What is structural glazing?
Structural glazing, more fully structural sealant glazing (SSG), is a way of glazing in which the glass is bonded with structural silicone to a support frame, usually aluminium, so that no pressure plates, caps or beads are visible on the outside. The bond transfers the loads on the glass, such as wind pressure and suction, self-weight and the differing thermal movement of glass and frame, into the metal structure.
Structural glazing and curtain walling are often mentioned together but are not the same thing. A curtain wall is a non-load-bearing facade hung in front of the structure. Structural glazing is a method of fixing the glass, often used within a curtain wall. A curtain wall can just as well have visible capped profiles.
Types
- Two-sided: two edges of each pane are bonded and the other two are held mechanically, so framing shows in one direction only.
- Four-sided: all edges are bonded and the facade shows only silicone joints.
- With or without mechanical restraint: self-weight can be carried on a support profile, and retaining devices can stop a pane falling out if the bond fails. National rules may require such restraint.
The European guideline for these systems is ETAG 002 for structural sealant glazing kits. Structural sealants are now assessed under its successor document, EAD 090010-00-0404.
Application
- Not a DIY job. Use only a certified facade contractor, with the design checked by a structural engineer.
- Bonding belongs in the factory. Structural bonding is done under controlled conditions (clean, dry surfaces, the right temperature and curing time), not on the scaffold.
- Check compatibility. The structural silicone must be compatible with the edge seal of the insulating glass units and with spacers and gaskets.
- Inspect the joints. Look periodically for loss of adhesion, cracks and discolouration. Clear silicone can discolour, which is why black is often chosen.
- Think about solar gain. A large glass facade without solar control glass or shading can overheat the space behind it.
Common mistake: having a broken pane replaced by a glazier with no SSG experience. Replacement panes must be bonded to the facade contractor’s system.
Related terms
- Curtain wall
- Glass fittings
- Sealant
- Dry glazing
- Aluminium in construction
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