Last updated: June 25, 2026
Quick Answer: From 31 July 2026, government secondary legislation removes the mandatory 10% Biodiversity Net Gain requirement from any development with a developable area of 0.2 hectares or below. A separate consultation on a broader brownfield exemption (covering residential sites up to 2.5 hectares) closed on 10 June 2026, with a government response expected shortly. Small housebuilders and brownfield developers should review their project pipelines now, as the rules differ depending on site size, land type, and whether planning permission was already granted. [1][7]
Key Takeaways
- From 31 July 2026, sites with a developable area of 0.2 hectares or below are exempt from mandatory BNG — the small site exemption applies regardless of whether the land is greenfield or brownfield.
- The 0.2 ha threshold is based on the developable area, not the total site area — a larger site with a small footprint may still qualify.
- A wider brownfield exemption for residential sites up to 2.5 hectares is under active consultation; no final decision has been published as of June 2026.
- BNG becomes mandatory for Nationally Significant Infrastructure Projects (NSIPs) from 2 November 2026.
- Developments primarily aimed at conserving or enhancing biodiversity, and works on parks, playing fields, and public gardens, will also become exempt later in 2026.
- BNG is projected to prevent 6,000–10,000 hectares of habitat loss annually across England.
- Developers who are not exempt still need a baseline biodiversity survey, a statutory metric calculation, and a secured delivery mechanism (on-site, off-site, or statutory credits).
- Brownfield developers should not assume exemption applies automatically — documentation is required to demonstrate eligibility.
What Is Biodiversity Net Gain and How Does It Work?
Biodiversity Net Gain (BNG) is a planning requirement in England that obliges developers to leave the natural environment in a measurably better state than before development. The legal basis is the Environment Act 2021, which made a minimum 10% net gain in biodiversity a condition of planning permission for most developments.
The process works as follows:
- Baseline survey: An ecologist surveys the existing habitats on and around the site using the DEFRA statutory biodiversity metric.
- Metric calculation: The pre-development biodiversity unit value is calculated, and a post-development plan must show at least 10% more units.
- Delivery hierarchy: Gains must first be delivered on-site, then off-site (via registered habitat banks or landowner agreements), and only as a last resort through government statutory credits.
- Legal securing: The biodiversity gain plan must be approved by the local planning authority (LPA) and secured through a planning condition or legal agreement.
- Monitoring: Habitat management and monitoring plans (HMMPs) run for a minimum of 30 years.
For a detailed breakdown of what goes into a BNG assessment, see what is in a Biodiversity Net Gain assessment.
What Changed with BNG Reforms in July 2026?
The Biodiversity Net Gain BNG reforms July 2026 small site exemption brownfield changes represent the most significant recalibration of the BNG regime since mandatory requirements came into force. The government confirmed via secondary legislation that the reforms take effect from 31 July 2026. [1][7]
Key changes confirmed for 31 July 2026:
- A new small site exemption for any development with a developable area of 0.2 hectares or below removes the mandatory 10% BNG requirement entirely.
- Developments primarily intended to conserve or enhance biodiversity become exempt.
- Works on parks, playing fields, and public gardens become exempt.
Changes confirmed for 2 November 2026:
- BNG becomes mandatory for Nationally Significant Infrastructure Projects (NSIPs) — the largest category of development in England, including major roads, railways, and energy installations. [1]
Still under consultation (as of June 2026):
- A broader brownfield exemption for residential sites up to 2.5 hectares. The consultation closed on 10 June 2026 and a government response is pending. [9]
These reforms follow a formal consultation process on improving BNG implementation for minor, medium, and brownfield development, to which the government published its response in April 2026. [7]
Small Site Exemption BNG: What Size Qualifies?
The small site exemption applies where the developable area of a site is 0.2 hectares (2,000 square metres) or below. This is a hard threshold set in secondary legislation taking effect 31 July 2026. [1][6]
Critical distinction: The 0.2 ha threshold applies to the developable area — the part of the site being built on — not the total land holding. A developer with a 0.5 ha plot who is only building on 0.18 ha of it may still qualify, provided the remaining land is not being developed.
Who this typically covers:
- Small infill plots in urban areas
- Single-dwelling or small cluster developments on tight sites
- Conversions where the external footprint is minimal
- Micro-commercial developments below the threshold
Who it does not cover:
- Sites where the developable area exceeds 0.2 ha, even marginally
- Sites that fall under a separate exemption category (these are assessed differently)
- Permitted development rights that have their own BNG rules
For more on how BNG applies to smaller projects, see BNG for small development projects.
How Do Brownfield Sites Get Exempted from BNG Requirements?
As of June 2026, there is no confirmed blanket brownfield exemption from BNG. The existing small site exemption (0.2 ha developable area) applies to brownfield sites just as it does to greenfield sites. However, the government has consulted on a wider brownfield-specific exemption. [9]
The proposed wider brownfield exemption:
- Would cover residential brownfield sites up to 2.5 hectares.
- The consultation closed on 10 June 2026.
- No final secondary legislation has been laid as of this article's publication.
Brownfield BNG exemption vs small site exemption — the key difference:
| Feature | Small Site Exemption | Proposed Brownfield Exemption |
|---|---|---|
| Threshold | 0.2 ha developable area | Up to 2.5 ha (residential) |
| Land type | Any (greenfield or brownfield) | Brownfield only |
| Status (June 2026) | Confirmed, in force 31 July 2026 | Consultation closed; awaiting response |
| Documentation needed | Exemption claim at planning stage | TBC — likely formal declaration |
Brownfield developers working on sites above 0.2 ha should not assume exemption applies. Until the government publishes its response to the brownfield consultation, mandatory BNG remains the default for those sites. [7]
What Documentation Do I Need for the Small Site BNG Exemption?
Claiming the small site exemption is not automatic. Developers must demonstrate eligibility to the local planning authority at the planning application stage. [6][7]
Typical documentation requirements:
- A site plan or drawing clearly delineating the developable area and confirming it does not exceed 0.2 ha.
- A completed BNG exemption declaration submitted alongside the planning application.
- Where the total site is larger than 0.2 ha, supporting information explaining how the developable area has been calculated.
Common mistake: Submitting a site area rather than a developable area figure. LPAs are increasingly scrutinising this distinction, and an incorrectly claimed exemption can cause significant delays. For a full overview of exempt project categories, see the exempt projects guidance.
Who Has to Comply with BNG vs Who Is Exempt?
Most new planning permissions in England require BNG compliance unless a specific exemption applies. The Environment Act 2021 sets the default; secondary legislation carves out exemptions. [1][10]
Exempt from BNG (from 31 July 2026):
- Sites with a developable area of 0.2 ha or below
- Householder applications (already exempt since February 2024)
- Developments of a dwelling or dwellings where the site area is below the de minimis threshold
- Developments primarily to conserve or enhance biodiversity
- Works on parks, playing fields, and public gardens (from later in 2026)
- Previously exempt categories: permitted development, heritage, self-build (subject to conditions)
Not exempt and must comply:
- Major residential and commercial developments above the threshold
- NSIPs (from 2 November 2026)
- Any development where none of the statutory exemptions apply
If there is any doubt, the safest course is to commission a biodiversity net gain assessment early, before the planning application is submitted.
How Much Does Biodiversity Net Gain Cost for Small Projects?
BNG costs vary considerably depending on whether gains can be delivered on-site or must be purchased off-site. For small projects that are not exempt, costs can be disproportionate relative to development value — which is part of the policy rationale for the new exemptions. [2][5]
Indicative cost ranges (2026):
- Baseline survey and metric calculation: Typically £800–£2,500 for a small site, depending on habitat complexity.
- On-site habitat creation: Variable; often the lowest-cost route if space allows.
- Off-site biodiversity units: Market prices vary by unit type and location. For current pricing, see cost of biodiversity units and statutory credits.
- Statutory credits (last resort): Government-set prices, generally significantly higher than the private market.
Decision rule: Choose on-site delivery if the site has sufficient space and the habitat type required is achievable within the development layout. Choose off-site units if on-site delivery would compromise the scheme's viability. Use statutory credits only when neither option is available — they are a deliberate last resort. For more on the trade-offs, see off-site or on-site BNG delivery.
Common Mistakes Developers Make with BNG Small Site Rules
The reforms reduce complexity for many small builders, but several pitfalls remain. [6][2]
- Assuming exemption without checking: The 0.2 ha threshold is specific. Developers who assume they qualify without calculating the developable area risk non-compliance.
- Confusing total site area with developable area: These are not the same figure, and LPAs will ask for evidence.
- Waiting until after planning to think about BNG: Even for non-exempt sites, late engagement with an ecologist increases cost and risk of delay.
- Overlooking irreplaceable habitats: Ancient woodland and other irreplaceable habitats trigger separate requirements regardless of site size or exemption status.
- Assuming the brownfield exemption already applies: It does not. Until the government responds to the June 2026 consultation and lays further secondary legislation, brownfield sites above 0.2 ha remain subject to mandatory BNG.
BNG July 2026 Reforms: Impact on Housebuilders and the Wider Market
The Biodiversity Net Gain BNG reforms July 2026 small site exemption brownfield changes are broadly welcomed by small housebuilders, who have argued since 2024 that the 10% requirement creates disproportionate cost and delay on micro-sites. [3][5][6]
For small housebuilders: The 0.2 ha exemption removes BNG compliance costs entirely from the smallest schemes. This is significant for custom builders, self-builders, and small regional developers who operate on tight margins.
For brownfield developers: The picture is more uncertain. The proposed 2.5 ha brownfield exemption, if confirmed, would remove BNG requirements from a substantial proportion of urban regeneration schemes. However, until the government publishes its response, developers should plan on the basis that BNG applies.
For ecological surveyors and BNG consultants: Demand for baseline surveys and metric calculations will concentrate on larger and more complex sites. The NSIP extension from November 2026 opens a significant new market for BNG professionals.
For the environment: BNG is projected to prevent 6,000–10,000 hectares of habitat loss annually. The exemptions are designed to reduce administrative burden without materially undermining that headline ambition, on the basis that micro-sites contribute a small proportion of total habitat loss. [1]
For practical guidance on achieving the 10% requirement where it still applies, see how to achieve 10% Biodiversity Net Gain.
Conclusion
The BNG reforms taking effect from 31 July 2026 represent a pragmatic recalibration rather than a wholesale retreat. Small builders working on sites with a developable area of 0.2 ha or below can now proceed without mandatory BNG compliance — a genuine reduction in cost and administrative burden. Brownfield developers on larger sites should monitor the government's response to the June 2026 consultation closely, but must plan for BNG to apply in the meantime.
Actionable next steps:
- Calculate the developable area of every project in your pipeline against the 0.2 ha threshold before assuming exemption.
- Prepare a BNG exemption declaration for qualifying sites and submit it with the planning application.
- For non-exempt sites, commission a baseline biodiversity survey early — ideally before the planning application is submitted.
- Monitor the government's response to the brownfield consultation; subscribe to DEFRA's planning and environment updates.
- If purchasing off-site units, engage with registered habitat banks early, as supply in some regions remains constrained.
- Engage a qualified ecologist to confirm whether any irreplaceable habitats are present, as these sit outside the standard exemption framework.
For tailored support on any of these steps, the guidance for developers section provides a practical starting point.
Frequently Asked Questions
Q: Does the small site exemption apply automatically, or do I need to claim it?
You must actively claim the exemption at the planning application stage by submitting a BNG exemption declaration. It is not applied automatically by the LPA.
Q: My site is 0.25 ha in total, but only 0.18 ha is being developed. Does the exemption apply?
Yes, provided the developable area — the part being built on — is 0.2 ha or below, the exemption applies. You will need to demonstrate this clearly on your site plans.
Q: Is the brownfield BNG exemption already in force?
No. As of June 2026, the brownfield exemption for sites up to 2.5 ha is still under consultation. The consultation closed on 10 June 2026, but no secondary legislation has been confirmed. Brownfield sites above 0.2 ha must currently comply with mandatory BNG.
Q: When does BNG become mandatory for NSIPs?
BNG becomes mandatory for Nationally Significant Infrastructure Projects from 2 November 2026.
Q: What if my site contains ancient woodland — does the small site exemption still apply?
The small site exemption removes the mandatory 10% BNG requirement, but ancient woodland and other irreplaceable habitats trigger separate planning policy requirements. You should still seek ecological advice regardless of exemption status.
Q: Can I appeal if the LPA rejects my BNG exemption claim?
Yes. A BNG exemption decision forms part of the planning determination, so it can be challenged through the standard planning appeal process via the Planning Inspectorate.
Q: What is the statutory biodiversity metric?
The statutory biodiversity metric is the government-approved calculation tool used to measure the biodiversity unit value of habitats before and after development. It is published by DEFRA and must be used for all mandatory BNG assessments in England.
References
[1] Biodiversity Net Gain: What's Changing and What It Means for You – https://defraenvironment.blog.gov.uk/2026/04/20/biodiversity-net-gain-whats-changing-and-what-it-means-for-you/
[2] Biodiversity Net Gain Changes 2026 – https://www.biodiverseconsulting.co.uk/post/biodiversity-net-gain-changes-2026
[3] Key Changes Confirmed to Biodiversity Net Gain – https://www.cla.org.uk/news/key-changes-confirmed-to-biodiversity-net-gain/
[5] Government Response Signals Refinements to BNG Regime – https://www.thrings.com/blog/government-response-signals-refinements-to-bng-regime
[6] BNG Simplified: Smaller Sites, Fewer Hurdles – https://lichfields.uk/blog/2026/april/17/bng-simplified-smaller-sites-fewer-hurdles
[7] Government Response and Summary of Responses – https://www.gov.uk/government/consultations/improving-the-implementation-of-biodiversity-net-gain-for-minor-medium-and-brownfield-development/outcome/government-response-and-summary-of-responses
[9] Improving the Implementation of Biodiversity Net Gain for Minor, Medium and Brownfield Development – https://www.gov.uk/government/consultations/improving-the-implementation-of-biodiversity-net-gain-for-minor-medium-and-brownfield-development
[10] Biodiversity Net Gain – https://www.gov.uk/government/collections/biodiversity-net-gain
