As the complexity of facade design continues to evolve, modern architecture requires wall cladding systems to have clean, distinguishable features with complex geometries that strive to achieve a high-performance system with limited maintenance. Although rain screen systems can meet these aesthetic and performance requirements, it is important to understand the fundamental concepts behind this type of wall system to produce and maintain this potentially complex cladding assembly during the life of the building.
Open-joint rain screen systems are a variation of the conventional drainage wall where moisture is allowed to pass beyond the surface of the cladding and drain within the panel cavity. While conventional drainage walls typically place the cladding material tight to the air and water barrier, occasionally impeding the drainage plane, open-joint rain screens create an air space that promotes drainage and ventilation. The design approach and choice of materials within an open-joint rain screen wall have important impacts on how the cladding will interact with the wall assembly and other building components, how the wall will resist air and water infiltration, and what level of performance and durability is achieved.
Contemporary open-joint rain screen assemblies generally consist of interchangeable panels held off the face of a sheathed and insulated structural backup wall via an engineered support system. The open joints between panels and the air space created between the panels and the face of the sheathing promote air movement, which allows the rain screen to function.
The intent is to have the solid panels deflect bulk water while only allowing incidental moisture to reach the panel cavity. Eventually, in some systems, limited moisture can also reach the primary water barrier. Water that reaches the cavity is contained and drained to the exterior at predesigned intervals using flashing elements. The void created by the air space minimizes the amount of moisture that reaches the water barrier, and also creates a space for active ventilation. With open joints between panels, air can circulate within the cavity, effectively drying the wall components after wet weather subsides.
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