The latest reforms introduce new exemptions for certain smaller and temporary developments, while also removing the previous exemption for self-build and custom-build housing. There is also greater flexibility for minor developments when considering how biodiversity gains can be delivered.
But what do these changes mean in practice for developers and landowners, and how should BNG be considered as part of the planning and design process?
Here William White, Planning Design Manager at RDC and our BNG lead, looks at the latest changes, clarifies what has changed and explains what developers need to be aware of when bringing forward new proposals.
1. Can you start by explaining your role and how it relates to Biodiversity Net Gain (BNG)?
My role involves advising developers and landowners on how Biodiversity Net Gain (BNG) requirements affect their schemes, including viability, planning strategy and delivery. This includes helping clients understand when BNG applies, what their obligations are, whether on-site or off-site delivery is most appropriate, and how to manage biodiversity requirements without delaying projects.
A key part of this is working closely with ecologists and the wider project team at the very outset. Early collaboration allows us to design BNG into a scheme from the beginning, rather than treating it as a constraint later in the process. By integrating ecological considerations alongside layout design, viability and planning strategy, we can identify opportunities to enhance biodiversity in a way that complements development, often ‘double stacking’ land uses to make the most efficient use of space.
As BNG has become embedded within the planning system, this kind of proactive, early-stage approach has become increasingly important. It helps ensure BNG is delivered efficiently, reduces the risk of redesign or delay, and ultimately leads to more coherent, sustainable and practical schemes.
2. The Government has announced some major BNG changes, can you explain the headline changes?
The changes that came into effect on 6 August 2026 are intended to make the BNG regime more proportionate, particularly for smaller developments.
The key changes are:
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introducing an exemption for developments on sites of 0.2 hectares or below, subject to the development not impacting onsite priority habitat;
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introducing an exemption for certain temporary developments where planning permission is granted for five years or less, again subject to priority habitat;
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removing the previous exemption for self-build and custom-build development for new planning applications; and
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giving minor developments that remain subject to BNG greater flexibility by allowing them to consider on-site and off-site biodiversity gains at the same time.
The changes apply to relevant planning applications made on or after 6 August 2026.
3. What does the Government hope to achieve with these changes?
The reforms are largely a response to concerns that BNG, while well-intentioned, can impose disproportionate burdens on some smaller developments.
With these changes, the Government is trying to strike a balance between:
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delivering environmental improvements; and
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maintaining development viability and reducing unnecessary burdens, particularly for smaller developers and projects where the costs of BNG can be disproportionate to the scale of development.
Importantly, the reforms do not remove the principle of BNG. Where a development remains within scope, the requirement to deliver at least 10% biodiversity net gain remains.
The changes are more about making the system proportionate and giving developers greater flexibility in how BNG is delivered.
4. What practical difference will the small site exemption make?
For smaller developers, it could make a really big difference.
Planning applications for developments on sites of 0.2 hectares or below are exempt from mandatory BNG, provided the development does not impact onsite priority habitat. This gives greater certainty to developers bringing forward smaller schemes and removes the need to meet the statutory BNG requirement where the exemption applies.
Previously, smaller developments could still be subject to BNG, meaning developers might have needed to consider:
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metric calculations,
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off-site unit costs, and
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the additional time involved in meeting the BNG requirements.
The new exemption could therefore reduce upfront costs and simplify the planning process for some smaller schemes, particularly infill and urban developments.
It is important, however, that developers check whether the exemption applies. In particular, the exemption does not apply where the development impacts onsite priority habitat. Protected species and other environmental legislation remain unaffected, regardless of whether a site is BNG exempt. Depending on site features and constraints developers may still need to undertake ecological surveys.
5. How important is this for developers?
This is especially important for smaller developers, because the new exemption could remove a significant additional consideration from some smaller sites.
For those developers, BNG has sometimes represented a relatively high cost compared to the scale of the development.
Where the new exemption applies, smaller projects may be:
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quicker to progress,
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cheaper to deliver, and
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simpler to bring forward.
That could improve the viability of some sites that might previously have been marginal.
However, it is important not to assume that every small development is exempt. The site area, the date of the planning application and the presence of priority habitat all need to be considered.
6. What are you hearing from developers about these changes?
The changes are likely to be welcomed particularly by SME housebuilders and promoters of smaller sites, where the cost and complexity of BNG can have a disproportionate impact.
The frustrations around BNG have often included:
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the cost of compliance,
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delays in securing off-site units, and
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uncertainty around how the requirements will affect individual schemes.
The new exemptions should address some of these concerns for smaller developments, while the greater flexibility around off-site delivery should give minor developments that remain within the BNG regime more options when deciding how to meet the requirement.
7. What changes are being proposed around off-site biodiversity units?
One of the important changes is to the way the biodiversity gain hierarchy applies to minor development. Previously, developers were expected to work through the hierarchy, considering on-site opportunities before moving to off-site delivery.
Now, minor developments that remain subject to BNG can consider on-site and off-site options at the same time. This means they can choose to use off-site biodiversity units without first having to demonstrate that on-site delivery has been considered and ruled out.
This could give developers greater flexibility when considering the most appropriate and cost-effective way of meeting the 10% requirement.
It does not mean that off-site delivery is now the only or preferred approach. Rather, it gives minor developments more choice and allows the most appropriate delivery option to be considered earlier in the process.
8. Does this mean BNG is becoming less important?
Not at all. BNG remains a mandatory requirement for most non-exempt development. What is changing is the proportionality of the system.
For developments that are not exempt, the requirement to achieve at least 10% BNG remains. The August changes do not reduce the target itself; instead, they change which developments are exempt and give certain minor developments more flexibility in how they achieve the requirement.
BNG should continue to deliver environmental gains, but in a way that is workable and proportionate for different scales of development.
9. How do these changes affect the way developers should approach BNG strategy?
Developers still need to think about BNG early, particularly on medium and larger sites and on smaller sites where the new exemption may not apply.
The reforms create more flexibility, but the core questions remain:
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what is the site's biodiversity baseline?
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does BNG apply to the development?
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if it does, how much gain is needed?
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what is the most efficient delivery route?
For smaller schemes, the first question should now be whether one of the exemptions applies. For developments of 0.2 hectares or below, for example, it is important to establish whether the site impacts priority habitat before assuming the exemption applies.
For schemes that remain within scope, early strategy is still critical to avoid unexpected cost and delay.
10. What opportunities do these reforms create for developers?
There are a few major opportunities:
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improved viability for some small sites;
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greater flexibility for minor developments that remain subject to BNG;
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potential reductions in the time and cost associated with BNG on exempt developments; and
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greater choice around on-site and off-site delivery for minor development.
For developers with constrained sites, these changes may make some projects more viable or provide greater flexibility in how biodiversity requirements are addressed.
11. Are there still risks or uncertainties developers need to watch?
Yes. Although the latest changes are now in force, developers still need to take care when assessing whether a development is exempt or remains subject to BNG.
In particular, developers should consider:
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whether the development falls within one of the current exemptions;
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whether onsite priority habitat could be impacted;
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the date on which the planning application is made; and
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whether transitional arrangements apply, particularly where an existing planning permission is being varied.
It is also important to remember that the removal of the self-build and custom-build exemption applies to new planning applications made on or after 6 August 2026. Existing applications and certain variations retain transitional protection.
Developers should therefore avoid assuming that a scheme is exempt without checking the current rules against the circumstances of the individual project.
12. What should developers be doing now?
Developers should be reviewing their pipelines to identify:
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sites that may now benefit from one of the new exemptions;
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schemes where the new flexibility around off-site delivery could be useful; and
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projects where the BNG strategy or cost assumptions could be revisited.
For any new proposal, it is worth establishing at an early stage whether BNG applies at all. If a site is 0.2 hectares or below, for example, the developer should check whether the new exemption applies and whether any onsite priority habitat is affected.
For schemes that remain within scope, BNG should still be incorporated into the design and planning strategy from the outset.
13. From your perspective, what do these changes suggest?
The reforms suggest that the Government is acknowledging some of the practical challenges that BNG implementation has created within the planning system, particularly for smaller developments.
The changes represent a more pragmatic and proportionate approach, while retaining the broader environmental objectives of BNG.
For developers, the key difference is that the system now provides greater flexibility in some circumstances, rather than applying the same approach across developments of very different scales.
That should be helpful, but it also makes it important for developers to understand exactly which rules apply to their individual scheme.
14. What is your key take away for developers?
The key takeaway is that BNG remains a major consideration for many developments, but the rules are now more flexible and proportionate.
Developers should:
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check at an early stage whether their scheme is exempt;
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understand the implications of the new 0.2 hectare and temporary development exemptions;
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be aware that the self-build and custom-build exemption has been removed for new applications; and
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where BNG still applies, consider both on-site and off-site delivery options early in the process.
The opportunity is to use the additional flexibility where it is available, while continuing to take a proactive approach to biodiversity on schemes that remain within the BNG regime.
In summary
The latest Biodiversity Net Gain reforms represent an important change in how BNG will apply to development in England.
Developments on sites of 0.2 hectares or below and certain temporary developments are exempt from mandatory BNG, subject to the relevant conditions. At the same time, the previous exemption for self-build and custom-build development has been removed for new planning applications. Minor developments that remain within the BNG regime also have greater flexibility when considering on-site and off-site delivery.
For developers, the message is the system has become more proportionate, with greater flexibility for some developments and new exemptions for others.
The first step for any new proposal should be to establish whether BNG applies and, if it does, what the most appropriate strategy for achieving the requirement will be. For larger schemes in particular, early consideration of biodiversity alongside planning, landscape and design remains important to avoid unnecessary cost, redesign and delay.
As BNG continues to evolve, understanding the detail of the latest requirements will be essential to bringing forward viable development while responding positively to the wider environmental objectives of the planning system.
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