How do structural movements, thermal expansion, and building sway impact curtain wall joint design and performance?

Curtain wall joint design must accommodate predictable and unpredictable movements to maintain weatherproofing, safety, and aesthetics. Thermal expansion causes aluminium frames and glazing to expand and contract; designers must provide movement allowances in joints and select sealants and gaskets with sufficient elongation and recovery properties. Building sway and interstory drift, which are especially relevant for tall or flexible structures, impose cyclic lateral displacements that require joints designed for shear, tension, and compression with appropriate movement capability. Vertical movement at floor slabs relative to the curtain wall (differential vertical movement) must be accommodated through slip-type anchors or floating mullion systems that allow axial movement while transferring gravity loads. Joints should be detailed so that primary structural anchors carry loads while secondary seals and gaskets handle air and water control without being overstressed. Specify joint sizes based on cumulative movement calculations from thermal, seismic, and service loads — typically sizing movement joints to accept the summation of max foreseeable strains plus safety factors. Use backer rods and bond-breaking geometry to ensure sealants move in shear rather than peel. For façades subject to wind-induced sway, limits on glazing deflection and joint rotation must be considered to prevent glass edge stress or gasket extrusion. Mock-ups and cyclic movement testing validate that joint assemblies retain adhesion and elasticity after repeated cycles. Detailed movement schedules and clear installation tolerances in contract documents minimise risk of field misalignment that could negate designed movement capacity.