Integrating the building structure to act as an energy-storage, thermally-activated building system (TABS) has proved to be energy efficient and economically viable for cooling and heating of buildings. However control has remained an issue to be improved. In this paper, a method is outlined allowing both for dimensioning and for automated control of TABS, with automatic switching between cooling/heating modes for variable comfort criteria. The method integrally considers both HVAC and building automation design aspects, as well as the fact that during design and operation heat-gains are unknown, but that bounds of them normally can be specified. This integral method is termed the Unknown-But-Bounded or UBB method. Applying the method guarantees that comfort can be maintained, as long as the actual heat-gains stay within the predefined range between the lower and upper bounds. The UBB method can also handle non-predictable day-to-day variations as well as room-to-room variations of the heat gains. The paper outlines the underlying thermal models and assumptions, and gives the procedure and an example for the application of the method. (c) 2007 Elsevier Ltd. All rights reserved.