What is the role of mullions in a curtain wall system?

Mullions—the vertical and horizontal aluminum members—form the skeletal framework of curtain walls, transferring loads to the building structure. In Gulf-region towers like those in Doha or Abu Dhabi, vertical mullions must resist wind pressures up to 3 kPa, requiring deep profiles with thermal-break polyamide cores to minimize heat transfer. Horizontal transoms tie mullions together, supporting glass and spandrel panels. At slab edges, mullions connect to stainless-steel anchors; sliding connections accommodate thermal and seismic movements. Pressure-equalization chambers within the mullion profiles manage rain intrusion and equalize internal/external pressures. Mullions also conceal drainage paths and integrate with aluminum ceiling perimeters, creating clean soffit transitions. Finish-coated mullions match ceiling colors for interior continuity—a signature of premium aluminum-ceiling and curtain-wall coordination.