Eligibility
The SSM applies to sites under 1 ha that meet either: a residential threshold of 1 to 9 dwellings or, where the number of dwellings is unknown, an area of less than 0.5 ha; or a non-residential floorspace under 1,000 sqm on a site under 1 ha. The SSM is not available for priority habitat or designated sites; those revert to the full SBM regardless of area.[S2]
Interaction with the 0.2 ha small-sites exemption (in force 6 August 2026)
A site below 0.2 ha containing no priority habitat is exempt from BNG entirely under the 0.2 ha exemption, which applies to planning applications made on or after 6 August 2026; the SSM is therefore only material for the 0.2 to 1 ha band.[S4] A self-builder remodelling a 0.15 ha curtilage does not need either tool; a 0.6 ha infill on lowland modified grassland does.
Input set
- Site boundary area in hectares.
- Dominant baseline habitat (UKHab Level 3).
- Condition (poor, moderate, good) per the SSM condition card.
- Post-development habitat composition.
Strategic significance defaults to medium where the LPA has not adopted a Local Nature Recovery Strategy mapping; this choice is conservative and tends to slightly under-state the post-development units.[S11]
Feasibility cost build-up for a self-builder
A 0.4 ha self-build on modified grassland needs a baseline survey and an SSM output prepared by the ecologist. Modified grassland is a Tier A1 habitat on the statutory credit price list at £42,000 per credit, and 2 credits are needed per unit, so every unit bought as statutory credits costs £84,000. On-site creation and off-site units are priced by the ecologist’s plan and the habitat bank’s quote; neither has a published rate.[S3]