The primary purpose of a curtain wall system is to protect the building interior against the exterior natural phenomena such as sun exposure, temperature changes, earthquake, rain, and wind. This protection can be separated into two major categories, namely structural safety and interior environmental control. The structural safety problems include failures of wall component, wall facing material, and fasteners. The interior environmental control problems include excessive energy loss, noise control, mold growth, interior water condensation, and water leakage. It is essential to maintain this protection for the life of the building ideally without periodic repairs or total renovation. Unfortunately experience indicated that the life of a curtain wall system can not outlive the building life due to complicated and intertwined multiple functional requirements of a curtain wall system. For example, sealing functional failure due to sun exposure and/or sealant line stress fatigue caused by various structural movements of wall components and building frame (such as thermal expansion or contraction, wind load deflection or rotation, dead load deflection, inter-floor live load deflection, and interfloor story drift) could produce a chain of functional failures, for example, water leakage leading to wetting of insulation material (energy loss) or mold growth (sick air building) or rusting of connection system leading to structural failure. The maintenance and renovation cost of the curtain wall system has a very significant impact on the life-cycle cost of the building. This cost impact can only be evaluated if the durability of all curtain wall functions can be determined. Unfortunately, little has been done in this regard due to the complexity of the intertwined curtain wall functions. This paper highlights the possibility of using Functional Isolation Concept (FIC) in designing a curtain wall system to greatly reduce the interferences among the various curtain wall functions. Continuing development of FIC in the future may lead to a reliable method of evaluating the cost impact of a curtain wall system on the life-cycle cost of a building.
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