Investigates the economically optimum window size and orientation for a daylit and non-daylit high-rise office building. Considers the effect of environmental variations on the building performance, of various energy charging schemes on life cycle cost and their effect on the optimum fenestration design. Notes a computer program using multiple regression techniques, numerical optimisation algorithms and building simulation results, to determine the optimum window design for a daylit or non-daylit building for the climatic locations studied. Concludes for optimisations for Boston, Denver and Saskatoon that the lowest life cycle cost building will be daylit with electric lighting controls, in all except cold, northerly sites. Describes how window orientation strongly affects life cycle costs. Provides recommendations. Does not consider non-quantifiable architectural factors.

KEYWORDS: Windows, offices, computer programs, calculating, designing, orientation.