Ask three architects what structural glazing means and you may get three answers. The term covers silicone-bonded curtain wall, point-supported and bolted assemblies, and glass acting as a structural member — fins, beams, floors, stairs. They share an aesthetic ambition and almost nothing else technically.
Here’s what separates them, and what each demands from the drawings.
The Two Meanings
What Is Structural Glazing?
Structural sealant glazing bonds glass to the frame with structural silicone instead of capturing it mechanically under a pressure plate and cap. The silicone transfers wind load from the glass into the framing. Nothing interrupts the exterior face on the bonded edges, which is the entire point — a flush plane of glass with shadow-line joints rather than aluminium caps.
Structural glass means glass carrying load beyond its own weight: fins stabilising a large glazed wall, beams, treads, floors, or point-supported assemblies where bolted fittings pass through the glass itself.
The first is about how glass is held. The second is about what glass is doing.
| System | What’s structural | Exterior appearance | Governing requirement |
| Captured (conventional) | Aluminium frame | Visible caps on all edges | Standard glazing practice |
| Two-sided SSG | Frame plus silicone on two edges | Caps on two edges only | Sealant bite by calculation |
| Four-sided SSG | Frame plus silicone on all edges | Fully flush glass plane | Factory glazing; often mechanical retention |
| Point-supported | Fittings and glass together | Minimal — fittings only | Fabricated holes; pre-temper processing |
| Structural glass elements | The glass itself | Frameless | Post-breakage capacity by design |
Structural Sealant Glazing
How Is Structural Silicone Bite Determined?
By calculation from wind load and glass size, not by convention.
Bite — the contact width between glass and frame — is derived from the design wind pressure, the short span of the lite, and the sealant’s published design stress. Larger lites and higher wind loads demand more bite, which in turn drives frame width and therefore sightline. That relationship is why the structural engineer and the architect need to be talking before the elevation is fixed: the visual result depends on a load calculation.
Design stress values vary by product and should come from the sealant manufacturer’s published data rather than a rule of thumb. Glueline thickness is a separate dimension, governed by movement — thermal expansion and differential deflection — rather than by load.
Two things follow that matter more than the arithmetic.
Only structural silicone qualifies. Weatherseal silicone, however similar it looks, is not rated to carry load. Substitution is a structural failure waiting for a storm.
Compatibility is not optional. Structural silicone must adhere to, and remain compatible with, every material it contacts — the frame finish, setting blocks, spacers, gaskets, insulating unit edge seals, even the cleaning agents used before application. The sealant manufacturer tests actual samples of each and issues adhesion and compatibility results, sometimes with a primer requirement.
That testing takes weeks and requires physical samples of specified products. On a compressed programme it is one of the earliest things that has to start and one of the most commonly left late.
Can Structural Silicone Glazing Be Done on Site?
Four-sided work should be factory-glazed. Assume that, and treat any exception as a question for the sealant manufacturer.
Structural bonding needs controlled temperature and humidity, clean surfaces, correct priming, verified bite and glueline, and undisturbed cure. A factory delivers all of that and can check each unit before it ships. A facade at height in variable weather delivers none of it reliably.
The consequence for design is sequencing. Factory glazing means unitized or pre-assembled panels, longer lead times, shop drawings resolved earlier, and a delivery-and-hoisting logic rather than a build-in-place one.
There’s also a retention question. For overhead applications and many four-sided systems, mechanical safety retention is required in addition to the bond — a captured edge, a retention clip, or a lip that holds the lite if adhesion fails. Confirm what the adopted code and the system manufacturer require rather than assuming the silicone stands alone.
Glass as Structure
Does Structural Glazing Require Laminated Glass?
For anything where glass carries load, effectively yes — and for a reason worth being precise about.
Structural glass elements are designed for post-breakage performance. The question isn’t only whether a fin or a tread resists the load; it’s what the assembly does once a ply has failed. Laminated construction with a stiff interlayer keeps the broken element bonded and load-carrying long enough to be discovered and replaced, rather than removing a structural member instantly.
That drives interlayer selection. Ionoplast interlayers retain substantially more stiffness after breakage than standard PVB, which is why they dominate structural applications, guards, and long-span point-supported assemblies. Redundancy is the design philosophy: multiple plies, sized so the assembly survives losing one.
Two related requirements come up on tempered structural glass. Holes for bolted fittings must be fabricated before tempering, since tempered glass cannot be cut or drilled afterwards — which means the fitting layout has to be final earlier than architects expect. And heat-soak testing is commonly specified to reduce the risk of spontaneous breakage from nickel sulfide inclusions, which matters far more when the lite is a structural member than when it’s infill.
What Has to Be Resolved at Design Stage?
Five things, and all of them get expensive late:
- Which meaning you’re specifying. Write “structural sealant glazing” or “point-supported glazing,” not “structural glazing.” The ambiguity produces bids that aren’t comparable.
- Compatibility testing. Samples of every contact material to the sealant manufacturer, weeks before fabrication.
- Factory versus field. This determines the whole procurement and erection logic, not just a glazing method.
- Mock-ups. Visual and performance mock-ups on flush facades reveal reflection, anisotropy, and roller-wave distortion that drawings cannot. Tempered glass in a large flush plane shows optical effects that never appear in a captured system.
- Reglazing access. A flush bonded facade is considerably harder to open than a captured one. Establish how a single lite gets replaced on the twentieth floor before the system is selected, not after the first breakage.
How Long Does Structural Silicone Glazing Last?
Decades, and it’s a maintained element rather than a permanent one — which is worth telling a client before they commission the building.
Structural silicone is chosen partly because it’s genuinely UV-stable, which matters when the bond line sits at a glass edge with sunlight reaching it. Properly specified, correctly primed, factory-applied, and compatible with everything it touches, a structural bond has a long service life and rarely becomes the reason a facade is replaced.
Where it fails, the cause is almost never chemistry. It’s adhesion failure from a missed primer or contaminated surface, incompatibility with a material nobody tested, insufficient bite from a load case that changed after the calculation, or movement exceeding what the glueline was sized for — design and fabrication decisions, not material limitations.
Practically, that means two things for the drawings. Structural bonded facades should be inspectable — a maintenance regime that looks at bond lines periodically rather than waiting for a symptom. And the building should have a documented record of the sealant product, the primer, and the compatibility results, because a replacement lite twenty years on has to be bonded with a compatible system, and the information is very difficult to reconstruct once the project team has dispersed.
Working Through It
Structural glazing rewards early engineering and punishes late decisions more than almost any other facade approach, because the aesthetic result is downstream of load calculations, sealant chemistry, and fabrication sequence.
Crystal Structures handles contract glazing including point-supported systems, curtain wall, and glass railing, and is frequently engaged on the conditions where standard systems run out — custom geometry, transitions, and interfaces between assemblies. Glazing options covers make-up selection, with editable specifications in the spec library.
Detailing a structural glazing condition where sightlines, load, and buildability all have to reconcile? Contact Crystal Structures for a no-cost design collaboration with our engineering team.
