Psi-values are required as part of the SAP calculation input. The accredited construction details can no longer be used so option is to use default psi-values (which makes BR compliance very tough) or calculated psi-values (or mixture of both). There is lots of published data on masonry and timber frame psi-values - see trade associations, building product manufacturers. For non-standard construction such as SIP, insulated formwork, light steel frame etc bespoke calculations may be only option, they are complex and time consuming hence costly!