Bill now law, there is a mandatory 10% biodiversity net gain requirement for new development projects. Developers will need to submit a biodiversity net gain plan alongside the usual planning application documents. Some local planning authorities are even asking for more than the legally required 10% net gain.

If net gain must be achieved off-site, the local authority will want any off-site improvements secured through a planning obligation or conservation covenant for at least 30 years.

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The mitigation hierarchy

Tackling biodiversity decline

Despite updates to policy, biodiversity is declining in the UK. The National Biodiversity Network’s State of Nature 2019 report outlines a 13% decrease in the abundance of species between 1970 and 2016.

To tackle this decline, developments should aim to follow this mitigation hierarchy:


The first option is to avoid any negative impacts on the habitat if possible. Examples include finding an alternative site, retaining habitat features, or changing work timings. This is the most preferred option.


The second option is to apply mitigation measures to reduce impacts to the point where they have no adverse effects.


If avoidance and mitigation is not achievable, the project should compensate for residual losses of biodiversity.


As a last resort only, offset measures are used when loss cannot be compensated for on site.

Calculating biodiversity net gain

Biodiversity units

Biodiversity itself isn’t measurable so we use units to understand the biodiversity value of a site. These take into account the size, location, and quality of a habitat. A biodiversity metric can calculate the number of units so we can understand the impact a development will have. This allows us to define any required offset action.

The use of a biodiversity metric is a requirement under the Environment Act.

At ADAS, we use Natural England’s Metric 3.0 Calculation tool, which is currently industry standard.

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Designing for Net Gain

By considering net gain as early as possible in the design process, you can reduce the risk of completing a scheme with a net loss. Creating a development with a net loss is not only a risk on the local biodiversity, but it could result in substantial offset costs.

At ADAS, we have a diverse team of biodiversity net gain experts to help you meet any biodiversity planning condition to achieve planning permission. We can assist with every stage, including:

Data collection

Our CIEEM accredited ecologists will visit the site to carry out a baseline survey and a habitat-condition assessment. They will also undertake desk-based studies to gather all the relevant information. These can be done alongside a preliminary ecological appraisal for the proposed development.

Data input

Our geographic information system (GIS) team will create accurate habitat measurements based on initial surveys. We will then feed this into the 3.0 metric to produce a biodiversity baseline value for the site. The proposed development will also be inputted to produce a final biodiversity value for the finished project.


Our landscape design team will inform you of any potential net losses as early as possible in the design process. We can also provide development plan recommendations on what habitats could work and where they should be located. While drawing up the design, we can layout the site in a way that maximises net gain.


Our team of Landscape Architects will work with you and the ecologists to design a scheme for net gain. Whether the initial calculations show a gain or a loss, the landscape team will aim to maximise the biodiversity output for the development.


On completion of the design process and finalisation of the calculations, we will produce a concise and robust biodiversity assessment report.

If it’s not possible to achieve Net Gain on-site

Unfortunately, it is not always possible to achieve net gain on a development. We can assist with finding a suitable off-site location to offset the loss. By working closely with the local authorities and landowners, we can ensure any long term requirements are met.

Implementation and long-term management

Under the new law, any habitats created for biodiversity net gain will need to be protected and managed as agreed for a minimum of 30 years.

Our team of experts will produce a long term management plan that will provide all the information and data needed to help achieve a successful programme.

Our Habitat Management team can help you with the implement any habitat improvements on site and assist with long-term site management.

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