Transom less Glazing (also known as “Vertical-Only” or “Ribbon” glazing) is a design approach that eliminates horizontal aluminum members (transoms) from the curtain wall grid. This results in uninterrupted vertical lines of glass, creating the illusion of a much taller, sleeker building.
How the System Works
- In a standard curtain wall, the glass is supported on all four sides by a “box” of aluminum (mullions on the sides, transoms at the top and bottom). In a transom less system:
- Vertical Support: The glass is held primarily by vertical mullions.
- Horizontal Joints: The horizontal gap between two glass panels is typically a
- butt-joint. This joint is filled only with structural silicone or a specialized weather-sealant, rather than a metal bar.
- Weight Transfer: Since there is no horizontal bar to sit on, the dead load of the glass is transferred to the vertical mullions via specialized “setting blocks” or internal “toggles” hidden within the vertical frame.
Key Components
- Heavy-Duty Mullion
Since the transoms are missing, the vertical mullions must handle all wind loads and glass weight. - Structural Silicone
Bonds the horizontal edges of the glass panels together to ensure water-tightness. - Setting Blocks
Small supports hidden at the base of the glass that transfer weight to the mullion. - Glass Fins (Optional)
In very high-end transom less systems, the vertical mullion is replaced by a glass strip for 100% transparency.
Benefits of Transom less Design
- Enhanced Aesthetics: It creates a “waterfall” effect where the glass appears to flow from the roof to the ground without horizontal breaks.
- Increased Natural Light: Removing the horizontal metal bars reduces shadows inside the building and maximizes the “vision area.”
- Lower External Maintenance: Horizontal transoms often act as “dust shelves” where dirt and bird droppings collect. Transom less systems stay cleaner as rain washes straight down the glass.
- Architectural “Stretch”: It is a favorite for designers who want to emphasize the verticality of a skyscraper or a double-height lobby.
