What is Biodiversity Net Gain?

And how will it affect new developments…

As we begin the new year 2024, we eagerly anticipate the challenges that this year will bring, beginning with the implementation of new Biodiversity Net Gain (BNG) regulations scheduled to take effect this January. Starting then, all developments in England falling under the Town and Country Planning Act 1990 will need to evaluate the existing biodiversity value of on-site natural habitats to guarantee compliance with the 10% Biodiversity Net Gain once the development or project reaches completion.

As part of the initial plans to achieve biodiversity net gain, a development must show evidence that the development will increase the biodiversity value of a site by at least 10%. This statistic is presented in the value of a biodiversity net gain metric called 'biodiversity units'.

So… What is Biodiversity Net Gain (BNG)?

BNG is a statutory approach to development to leave biodiversity in a measurably better state than it was before.

Why do we need added complexity to new developments?

Although certain sites are protected, there are limited mechanisms to value, maintain, enhance or create wider habitats. As a result, habitats continue to be lost to development, reducing nature's ability to connect and thrive. 

Image source: biofarm.co.uk

What sort of planning applications are affected?

From January 2024, all major sites will comply with the Town and Country Planning Act. From April 2024, minor applications will comply, and then in 2025, they will apply to Nationally Significant Infrastructure Projects (NSIPs). See below for the criteria for a small site.

A raft of new guidance and secondary legislation has recently been released in draft form, and one of them sets out a longer list of exemptions, including Householder applications, permitted development, and a few others. Find more information on the government website here.

What will need to be provided?

At pre-planning, we'd work closely with an ecologist who would visit your site and prepare an initial assessment of the current site. Together, we'd look at the project proposal and determine whether you're looking at a net gain or loss. We'd consider if any improvements could be made regarding green infrastructure design and if you need to offset to hit the minimum statutory 10% BNG. The ecologist will also consider the proposal regarding longer-term obligations, as it is a 30-year commitment on and off-site. Net gains can be secured legally, likely through Section 106, and the BNG proposal will be a detailed habitat management plan.

Small scale developments - Small Site Metric (SSM)

Small sites, defined as residential developments with 1 to 9 dwellings or sites with an area of less than 0.5 hectares, are required to achieve a Biodiversity Net Gain (BNG) of 10% starting from April 2024. They cover:

• Commercial development where floor space created is less than 1,000 square metres, or total site area is less than 1 hectare 

• Development that is not the mining and working of minerals or the use of land for mineral-working deposits 

• Development that is not waste development 

• If your project qualifies as a small site, you can use a simpler version of the metric tool called the small sites metric (SSM).  

However, where the following are present, the site won't be considered under the small site metric:

• Habitats not available in the SSM

• Priority habitats (excluding some hedgerows and arable field margins) 

• Protected sites

• European protected species

Large-scale developments - Biodiversity Metric

Any sites beyond the small-scale metric will be classified as large developments and will be required to achieve a Biodiversity Net Gain (BNG) of 10% starting from January 2024.

How is Biodiversity measured?

When an ecologist comes to site, they will assess it in line with Natural England's Biodiversity Metric 4.0. We've outlined this below:

• Distinctiveness – this includes species richness, diversity, rarity and whether it supports species rarely found in other habitats

• Condition – the quality of the habitat

• Connectivity – how connected the habitat is to other similar habitats

• Strategic significance – whether the habitat occurs within an ecologically desirable area and has been identified by a local strategy.

The Metric also measures all types of habitats, including: 

• Grassland 

• Hedgerows 

• Lakes  

• Woodland 

• Watercourses such as rivers and streams 

The biodiversity metric measures the biodiversity value of habitats by calculating the number of biodiversity units. It calculates: 

• How many units a habitat contains before development takes place 

• How many units are needed to replace the units of habitat lost and to achieve 10% BNG through the creation or enhancement of habitat 

The calculation also considers other variables such as: 

• Size 

• Quality 

• Location 

• Type

• For created or enhanced habitats 

• Difficulty of creation or enhancement 

• The time it takes a habitat to reach its target condition 

• Distance from the habitat loss  

There are metric tools and guidance for both large and small-scale sites on the following Government website. If you have any concerns or questions about how these regulations might affect you or your development, get in touch today, and the team will help you navigate Biodiversity Net Gain.

What are our thoughts?

At Arbor Architects, we see this legislation as a positive step in the right direction. We feel as Architects it's become imperative that we address biodiversity collapse in the context of climate change. The UK has lost around half of its biodiversity since the Industrial Revolution. Having a standardised mechanism to measure and monitor biodiversity is going to be a powerful tool and will provide a chance to turn this around through habitat restoration.

In our experience it's not always easy to achieve a biodiversity net gain, especially on inner city tight sites. But that being said, is easy the best answer? One could argue it’s not easy to achieve Passivhaus or EnerPHit certification and at Arbor Architects this is something we have embraced in our mission to build more responsibly. 

The new legislation means that at pre-planning stage an ecological assessment of the site will be made and this will establish a baseline from which proposed enhancements of at least 10% Biodiversity net gain can be made within development proposals. For smaller sites the impact of this is likely to be greater as it inevitably adds a layer of complexity and cost to projects, but accountability is important.

We also know how important the natural environment is to our wellbeing, so these changes can only be a good thing. At Arbor Architects we have partnered with the Herefordshire Wildlife Trust to demonstrate our commitment to local wildlife habitat renewal and have the ambition to exceed the 10% BNG.