The Government's small-site BNG changes are now in force. Development within a red-line area of 0.2 hectares or less can qualify for the area-based exemption where onsite priority habitat is not affected. The former self-build and custom-build exemption has been removed for applications made from 6 August 2026.
What changed on 6 August 2026
The Government's small-site BNG changes are now in force. Development within a red-line area of 0.2 hectares or less can qualify for the area-based exemption where onsite priority habitat is not affected. The former self-build and custom-build exemption has been removed for applications made from 6 August 2026.
This changes the position described when the original article was published in April. The threshold concerns the whole red-line site area rather than only the habitat footprint, so applicants still need an accurate boundary and an early ecological check.
The 0.2 hectare exemption
The exemption applies across development types and is expected to remove many small residential permissions from mandatory BNG. In announcing the change, the Government estimated that around half of residential permissions previously subject to mandatory BNG could be exempt, with around 12% fewer baseline units requiring mandatory compensation and an estimated 10% reduction in demand for offsite units.
It does not apply where onsite priority habitat is affected. A small site can therefore remain ecologically complex even when its area is below the threshold. Trees, watercourses, protected species, designated sites and ordinary development-plan biodiversity policies remain relevant. An exemption from mandatory net gain is not an exemption from assessing or mitigating ecological harm.
Self-build and custom-build
The former small-scale self-build and custom-build exemption no longer applies to applications made from 6 August 2026. Many single-dwelling schemes may instead fall within the area-based exemption, but only where its threshold and habitat conditions are met.
Applicants should record which exemption is relied upon and why. A description such as ‘self-build’ is no longer enough to establish the current position.
Minor development is not fully exempt
The Government did not exempt all minor development. A small residential scheme of up to nine dwellings can still require mandatory BNG where the red-line site exceeds 0.2 hectares or the exemption otherwise does not apply. Site area, ecological baseline and the emerging layout should therefore be tested before the scheme is fixed.
For minor development that remains in scope, the rules provide greater flexibility between onsite and registered offsite gains, while statutory biodiversity credits remain a last resort. That can help constrained urban sites where small onsite habitat fragments would be difficult to maintain. The wider mitigation hierarchy continues to require harm to be avoided and mitigated before compensation is considered.
Temporary permissions
A qualifying development granted temporary permission for no more than five years can be exempt. The route is aimed at development that is wholly temporary; it should not be assumed to cover a permanent operation merely because one element is time-limited.
Priority habitat and other ecological controls still need to be checked, and a later proposal to retain the use permanently would require its own assessment.
Brownfield land and open mosaic habitat
Brownfield land can support valuable open mosaic habitat. The small-site exemption does not make that habitat irrelevant, and the presence of priority habitat can prevent reliance on the exemption.
The Government has also been reviewing the metric definition, guidance and condition assessment for open mosaic habitat, together with possible urban habitat categories and proxy habitats. A separate brownfield proposal has been considered for some residential sites. Those technical strands should be checked against the latest final guidance rather than assumed to apply.
A site that looks vacant or previously developed may therefore need competent ecological assessment before acquisition, design or submission decisions are made.
What applicants should do now
Check the application date, red-line area and habitat position against the regulations and current guidance. Where BNG applies, establish the baseline and delivery route early. Where an exemption applies, explain it clearly and submit any ecological evidence still needed to assess the proposal.
Applications already subject to the biodiversity gain condition still require an approved biodiversity gain plan before development begins. The practical planning strategy should address biodiversity together with layout, landscape, drainage, trees and viability.
Rubix Planning commentary
The new threshold makes the system more proportionate for many smaller schemes, but it does not make ecology a late-stage formality. The strongest approach is to identify the route early, record the evidence and design around genuine constraints rather than relying on an exemption label alone.