Changes to BNG Coming in August 2026
New statutory regulations affecting biodiversity net gain (BNG) under the Town and Country Planning Act 1990 (TCPA) and the Environment Act 2021 are coming into force on 6th August 2026.
Following DEFRA’s major consultation response aimed at easing administrative burdens and accelerating housing delivery for SME housebuilders, the updates specifically target smaller sites and minor developments.
Background to the BNG Reforms
Based on the standard BNG framework, developers must establish a development site’s pre-development baseline biodiversity value at the pre-application stage.
Comparing the baseline against the proposed post-development layout confirms if the scheme results in a net loss or gain, with a formal biodiversity gain plan proving how a minimum 10% net gain will be achieved.
Ecological modelling can be worked into major developments, but feedback from local planning authorities and SME housebuilders has shown that mandatory BNG created disproportionate financial bottlenecks on small plots.
Between high baseline survey costs, complex metric calculations and 30-year site management obligations, small-scale developments inadvertently faced numerous stumbling blocks.
Confirmed Changes Coming 6 August 2026
New 0.2 Hectare Area-Based Exemption
The primary change for housebuilders is a new area-based exemption for developments with a total red-line site boundary of 0.2 hectares or less.
It means that qualifying sites are exempt from mandatory BNG using the statutory metric, meaning formal calculations and 10% gain conditions are not required.
According to DEFRA, the exemption could cover around 50% of residential planning applications across England. Developers must, however, watch out for two critical thresholds:
- Red-Line Boundary Rule: To qualify under this exemption category, the entire red-line boundary (RLB) of the application must be under 0.2 hectares, meaning that all impacts within the RLB count – not just the net developable area.
- Priority Habitat Safeguard: No priority habitats (such as deciduous woodland) can be impacted. If a priority habitat exists on site but will be retained and protected in full, the site remains exempt – it is only if the habitat will be impacted that the exemption is lost.
That said, applicants still have an obligation under the National Planning Policy Framework (NPPF) to avoid and minimise on-site ecological harm first and demonstrate non-quantified net gains through nature-friendly features, and statutory credits remain a strict last resort.
The changes will come as a welcome relief to SME housebuilders who are already grappling with rising costs in other areas. It is, however, worth being crystal clear on what the new 0.2ha exemption covers and what it doesn’t to avoid an unwelcome BNG surprise late in the game.
If any on-site priority habitat is impacted by the works, the development will not be exempt. The priority habitat definition is far broader than many developers expect; the most likely priority habitat on-site is hedgerow, as any hedgerow made up of predominantly native species may be classified as important. This means that even cutting through a small section of hedgerow for a new visibility splay may trigger BNG.
Our advice to developers is unchanged: seek ecological advice as early as possible to avoid costly delays and offsite unit costs.
Nicole Gullan MRSB TechArborA, Associate Director at Arbtech
Equal Preference for Minor Schemes (>0.2ha)
For non-exempt minor schemes with sites of over 0.2 hectares up to major development thresholds, DEFRA is updating the biodiversity gain hierarchy.
On-site and off-site BNG units are considered equal, but the mitigation hierarchy still applies. Due to this, developers need to demonstrate that they’ve made an effort to achieve BNG on-site before moving to off-site solutions.
Housebuilders no longer need to prove that on-site delivery is impossible before resorting to purchasing off-site units, protecting the usable developable space.
Extended Exemption for Temporary Permissions
The existing exemption for temporary planning permissions has been extended from 2 years to up to 5 years, as long as the land can be reinstated to its former condition.
Integration of Self-Build and Custom-Build Plots
The standalone exemption for self-build and custom-build schemes is being removed.
Instead, single-dwelling self-build sites are now expected to be covered under the broader 0.2 hectare area-based exemption.
Larger Sites and Future Changes
Although changes are confirmed for August, other upcoming policy milestones are coming:
Brownfield Residential Housing (Up to 2.5 Hectares)
DEFRA’s consultation (Considering a Targeted Exemption for Residential Brownfield Development) closed in June 2026.
Government responses are expected early next year. Until then, there will be a lot of speculation surrounding the definition of brownfield land, the size of the exemption, and the finer details of how the change will apply.
Major Infrastructure and Nationally Significant Infrastructure Projects (NSIPs)
Mandatory BNG requirements for NSIPs take effect in November 2026.
Conservation and Municipal Exemptions
Dedicated exemptions for conservation-led habitat restoration projects (e.g. dedicated nature reserves) and developments that enhance municipal public parks, playing fields and gardens will follow later in 2026.
Get Early Advice from Our Team
The 0.2 hectare exemption could potentially save SME developers thousands in the cost of biodiversity net gain surveying and monitoring. Assuming your site is exempt without the correct verification, however, could be a costly mistake.
A site boundary slightly over 0.2 hectares or the presence of an unidentified priority habitat can immediately pull your project back into mandatory BNG territory. Trying to resolve BNG at the final hour creates unnecessary planning friction, delays consent and inflates project costs.
If an ecologist or planning officer discovers a biodiversity net gain requirement right before your submission deadline, scrambling to shoehorn metric calculations or off-site units in at the last minute could create severe delays and unexpected costs.
Refer to Arbtech for Help with Protecting Your Pipeline
As the country’s leading ecology and biodiversity net gain consultancy, we help developers, planners and landowners navigate regulatory updates with total confidence.
If your development site isn’t exempt, we can deliver rapid baseline surveys, clear metric plans and hassle-free off-site unit sourcing. We can also review your red-line boundaries and site baseline early to confirm whether you qualify for the 0.2 hectare exemption for you to submit.
For expert BNG advice, a free quote for the services you need or an exemption statement for your planning officer, contact Arbtech via our website, over email or by calling us directly.
We’re also running a series of invitation-only BNG briefings for housebuilders across the UK in autumn. The talks have limited spaces, so please contact Nicole Gullan at [email protected] as soon as you can to receive an invite and secure your place.
