BNG Across Housing Sees Major Shift
The latest Defra consultation features a number of changes that will affect SME developers and self-builders…
The UK government has confirmed a significant shift in how Biodiversity Net Gain (BNG) will be applied across the housing sector – balancing environmental ambition with development practicality.
Introduced under the Environment Act 2021 and enforced from 2024, BNG requires developers to commit to the delivery of at least a 10% improvement in biodiversity before securing planning approval. The policy has been widely regarded as a cornerstone of the UK’s environmental strategy, but its implementation has not been without friction – particularly for smaller developers and self-builders.
The latest consultation on the changes, released in April 2026, has decided to bring to an end the exemption of self-build and custom housebuilding projects from BNG requirements. This decision might be viewed as a signal of a firm commitment to maintaining environmental standards across all development types, regardless of scale or ownership structure.
Defra (Department for Environment Food and Rural Affairs) argues that by applying consistent rules across the board, local planning authorities can avoid navigating a patchwork of exceptions, which has previously slowed down decision-making.
Housing minister Matthew Pennycook had earlier indicated the government’s intention to streamline planning processes, and this move aligns with that broader agenda.
For self-builders, this is a mixed outcome. On the one hand, the lack of exemption means additional cost, complexity, and potentially longer planning timelines. Many self-build projects operate on tight budgets, and commissioning ecological assessments or securing biodiversity units – especially off-site – could add several thousand pounds to project costs.
On the other hand, the simplification of rules may actually reduce confusion. Previously, navigating whether a project qualified for exemptions could be unclear. A more uniform system, combined with increased flexibility around off-site biodiversity gains, could make compliance more predictable – even if not cheaper.
There is also a design implication: self-builders may increasingly need to factor biodiversity into the site layout from the outset, integrating features such as native planting, green roofs, or habitat corridors to meet requirements in a cost-effective way.
BNG Exemptions
While self-builders won’t be let off the hook, Defra has introduced several targeted exemptions set to take effect from 31 July 2026 (subject to parliamentary approval). These include developments where biodiversity enhancement is the primary goal, temporary planning permissions (up to five years) and projects improving public green spaces such as parks and playing fields.
Perhaps most impactful, though, is the exemption for small residential developments. Sites delivering between one and nine homes – now capped at 0.2 hectares, down from the previously proposed 0.5 hectares – will no longer need to meet BNG requirements (Defra consultation response, April 2026). According to Defra, this could exempt around 50% of residential planning applications that were previously subject to the rules, in effect meaning self-builders could still see their proposed development to be exempt.
For SME developers, this threshold change is likely to be significant. Many small builders operate on sites just above or below these limits, so the revised 0.2-hectare cap becomes a critical dividing line.
Those who fall within the exemption will benefit from reduced costs and faster planning decisions – potentially improving viability for marginal sites – because it is rare for a SME developer’s site to be large enough to provide on-site BNG (because BNG cannot be provided within gardens) therefore purchasing off-site credits is normal and far from inexpensive. However, developers just above the threshold may feel disproportionately impacted, facing full BNG requirements while competing with exempt schemes nearby.
This could unintentionally influence land-acquisition strategies, with developers favouring smaller, sub-threshold sites to avoid BNG obligations. Over time, this may reshape the type and scale of residential development coming forward, particularly in rural and edge-of-settlement locations.
Off-site Provisions
At the same time, the ability to rely more on off-site biodiversity gains could help SME developers who lack the space or expertise to deliver ecological improvements on-site. Still, access to affordable off-site units – and a transparent market for them – will be key to ensuring this flexibility translates into real-world benefits.
Another notable reform involves the ‘biodiversity gain hierarchy’, a framework guiding how developers meet their obligations. Traditionally, according to guidance on the Environment Act 2021, developers were expected to prioritise on-site biodiversity improvements, followed by off-site measures, and finally statutory credits.
Under the new changes, according to the consultation response, Defra plans to make it easier to use off-site biodiversity gains earlier in the process. This flexibility could unlock more efficient delivery, especially for urban or constrained sites where on-site enhancements are difficult.
In parallel, the government has delayed the rollout of BNG requirements for nationally significant infrastructure projects until November 2026. This marks another postponement, reflecting ongoing challenges in aligning large-scale development with biodiversity goals.
Overall, for self-builders and small developers, the picture is nuanced. While some will benefit from exemptions and increased flexibility, others will face new costs and strategic decisions. Ultimately, success will depend on how clearly the system is implemented – and whether the emerging biodiversity market can support projects of all sizes without becoming a barrier to delivery.
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