BNG Exemptions & Thresholds – Who Is Exempt from Biodiversity Net Gain?
Biodiversity Net Gain (BNG) is a UK planning policy that requires most developments to leave nature better off by at least 10%. In practice, developers must deliver a 10% net gain in biodiversity value on or off site as a condition of planning permission. However, not all projects fall under these rules. There are specific BNG exemptions and thresholds in place to ensure that very small or special-case developments aren’t unduly burdened by biodiversity net gain requirements. If you’re planning a project in England, it’s vital to know whether BNG applies to you or if your development might be exempt from BNG altogether. This guide will walk you through the official biodiversity net gain exemptions, from de minimis thresholds for tiny sites to special provisions for self-build homes and more.
By understanding who is exempt from BNG, you can save time, reduce costs, and focus on compliance measures only when they truly apply. Let’s explore why these exemptions exist and which developments qualify, so you can determine if your project needs to factor in that 10% biodiversity increase or if you can confidently proceed without a BNG plan.
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Why Do Biodiversity Net Gain (BNG) Exemptions Exist?
The mandatory BNG requirement is designed to make most new developments contribute positively to nature. But policymakers recognised that a one-size-fits-all approach could place an unnecessary burden on certain small or low-impact projects. For example, forcing a homeowner building a small kitchen extension to go through ecological surveys and habitat compensation could be disproportionate. Similarly, tiny habitat impacts or very specific projects might not justify the full BNG process. Therefore, exemptions to BNG were created to keep the net gain policy ambitious yet proportionate. These narrowly defined exemptions ensure that minor works, self-builders, and certain special cases can proceed without the complexity of biodiversity calculations, while larger and impactful developments still deliver net gains. In short, BNG exemptions exist to focus efforts where they matter most, and to avoid penalising projects that have minimal or specialised impacts on biodiversity.
Official BNG Exemption Categories (England 2024)
Under the Environment Act 2021 and the subsequent BNG regulations, only a limited set of development types are exempt from the mandatory net gain rules. It’s a narrow list, intended to cover very specific scenarios. The main categories of BNG exemptions are:
- De minimis developments – Projects with tiny habitat impacts below defined thresholds (often <25 m² of habitat or <5 m of hedgerow affected), and no impact on any priority habitat. These very small-scale works are exempt from BNG requirements.
- Householder applications – Small projects within the curtilage of a single existing dwelling (e.g. home extensions, garden buildings, loft conversions) do not need to deliver BNG. This covers typical householder developments, but not changes of use or proposals creating new dwellings.
- Self-build and custom housing – Small-scale self-build projects can be exempt, provided they meet specific size criteria (generally sites ≤0.5 hectares and 9 or fewer dwellings, all intended as self/custom build homes). This exemption helps individual builders and community projects.
- Biodiversity gain sites – Developments undertaken purely to create or enhance habitat for another project’s offset (i.e. building a habitat bank or BNG off-site compensation area) are exempt, so they don’t need to achieve an additional 10% on top.
- Infrastructure and other statutory exemptions – Certain major infrastructure works like the High Speed 2 (HS2) rail network are excluded from BNG rules. Also, urgent Crown developments (e.g. emergency works by government) and developments permitted by a development order (including many permitted development rights) are exempt.
These are the core exemptions defined in the Biodiversity Gain (Exemptions) Regulations 2024. Let’s unpack each in more detail to understand the exact thresholds and criteria.
De Minimis Exemption (Tiny Habitat Impacts)
The de minimis exemption is all about very small impacts. If your development only affects a negligible amount of habitat, it may be BNG exempt as de minimis. Under the regulations, this means the project:
- Impacts less than 25 square metres of habitat in total (about a 5 m × 5 m area), and
- Affects less than 5 metres length of any “linear habitat” (such as hedgerow or ditch), and
- Does not impact any priority habitat on the site. (“Priority habitats” are sensitive or important habitat types listed under the Natural Environment and Rural Communities Act 2006.)
If all of those conditions are met essentially, no significant habitat loss and nothing of high ecological value disturbed then the development is treated as de minimis for BNG. In plain terms, it’s too small to warrant the full net gain process. This BNG de minimis exemption ensures truly minor works aren’t bogged down by ecology reports and unit calculations. It encourages developers to design schemes that avoid habitat loss altogether when possible, since a project that stays within these limits can skip the BNG requirement. Conversely, if you exceed either the 25 m² area or 5 m hedgerow threshold (even slightly), or if any priority habitat is affected, then de minimis exemption does not apply the full BNG rules kick in for the whole site.
Examples of De Minimis Developments
What might qualify as de minimis? Consider a small wheelchair ramp and new entrance lobby added onto an existing building, built entirely on already-paved ground. If no green habitat is lost or only a few square metres of amenity grass are affected, this could fall under the de minimis threshold. Another example is laying a short stretch of pipe or cable through a garden where only a tiny strip of lawn is temporarily disturbed. Because these works impact minimal habitat area, they likely qualify as exempt from BNG. It’s worth noting that existing hard surfaces (like tarmac, concrete, buildings) count as zero biodiversity value replacing or building on an already sealed surface often means you’re not reducing any habitat, which effectively puts you in de minimis territory by default.
Householder Projects (Home Extensions)
If you’re a homeowner extending or altering your house, good news: most householder applications are exempt from BNG. In the planning context, a “householder” development means work within the curtilage (the property boundary) of an existing dwelling that is used for purposes incidental to the dwelling. Typical examples include: adding an extension or conservatory, converting a loft or garage, building a garden room or shed, or similar improvements to a home. These types of projects do not require biodiversity net gain calculations or offsets. The rationale is that such small-scale domestic works usually have very limited ecological impact, and it wouldn’t be proportionate to force every home improvement to create new habitats.
However, be careful: the householder exemption is narrowly defined. It does not cover proposals that change the use of a house (for instance, converting a single house into flats or a shop), nor does it cover projects that create new dwellings in a garden or on the plot. Those would fall outside “incidental to an existing house” and wouldn’t count as householder for BNG purposes. In those cases, you’d need to assess BNG like any other development (unless another exemption applies). But for a straightforward house extension or similar, you can rest assured Biodiversity Net Gain is not required no need to worry about habitat unit metrics for your small home project. Just ensure any landscaping changes are minimal, or you might want to double-check the de minimis rules if you’re digging up part of a large garden.
Self-Build and Custom Build Exemption
One of the most significant BNG exemptions is for small self-build and custom-build housing projects. This was introduced to support individuals and communities building their own homes, who might otherwise struggle with the extra costs and complexity of delivering net gain. To qualify for the BNG self-build exemption, a development must meet all of the following criteria:
- It consists of no more than 9 dwellings in total;
- The entire site is 0.5 hectares or less in area (roughly, up to about 1.2 acres);
- Every dwelling in the development is to be built as self-build or custom housebuilding, as legally defined (meaning the people who will live in the homes have had a primary input into their design and are building them for their own use).
If your project ticks those boxes, it is exempt from the BNG requirement. In practice, this covers things like a small group of self-build homes or a single custom home on a modest plot. The exemption won’t apply if you’re building 10 or more units, or if you exceed the 0.5 ha site size larger sites are expected to provide net gains because they likely impact more habitat and have more scope to deliver enhancements. Also, the self-build exemption isn’t a loophole to avoid BNG on commercial developments; it’s specifically tied to the Self-build and Custom Housebuilding Act 2015 definition. Local planners will require evidence that a proposal truly is self-build/custom-build (for example, being on the authority’s self-build register, or via planning conditions tying the permission to self-build occupancy).
Benefits for Self-Builders
This exemption is a big win for individual homebuilders and small developers. Without it, even a single self-built house would have to go through ecology surveys and potentially buy biodiversity credits or create habitat which can add tens of thousands of pounds and significant delays. By exempting bona fide self-build projects, the rules reduce barriers to entry for those looking to build their own home. It strikes a balance: small self-build sites generally have limited ecological impact (often they’re infill plots or small parcels), and they typically lack the economies of scale to easily absorb net gain costs. The exemption acknowledges this, helping to keep housing delivery for self-builders viable while still ensuring larger developments shoulder the responsibility for biodiversity. Self-builders can thus focus on sustainable design and good landscaping practices voluntarily, rather than navigating formal BNG metrics.
Biodiversity Gain Sites
This is a niche but important category: if a development’s main purpose is to create or enhance habitats to provide biodiversity gain for another development, it is itself exempt from needing a further 10% net gain. These are often called biodiversity gain sites or habitat banks. For example, suppose a developer secures a separate plot of land to undertake habitat creation as offsetting for a larger project’s BNG requirement. That habitat project may need its own planning permission (for change of land use or earthworks, etc.), but it wouldn’t make sense to require the habitat-creation project to also deliver an extra 10% gain on itself. Therefore, the law exempts developments that are solely for biodiversity gain or environmental improvement purposes from having to additionally meet BNG.
In practice, this means if you are establishing an off-site compensation area (a wildflower meadow, wetland, woodland planting, etc.) to fulfil a BNG obligation, that specific project won’t need to calculate another net gain on top of what it’s already delivering. It removes a potential Catch-22 and ensures that BNG offset projects can fully count their improvements for the development they’re serving, without being penalized by their own separate net gain target. Do note, this exemption typically applies when the project is purely for biodiversity or also for public amenities related to nature (like creating a nature reserve or park for community use). If you’re doing mixed-use (say, part housing, part nature area), only a dedicated gain site is exempt.
Major Infrastructure & Other Exemptions
A few other BNG exemptions exist to cover nationally significant or regulated scenarios:
- High-Speed Rail (HS2) – Any development that is part of or works ancillary to the HS2 high-speed rail network is exempt from BNG. Large infrastructure projects often have their own bespoke environmental mitigation regimes, so the BNG requirement was not additionally applied to HS2 phases by law.
- Urgent Crown Developments – If the Government (Crown) urgently needs to carry out development (for instance, emergency works or fast-tracked projects of national importance), such projects are exempt from the net gain rules. This ensures that, in a crisis or urgent public need, BNG obligations don’t delay necessary action.
- Development Orders & Permitted Development Developments that are granted by general development order including many forms of permitted development (PD) that don’t require a normal planning application – are not subject to BNG. Essentially, if you don’t need full planning permission (because your project is allowed under national permitted development rights or a local development order), then the mandatory BNG condition doesn’t apply. One example might be certain rail or road maintenance works under permitted development, or a small PD housing extension (which would be exempt anyway as householder).
It’s important to stress that beyond these listed cases, almost all other developments must comply with BNG. The exemption list is intentionally limited. For instance, projects by NHS Trusts or local authorities are not automatically exempt (unless they fall in one of the categories above); they are expected to follow BNG rules just like private developments. So a new hospital building or school, for example, would need to achieve net gain unless perhaps it’s delivered under an order or special urgent provision. Always check if a particular public-sector project has any special status, but generally, BNG regulations apply across the board outside the specific exemptions.
Are Small Sites Exempt from BNG?
There’s been some confusion around “small sites” and BNG, so let’s clear that up. Originally, when the BNG policy was being rolled out, small site developments (typically defined as those creating fewer than 10 homes or under 0.5 hectares, i.e. minor applications) were given a slightly later start date for mandatory BNG. Major developments had to comply from 12 November 2023 (later adjusted to February 2024), and small sites from 2 April 2024. This grace period led some to believe small sites were entirely exempt but that’s not the case. It was a temporary exemption or deferral, only until April 2024. As of now (2025 onward), small sites are not exempt from biodiversity net gain. If you submit a planning application for a housing development of, say, 5 homes on a 0.3 ha site, you will need to deliver 10% net gain just like a larger project would.
Small Sites Metric (SSM)
However, small sites do benefit from a different process. There is a Small Sites Metric (SSM) a simplified biodiversity metric tool – which small projects can use instead of the more complex standard metric. The SSM is designed to be completed by a “competent person” (not necessarily a fully qualified ecologist) and is generally more user-friendly for minor developments. This helps to reduce the burden on small site developers. So while you’re not exempt from BNG on a small site, you have a streamlined way to comply. Additionally, many local planning authorities are being pragmatic with small developers, sometimes offering guidance or standard approaches to achieve net gain on-site or via local offset schemes.
Remember, if your small site project qualifies under another exemption (for example, it’s all self-build homes, or the habitat loss is under the de minimis threshold), then those specific exemptions still apply. But “smallness” alone is not an automatic BNG exemption after April 2024. In summary: small sites must deliver BNG, but the process is scaled appropriately. Always double-check if your site might hit the de minimis criteria or if it’s a pure self-build that could change things. Otherwise, be prepared to use the small-sites BNG metric and factor in some ecological enhancements, even for minor developments.
Retrospective Applications & Section 73 Variations
What if you’re seeking permission after work has started or for a tweak to an existing permission? Current guidance indicates that BNG does not apply to retrospective planning applications at least for now. If a development is essentially already carried out (without prior permission) and you apply under Section 73A of the Town and Country Planning Act 1990 to regularise it, there isn’t a practical way to enforce net gain (since the baseline habitat was likely already altered). As a result, retrospective permissions are temporarily exempt from BNG requirements. This is seen as a loophole by some, and the government may close it with future regulations, but as of 2025 there is no end-date yet for the retrospective exemption. Developers shouldn’t abuse this intentionally, though proceeding without permission has many risks beyond BNG.
Section 73 applications
Similarly, Section 73 applications (which are applications to vary or remove conditions on an existing planning permission) do not usually trigger a new BNG requirement, provided the original permission pre-dated mandatory BNG. For example, if you got permission in 2023 (when BNG wasn’t mandatory) and in 2025 you apply under s.73 to make a minor material change, you wouldn’t suddenly be forced to add 10% net gain to that project.
The principle is that the BNG condition applies based on when the original planning application was made. Indeed, any project with a full planning application submitted before 12 February 2024 is exempt from the new net gain rules entirely, thanks to transitional provisions. The key date is when the application was lodged, not when construction starts. So if you’re varying an older permission or finalising reserved matters on an outline that was submitted before BNG kicked in, you generally won’t need to retrofit BNG into it.
Do note: if your Section 73 change significantly increases the development’s impact on biodiversity (say you enlarge the site boundary or remove extra habitat compared to the original plan), the local authority might require some form of compensation or enhancement via other policies. But there is currently no statutory 10% BNG requirement on s.73 variations or s.73A retrospectives. Keep an eye on policy updates, though, because there have been calls to address this gap to prevent misuse (for instance, a developer might otherwise intentionally build first and apply later to evade BNG something authorities will want to discourage). For now, it remains one of the few situations where biodiversity net gain is not enforced.
Irreplaceable Habitats – A Special Case
One thing to understand is that irreplaceable habitats are treated differently in the world of biodiversity net gain. Irreplaceable habitats include things like ancient woodlands, ancient hedgerows, peat bogs, veteran trees, and other ecosystems that cannot be recreated or compensated within a human lifetime. The loss of an irreplaceable habitat can’t be offset by simply creating a 10% gain elsewhere by definition, it’s irreplaceable.
Therefore, developments that would damage or destroy irreplaceable habitat are not subject to the standard 10% BNG metric. because something more stringent applies. In fact, BNG regulations exclude irreplaceable habitats from the net gain requirement. This does not mean you get a free pass to impact them quite the opposite. It means if such a habitat is in your site, you cannot just do a biodiversity calculation and pay for credits to make it okay. Instead, planning policy and the Environment Act impose stricter tests: usually, you must demonstrate wholly exceptional circumstances to even be allowed to affect an irreplaceable habitat, and you must provide comprehensive compensation and mitigation bespoke to that impact (often involving things like habitat translocation, long-term management elsewhere, etc., which go beyond simple metrics).
Summary: Application Involving Irreplaceable Habitat
In summary, an application involving irreplaceable habitat is handled outside the normal BNG process. You won’t be calculating a 10% improvement because the law recognises that you can’t put a numeric value on such losses. If you find yourself in this scenario (e.g. your site has ancient woodland or a very rare habitat), expect a tougher planning route likely needing extensive environmental impact assessments and facing possible refusal unless truly exceptional. For our purposes here: you can think of it as an “exemption” from BNG only in the sense that the usual net gain requirement isn’t applied. But it’s not an exemption that makes life easier; rather, it flags a situation that’s beyond the scope of net gain and into the realm of strict conservation law. Always seek specialist ecological and legal advice if irreplaceable habitats are in play.
How to Check if You’re Exempt (Process & Next Steps)
Given all these categories, how do you determine if your particular development is exempt from BNG? The first step is to review the criteria above against your project: size of habitat impact, type of application, etc. Here’s a quick process to follow:
- Measure your habitat impact – Estimate the area of land and length of any hedgerows or watercourses your project will affect. If it’s below the de minimis thresholds and no priority habitat is involved, you likely qualify for that exemption.
- Identify your application type – Is it a straightforward householder planning application for your own home? If yes, BNG won’t apply. If it’s a new build housing, check if it could count as self-build/custom-build and if it’s within the 9 units/0.5 ha limit. If yes, that exemption could apply (make sure to declare it’s self-build on your forms!).
- Consider timing and permission route – Was the planning application submitted before the mandatory BNG start date? Or is it a modification of an older permission? If so, note those transitional exemptions. Also, if your project doesn’t even require full planning permission (e.g. permitted development), BNG isn’t required.
- Check for special designations – Are there any irreplaceable habitats on site? If yes, normal BNG rules don’t apply (but you have other serious considerations). Are you part of HS2 or an urgent government scheme? Those special cases aside, most typical developments won’t fall in this category.
BNG exempt developments guidance
It can be very useful to consult the official BNG exempt developments guidance (available on GOV.UK) or the legislation text to double-check definitions. Many local planning authority websites also summarize BNG exemption criteria. If you think an exemption applies, you must clearly state this in your planning application.
There’s usually a question on the application form (or a local validation requirement) asking if the development is subject to BNG. If claiming an exemption, you should provide a brief statement or BNG exemption form explaining why for example, “This is a householder application for a rear extension, which is exempt from BNG” or “The development impacts only 10 m² of amenity grassland with no priority habitat (below de minimis threshold), thus BNG does not apply.” Attaching a short BNG exemption statement with those details and any evidence (like a map highlighting habitat areas) can help the planning officer agree that no net gain condition is needed.
If you are unsure about your status, consider getting expert advice. Our team, for instance, can assess your site and plans to confirm BNG applicability or exemption. It’s much better to confirm early on than to assume wrongly and face surprises later. Authorities are becoming familiar with these rules, but it’s still new so proactively making the case for your exemption (with references to the regulation criteria) is wise. Once you know you’re exempt, you can focus on other aspects of your application. If you’re not exempt, then you know to proceed with a Biodiversity Gain Plan or consider design tweaks to reduce impacts. Either way, knowing where you stand saves time and hassle.
Our BNG Compliance Services
Navigating the ins and outs of biodiversity net gain regulations can be challenging, especially as the rules continue to evolve. This is where our expertise comes in. We offer comprehensive support to ensure your development meets all BNG requirements or properly documents a valid exemption. Our services include:
BNG Feasibility Assessments
At the early stage of your project, our ecologists and planners will review your site for any BNG obligations or exemptions. We identify whether your proposal hits any exemption criteria (such as de minimis impact or self-build status) and advise on the best course of action.
Small Sites Metric Assistance
If your development is a minor project that needs to deliver net gain, we can help you use the Small Sites Metric (SSM) effectively. Our team will guide you through the simplified calculations, ensuring you understand how to achieve the required units without overcomplicating things.
Biodiversity Gain Plan Preparation
For projects that do require BNG, we prepare full Biodiversity Gain Plans and Habitat Management Plans. This includes baseline habitat surveys, metric calculations, and designing on-site enhancements or liaising to purchase off-site units. We make sure your plan will satisfy council requirements on the first submission.
Exemption Documentation
When an exemption from BNG applies, we compile the necessary evidence and a clear statement to accompany your planning application. This might involve mapping the affected area to prove it’s under the threshold, or assembling proof of self-build status. We handle the paperwork so you have peace of mind.
Regulatory Liaison
Our experts stay up-to-date with the latest BNG regulations and local policies. We frequently communicate with Local Planning Authorities on our clients’ behalf to confirm interpretations of the rules (for example, confirming a retrospective exemption or negotiating reasonable BNG conditions). This proactive liaison can prevent delays and ensure your project isn’t over-burdened by misapplied requirements.
Whether you’re a homeowner extending your property, a small developer building a handful of houses, or a landowner creating a habitat bank, we tailor our services to your needs. The goal is simple: keep your project compliant, on schedule, and cost-effective with respect to biodiversity net gain. We take pride in demystifying BNG for our clients. With our support, you can confidently address any net gain obligations or confirm that none are needed well before you break ground.
Why Choose Us for BNG Guidance?
When it comes to biodiversity net gain and ecological planning, you need a partner who combines deep technical know-how with practical experience. Here’s why clients trust us to steer them through BNG exemptions and requirements:
- BNG Expertise & Experience: Our team includes certified ecologists and planning consultants who specialise in UK BNG regulations. We have been involved with BNG since its early pilot days and stay current on every update, so you get advice based on the latest rules and real-world practice.
- Tailored Strategies: We understand that every development is unique. We don’t do one-size-fits-all. Instead, we evaluate your project’s specifics location, size, habitat value, timelines and provide bespoke guidance. Whether that means securing an exemption or crafting a gain plan, our solutions fit your context.
- Save Time & Cost: Misinterpreting BNG rules can be expensive. By clarifying upfront if you’re exempt or, if not, the simplest way to comply, we save you from unnecessary surveys or over-engineered solutions. Our efficient approach often accelerates planning approval and minimises costly delays or unit purchases.
- Collaborative Approach: We liaise closely with local authorities, stakeholders, and other consultants on your behalf. Our clear reports and proactive communication help smooth the planning process. Councils appreciate our thorough, policy-compliant submissions meaning fewer headaches for you.
- Commitment to Nature: Beyond just ticking boxes, we genuinely care about achieving positive outcomes for nature. If your project does need to deliver net gain, we’ll identify creative yet feasible ways to enhance biodiversity on-site or locally. If you’re exempt, we can still suggest voluntary improvements (like native planting) to add value without obligation. It’s this balanced approach that earns us the respect of both clients and regulators.
Ready to ensure your project is on the right side of biodiversity net gain regulations?
Whether you need a quick exemption check or full-service BNG plan, we’re here to help. Get in touch with our team today to discuss your project and find out how we can assist, from confirming “no net gain required” to delivering comprehensive ecological solutions. Let’s work together to achieve your goals while safeguarding nature. With our guidance, you can proceed with confidence knowing that your BNG matters are in expert hands. We help you navigate the complexity so that you can focus on the bigger picture of your development.
In the past year, we’ve delivered over 750 audit-ready reports supporting 400+ projects for developers, planners, and architects nationwide. We put quality over quantity and build lasting relationships based on trust, ensuring your planning applications are backed by robust evidence and delivered on time.
You can also drop us an email at hello@acp-consultants.com and we’ll get back to you within 24 hours to help with your inquiry!
FAQs: Biodiversity Net Gain (BNG) exemptions?
Got questions about Biodiversity Net Gain (BNG) exemptions? This FAQ explains how the rules apply to householder projects, small sites, self-build and custom-build housing, de minimis thresholds, Section 73 variations and retrospective applications. Use these answers to quickly check whether your development is likely to be exempt, what evidence you may need, and the next steps to stay compliant.
What developments are exempt from Biodiversity Net Gain?
In England, only a narrow set of developments are exempt from BNG. These include very small projects (impacting <25 m² habitat and no priority habitat), householder applications (like home extensions), qualifying small-scale self-build or custom-build housing (≤9 homes on ≤0.5 ha site), dedicated biodiversity gain sites (habitat creation for offsets), and certain infrastructure or permitted developments (e.g. HS2, urgent Crown projects). If your project doesn’t fit one of these categories, it likely must comply with the 10% net gain requirement.
Are small sites exempt from BNG requirements?
Not anymore. Small sites (e.g. developments of 1–9 homes) had a delayed start but as of April 2024 they also must deliver 10% net gain. There is no permanent blanket exemption just for being a “small site.” However, small projects can use a simplified Small Sites Metric to comply, and if a small project meets another exemption (like being self-build or under the de minimis habitat threshold) then that specific exemption would apply.
Does a house extension need to provide Biodiversity Net Gain?
No, typical householder projects such as extensions, loft conversions, or garden outbuildings are exempt. These are considered householder applications and do not require a BNG assessment or a 10% net gain. Just be sure your proposal is strictly within your home’s curtilage and doesn’t create new dwellings. If it’s a straightforward home improvement, you won’t need to worry about BNG.
What is the BNG de minimis exemption?
The de minimis exemption means very small habitat impacts don’t trigger BNG. If your project affects less than 25 m² of habitat (and under 5 m length of any hedgerow) and no priority habitats at all, it’s considered de minimis. Such minor works are exempt from the 10% net gain rule. It basically acknowledges that the impact is too small for the formal BNG process.
Is there a Biodiversity Net Gain exemption for self-build homes?
Yes a development exclusively of self-build or custom-build homes can be exempt, provided it’s no more than 9 homes on a site no larger than 0.5 ha. This BNG self-build exemption aims to ease the burden on individuals building their own homes. If you meet the criteria (and are truly building for yourself to live in), you won’t need to deliver net gain on that project. Be prepared to demonstrate that status in your planning application.
Do change-of-use applications need to comply with BNG?
Generally, yes. Changing the use of land or a building (for example, converting offices to flats) is not listed among the exemptions, so BNG will apply if the change of use leads to habitat loss or gain within the site. However, if the change of use is entirely internal (say, repurposing an existing building with no external works), then there may be effectively no habitat impact potentially falling under de minimis if negligible. Importantly, the householder exemption does not cover change-of-use of a house or increasing dwelling numbers, so those scenarios would need BNG consideration. Always check if any habitat is affected by the change of use; if not, you might argue no net gain needed, but it isn’t an automatic official exemption.
Are retrospective planning applications exempt from BNG?
At present, yes if you are applying for permission after the fact (a retrospective application under Section 73A), the law currently does not enforce BNG on that. The rationale is that the development’s impacts have already occurred, so a net gain condition would be difficult to implement. However, this is seen as a loophole and regulations might change in future. Councils will still encourage some biodiversity enhancements informally, but as of now there is no mandatory 10% requirement for retrospective permissions.
How do I declare a BNG exemption on my application?
When submitting your planning application, there will typically be a section or question about biodiversity net gain. If you believe your project is exempt, you should clearly state the exemption category and why it applies (e.g. “This proposal is a householder development exempt from BNG” or “Impacts <25m², below de minimis threshold”). It’s wise to include a brief cover note or BNG exemption statement detailing the evidence (like habitat area calculations or confirmation of self-build status). This helps the planning authority validate your claim. If you don’t mention it, the default assumption might be that BNG applies, so always communicate it upfront.
What if my project impacts an irreplaceable habitat?
If an irreplaceable habitat (such as ancient woodland or a veteran tree) is on your site and would be impacted, the standard BNG process does not apply you can’t simply offset it with 10% net gain elsewhere. In fact, your project will face a much stricter regime. You’ll likely need to prove exceptional circumstances and propose bespoke compensation. Essentially, irreplaceable habitats are excluded from BNG metrics because their loss can’t be quantified or replaced. This isn’t an exemption that removes obligations; instead, it elevates the level of scrutiny. It’s best to redesign to avoid any harm to such habitats, as permission could be refused outright regardless of net gain.
Will BNG exemptions change in the future?
The list of exemptions is set in legislation, but there is ongoing discussion about certain aspects (like the retrospective exemption). It’s possible that regulations could be updated for example, to eventually require net gain for retrospective applications, or to tweak definitions. Also, new policy could introduce additional categories (though none are proposed at the moment). For now, the exemptions in place are expected to remain as is, at least in the short term, apart from any minor clarifications. It’s important to stay informed through official guidance or consult experts, because biodiversity net gain is a evolving area of policy.
Additional FAQs on BNG Exemptions & Forms
Alongside the most common questions, developers and homeowners often search for more specific points about BNG exemptions. These include queries on small sites, retrospective permissions, NHS projects, and exemption forms. The answers below cover these additional scenarios so you can be clear on when biodiversity net gain does or does not apply.
Are there BNG exemptions for small sites?
No permanent BNG exemptions small sites exist. While small projects (1–9 dwellings or under 0.5 ha) once had a BNG exemptions temporary delay until April 2024, they must now comply using the Small Sites Metric.
What is meant by “BNG small sites”?
The phrase BNG small sites usually refers to minor residential schemes under 10 dwellings or 0.5 hectares. These projects are required to deliver net gain, but can use the simplified Small Sites Metric.
Does “biodiversity net gain small sites” mean no BNG applies?
No. The term biodiversity net gain small sites highlights that small developments must follow BNG rules. They are not automatically exempt, though other exemptions (like self-build or de minimis) might still apply.
What about retrospective projects? Do they get BNG exemptions?
Yes, at present BNG exemptions retrospective apply to Section 73A applications, and biodiversity net gain exemptions retrospective mean councils don’t impose net gain on works already carried out. This may change in future updates.
Is there an official BNG exemptions form?
Many councils provide a template BNG exemptions form. You may also see it listed as a biodiversity net gain exemptions form, where you confirm your project type (e.g. householder or de minimis) and supply supporting evidence.
Do Section 73 applications qualify as BNG exemptions?
Yes, some applicants ask about BNG exemptions s73. If your original permission was submitted before mandatory BNG began, a Section 73 variation does not normally trigger new biodiversity net gain requirements.
Are there biodiversity net gain exemptions for NHS projects?
Despite common searches for biodiversity net gain exemptions NHS, there is no general exemption for hospitals, GP surgeries, or other NHS developments. They must comply unless another valid exemption applies.
Where can I find official government guidance on exemptions?
The most authoritative source is the biodiversity net gain exemptions GOV UK webpage, which lists all recognised categories. It’s always best to check that page alongside local planning advice.
Is there such a thing as a general “biodiversity net gain exemption”?
The phrase biodiversity net gain exemption refers collectively to the small number of development types legally excluded from BNG such as de minimis cases, self-build, or householder projects.
Do small home extensions fall under “small developments exemptions”?
Yes. The category of small developments exemptions mainly covers householder planning applications like single-storey extensions, loft conversions, or sheds within a dwelling’s curtilage.
References
- Guidance: Statutory biodiversity credit prices.
- Guidance: Estimate the cost of statutory biodiversity credits.
- Biodiversity Net Gain Monitoring Fees. Torridge District Council.
- Biodiversity net gain legislation 2024. UK Statutory Instruments.
- Guidance: Understanding biodiversity net gain.
- Creating a habitat management and monitoring plan for BNG. Defra.
- Register your interest in a legal agreement to regulate an off-site biodiversity net gain site. Buckinghamshire Council.
- Guidance: Biodiversity net gain: exempt developments. Defra.
- Biodiversity Net Gain – what are the exemptions?. Defra.
- The Biodiversity Gain Requirements (Exemptions) Regulations 2024. UK Statutory Instruments.
- Biodiversity net gain planning advice. Westmorland & Furness Council.
- Biodiversity Net Gain (BNG) Exemption Statement. Defra.
- New research shows government should not exempt all small BNG sites. CIEEM.
- Exemptions & de minimis thresholds – Householder, small self-build, and very small impacts where no priority habitat is affected. Exemptions Guidance (GOV.UK) and Defra Environment Blog.
- Statutory biodiversity metric – How units are calculated, modules, factors, and guidance on early use. Statutory Metric and User Guide (GOV.UK).
- Statutory framework & planning condition – Biodiversity Net Gain under Schedule 7A of the Town and Country Planning Act 1990; statutory regime explained in Planning Practice Guidance (GOV.UK)
- Securing off-site Biodiversity Net Gain: Expert legal perspectives. Natural England.
- Guidance: Make off-site biodiversity gains as a developer. Defra.
- BNG in Practice Report (2025) – Case studies showing how BNG is being delivered in real projects. Institute of Environmental Sciences.
- Biodiversity Net Gain – Principles and Guidance for UK Construction and Developments. Chartered Institute of Ecology and Environmental Management.
- Biodiversity net gain: where to start. Natural England.
- Biodiversity Net Gain Report and Audit Templates- CIEEM.
- Implementing statutory biodiversity net gain. NAO.
- Mandatory Biodiversity Net Gain in England. A Guide by CIEEM.
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Explore Related Biodiversity Net Gain Resources
Not all projects fall within mandatory Biodiversity Net Gain (BNG) requirements, but understanding the exemptions and thresholds is only one step. To see how BNG applies when it is required, start with the Biodiversity Net Gain Overview and BNG Legislation & Guidance, which explain the policy context under the Environment Act 2021.
For smaller developments, learn how the Small Sites Metric (SSM) simplifies calculations, or use the Statutory Biodiversity Metric 4.0 for full-scale applications. If your proposal requires formal reporting, our Biodiversity Gain Plan (BGP) and Habitat Management and Monitoring Plan (HMMP) templates show how to evidence compliance.
For cost and implementation insight, explore the BNG Costs & Pricing and BNG Monitoring Fee Calculator. You can also review BNG Case Studies to see how exemptions, thresholds, and discretionary approaches are applied in practice, or download reference materials from our BNG Templates & Downloads.
You can also drop us an email at hello@acp-consultants.com and we’ll get back to you within 24 hours to help with your inquiry!
- Last Updated:
- October 2025
Disclaimer: Our content is prepared by ACP Consultants’ in-house specialists and is based on current guidance, standards, and best practice in environmental consultancy. While we make every effort to keep information accurate and up to date, it is provided for general guidance only and should not be relied upon as a substitute for professional advice on specific projects. Planning authorities retain final decision-making powers, and requirements may vary between local authorities and over time. ACP Consultants accepts no liability for any loss arising from reliance on this content without obtaining tailored advice for your project.