The biodiversity net gain (BNG) rules mean developers are now legally required to increase net biodiversity by 10 per cent on residential developments with either 10 or more dwellings or where the site is larger than 0.5ha. The rules also apply to commercial developments where the site is larger than 1ha.
Now mandatory under the Environment Act, the BNG rules are designed to ensure development has a ‘measurably positive impact’ on biodiversity compared with what was there before in order to ‘halt species decline by 2030’.
The rules do not apply to planning applications submitted before 12 February.
Biodiversity on a site will be measured via a statutory biodiversity metric, which is a standardised way of measuring the units of biodiversity – and range of habitats – on any given site, and the units needed to achieve 10 per cent BNG.
The Department for Environment, Food & Rural Affairs (Defra) has suggested three ways developers can deliver 10 per cent BNG:
- By enhancing and restoring biodiversity on-site, ie within the red-line boundary of a development site.
- By delivering a mix of on-site and off-site biodiversity, ie with biodiversity gains on land they own outside the development site.
- Only as a last resort, by purchasing statutory biodiversity credits from the government, which ‘will use the revenue to invest in habitat creation in England’.
While developers can combine more than one of these options, they must follow the steps in order, described as the biodiversity gain hierarchy.
Sustainable construction consultant Saul Humphrey told the AJ that ‘early consideration of a site’s existing ecological characteristics will be absolutely necessary’ for architects.
He added any new site’s master plan and development density ‘may have to be limited’ to meet the BNG rules, explaining ‘it is probable that plans will have to change – or as a last and costly resort, off-site solutions be found’ to meet the 10 per cent metric.
‘Avoiding any biodiversity loss in the first place is the target,’ explained Humphrey.
The sustainability expert predicts the ‘initial response’ to brownfield sites from developers will be the introduction of green roofs, while greenfield sites will be more challenging, and ‘early dialogue with ecologists will be critical’.
He explained: ‘In the short-term I expect greater rewilding, the introduction of wetlands, more landscaping, hedgerows and green corridors will all become quite ubiquitous.’
As well as major development sites, from April the new rules will also apply to small development sites, and to ‘nationally significant infrastructure projects’ from late November 2025.
Defra has confirmed small developments will be defined as residential development where the number of dwellings is between one and nine, or if unknown where the site area is less than 0.5ha, and commercial developments of less than 1,000m² GIA, or less than 1ha overall across the site.
The government says the changes ‘will be fundamental in helping the country meet our target to halt the decline in species abundance by 2030’.
It has committed a £10.6 million funding injection ‘to help local authorities recruit and expand ecologist teams, investing in green jobs and increasing capacity to create new wildlife-rich habitats alongside developments’.
Natural England chair Tony Juniper described BNG coming into force as ‘a key moment on our path to halting the decline of nature, enabling developers to make a positive contribution through creating new habitats, increasing access to green spaces, and building healthy and resilient places for people to live and work’.
Rob Perrins, chief executive of developer Berkeley Group, which became the first homebuilder to commit to achieving biodiversity net gain on every site in 2017 (and has since calculated BNG on 55 masterplans) described the new law as ‘a positive step for the homebuilding industry [which] will bring nature back to our towns and cities’.
He added: ‘The challenge now is to make sure that developers and planning authorities take a positive and collaborative approach to delivering biodiversity net gain across the country.’