How is moisture managed within a curtain wall system to prevent leaks?

Effective moisture management within a curtain wall system is achieved through a sophisticated, multi-layered strategy that anticipates water penetration and provides controlled pathways for it to drain away harmlessly. The fundamental principle is often referred to as a "zone-drained" or "pressure-equalized rainscreen" system. The first line of defense is the outer set of gaskets and seals, which are designed to minimize the amount of water and air that enters the system. However, it is assumed that under extreme conditions, such as the wind-driven rain sometimes experienced in the region, some water may bypass these primary seals. This is where the internal drainage system becomes critical. Any water that enters is collected in an internal gutter system, which is integrated within the horizontal aluminum transoms. These transoms are designed to slope slightly towards the exterior. The collected water is then channeled vertically down through the hollow chambers of the mullions and finally expelled to the exterior through strategically placed weep holes at the bottom of each drained area. This internal "weep" system ensures that water never reaches the interior of the building. The concept of pressure equalization further enhances this by reducing the forces that drive water into the system. For a curtain wall in a humid coastal city like Jeddah, this comprehensive water management is essential for preventing leaks, mitigating the risk of material degradation, and ensuring the long-term durability and performance of the building's facade.