BNG Exemptions: Does Biodiversity Net Gain Apply?

BNG exemptions: does BNG apply to my development?

BNG exemptions determine whether a development must meet England's statutory biodiversity gain condition. If you are asking, “does BNG apply to my development?”, the answer depends on the planning route, application history, development description and habitat impacts. Biodiversity net gain exemptions should be checked against the actual proposal rather than assumed from a small site area or a limited construction budget. Collington Winter Environmental helps applicants understand the ecological evidence needed to explain their position clearly to the planning authority.

This guide explains the established mandatory BNG framework and its principal exemptions and exclusions. Requirements can change, so confirm the legislation and guidance applicable to the submission date before relying on a particular route. A proposal or consultation about changing exemptions is not the same as an exemption already in force. Where a scheme is unusual or the planning history is complex, ecological advice may need to be combined with specialist planning or legal advice.

Start with the scope of mandatory biodiversity net gain

The Environment Act 2021 introduced the statutory framework through Schedule 7A of the Town and Country Planning Act 1990. For development within scope, the biodiversity gain objective is at least a 10% increase in biodiversity value. Mandatory BNG commenced for major development from 12 February 2024 and for small sites from 2 April 2024, subject to the relevant exemptions and transitional arrangements.

The biodiversity gain plan is normally submitted after permission and must be approved before development commences. Where an exemption genuinely applies, that statutory condition does not apply to the permission. However, other ecological requirements remain relevant. Protected species legislation, designated site safeguards, tree controls and local planning policy can still require investigation or mitigation. Read whether biodiversity net gain is mandatory for the wider context.

Householder development exemption

Householder applications are exempt from mandatory BNG. These are applications within the statutory householder definition, typically covering works to an existing home or within its curtilage for purposes incidental to its enjoyment. Extensions, conservatories and certain alterations may fall within this route. The exemption relates to the application category, not a general principle that all residential development is outside BNG.

A new dwelling, a conversion creating separate accommodation or a wider development involving residential land is not automatically a householder application. Check how the proposal is legally classified before relying on the exemption. An exempt extension can still affect bats, nesting birds, trees or other ecological interests, so exemption from the biodiversity gain condition does not establish that no survey work is needed.

De minimis BNG exemption

The habitat impact thresholds

The established de minimis exemption applies where development does not impact priority habitat and impacts less than 25 square metres of relevant on-site area habitat and less than five metres of relevant on-site linear habitat. The assessment concerns habitat impacts, not simply the footprint of the building or the total size of the landholding. All applicable thresholds must be satisfied.

The word “less” matters. An impact of exactly 25 square metres does not fall below the area threshold, and exactly five metres does not fall below the linear threshold. Where both area and linear habitats are affected, consider both rather than choosing whichever gives the more favourable result. Priority habitat impact prevents reliance on this exemption even where the affected area is small.

What counts as an impact?

Review the whole development and its associated works. Access changes, service trenches, drainage, construction activity, storage and other interventions can affect habitats outside the proposed building footprint. A small structure on a large lawn is not automatically exempt if its associated works affect a larger area of habitat. Conversely, existing sealed surfaces may have no biodiversity value in the metric, but the surrounding works still need checking.

A proportionate exemption statement should identify the habitats, describe the proposed impacts and show how the thresholds are met. Plans, photographs and survey evidence can support the explanation. Avoid presenting the exemption as an automatic entitlement for every brownfield or urban site: these sites can contain habitats with biodiversity value, including valuable vegetation within apparently developed land.

Self-build and custom-build exemption

Qualifying self-build and custom-build development is exempt where it consists of no more than nine dwellings, is on a site no larger than 0.5 hectares and consists exclusively of qualifying self-build or custom-build housing. All parts of the test must be met. A low dwelling count alone does not establish the exemption, and a conventional speculative housing scheme does not qualify simply because the homes will eventually be privately owned.

The housing must meet the relevant statutory meaning of self-build or custom housebuilding. Explain how the proposal satisfies that definition and how its qualifying nature will be secured or evidenced through the planning process. A mixed scheme containing ordinary market housing cannot rely on this exemption merely because some plots are intended for self-build. Obtain advice if ownership, procurement or delivery arrangements make the classification uncertain.

Development undertaken primarily to provide biodiversity gain

Development undertaken solely or mainly to meet the biodiversity gain objective for another development can fall within the biodiversity gain site exemption. This enables relevant habitat delivery works to be treated appropriately where their purpose is to provide the gains required elsewhere. It is not a general exemption for any commercial development that happens to include landscaping or claims to be environmentally beneficial.

The primary purpose and nature of the works matter. An application for habitat creation associated with a gain site should explain the relationship to biodiversity delivery. Wider infrastructure or built development on the same land may require separate consideration. Read our habitat banking guide for an introduction to the legal, management and registration arrangements associated with supplying off-site biodiversity gains.

High Speed 2 exemption

The exemptions regulations include development forming part of, or ancillary to, the high-speed railway network specified in the High Speed Rail (Preparation) Act 2013. This is a specific statutory exemption relating to that network, rather than a blanket exemption for transport schemes or railway-related development generally. Ordinary road, rail or infrastructure proposals need to be assessed through their own planning route.

An exemption from the mandatory BNG condition does not remove other environmental commitments or project-specific requirements. For major infrastructure, the relevant consenting legislation and environmental assessment framework may be different from an ordinary planning application. Avoid drawing conclusions for a local transport development from an exemption designed for a particular nationally significant railway programme. The statutory exemption categories are set out in the Exemptions Regulations.

Permitted development and other routes outside the condition

Mandatory BNG under this framework does not apply to permitted development, including development proceeding through the relevant prior approval route. This is distinct from claiming a de minimis exemption. First establish whether the proposal genuinely benefits from permitted development rights and meets their limitations and conditions. A development needing a full planning application cannot rely on an assumed permitted development exclusion if those rights are unavailable.

Retrospective permissions under section 73A are outside the statutory biodiversity gain condition. This should not be treated as a strategy for avoiding BNG: carrying out unauthorised development can create serious planning and other legal consequences. Other consent routes, including nationally significant infrastructure projects, have their own framework and later commencement arrangements. The ordinary 2024 planning dates do not automatically settle their position.

Transitional applications and variations of permission

Applications made before the relevant commencement date can benefit from transitional arrangements. Major development applications made before 12 February 2024 and qualifying small development applications made before 2 April 2024 need to be considered in that context. The application history is therefore important: a later decision date does not necessarily bring an earlier application within mandatory BNG.

Section 73 permissions varying conditions have specific transitional rules. Where the original permission or application falls outside the regime under the applicable provisions, a later variation may also remain outside it. However, do not assume every amendment is protected or every later application inherits the original position. Review the original application, decision, proposed procedure and relevant legislation together, particularly where a materially different development is proposed.

Common mistakes when assessing BNG exemptions

Small sites are not automatically exempt, and using the Small Sites Metric is not an exemption. The simplified metric is an assessment tool for eligible development that still needs to meet the gain objective. Similarly, a site described as previously developed land can still contain habitats affected by construction. A planning label is not a substitute for examining what is present.

Another mistake is assuming that no protected species records means there is no biodiversity value. BNG measures habitats through the metric, while species assessment addresses separate issues. An exemption statement should focus on the correct legal test and supporting evidence. If the test is not met, a proportionate BNG assessment is usually a better route than trying to force the proposal into an unsuitable exemption.

Why choose Collington Winter

Collington Winter Environmental is based in Bolton and works throughout England. Our Managing Director, Olivia Collington, is a Chartered Environmentalist with the IES and holds Natural England bat and great crested newt licences, together with GCN and badger mitigation licences. Her experience includes the DEFRA Statutory Biodiversity Metric and habitat bank offsetting, helping connect applicability advice with the next steps where assessment is required.

Explore what biodiversity net gain means, when assessments are required and biodiversity metric calculations. If you need help understanding BNG exemptions for your proposal, call 01204 939 608 or use our contact page.