Structural Glazing
Glass bonded to its frame with structural silicone for a flush exterior.
Quick Answer
Structural glazing is a method of attaching glass to a supporting frame using structural silicone sealant instead of exterior pressure plates or caps. The adhesive transfers wind and other loads from the glass to the framing, producing a smooth, flush facade with no visible exterior frame. It requires careful engineering, testing, and controlled application.
The Full Picture
In a conventional curtain wall, glass is held by exterior metal caps. Structural glazing replaces those with a bead of structural silicone that bonds the glass edge to the frame. The silicone is a load-carrying element, so it is engineered for wind, dead load, and movement, and the exterior shows only glass and narrow joints of weatherseal.
Systems vary by how many edges are bonded. Four-sided structural glazing bonds all edges for a fully flush look. Two-sided systems bond two edges and mechanically capture the other two. Some projects use point-supported or spider fittings, which are a different structural approach to frameless glass.
Because the silicone carries load, installation is tightly controlled. Manufacturers typically require adhesion testing and compatibility testing with the materials it touches, and structural glazing is often done in a shop under controlled conditions and then shipped as unitized panels. Specifiers refer to standards and guides, including ASTM C1401, for structural sealant glazing.
Design considerations include thermal movement, glass weight, long-term sealant durability, and fire and safety provisions. The look is appealing, but repairs and replacement can be more involved than for capped systems, and some codes and owners require redundant mechanical retention for added safety on tall buildings.
Real Examples
Common Misconceptions
People assume: Structural glazing means no framing behind the glass.
Actually: The frame is still there, just hidden. The glass is bonded to it with silicone, which carries the loads.
People assume: Structural silicone is just ordinary sealant.
Actually: It is a specialized structural adhesive that must be designed, tested for adhesion and compatibility, and applied under quality control.
Frequently Asked Questions
What is structural silicone glazing?
A glazing method in which structural silicone bonds glass to a metal frame and carries wind and other loads, rather than exterior caps or gaskets.
What is the difference between two-sided and four-sided structural glazing?
Four-sided bonds every edge for a fully flush appearance. Two-sided bonds two edges and uses mechanical capture on the other two.
Is structural glazing done on site or in a shop?
Frequently in a shop under controlled conditions, with unitized panels delivered to site. Field application is possible but harder to control.
What standards cover structural sealant glazing?
ASTM C1401 is the commonly referenced guide for structural sealant glazing, alongside manufacturer testing and the project's wind load requirements.