SBEM 3.3.b now allows some domestic activities in predominantly non-domestic buildings such as flats above pubs. This is first implemented in DesignBuilder v.1.9.2. For earlier versions the comment from BRE applies:

"SBEM can currently be used for non-domestic buildings energy calculations only (although this might change in the next version of SBEM). The only domestic activity that can be modelled in SBEM is the common circulation areas in apartment blocks by selecting the Building type as "Dwelling" and the Activity type as "Common circulation areas". It is our understanding that the apartments themselves should be modelled using SAP. We are currently in discussion with CLG regarding the introduction of some domestic activities into SBEM to be used in a particular case only, which is when one EPC is required for a building where there is residential accommodation above a non-domestic space (e.g., a shop or a pub) provided that the residential space can only be accessed from within the non-domestic space. If this is agreed upon, then the necessary modifications would be made to the NCM Activity Database."