Why to use curtain wall system instead of window wall system？

In the modern construction industry, curtain wall system and window wall system are commonly used methods of exterior cladding for mid-rise and high-rise buildings. In practical applications, both curtain wall system and window wall system are intended as all-in-one cladding systems. While most people think first of the glazing or window component of these systems, they both encompass many aspects and functions common to any exterior wall, including:
-Enclosure/Barrier – These systems inherently act as the primary air/vapor/weather-resistive barrier for the building envelope.
-Cladding – Beyond clear glass, these systems can incorporate panels of metal, stone, opaque glass, etc.
-Insulation – While they do not have the same insulation value as a solid or framed wall, these systems do provide some degree of insulation value.
-Structural – While these are not bearing walls (i.e. they do not support the floors above, and can be removed without any detrimental effect on the overall building structural system), they transfer their loads to the main building structure, and need to be designed to resist wind and other lateral loads.

What’s the Difference between Curtain Wall System and Window Wall System?
A window wall system spans only a single floor, is supported by the slab below and above, and is therefore installed within the slab edge while a curtain wall is a structurally independent/self-supporting system, typically spanning multiple stories, and is installed proud of/beyond the slab edge. In addition, curtain wall cost is relatively higher than window wall cost in building budget. Specifically speaking, curtain walls are more often used in commercial buildings, while window walls are often used in residential buildings due to their lower cost, installation from the building interior and customization potential. Especially in some tall residential and commercial buildings, wind driven rain and strong winds will be major concerns and proper design of either curtain wall or window wall is needed to achieve strong performance. In regard to water penetration and air leakage, aluminium curtain wall has an advantage due to its less exposed parts and simpler connections to the structure.

In most cases, people have the false perception that window wall is a lesser form of glazed cladding. However, it proves that window wall not only has a vital place in high-rise construction, it can also outperform a typical curtain wall system in applications. The unique characteristics of window wall make it ideally suited for residential applications, which is why it dominates the condo cladding marketplace today while for commercial buildings, structural glass curtain wall performs better than the window wall and has a stronger R-value at the clear wall and the slab intersection according to the modeling.