Functional elements constituting buildings are delegated by functional requirements, affected by agents and finally evaluated by performance requirements. These elements can be represented by conceptual object oriented product models. Work is undertaken to elaborate on the element model and subsequently to develop a method for the evaluation in terms of and comparison of the life cycle performance in terms of multiple indicators pertaining to element alternatives illustrated here by glazed building envelope systems. Components as discrete parts of any one element are intended to satisfy one or more of the functional requirements pertaining to that element. Thus the resultant overall element performance depends on the performances of individual components. Conversely, any one requirement may implicate one or more components. Appropriate performance requirements for evaluating elements are identified for each phase of the life cycle. These requirements are measured by performance indicators to which relative weights are then assigned. Component performance is evaluated in two consecutive stages. These stages employ the same procedure, but life cycle and statistical indicators are substituted respectively. Multiple statistical parameters are utilized to supplement the average utility value of that component in order to account for the deviation of indicator values. Hence a single overall indicator value is obtained that allows component performances to be in effect combined through enhanced aggregation to yield the overall element performance. Consequently the method allows the following entities to be appraised: 1. Relative component performances over the complete life cycle, 2. Relative element performances in any one phase or over the complete life cycle. This approach is demonstrated by means of an implementation on envelope systems.