Biodiversity Net Gain Changes in 2026: What London and Surrey Homeowners Need to Know

Biodiversity Net Gain rules changed significantly in England on 6 August 2026.

The changes reduce the regulatory burden for some smaller and temporary developments. However, eligibility depends on the application type, site area, existing habitat and the requirements of the relevant local planning authority.

This article explains the key changes for homeowners, small developers and property owners planning extensions, conversions, infill schemes or new homes across London and Surrey.

Important: This is general information, not legal or planning advice. A project's BNG position must be confirmed against the application documents, site conditions, legislation and local planning authority requirements.

What is Biodiversity Net Gain?

Biodiversity Net Gain is a statutory planning framework intended to ensure that eligible development leaves biodiversity in a measurably better condition.

For developments within scope, the requirement remains a minimum 10% increase in biodiversity value compared with the pre-development habitat baseline. This gain may be delivered through:

• Habitat retained, enhanced or created onsite.
• Registered biodiversity gains delivered offsite.
• Statutory biodiversity credits, where other routes cannot deliver the required gain.

The requirement is generally secured through a Biodiversity Gain Plan, which must be approved before development begins. The official Planning Practice Guidance on Biodiversity Net Gain explains the statutory process, exemptions and information requirements.

The 2026 regulations do not remove BNG altogether. Instead, they change who is exempt, how some minor developments can meet the requirement and how applications submitted before the changes are treated.

1. New exemption for sites of 0.2 hectares or less

The most significant change is a new exemption for qualifying development on sites measuring 0.2 hectares or less.

That is equivalent to:

• 0.2 hectares
• 2,000 square metres
• Approximately half an acre

For applications submitted on or after 6 August 2026, development on a site at or below this threshold is generally exempt from mandatory BNG where it does not negatively impact onsite priority habitat.

This exemption is not limited to one type of development. It can be relevant to certain new homes, infill schemes, conversions, commercial proposals and other applications, provided the development satisfies the applicable criteria.

The priority habitat exception is crucial. If onsite priority habitat would be negatively impacted, the 0.2-hectare exemption does not apply simply because the site is small.

The Defra update on the 2026 amendments confirms that the exemption is intended to focus mandatory BNG requirements on larger developments while retaining wider environmental protections.

The site area is not the building footprint

A common misunderstanding is that the 0.2-hectare threshold refers only to the size of an extension or new building.

It does not.

The relevant measurement is generally the area within the red-line boundary shown on the planning application location plan. This means a proposed extension measuring 40 square metres could still be part of an application site exceeding 2,000 square metres.

Conversely, a development involving more than one building may still fall within the threshold if the complete application site remains at or below 0.2 hectares.

The red-line boundary therefore deserves careful attention at the earliest design stage. It should accurately reflect the land to which the application relates, including relevant gardens, access areas, parking spaces and other land included in the proposal.

2. New exemption for certain temporary developments

A second exemption applies to qualifying temporary development where the land will be reinstated within five years or less.

This is narrower than simply describing a proposal as “temporary”. The exemption generally requires:

• The whole development to consist solely of temporary development.
• Planning permission to be granted for a period of five years or less.
• A condition requiring buildings or works to be removed.
• Any authorised use to cease.
• The land to be reinstated within the relevant period.
• No negative impact on onsite priority habitat.

The rules also prevent successive permissions from being used to extend the same temporary development indefinitely. Where earlier and later permissions together exceed five years, the exemption may not apply.

For property owners and developers, the practical point is that the planning permission, conditions and actual nature of the proposal must all align. A proposal that has a temporary effect on habitat is not necessarily the same as a qualifying temporary development under the new exemption.

3. The self-build and custom-build exemption has been removed

Before 6 August 2026, certain small-scale self-build and custom-build housing schemes could benefit from a specific BNG exemption.

That exemption has now been removed for new applications.

New self-build and custom-build applications must therefore be assessed like other development proposals. They will generally need to meet the 10% BNG requirement unless another exemption applies.

For example, a self-build scheme may still qualify for the new 0.2-hectare exemption if:

• The application site measures 2,000 square metres or less.
• No onsite priority habitat is negatively impacted.
• The application is submitted on or after 6 August 2026.
• No other aspect of the proposal prevents reliance on that exemption.

The change does not mean every self-build project now requires a Biodiversity Gain Plan. It means the former self-build category can no longer be relied upon for new applications without checking whether another exemption is available.

Applications made before 6 August 2026 remain subject to the rules that applied when they were submitted.

4. More flexibility for minor developments that remain within BNG

Some minor, or non-major, developments will remain subject to BNG. This may include schemes that exceed 0.2 hectares or affect habitat in a way that prevents reliance on an exemption.

For applications submitted on or after 6 August 2026, the biodiversity gain hierarchy has been modified for these non-major developments.

Onsite habitat enhancement, onsite habitat creation and registered offsite biodiversity gains can now be considered at the same level of preference. This means an eligible minor development may be able to select an offsite gain strategy from the outset, rather than first demonstrating that all onsite opportunities have been maximised.

Statutory biodiversity credits remain the final option.

The change may be particularly relevant to constrained London sites, where gardens are small, access is limited and onsite habitat creation could conflict with layout, daylight, drainage, amenity or other planning requirements.

The hierarchy does not remove the need to avoid and mitigate harm. The GOV.UK guidance distinguishes the Biodiversity Gain Hierarchy from the wider mitigation hierarchy applied to planning decisions.

Major development remains subject to the original hierarchy, with onsite enhancement and creation generally prioritised ahead of registered offsite gains.

5. The application date controls the transitional position

The new exemptions and hierarchy changes generally apply to new planning applications submitted from 6 August 2026.

Applications already submitted remain subject to the BNG rules that applied when they were made. The new 0.2-hectare and temporary development exemptions do not automatically remove requirements attached to an earlier application or permission.

This distinction matters where a proposal has already been submitted, approved or made subject to a Biodiversity Gain Plan or related planning obligation.

A later amendment, variation or Section 73 application can have its own technical treatment. The updated guidance includes specific rules for Section 73 permissions, and the new exemptions do not automatically apply to every variation of an earlier permission.

The relevant legislation is set out in The Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026.

What has not changed?

The 2026 amendments do not remove the wider planning responsibilities associated with development.

Even where mandatory BNG does not apply:

• Planning permission may still be required.
• Local planning policies may still require landscaping, tree protection or ecological information.
• The mitigation hierarchy still applies.
• Significant harm to biodiversity may still affect the planning decision.
• Protected species, trees, habitats and other environmental regimes remain relevant.
• Nature-friendly design remains an important part of responsible development.

Defra states that exempt developments remain subject to existing environmental protections and policies. A small extension or infill scheme can therefore be exempt from mandatory BNG while still needing to retain trees, protect habitat, provide suitable planting or address other local requirements.

A practical BNG checklist for London and Surrey projects

Before submitting a planning application, consider the following:

1. 1Confirm the application type. A typical householder application for an extension or loft conversion may already fall within the householder exemption. A new dwelling, infill scheme, change of use or larger redevelopment may be treated differently.
2. 2Measure the complete red-line site area. Do not measure only the proposed building or extension. Check the full application boundary against the 0.2-hectare, or 2,000-square-metre, threshold.
3. 3Check for onsite priority habitat. The small-site and temporary development exemptions do not apply where qualifying priority habitat is negatively impacted.
4. 4Confirm when the application was submitted. Applications submitted before 6 August 2026 remain subject to the earlier rules. New applications from that date are assessed under the amended framework.
5. 5Consider whether the development is major or non-major. The modified hierarchy for offsite gains applies to qualifying non-major development. Major schemes continue to follow the original hierarchy.
6. 6Review local requirements. Each local planning authority may have its own validation requirements, local information list and approach to ecological matters.
7. 7Get the position confirmed before submission. Discuss the proposal with the relevant local planning authority or a suitably qualified planning or ecology professional where the position is uncertain.

Early assessment is valuable because the red-line boundary, layout and landscaping strategy can all influence the BNG position. It is usually more efficient to address these matters before the planning drawings and application documents are finalised.

How Shorplans can help

BNG is one part of a wider planning and construction process. A successful proposal also needs accurate site information, clear architectural design and coordinated technical documentation.

Shorplans supports homeowners, property owners and developers across London and Surrey with:

• Measured surveys and existing-condition drawings.
• Residential extensions, loft conversions and renovations.
• Infill and new-build housing design.
• Planning applications and supporting drawings.
• Detailed Building Control and construction information.
• Structural engineering coordination, including structural calculations and drawings.
• In-house coordination between architectural and structural engineering services.

Our integrated approach helps reduce gaps between the architectural proposal, planning submission and technical design. It also allows environmental considerations, access, structure, layout and practical construction requirements to be considered together.

For an initial discussion about a project and its likely planning requirements, book a consultation with Shorplans. Alternatively, request a quote and provide details of the proposed site, development type and location.

The 2026 BNG changes create more flexibility for some smaller schemes, but the correct answer depends on the individual application. Early, accurate project information remains the clearest route to a proportionate and compliant design.