Updated: July 2026
Important changes to England’s mandatory Biodiversity Net Gain requirements come into force on 6 August 2026. The changes introduce a new exemption for qualifying sites of 0.2 hectares or less, alter the rules for temporary development and remove the existing exemption for self-build and custom-build projects.
This guide explains what is changing, which developments may be exempt and why ecological advice may still be required even where mandatory Biodiversity Net Gain does not apply.
Contents
- What is Biodiversity Net Gain?
- What is changing on 6 August 2026?
- The new 0.2-hectare exemption
- What if priority habitat is present?
- Changes for self-build development
- Temporary development
- Changes for minor development
- Will ecological surveys still be needed?
- What about existing applications?
- How Crossman Ecology can help
- Frequently asked questions
What is Biodiversity Net Gain?
Biodiversity Net Gain, commonly shortened to BNG, is a planning requirement intended to leave biodiversity in a measurably better condition than it was before development.
Unless an exemption applies, developments covered by the statutory framework must normally achieve at least a 10% increase in biodiversity value. This is calculated using the statutory biodiversity metric.
The required gain may be delivered through:
- retaining, creating or enhancing habitats within the development site;
- using registered off-site biodiversity units; or
- purchasing statutory biodiversity credits as a last resort.
What is changing on 6 August 2026?
The main changes applying to relevant planning applications made on or after 6 August 2026 are:
- A new BNG exemption for qualifying development sites of 0.2 hectares or less.
- A new exemption for certain temporary developments permitted for five years or less.
- The removal of the existing exemption for self-build and custom-build development.
- Changes to the biodiversity gain hierarchy for development that is not classed as major development.
Important: The 0.2-hectare exemption is based on the development site area. It is not simply a threshold based on the area of habitat being removed.
The new 0.2-hectare BNG exemption
From 6 August 2026, mandatory Biodiversity Net Gain will generally not apply to a planning application where the relevant development site is 0.2 hectares or smaller, provided the development does not affect onsite priority habitat.
A site area of 0.2 hectares is equivalent to:
- 2,000 square metres;
- approximately one-third of a typical football pitch; or
- a rectangular site measuring approximately 40 metres by 50 metres.
This exemption is likely to apply to many smaller projects, including some:
- single-house developments;
- small residential schemes;
- barn conversions;
- commercial extensions;
- agricultural developments; and
- changes of use involving limited land.
However, a development is not automatically exempt simply because it appears small. The correct application boundary and the presence of priority habitat must both be considered.
What if priority habitat is present?
The new small-site exemption does not apply where the development affects onsite priority habitat.
Priority habitats are habitats identified as being of particular importance for biodiversity conservation. Examples can include:
- lowland meadows;
- traditional orchards;
- lowland calcareous grassland;
- coastal and floodplain grazing marsh;
- certain ponds;
- ancient and species-rich hedgerows; and
- some types of woodland.
Identifying priority habitat is not always straightforward. A site that looks like an ordinary field, paddock, garden or area of scrub may contain habitat with greater ecological importance than is immediately apparent.
Where there is uncertainty, an ecological site assessment can establish whether priority habitat is present and whether the exemption can reasonably be relied upon.
BNG changes for self-build and custom-build development
One of the most important changes is the removal of the existing exemption for qualifying self-build and custom-build development.
From 6 August 2026, a project will not be exempt from BNG merely because it is a self-build or custom-build development.
However, many individual self-build plots may fall within the new 0.2-hectare site-area exemption. This means the size of the site and the habitats affected will become particularly important.
Example: A self-build dwelling on a 1,500m² site may qualify for the new area-based exemption, provided priority habitat is not affected. A self-build dwelling on a 3,000m² site would not qualify for that exemption solely based on site size.
New exemption for temporary development
A further exemption is being introduced for certain developments granted temporary planning permission for a period of five years or less.
As with the small-site exemption, the temporary development exemption will not apply where onsite priority habitat is affected.
The exemption may be relevant to projects such as temporary buildings, compounds, uses of land or other time-limited planning permissions. The specific circumstances of the application should still be reviewed before an exemption is claimed.
Changes to the biodiversity gain hierarchy for minor development
The biodiversity gain hierarchy determines the order in which developers should consider ways of delivering BNG.
For development that is not classed as major development, the amended rules place:
- the creation of onsite habitat;
- the enhancement of onsite habitat; and
- the use of registered off-site biodiversity gains
at the same level of preference. Statutory biodiversity credits remain a last-resort option.
In practice, this should give smaller developments greater flexibility to purchase off-site biodiversity units where providing appropriate habitats within a constrained site would be impractical or disproportionately complex.
Does a BNG exemption mean ecological surveys are no longer needed?
No.
Biodiversity Net Gain is only one part of the ecological planning process. An exemption from mandatory BNG does not remove the need to consider:
- protected species legislation;
- designated wildlife sites;
- local planning policy;
- the National Planning Policy Framework;
- priority habitats and species;
- the mitigation hierarchy; or
- locally required biodiversity enhancements.
Depending on the site and proposals, ecological work could still include:
- a Preliminary Ecological Appraisal;
- a Preliminary Roost Assessment or bat survey;
- bat emergence surveys;
- great crested newt assessment or eDNA testing;
- reptile surveys;
- dormouse surveys;
- badger surveys;
- breeding bird surveys; or
- an Ecological Impact Assessment.
A local planning authority may therefore still request ecological information even when the development is exempt from the statutory BNG condition.
What happens to applications submitted before 6 August 2026?
The amended rules apply to relevant planning applications made on or after 6 August 2026.
Applications made before that date will generally continue to be considered under the previous BNG arrangements. Applicants with a project close to the threshold should therefore consider the application date when planning their ecological work and submission programme.
Delaying an application solely to obtain an exemption may not always be advisable. Seasonal ecological surveys, design requirements and other planning constraints should also be taken into account.
How do I know whether my development is exempt?
Before relying on the new exemption, applicants should establish:
- the correct red-line area of the development site;
- whether the site is 0.2 hectares or less;
- whether any onsite priority habitat will be affected;
- whether another exemption or exclusion applies;
- the date on which the planning application will be made; and
- whether ecological information is required for another reason.
Where the position is unclear, early advice can prevent unnecessary metric calculations while reducing the risk of an application being delayed because insufficient ecological information has been submitted.
How Crossman Ecology can help
Crossman Ecology advises homeowners, architects, planning consultants and developers across the South of England.
We can review your site and proposals to determine:
- whether the new 0.2-hectare exemption is likely to apply;
- whether priority habitat could be affected;
- whether a BNG assessment and biodiversity metric are required;
- what protected species surveys may be needed;
- whether BNG can be delivered onsite; and
- whether off-site biodiversity units are likely to be required.
Our aim is to provide clear advice at an early stage, so that you understand the likely ecological requirements and costs before submitting your planning application.
Unsure whether your development needs BNG?
Send us your site location and proposed plans. We can review the project and advise what ecological work is likely to be required.
Frequently asked questions about the 2026 BNG changes
When do the new Biodiversity Net Gain rules start?
The changes apply to relevant planning applications made on or after 6 August 2026.
Are all sites below 0.2 hectares exempt from BNG?
Not necessarily. The new exemption will not apply if the development affects onsite priority habitat. Other details of the proposal and application may also need to be considered.
Does the 0.2-hectare threshold relate to the building footprint?
No. The exemption concerns the area of the development site, rather than only the footprint of the proposed building.
How many square metres are in 0.2 hectares?
There are 2,000 square metres in 0.2 hectares.
Will self-build homes be exempt from BNG?
The specific self-build and custom-build exemption is being removed. A self-build project may nevertheless qualify for the new 0.2-hectare exemption if it meets the relevant criteria.
Do I still need a bat survey if my development is exempt from BNG?
Potentially, yes. Bats and their roosts remain legally protected. The need for a bat survey depends on the buildings, trees, habitats and proposed works, not on whether mandatory BNG applies.
Can a small development use off-site biodiversity units?
Where BNG still applies, the amended biodiversity gain hierarchy gives non-major development greater flexibility to use registered off-site biodiversity gains. Statutory credits remain a last resort.
Do local planning authorities still expect biodiversity enhancements?
They may do. An exemption from statutory BNG does not necessarily remove requirements arising from planning policy, protected species mitigation or site-specific ecological considerations.
Official guidance
Further information is available through the Government’s Biodiversity Net Gain guidance:
This article provides general guidance and does not constitute legal or planning advice. The application of an exemption will depend on the circumstances of the individual development.