To facilitate multi-variate performance appraisal all aspects of a building must be treated simultaneously. This paper gives examples of how the principal technical domains relating to a building's environmental performance are coupled within the ESP-r integrated simulation package. Essentially, the equation-sets defining each domain an processed by customised solvers, while the domain interactions are handled by ensuring that the equation-sets for a given domain an established and solved as a function of information defining the evolution of any coupled domains. An earlier version of this paper appears in the proceedings of Building Simulation'99 [J.A. Clarke, Proc. Building Simulation'99, 1999] [1]. (C) 2001 Elsevier Science B.V. All rights reserved.