Statutory Exemptions from Mandatory BNG
While BNG is universal for new developments, the Environment Act 2021 provides specific statutory exemptions where 10% uplift is not required:
1. Householder Applications: Minor domestic house alterations, loft conversions, detached single garages, and conservatories.
2. De Minimis Threshold: Developments that do not impact any priority habitat and impact less than 25 square metres of non-priority habitat (or less than 5 metres of linear habitat).
3. Self-Build and Custom Build: Sites comprising 9 or fewer dwellings on sites no larger than 0.5 hectares, carried out by self-builders.
4. Biodiversity Gain Sites: Developments undertaken solely to enhance biodiversity habitats.
5. High Speed 2 (HS2): Specific statutory railway works exempt under royal assent legislation.
| Development Category | Site Threshold Criteria | Metric Calculation Tool | Statutory Deadline |
|---|---|---|---|
| Major Residential | 10+ dwellings or site area >= 0.5 ha | Statutory Biodiversity Metric (Full) | Mandatory since 12 Feb 2024 |
| Major Commercial | Floor space >= 1,000 m² or area >= 1 ha | Statutory Biodiversity Metric (Full) | Mandatory since 12 Feb 2024 |
| Small Residential | 1 to 9 dwellings on sites < 0.5 ha | Small Sites Metric (SSM) | Mandatory since 2 April 2024 |
| Householder Works | Domestic extensions, outbuildings | Exempt (No metric required) | Statutorily Exempt |
| De Minimis Sites | Impacts < 25 m² non-priority habitat | Exempt (Exemption self-declaration) | Statutorily Exempt |
Legal Enforcement: The 30-Year Conservation Covenant
Habitat gains cannot be temporary. The developer must enter into a formal Section 106 planning obligation with the council or execute a statutory Conservation Covenant under Part 7 of the Environment Act 2021 with a designated Responsible Body.
The covenant binds the land for at least 30 years and requires monitoring reports to be submitted to the local authority at years 1, 2, 5, 10, 20, and 30.