There is no separate Simple Buildings (SB) licence, because assessment of simple buildings is under the relevant scheme (UK 2011, 2014 New Construction Non-Domestic and 2014 UK Refurbishment and Fit-Out).
Assessment of SB is building type specific, so for instance to assess a new construction Offices development to SB, the assessor must hold a Commercial license. Equally, if it was an Education building, the assessor must hold a Public license.