SSG Curtain Wall: Structural Glazing Systems Explained

The Engineering View

What Structural Glazing Actually Means

In a conventional captured curtain wall, glass is held in the frame by aluminum pressure plates and gaskets, which visibly outline every pane. Structural silicone glazing changes that: the glass edge is bonded directly to an aluminum or steel setting block with structural silicone, and the bonding bead — not a mechanical clamp — carries the wind load from the glass into the frame. SSG curtain wall facades therefore present glass-to-glass or glass-to-insulated-panel surfaces with no aluminium on the outside face: an all-glass, frameless curtain wall — in effect a hidden frame curtain wall, because the support exists but is invisible. This is what a structural glazed curtain wall delivers: transparency without visible metal, achieved by engineering rather than by removing the structure.

SSG is not a single product; it is a family of configurations. In a two-sided SSG , the two vertical edges are structurally bonded and the horizontal edges are still captured or drained. In four-sided SSG , all four edges of the unit are bonded, giving the fully frameless reading. There is also SSG in unitised systems , where each factory-assembled panel is glazed under controlled factory conditions and bonded to the frame before dispatch — by far the most common SSG route on high-rise buildings because site glazing of four-sided bonds is weather and labour dependent.

The Silicone Joint as a Structural Element

Structural silicone is an elastomer with a design tensile strength typically taken as one-tenth to one-eighth of its ultimate strength, per the industry factor of safety of about 5–6 against ultimate. A correctly sized SSG joint resists three concurrent demands. The wind suction pulls the glass away from the frame and stresses the bond in tension; the positive wind pressure pushes the glass inward and stresses the bond in compression and shear; and thermal and drift movement between frame and glass strains the bead in shear. The design width and depth of the bead must satisfy all three together, with the tension case almost always governing on tall buildings.

Joint sizing follows a simple but unforgiving logic. The required bite (the width of the bond on the glass) is proportional to the design wind pressure times the pane area divided by the allowable strength of the silicone divided by the length of the bonded edge. Doubling the pane area therefore doubles the required bite on the same edge, which is why very large panes are either bonded on four sides or moved to point-supported systems. Four-sided SSG redistributes load better but turns every edge into a QC-critical seam; two-sided SSG keeps the structural seams to two edges but puts the full pane width on each bond. Neither is "better" in the abstract — each is a trade between sightlines, pane size and test evidence.

Design Rules: Bite, Edge Clearance & Movement

Three dimensions control an SSG design. First, the structural bite described above — typically 6–19 mm depending on pane size and wind zone. Second, the edge clearance between glass edge and frame, which gives the silicone room to deform in shear without the glass kissing the metal at the corner — usually 4–8 mm. Third, the back-up depth and the perimeter sealant that protects the structural bead from UV and water. The structural silicone itself must never be exposed to sunlight or standing water: UV degrades the surface, and water in the bond line is both a durability and an adhesion risk.

Because silicone adheres tenaciously but not indiscriminately, the substrates matter as much as the geometry. The glass edge must be clean, dry and free of any release agent; the aluminum must be degreased and, if anodised or coated, verified coat-to-silicone adhesion. Ionomer, certain laminated glass interlayers and some decorative coatings are incompatible with standard structural silicones and require compatibility testing before anything is bonded. This is why SSG design on landmark projects is always a package: glass supplier, silicone manufacturer and system manufacturer must sign off on the same bond schedule.

Stage by Stage

1. Specify SSG with Verified Engineering

   Send your drawings and wind data. Hanart's engineers will size the structural joints, propose a factory-glazing sequence and provide a compliance statement to EN 13022 / GB/T 21086 — free, within 48 hours.

Specifications & Standards Referenced

• EN 13022
• GB/T 21086

Traceability & Sources

• Read the full source article: SSG Curtain Wall: Structural Glazing Systems Explained — source page
• Project file: Senlan International Plaza, Shanghai — Unitized curtain wall on a mixed-use Pudong tower — Luban Prize 2015.
• Point-Supported Glass & Cable-Net Systems — related note
• Curtain Wall Structural Design: Loads & Deflection — related note
• Facade Standards Hub — test methods cited across the library