This paper presents interim results of the currently ongoing "Building as a Service" (BaaS) EU project. The BaaS project aims at optimising energy performance of non-residential buildings, e.g. schools, universities, hotels, shopping centres, or sports facilities.

An ICT platform is being developed that integrates IT systems that already exist in infrastructure assets with new IT components delivering novel functionalities extending the performance assessment of buildings. The former include building management systems (BMSs), access control systems, or systems providing weather data. The latter are mostly concerned with the assessment, prediction, and optimisation (APO) of energy usage and modelling. The IT infrastructure systems and APO services are linked by an integration middleware. The main features of this middleware are standardised interfaces via which all communication between the components of the system is routed. Functioning and characteristics of the middleware and its interfaces will be explained in the present paper.