What has changed?
Mandatory BNG has required most new developments in England to deliver a 10% increase in biodiversity since February 2024 (major sites) and April 2024 (small sites). For small builders, the cost of ecological surveys, metric calculations and off-site units was often out of proportion to the scheme.
Following its consultation on BNG for minor, medium and brownfield development, the government has introduced an area-based exemption. If your application site is 0.2 hectares or smaller, BNG does not apply. Defra expects this to remove around half of the residential planning permissions that were previously caught.
How the 0.2 hectare test works
The test covers the whole area inside the red line boundary of your planning application, not just the green or habitat areas. Existing buildings, hardstanding and gardens all count towards the 0.2 hectares.
That makes the red line important. It must include all land needed to carry out the development, such as access and visibility splays, so it can’t simply be drawn tightly to squeeze under the threshold.
The catch: priority habitat
The exemption does not apply if the development would negatively impact onsite priority habitat, which is habitat of principal importance for conservation in England. On small sites this most often means features such as hedgerows, traditional orchards or certain ponds. The same caveat applies to the de minimis and temporary development exemptions.
An early ecological check is still worthwhile on greenfield or garden-land sites. It is far cheaper to confirm there is no priority habitat, or design to avoid it, than to discover it after submission.
Self-build and custom build
The previous exemption for self-build and custom build housing has been removed. Most single self-build plots are under 0.2 hectares and remain exempt under the new test. Larger plots, or schemes that affect priority habitat, may now need to deliver BNG.
Temporary development
A new exemption covers temporary development where the land will be reinstated within 5 years or less, again unless priority habitat is negatively impacted. It suits construction compounds, temporary uses and meanwhile projects.
What stays the same
- Householder applications (extensions, loft conversions, outbuildings) remain exempt.
- The de minimis exemption remains for development affecting less than 25 m² of onsite habitat or 5 metres of linear habitat such as hedgerows.
- Development under permitted development rights remains outside BNG.
- Sites over 0.2 hectares still need to deliver 10% BNG. Defra has said minor sites can go straight to off-site provision in the first instance.
Applications already in the system
The exemption applies only to applications made on or after 6 August 2026. A small-site application submitted before then is still assessed under the old rules, even if it hasn’t been decided.
In some cases it may be worth withdrawing and resubmitting to benefit from the exemption. Whether that makes sense depends on the stage of the application, fees, timescales and any change in policy, so take advice before acting.
Want advice on your site?
Tell us what you’re planning and we’ll explain where you stand, in plain English.
Sources
- GOV.UK: Biodiversity net gain: exempt developments
- Defra: BNG amendments and transitional arrangements published (14 July 2026)
- The Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026
- GOV.UK: Government response on BNG for minor, medium and brownfield development
This article is general information about planning in England at the date shown. It is not advice on any particular site, and the law and policy may have changed since. Please speak to us before relying on it.