States that an intelligent building system must react automatically, correctly and appropriately to the frequent changes that occur during building development. Identifies building software characteristics that will produce effective reaction. States they are information databases corresponding to human knowledge, historical information representing experience, integration for automatic responses to changes, simulation representing the operating world of building systems, feedback for corrective action by originating modules of the building system, and communication between the system and system users. Uses the term 'reactive intelligence of building systems' (RIBS) to describe these characteristics and emphasises the need for reaction from building software systems. Shows how RIBS characteristics can be used to develop building services engineering design programs.

KEYWORDS: USA, computer programs, buildings, building services, designing.