The mullion-transom construction is the classic system for large-format glass façades, conservatories, and rooflights. Vertical mullions carry loads from wind, self-weight, and where applicable snow, transferring them to the building structure. Horizontal transoms connect the mullions and support the weight of the glazing units. Profiles are predominantly aluminium with thermal break inserts to reduce heat transmission. Clamping or pressure-cap sealing systems ensure weathertightness. Fire protection, acoustic, and burglar-resistance requirements can be met through specially designed system profiles and inserts. The standard EN 13830 governs performance requirements for curtain wall systems of this type.