How does a unitized curtain wall accommodate building movement, deflection, and thermal expansion?

Question

Accepted Answer

Unitized curtain walls accommodate building movement through designed movement joints, flexible anchor details, and compressible seals. Each panel-to-structure interface typically includes attachments that allow for horizontal and vertical movement: slotted anchors for translation, rotating anchors for angular adjustment, and sliding plates for thermal expansion. Panel-to-panel joints use compression gaskets, backer rods, and sealant profiles sized to accept predicted movements without exceeding sealant elongation limits. The design process quantifies expected interstory drift, thermal growth, and differential movement between materials; allowable movement is then compared to joint capacity to prevent overstrain. Framing members incorporate thermal breaks to minimize expansion-induced stress transfer and are detailed so that perimeter covers can slide relative to the pressure plate. For heavy wind or seismic actions, flexible mullion intersections and calculated load transfer paths prevent excessive stresses in glass and seals. Tolerances in factory assembly are set to allow field alignment without undue preload on anchors or seals. Where continuous insulation or cladding interfaces exist, transition details treat movement with compressible substrates and movement-accommodating flashings. Regular maintenance ensures that gaskets and sealants retain elasticity; loss of elasticity diminishes movement capability and leads to premature failure. Overall, successful accommodation of movement combines accurate movement modelling, appropriately sized joints, and field-correct installation.