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Biodiversity net gain (BNG) laws have been introduced by the government throughout England to ensure that housebuilding developments do not damage wildlife habitats. BNG aims to improve the biodiversity of the surrounding land by 10% upon the build’s completion. The new law is part of the government’s Environment Act (2021) and sets out to quantifiably improve ecosystems throughout the UK.
The word biodiversity refers to the variety of living organisms that are present in a particular habitat. This includes animals (such as birds, bats and moles), insects, plants, bacteria and fungi – all of which play a fundamental role in creating a heathy, happy local ecosystem.
Actively promoting the growth and protection of these living organisms throughout development projects will preserve biodiversity for both current and future generations.
So, what does biodiversity net gain mean for self builders looking to build their own home? Here are the key details you need to know.
As of the 12th February 2024, it became a legal requirement achieve an increase in the biodiversity of a building development’s area by 10% upon its completion. This means that the development will positively impact the local environment.
A site’s biodiversity value can be measured in standardised biodiversity units. This depends on features such as the size, quality, location and type of site. These biodiversity units can be lost when undertaking a housebuilding project or generated by promoting growth of the local ecosystem through initiatives such as planting or conservation.
The government has introduced a statutory (official) biodiversity metric. This is used to measure how many units a habitat contains before development, as well as how many units are needed to replace lost habitat and to achieve 10% biodiversity net gain.
CLICK HERE TO USE THE GOVERNMENT’S BIODIVERSITY METRIC TOOL
You can reach the 10% net gain in biodiversity by adopting a variety of measures. For example, you could:
The basic principle of preserving and encouraging biodiverse habitats is something to be encouraged. However, developing and implementing BNG plans can be complex and costly – potentially adding a significant burden that large developers can bear much more easily than self builders.
When you apply to your local planning authority for planning permission for your project, you will need to confirm whether your development is exempt from biodiversity net gain (BNG) – keep scrolling to find out more about exemptions.
If your project isn’t exempt from BNG rules, you’ll have to provide details on how you’re planning on meeting the BNG objective, including information about the site-specific enhancements that you are going to make.
Toby Diggens and Bella Lowes restored and rebuilt a derelict barn in Dorset under the Living Building Challenge, which celebrates the wider setting of a building and its ecological impact. This encouraged them to embrace natural materials and a sensitive design both inside and out, giving back to the environment throughout the build. “We chose mostly native plants, plus European species from similar landscapes, and left some bare ground for solitary bees and blow-ins,” says Toby. Photo: Simon Burt
If your local planning authority grants your project planning permission, you’ll need to put together a comprehensive plan, with supporting evidence, demonstrating how you will achieve the 10% increase in biodiversity. The local planning authority will then either approve or refuse your biodiversity net gain plan within 8 weeks. You won’t be able to start your build until the authority has come to a decision.
This plan must be managed and maintained for 30 years, commencing on the date you complete the development. If you do not meet these requirements, then the local planning authority could take action.
FIND YOUR LOCAL PLANNING AUTHORITY
The introduction of biodiversity net gain laws aims to cover the majority of housebuilding developments. However, there are certain exemptions. These include:
As of the 6th August 2026, the Biodiversity Net Gain exemption for self build and custom build developments is no longer in valid.
If your planning application was submitted before the 6th August 2026, the previous exemption may still apply under transitional arrangements. Under these rules, bespoke self build homes and small custom build developments were exempt from biodiversity net gain, provided they met the following conditions:
Martin Gaine is one of Build It’s planning experts. He runs planning consultancy Just Planning. A former case officer, he has experience on both sides of the planning divide and now specialises in helping homeowners win consent at appeal. He is the author of How to Get Planning Permission: An Insider’s Secrets.
The BNG system proved to be a real pain for smaller developers because, even if you’re only proposing a small development, you had to invest in ecology reports and BNG assessments and implement the findings. That could mean additional works on site to improve biodiversity, or the purchase of off-site credits. These reports and consultants created a heavy administrative burden and slowed down the planning process.
Self builders had a better time of it because there was a specific self-build exemption, but that created its own problems. For example, many councils would require that the self-builder enter into a legal agreement so that the council could be sure that the project ended up being a self build. That legal agreement was complicated, delayed the process of getting planning permission, and meant the applicant paying for two sets of legal fees, their own and the council’s. So, whether you were a self builder or not, it was bureaucratic, expensive, complicated and had become a burden on the sector.
The change to the BNG rules is very welcome, because from 6th of August, there is no longer any specific self build exemption, but any site below 0.2 is exempt, provided there is no adverse impact on on-site habitats. Of course, there is the wrinkle that if you’re a self builder with a site over 0.2 hectares, you now become liable where you wouldn’t have before.
The other frustration that has emerged is that the change is not retrospective, so if you have a planning application that was submitted before the 6th of August this year, it still follows the old system. It is very frustrating for people who are midway through the planning application process. Some clients are simply holding off until the 6th of August before making their submission.
Featured image: Toby Diggens and Bella Lowes‘ barn restoration project in Dorset. Photo: Simon Burt
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