BNG for Sites Under 2,000 m²: Does the Exemption Apply?

A practical guide to the new small-site exemption and the priority habitat exception.

The short answer: usually not, provided the planning application was made on or after 6 August 2026, the entire site within the red-line boundary is no larger than 0.2 hectares (2,000 m²), and the development does not impact an onsite priority habitat.

That is welcome news for many small developments. However, site size alone is not enough to establish the exemption. A small site can still fall within mandatory Biodiversity Net Gain (BNG) if the proposals would cause the loss or degradation of priority habitat.

What changed?

For planning applications made on or after 6 August 2026, development on a site no larger than 0.2 hectares is exempt from the statutory BNG condition, as long as it does not impact priority habitat on the site. The threshold includes a site of exactly 0.2 hectares.

The relevant area is the whole site shown inside the planning application’s red-line boundary—not just the building footprint, access road or area of vegetation being removed. If the red-line area is greater than 2,000 m², this particular exemption is unavailable, although another exemption, such as the de minimis exemption, may sometimes apply.

The priority habitat exception

The 2,000 m² exemption has two conditions: the site must be no larger than 0.2 hectares, and the development must not impact an onsite priority habitat. Both conditions must be met.

For BNG purposes, priority habitat means habitat included on the Secretary of State’s list under section 41 of the Natural Environment and Rural Communities Act 2006. England’s list contains 56 priority habitat types. Examples that may occur on smaller development sites include certain hedgerows, traditional orchards, ponds, lowland meadows, lowland calcareous grassland, deciduous woodland, wood-pasture and parkland, and open mosaic habitat on previously developed land.

Important: a habitat is not priority habitat simply because it looks green or is valuable to wildlife. Equally, an unmapped or modest-looking feature may meet a priority habitat definition. The habitat type and the relevant criteria need to be checked.

Does the presence of priority habitat automatically mean BNG applies?

Not necessarily. The legal test is whether the development impacts the priority habitat. Government guidance says a habitat is impacted where it is lost or degraded so that its biodiversity value decreases. This can include a change in habitat type, extent or condition that produces a negative biodiversity unit score in the statutory metric.

A scheme may therefore remain within the exemption if priority habitat is present but genuinely unaffected. The design and all associated works need to be considered, including access, services, drainage, landscaping, construction compounds and other activities that could cause loss or degradation. A clear avoidance plan and appropriate protection measures may be important evidence.

What about other, non-priority habitats?

For the new area-based exemption, impacts to non-priority habitat do not themselves switch mandatory BNG back on. If the red-line site is 2,000 m² or less and no onsite priority habitat is impacted, the development can qualify for this exemption even where other habitat is affected.

This is different from the separate de minimis exemption, which is generally used for larger sites and limits impacts to habitat with a biodiversity value greater than zero to less than 25 m², and impacts to linear habitat such as hedgerows to less than 5 metres. For a non-householder development on a site no larger than 0.2 hectares, national planning guidance says the area-based exemption should normally be considered before the de minimis exemption.

Why might an ecological check still be needed?

An exemption from mandatory BNG does not necessarily mean that no ecological work is required. The planning authority must be satisfied that the exemption has been correctly claimed, particularly where priority habitat may be present or the proposals sit close to a potentially important feature. Online habitat maps are useful for screening, but they are not a substitute for checking the habitat on the ground.

A proportionate site appraisal can identify the habitats present, establish whether any meet a priority habitat definition, and compare them with the proposed works. The result may be a short, evidence-based exemption statement rather than a full BNG metric and report. Where priority habitat would be impacted, a full BNG assessment will normally be required.

The statutory BNG exemption also does not remove other obligations relating to protected species, designated sites, trees, hedgerows or wider planning policy. Those matters should still be considered where relevant.

A sensible process for sites under 2,000 m²

Confirm the application date. The new exemption applies only where the planning application was made on or after 6 August 2026. Special rules apply to section 73 applications.
Measure the red-line boundary. Check the total application site area, not only the works footprint. It must be no larger than 0.2 hectares.
Screen for priority habitat. Review available records, maps, aerial photography and the site’s context.
Check the site where necessary. If priority habitat cannot confidently be ruled out, arrange a proportionate habitat survey by a competent ecologist.
Compare the habitats with the proposals. Establish whether any priority habitat would be lost or degraded, including through associated works.
Use the right output. If there is no impact on priority habitat, prepare a clear exemption justification. If there is an impact, proceed with a statutory BNG assessment and metric.

Two quick examples

Example 1: small site with ordinary grassland

A 1,600 m² site contains a building, hardstanding and modified grassland. The application is made after 6 August 2026. A habitat check confirms that no priority habitat is present. The scheme can qualify for the 0.2-hectare exemption, even if some of the non-priority grassland is lost. Other ecological constraints still need to be considered.

Example 2: small site affecting a priority hedgerow

A 1,900 m² site includes a hedgerow that meets the relevant priority habitat definition. The proposed access requires part of that hedgerow to be removed, reducing its biodiversity value. The priority habitat condition is not met, so the area-based exemption does not apply and mandatory BNG must be addressed, unless a different exemption applies.

How Crossman Ecology can help

The new exemption should make many smaller planning applications simpler and more proportionate. The key is establishing early whether the site and proposals genuinely meet the conditions.

Crossman Ecology can review the red-line boundary, screen the site for priority habitat and advise on the most proportionate next step. Where the exemption applies, we can provide clear evidence to support it. Where BNG is triggered, we can complete the assessment and guide the project through the process—keeping the advice practical, straightforward and focused on what is actually needed.

Not sure whether your small site is exempt from BNG?

Contact Crossman Ecology for a proportionate review before you commission a full assessment.

Sources and scope

Information checked: 15 September 2026. This article concerns the statutory BNG regime for planning permissions in England and provides general information, not site-specific legal or ecological advice.