Biodiversity Net Gain has been one of the biggest changes to the planning system in England in recent years.
But from 6 August 2026, the rules changed significantly. For many homeowners, landowners and small-scale developers, the changes could make smaller development projects considerably simpler.
The headline change is straightforward: development sites measuring 0.2 hectares — 2,000m² — or less are now generally exempt from mandatory Biodiversity Net Gain. There are important exceptions, however, so the size of the site should never be considered in isolation.
What is Biodiversity Net Gain?
Biodiversity Net Gain, usually referred to as BNG, is a planning requirement designed to ensure that qualifying development leaves biodiversity in a measurably better condition than before development took place.
Where mandatory BNG applies, development is normally required to achieve at least 10% Biodiversity Net Gain. The biodiversity value of a site is calculated using the Government's statutory biodiversity metric. This looks at the type, size, condition and strategic importance of habitats rather than simply counting trees or the amount of landscaping proposed.
For developments caught by the legislation, BNG can therefore influence:
- site layout;
- landscaping;
- development capacity;
- ecological survey requirements;
- planning documentation;
- legal agreements;
- project costs; and
- long-term habitat management.
The important new 0.2-hectare exemption
From 6 August 2026, development carried out on a site measuring 0.2 hectares or less is generally exempt from mandatory Biodiversity Net Gain.
The important point is that the calculation relates to the development site within the planning application's red-line boundary. It is not simply the footprint of the proposed building.
For example, a new house might only occupy 150m², but if the planning application includes a 3,000m² site within the red-line boundary, it would not qualify for the new exemption solely on the basis of its small building footprint. This makes the definition of the planning application site an important consideration during early planning feasibility work.
Which developments could benefit?
The change is particularly relevant to smaller developments such as:
- individual new-build houses;
- small infill sites;
- backland development;
- redevelopment of small plots;
- small commercial developments;
- certain conversions requiring planning permission; and
- small developer-led residential schemes.
For developers looking at land across Birmingham, Solihull, Sutton Coldfield, Warwickshire, Worcestershire and the wider West Midlands, this could remove a significant layer of planning complexity from many smaller sites. The Government estimated that the new exemption could remove around half of residential planning permissions previously required to undertake mandatory BNG from the system.
Does every site below 2,000m² automatically qualify?
No. There is an important exception relating to priority habitat. The new exemption cannot normally be relied upon where development would negatively affect priority habitat located within the site.
Examples can include certain species-rich grasslands, traditional orchards, ancient and veteran woodland habitats, ponds, wetlands and particular hedgerow or woodland habitats. This is why a small site should not automatically be assumed to have no ecological constraints.
BNG exemption does not mean ecology can be ignored
Being exempt from mandatory Biodiversity Net Gain does not mean a development is exempt from wider environmental or ecological legislation.
Planning applications may still need to consider protected species, bats, nesting birds, badgers, important trees, hedgerows, designated habitats, Local Wildlife Sites, ancient woodland and other ecological constraints. A local planning authority can still request appropriate ecological information where there is a reasonable ecological issue affecting a site.
Good feasibility work should establish the likely ecological position before detailed design begins. Our planning application service explains how we coordinate the early planning route and supporting information.
What about normal house extensions?
Most ordinary householder development was already exempt from mandatory BNG. This includes typical works to an existing home such as extensions, loft conversions, conservatories and other qualifying householder development.
For most homeowners planning an extension, therefore, the August 2026 changes will have relatively little direct effect. The real significance of the new rules is for new development and smaller development sites.
The self-build rules have changed
Previously, certain small-scale self-build and custom-build housing developments had their own specific BNG exemption. That exemption has now been removed for new planning applications from 6 August 2026. However, many individual self-build projects could still be exempt under the new 0.2-hectare site exemption.
Example A — Small self-build site
A proposed individual house sits within a planning application site of 1,600m². If no priority habitat is negatively affected, the development may qualify for the new 0.2-hectare exemption.
Example B — Large self-build plot
A proposed individual house sits within a 4,000m² plot. Being a self-build project no longer provides its own exemption. BNG will therefore need to be considered unless another exemption applies.
This makes early assessment particularly important for anyone purchasing larger building plots. Explore our new-build homes service for the design, planning and technical stages involved.
What if the site is larger than 0.2 hectares?
A site exceeding 2,000m² is not automatically problematic. It simply means that the new area-based exemption cannot be relied upon. Other exemptions may still be relevant depending on the circumstances.
Where mandatory BNG does apply, the development will normally need to demonstrate a minimum 10% Biodiversity Net Gain. That gain can potentially be achieved through on-site biodiversity, registered off-site biodiversity units or, as a last resort, statutory biodiversity credits.
Another useful change for small developers
The Government has also changed the Biodiversity Gain Hierarchy for minor development. From 6 August 2026, qualifying minor developments which remain subject to BNG have greater flexibility: on-site habitat creation and registered off-site biodiversity gains can now be considered at the same stage.
This can be particularly useful on constrained urban and suburban sites, where habitat areas can conflict with parking, access, private amenity space, drainage, landscaping, building positioning or overall viability.
Temporary development exemption
A further new exemption applies to certain temporary development. Where the whole development is temporary and the land is to be reinstated within five years or less, mandatory BNG may not apply. The exemption cannot be relied upon where priority habitat would be negatively affected.
What about applications already submitted?
The changes broadly apply to new planning applications submitted from 6 August 2026 onwards. Applications submitted before the change remain subject to the previous BNG regime and relevant transitional arrangements.
What happens where BNG still applies?
Where mandatory BNG applies, a Biodiversity Gain Plan will normally need to be approved before development can commence. Significant habitat used to secure mandatory BNG may also need to be maintained for a minimum period of 30 years.
BNG can therefore have financial and legal consequences extending far beyond obtaining the initial planning permission.
What does this mean when buying development land?
For anyone considering buying a plot, one early question is particularly important: how large is the planning application site? If it is 2,000m² or less, mandatory BNG may no longer apply.
That could remove biodiversity metric calculations, elements of ecological consultancy, Biodiversity Gain Plan requirements, off-site biodiversity unit costs and associated long-term management obligations.
However, BNG is only one part of a development feasibility assessment. Planning policy, the development principle, access and highways, neighbouring amenity, trees, ecology, flood risk, drainage, heritage, levels, design constraints and likely capacity all remain relevant.
Our view
For smaller developments, the August 2026 reforms are a welcome simplification. The new rules should allow many straightforward small sites to progress more efficiently while retaining protection for ecologically important land.
The most important lesson is to establish the BNG position at feasibility stage — not after the scheme has already been designed.
Considering a development site in the West Midlands?
Hepburn Architects provides architectural and planning feasibility advice for homeowners, landowners and developers across Birmingham, Solihull and the wider West Midlands. We assess new-build homes, small residential developments, infill and backland sites, redevelopment opportunities, extensions and conversions.
If you are considering purchasing or developing land, establishing the planning constraints early can help you understand its realistic development potential before significant money is committed. Discuss a potential site with us.
This article provides general information on the Biodiversity Net Gain rules applying in England from 6 August 2026. Planning and ecological requirements vary according to the circumstances of individual sites and professional advice should be sought where appropriate.