Structural Glazing Systems: Glass Held by Silicone, Not by Frames

What the system is doing

In a conventional curtain wall, a pressure plate clamps the glass mechanically and a cap covers it. That cap is what you see as a grid on the outside.

Structural glazing removes it. The glass is bonded to the frame behind with structural silicone, and wind load passes through the adhesive. From outside, the facade reads as a flush plane of glass with only silicone joints between panes.

The appearance is the reason clients choose it. The engineering consequence is that an adhesive joint has become a structural element.

What that changes

	Conventional glazed system	Structural glazing
Load path	Glass → pressure plate → frame	Glass → silicone bond → frame
External appearance	Visible capping grid	Flush glass, silicone joints
Critical quality item	Gasket and fixing	The silicone bond
Where it is made	Partly on site	Bonding in the factory
Inspection	Visual, mechanical	Bond geometry, adhesion, compatibility
Repair of a pane	Unclip and replace	Remove and re-bond the unit

Bond geometry is calculated, not chosen

The bite — the width of the silicone bond — and its thickness are derived from the design wind pressure, the pane size and the silicone's rated strength.

Design wind pressure comes from IS 875 (Part 3) for the specific site, height and terrain, and varies across a building, with corners and upper levels highest. So the bond dimensions on one project do not transfer to another, and within one building they may differ by elevation.

Design practice is addressed by guidance such as ASTM C1401 and the structural sealant glazing standard EN 13022, within the curtain walling framework of EN 13830. The values must come from the project's facade engineer.

Compatibility is a real failure mode

Structural silicone touches several other materials: the glass coating, the frame finish, setting blocks, spacers, gaskets, the insulating unit's edge seal, and any weather seal beside it.

Some combinations degrade the bond. This is why compatibility and adhesion testing between the actual silicone and the actual materials being used is part of the design process, not a formality — and why a substitution of any component late in procurement requires the testing to be revisited.

Fabrication control

Because the bond is structural, factory conditions matter:

• Surfaces cleaned and primed to the silicone manufacturer's procedure
• Controlled temperature and humidity during application and cure
• Bead geometry verified, not assumed
• Cure time respected before handling or transport
• Records kept per unit, so the fabrication of any panel can be traced

A facade whose structural bonding was done on site, in ambient conditions, to unrecorded procedures, is not a structurally glazed facade in any meaningful engineering sense.

What to ask for

• The design wind pressures used, and who established them
• The bond calculation, and the silicone's rated values
• Compatibility and adhesion test results for the actual material combination
• The fabrication procedure and quality records
• Whether mechanical retention is provided, and on what basis
• A performance mock-up, tested before production
• The inspection and cleaning regime for handover

Where it suits, and where it does not

It suits buildings where a flush, uninterrupted glass plane is the architectural intent and the budget supports the fabrication control that requires.

It suits less well where the facade is highly irregular with many one-off panes, where the programme cannot accommodate factory bonding and curing, or where the project cannot support the quality regime the system depends on. In those cases a captured or partly captured system is the more honest choice.

Standards referenced

Structural sealant glazing guidance in ASTM C1401 and EN 13022; curtain walling product standard EN 13830; wind loading to IS 875 (Part 3). Bond design, wind pressures, retention provisions and compatibility for a specific building must be established by the project's facade engineer and the silicone manufacturer.