Biodiversity Net Gain Small-Site 0.2 Hectare Exemption August 2026 Developer Guide

Last updated: August 10, 2026

Quick Answer: From 6 August 2026, developments affecting less than 0.2 hectares of habitat and not impacting priority habitat are exempt from mandatory Biodiversity Net Gain requirements under the Environment Act 2021. The same date saw the removal of the self-build and custom-build exemption, meaning those projects now fall under standard BNG rules unless they qualify on site-size grounds. Developers must still confirm the absence of priority habitat before relying on any exemption.

Key Takeaways

• The 0.2 hectare small-site exemption applies to non-major developments where the total area of habitat affected is under 0.2 ha and no priority habitat is present.
• The self-build and custom-build exemption was removed on 6 August 2026; those projects must now meet BNG obligations or qualify under another exemption.
• A new temporary-development exemption covers planning permissions granted for five years or less.
• For non-major development, off-site BNG gains are now on equal footing with on-site habitat creation, the strict hierarchy no longer applies.
• Priority habitat is the critical trigger: even a tiny site containing priority habitat is not exempt.
• Developers cannot artificially split a site into sub-0.2 ha parcels to avoid BNG obligations.
• A Biodiversity Gain Site Register entry is still required when off-site units are used to discharge a BNG condition.
• Early reports from the first week of implementation suggest local planning authorities are scrutinising priority habitat checks more closely than site-area calculations.

What Is the 0.2 Hectare Exemption for Biodiversity Net Gain?

The 0.2 hectare exemption is a statutory threshold below which non-major developments are not required to deliver a mandatory 10% Biodiversity Net Gain under the Environment Act 2021. Specifically, if the total area of onsite habitat affected by a proposed development is less than 0.2 hectares, and the site does not contain or impact priority habitat, the development is exempt from BNG obligations.

This threshold sits alongside the pre-existing 0.5 hectare threshold for major development. The two are distinct:

The exemption does not mean a developer can ignore ecology entirely. A baseline habitat assessment is still needed to confirm the site qualifies. See our overview of exempt projects for a full list of categories.

What Changed with BNG Exemptions in August 2026?

Three significant changes took effect on 6 August 2026, making this the most consequential update to BNG regulations since mandatory requirements were extended to small sites in April 2024.

1. The 0.2 hectare small-site exemption became operative. Previously, small sites had a transitional period with limited regulatory clarity. From 6 August 2026, the 0.2 ha threshold is the definitive statutory test for non-major development.

2. The self-build and custom-build exemption was removed. Until 5 August 2026, self-build and custom-build projects benefited from a specific carve-out. That exemption no longer exists. Self-builders must now either demonstrate their site qualifies under the 0.2 ha threshold or comply with full BNG obligations. This change affects a significant number of single-plot residential projects across England.

3. A temporary-development exemption was introduced. Planning permissions with a duration of five years or less are now exempt from mandatory BNG, regardless of site size. This covers short-term infrastructure, meanwhile uses, and certain construction compounds.

Additionally, the planning policy hierarchy for non-major development was relaxed. Developers of smaller schemes are no longer required to exhaust on-site habitat creation options before turning to off-site solutions. On-site and off-site gains now carry equal weight, which gives smaller developers considerably more flexibility. For a detailed comparison of delivery routes, see Biodiversity Net Gain off-site or on-site delivery.

Does My Small Development Site Qualify for the BNG Exemption?

A site qualifies for the 0.2 ha small-site exemption if it meets all three of the following conditions simultaneously:

1. The application is for non-major development (typically fewer than 10 dwellings or under 1,000 sq m of commercial floorspace).
2. The total area of habitat affected, not the total site area, is less than 0.2 hectares.
3. No priority habitat is present on or directly adjacent to the development footprint in a way that would be impacted.

If any one of these conditions fails, BNG obligations apply in full.

Common edge case: A 0.15 ha garden plot sounds straightforwardly exempt. But if part of that garden contains a patch of species-rich grassland classified as priority habitat, the exemption falls away entirely. The priority habitat test is binary: present and impacted means BNG applies, regardless of area.

For guidance on how to conduct the baseline assessment that underpins this determination, see how to conduct a biodiversity impact assessment.

How Do I Calculate Whether My Site Is Under 0.2 Hectares?

The 0.2 ha test applies to the area of habitat affected, not the gross site area or the red-line boundary. One hectare equals 10,000 square metres, so 0.2 ha equals 2,000 square metres, roughly the footprint of four average semi-detached houses and their gardens.

Step-by-step calculation:

1. Define the development footprint, including any areas of ground disturbance, access works, and drainage.
2. Map existing habitat types within that footprint using the UK Habitat Classification.
3. Calculate the total area of habitat (excluding hard standing, buildings, and other non-habitat surfaces already present).
4. If the total habitat area within the footprint is below 2,000 sq m and no priority habitat is present, the exemption applies.

A qualified ecologist should carry out or verify this calculation. Errors at this stage are the most common reason local planning authorities (LPAs) reject exemption claims.

What Is the Difference Between the 0.2 Hectare and 0.5 Hectare Exemptions?

The 0.5 ha exemption applies to major development only. Major development is defined in the Town and Country Planning (Development Management Procedure) Order 2015 as schemes involving 10 or more dwellings, sites of 0.5 ha or more for residential use, or commercial floorspace of 1,000 sq m or more.

The 0.2 ha exemption applies to non-major development. Both exemptions share the same priority habitat override: the moment priority habitat is affected, neither threshold provides protection from BNG obligations.

In practice, a developer building eight houses on a 0.18 ha brownfield site with no priority habitat would rely on the 0.2 ha non-major exemption. A developer building 12 houses on a 0.4 ha greenfield site would need to check the 0.5 ha major threshold, and would likely fail it if the site contains significant habitat.

Does Priority Habitat Still Trigger BNG on Small Sites?

Yes, and this is the single most important point in the entire Biodiversity Net Gain small-site 0.2 hectare exemption August 2026 developer guide. Priority habitat overrides both the 0.2 ha and 0.5 ha exemptions without exception.

Priority habitats in England are listed under Section 41 of the Natural Environment and Rural Communities Act 2006. They include:

• Traditional orchards
• Ancient and veteran trees
• Species-rich grassland
• Lowland heathland
• Blanket bog
• Coastal and floodplain grazing marsh
• Hedgerows (where meeting the Hedgerow Regulations 1997 criteria)

If a Phase 1 habitat survey or desk study reveals any of these on or adjacent to the site, a full BNG assessment is required regardless of site size. This is why a preliminary ecological appraisal is never truly optional, even for apparently exempt sites.

Are Residential Extensions Covered by the Small-Site Exemption?

Residential extensions that require planning permission and affect less than 0.2 ha of habitat, with no priority habitat present, can qualify for the exemption. However, many householder extensions fall under permitted development rights and are therefore outside the BNG regime entirely, BNG applies only to developments requiring a planning application.

Where a householder does submit a planning application (for example, because permitted development rights have been removed by an Article 4 Direction), the 0.2 ha test applies in the same way as for any other non-major development.

Can I Combine Multiple Small Sites to Avoid the BNG Requirement?

No. Deliberately splitting a larger development into sub-0.2 ha parcels to circumvent BNG is not permitted. LPAs are instructed to treat artificially fragmented applications as a single development for the purposes of BNG assessment. This is sometimes called "salami slicing" and planning authorities are alert to it.

Where a developer has genuinely separate, unrelated projects that each fall below the threshold, each is assessed independently. The test is whether the sites are functionally and commercially linked, not merely whether they are physically adjacent.

Do I Still Need a Biodiversity Survey If I'm Exempt?

Yes, in practice. The exemption does not remove the need for ecological due diligence, it removes the obligation to deliver a 10% net gain. To claim the exemption, a developer must be able to demonstrate to the LPA that the site qualifies. That demonstration requires a habitat survey or preliminary ecological appraisal confirming:

• The area of habitat affected is below 0.2 ha.
• No priority habitat is present or affected.

Without that evidence, an LPA can refuse to accept the exemption claim and require a full BNG assessment. See what is in a Biodiversity Net Gain assessment for a breakdown of what that process involves.

How Do I Apply for a Small-Site Exemption?

There is no separate formal application for a BNG exemption. Instead, the developer declares the exemption within the planning application, typically through the biodiversity net gain statement or a covering letter from a qualified ecologist.

The declaration should include:

• A site plan showing the development footprint.
• A habitat map or Phase 1 survey confirming habitat types and areas.
• A written statement confirming no priority habitat is present.
• The calculated habitat area, showing it falls below 0.2 ha.

Some LPAs have their own checklists or validation requirements, so it is worth checking local validation guidance before submission.

If off-site BNG units are needed (because the site does not qualify for exemption), those units must be registered on the Biodiversity Gain Site Register before they can be used to discharge a planning condition. For guidance on sourcing off-site units, see our guide to biodiversity credits for developers.

Early Observations from the First Week Post-Implementation

One week into the new regime, several patterns are already emerging from developer and planning consultant reports.

LPA scrutiny of priority habitat checks is high. Planning officers are requesting supporting evidence for exemption claims more frequently than anticipated, particularly where sites are near hedgerows or semi-improved grassland. Developers relying on desk-study data alone are finding their claims challenged.

Self-build applicants are caught off-guard. The removal of the self-build exemption has generated a notable volume of enquiries from individuals who were unaware of the change. Single-plot applications that were assumed to be exempt are now requiring full BNG assessments or habitat surveys to confirm the 0.2 ha threshold applies.

The relaxed hierarchy is being welcomed. Smaller developers and housing associations report that the equal footing given to off-site gains for non-major development is reducing project complexity. Rather than attempting to retrofit on-site habitat creation into constrained urban plots, developers can now proceed directly to off-site solutions without needing to justify the decision. This aligns with broader guidance on BNG for small development projects.

Temporary permission exemptions are being used for construction compounds. Infrastructure contractors have moved quickly to apply the five-year temporary permission exemption to ancillary works areas, reducing BNG liability on large projects.

What Documentation Do I Need to Prove My Site Qualifies?

To support an exemption claim, developers should prepare the following:

• Preliminary Ecological Appraisal (PEA) or Phase 1 Habitat Survey, dated within the last two years.
• Habitat area calculation, clearly showing the methodology used to arrive at the figure.
• Priority habitat confirmation, including a check against Natural England's Priority Habitat Inventory and a site walkover.
• Site location plan at 1:1250 or 1:2500 scale with the development footprint clearly marked.
• Written declaration signed by a suitably qualified ecologist (SQE or CIEEM member).

Keeping this documentation on file is also important for due diligence purposes if the site is sold or refinanced before or during development.

What Are Common Mistakes Developers Make with BNG Exemptions?

Based on early post-August 2026 experience and patterns from the preceding two years of mandatory BNG, the most frequent errors are:

1. Measuring site area instead of habitat area. The threshold applies to habitat, not the red-line boundary. A 0.3 ha site that is 80% hard standing may have only 0.06 ha of habitat and qualify for exemption.
2. Overlooking hedgerows. Hedgerows meeting the Hedgerow Regulations criteria are priority habitat. A single mature hedgerow bordering a small plot can invalidate an exemption claim.
3. Using outdated survey data. Surveys more than two years old may not reflect current habitat conditions and are unlikely to be accepted by LPAs.
4. Assuming self-build projects are still exempt. This exemption ended on 6 August 2026.
5. Failing to register off-site units. Where BNG is required, off-site units must appear on the Biodiversity Gain Site Register before a condition can be discharged.
6. Not checking for ancient trees. A single ancient or veteran tree on or adjacent to the site triggers priority habitat status.

Is the 0.2 Hectare Exemption Still in Effect After August 2026?

Yes. The 0.2 ha small-site exemption is a permanent feature of the BNG framework as it stands in August 2026, not a transitional measure. It was introduced to ensure that very small developments are not disproportionately burdened by BNG compliance costs, while still protecting ecologically sensitive land through the priority habitat override.

There is no current government indication that this threshold will be revised in the near term. However, the Environment Act 2021 gives the Secretary of State power to amend exemption thresholds by secondary legislation, so developers with long-term pipelines should monitor for any future changes.

For a broader understanding of how BNG obligations work across different project types, the Biodiversity Net Gain explained resource provides a useful foundation.

BNG Small-Site Exemption Checker

Use this tool to get a quick indication of whether your development may qualify for the 0.2 ha exemption.

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function cg_check(){
var major=document.getElementById(‘cg-major’).value;
var area=document.getElementById(‘cg-area’).value;
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el.style.display=’block’;
if(!major||!area||!priority||!temp){el.className=’cg-bng-result cg-bng-required’;el.innerHTML=’Please answer all four questions.’;return;}
if(temp===’yes’){el.className=’cg-bng-result cg-bng-exempt’;el.innerHTML=’Likely exempt, temporary permissions of 5 years or less are exempt from mandatory BNG (from 6 August 2026). Confirm with your ecologist.’;return;}
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if(priority===’unsure’){el.className=’cg-bng-result cg-bng-required’;el.innerHTML=’Survey required, you must confirm the absence of priority habitat before claiming exemption. Commission a Preliminary Ecological Appraisal.’;return;}
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if(major===’no’&&area===’yes’){el.className=’cg-bng-result cg-bng-required’;el.innerHTML=’Check major threshold, this is major development. The 0.5 ha threshold applies, not 0.2 ha. If habitat affected is under 0.5 ha and no priority habitat is present, you may still qualify.’;return;}
el.className=’cg-bng-result cg-bng-required’;el.innerHTML=’BNG likely required, the habitat area exceeds the relevant threshold. A full BNG assessment and 10% net gain delivery plan will be needed.’;
}

Frequently Asked Questions

Q: Does the 0.2 ha exemption apply to all of England?
A: Yes. The exemption applies across England under the Environment Act 2021 framework. It does not apply in Wales, Scotland, or Northern Ireland, which have separate biodiversity legislation.

Q: My self-build project was in progress before 6 August 2026. Am I still covered by the old exemption?
A: If your planning permission was granted before 6 August 2026 and the self-build exemption applied at the time of permission, you should seek legal and ecological advice on transitional provisions. New applications submitted from 6 August 2026 onwards cannot rely on the self-build exemption.

Q: Can I use statutory biodiversity credits instead of finding off-site habitat units?
A: Yes, statutory biodiversity credits purchased from Natural England are a last-resort option where on-site and off-site solutions are not available or viable. They are significantly more expensive than market-rate biodiversity units. See the cost of biodiversity units and statutory credits for current pricing context.

Q: What is the Biodiversity Gain Site Register?
A: The Biodiversity Gain Site Register is a public register maintained by Natural England. It records off-site habitat enhancement sites that have been approved to generate biodiversity units for use in discharging BNG planning conditions. Off-site units cannot be used to satisfy a BNG condition unless the gain site is registered.

Q: Does the relaxed hierarchy mean I never have to consider on-site habitat creation for non-major development?
A: Not exactly. The relaxed hierarchy means on-site and off-site options are treated equally, neither is mandated as the first step. However, LPAs may still encourage on-site creation where it is genuinely feasible, and some local policies may set higher expectations. The change removes the legal obligation to exhaust on-site options first, not the planning authority's discretion.

Q: How long does a Preliminary Ecological Appraisal take to commission?
A: A PEA for a small site typically takes two to four weeks from instruction to report, depending on ecologist availability and seasonal survey constraints. It is advisable to commission one at pre-application stage to avoid delays.

Conclusion

The Biodiversity Net Gain small-site 0.2 hectare exemption August 2026 developer guide reflects a regulatory landscape that is becoming more nuanced, not simpler. The 6 August 2026 changes introduce genuine relief for small developers through the 0.2 ha threshold and the new temporary-development exemption, while simultaneously closing the self-build loophole and sharpening the priority habitat test.

The central message for developers is this: the exemption is real and usable, but it is not self-certifying. Every exemption claim rests on a habitat survey that confirms two things, the area of habitat affected is below 2,000 square metres, and no priority habitat is present. Without that evidence, an LPA can and will require a full BNG assessment.

For non-major projects that do not qualify for exemption, the relaxed hierarchy is a practical improvement. The ability to move directly to off-site solutions without justifying the decision opens up faster, simpler compliance routes, particularly for urban infill and brownfield development.

Next steps for developers:

• Commission a Preliminary Ecological Appraisal before submitting any planning application on a site where exemption status is uncertain.
• Check the Priority Habitat Inventory via Magic Map or Natural England's data portal at the earliest opportunity.
• If off-site BNG units are needed, begin sourcing them early, the Biodiversity Gain Site Register lists available sites, but supply in some areas remains constrained.
• Review any live self-build applications to ensure they now comply with standard BNG obligations.

To get a clear picture of your project's BNG obligations and exemption eligibility, book a BNG feasibility assessment with our specialist team at Biodiversity Surveyors. Early advice prevents costly delays at the planning stage.

References

• HM Government. Environment Act 2021. London: HMSO, 2021. https://www.legislation.gov.uk/ukpga/2021/30/contents
• Natural England. Biodiversity Net Gain: Guidance for developers. 2024. https://www.gov.uk/guidance/biodiversity-net-gain
• Natural England. Biodiversity Gain Site Register. 2024. https://www.gov.uk/guidance/biodiversity-gain-sites-register
• Department for Levelling Up, Housing and Communities. Biodiversity Net Gain: Small sites regulations. 2024. https://www.gov.uk/guidance/biodiversity-net-gain
• HM Government. Town and Country Planning (Development Management Procedure) (England) Order 2015. London: HMSO, 2015.
• Natural Environment and Rural Communities Act 2006, Section 41. London: HMSO, 2006.