Exemptions to Biodiversity Net Gain (BNG) are detailed in the Biodiversity Gain Requirements (Exemptions) Regulations 2024. When these exemptions apply, the statutory requirement to achieve 10% BNG is waived, although compliance with local BNG policies may still be necessary.

The exemptions are many and include:

• applications submitted before 12 February 2024 (though these applications may still be subject to local policies);
• the de minimis exemption;
• householder applications (excluding changes of use or change in dwelling numbers);
• self-build developments;
• sites needing planning permission to fulfil a BNG condition;
• high-speed railway projects; and
• urgent crown development.

Planning permissions granted through development orders and rights are also exempt.

These exemptions were intended to ensure that BNG requirements are applied proportionately, avoiding undue burdens on certain developments, such as small-scale projects.

In autumn 2024, the government reported collecting data on the use of these exemptions, as most planning applications submitted in 2024 were exempt from BNG.  Interested parties – particularly those seeking to deliver BNG units, relying on a material level of stable demand – have also voiced concerns that the exemptions are too broad.

Ironically, these exemptions were designed to ease the burden on SME builders but there is a risk of perverse outcomes/ incentives. There are some cautionary examples emerging that illustrate the need to take care with BNG assumptions.

The most frequently used exemptions are the de minimis exemption and the self-build/custom-build housing exemption. There have been calls to reduce the 25m² threshold for the de minimis exemption, in light of concerns that site boundaries / development design are being adjusted to avoid BNG requirements.

Additionally, many small developers are using the self-build/custom-build housing exemption for small-scale developments to avoid BNG. With many local planning authorities having limited resources, the information provided in planning applications cannot always be verified, meaning there is currently no guarantee that the exemptions are being applied correctly.

An example of that is a DEFRA-funded scheme to construct open-sided agricultural buildings to cover open manure heaps on a large-scale pig farm (mitigating air pollution from ammonia emissions and watercourse pollution from run-off). The application had been made on the basis that there would be no new hardstanding, and the council validated it without a biodiversity metric. It later realised its error and, at appeal the applicant claimed the proposal met the de minimis size exemption. The inspector did not agree that it should be engaged simply because the only groundworks outside of the existing hardstanding would be post support pads covering less than 25m².  Part of each building (to be used for storage) covered the edge of a field which would therefore no longer receive the same rainfall/ sunlight.

In refusing permission, the inspector appears to have taken a mixed approach to the statutory requirement (which could have been fixed by a condition discharge scheme showing BNG woven into the scheme at pre-commencement stage) and the policy requirements under the NPPF for BNG.

Whilst the exemptions for BNG were drafted to provide some flexibility and prevent undue burdens on smaller developments, their broad application has raised concerns about the impact of mandatory BNG.  Balance is needed between facilitating development and ensuring the biodiversity objective is still met. Despite the issues that have been raised, there has been no formal confirmation of forthcoming amendments to the exemptions. Nevertheless, it will be worth monitoring future changes to ensure the thresholds or requirements have not changed.