From 6 August 2026, the biodiversity gain hierarchy changes for minor developments in England: smaller schemes will be able to buy off-site biodiversity units without first proving that on-site habitat delivery was ruled out. The change comes from the Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026, made on 9 July 2026 and in force from 6 August 2026 — and it is one of the most practical cost-savers in this summer's package of BNG reforms.
This post explains what the biodiversity gain hierarchy is, exactly what changes for minor sites, the transitional arrangements that decide which rules your application falls under, and how to plan a compliant sustainability statement either side of the switch.
What is the biodiversity gain hierarchy?
Mandatory biodiversity net gain under the Environment Act 2021 requires most developments to deliver a 10% improvement in biodiversity value. The biodiversity gain hierarchy governs where that gain must be delivered, in order of preference:
- On-site — habitat created or enhanced within the red line boundary;
- Off-site — registered biodiversity gain sites elsewhere, or purchased off-site units;
- Statutory biodiversity credits — bought from government as a genuine last resort, priced deliberately high to discourage use.
Until now, every applicant — from a national housebuilder to someone building two houses on a backland plot — was expected to work down that ladder, evidencing why on-site delivery could not reasonably provide the gain before relying on off-site units. Our comparison of on-site vs off-site BNG units explains the trade-offs.
What changes on 6 August 2026?
For minor development only, the 2026 Regulations revise the hierarchy so that off-site biodiversity gains are treated on an equal footing with on-site creation and enhancement. In practice, a minor scheme can go straight to purchasing off-site units without demonstrating that on-site provision was considered and rejected first.
According to Defra's announcement of the amendments and transitional arrangements, the aim is flexibility where on-site delivery is genuinely constrained — which is the norm on small sites, where a strip of enhanced grassland squeezed around a house plot often delivers poor ecological outcomes at disproportionate cost, and then has to be legally secured and managed for 30 years.
Two important limits:
- Statutory credits remain the last resort for developments of every size — the equal footing applies between on-site and off-site delivery only.
- Major developments keep the full hierarchy — they must still prioritise on-site delivery and evidence the steps down the ladder.
Which developments count as minor?
Minor development for these purposes follows the established planning definition: residential schemes of fewer than 10 dwellings (or under 0.5 hectares where the number is unknown), and non-residential schemes creating less than 1,000 square metres of floorspace or under 1 hectare of site area. Many of the smallest sites will now fall out of mandatory BNG altogether under the new 0.2 hectare exemption — the hierarchy change matters for the band above that: too big to be exempt, too small to make on-site delivery sensible.
Transitional arrangements: which rules apply to your application?
The Regulations include transitional provisions, and the operative date is the date your planning application is made:
- Applications submitted before 6 August 2026 are determined under the existing rules — the full hierarchy, the current exemptions, and (for self-builders) the outgoing self-build exemption.
- Applications submitted on or after 6 August 2026 fall under the new regime: revised hierarchy for minor development, the 0.2 hectare exemption, and no self-build exemption.
That cut-off pulls in two directions. A self-build project that would lose its exemption has a strong incentive to submit before 6 August — see our explainer on the end of the self-build BNG exemption. A minor scheme that would benefit from the 0.2 hectare exemption or the straight-to-off-site route may prefer to wait and submit after. If your application is near the boundary, run both scenarios before choosing a submission date — our free BNG exemption checker covers the August 2026 rules.
What does the change mean in practice?
- Simpler biodiversity gain plans. Minor applicants can propose an off-site unit purchase as the primary strategy, cutting survey-to-strategy time and removing marginal on-site habitat schemes that existed only to satisfy the hierarchy.
- Lower long-term liabilities. Off-site units transfer the 30-year management obligation to a habitat bank, rather than leaving it with a homeowner or small developer.
- Costs become more predictable. Off-site unit prices vary by habitat type and location but are quoted up front; our summary of statutory credit prices shows why the government-backed fallback remains the expensive option.
- Ecology input is still needed. The baseline still has to be measured with the statutory metric, priority habitats still bar the new exemption, and the 10% requirement itself is unchanged.
Key takeaways
- From 6 August 2026, minor developments can use off-site BNG units on an equal footing with on-site delivery — no need to rule out on-site provision first.
- The change comes from the Biodiversity Gain (TCP) (Amendments and Transitional Provisions) (England) Regulations 2026, made 9 July 2026.
- Statutory credits stay the last resort, and major developments keep the full hierarchy.
- The rules that apply are fixed by your application submission date — check whether submitting before or after 6 August works better for your site.
How Fortress Associates can help
Fortress Associates' automated sustainability statement service produces a free, site-specific report in minutes for any UK local authority — covering 10% biodiversity net gain under the Environment Act 2021, water efficiency against the 110 litres per person per day standard, urban greening and BREEAM where required. It reflects the current BNG rules, including the August 2026 changes, so your planning submission states the right obligations for your application date. Contact us to talk through a site that straddles the transition.
Sources & further reading
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