Structured, generalised, digital modelling and simulation software tools that enable engineers to more easily produce formalised, documented and transferable software for prediction of thermal performance and energy use in buildings are described. The basis for these tools is modern state-space analysis techniques that cast modelling equations into a vector-matrix form ideally suited for digital computation. An automated building modelling capability generates detailed and simplified models directly from building plans through use of a library of construction element models (walls, floors, etc.). A user-oriented program interface enables interconnection of the building model with other component models selected from a library of HVAC equipment. controls, internal load schedules, and weather data to construct a closed-loop system simulation. Theoretical considerations for the modelling methodologies implemented in these tools are discussed, along with techniques to systematically reduce the modelling complexity and simulation costs without loss of accuracy. Plans to implement the simulation tools on a minicomputer with an array processor are overviewed.