Tempered vs Laminated Glass: Which Goes Where?

Two terms appear most often in a glass system quotation and are least understood: tempered and laminated. Most customers hear both as "safety glass" and assume there is no difference between them. In fact these two types go through different production processes, break in different ways and need to be used in different places. Glass used in the wrong place stops the system being safe. In this article we explain the difference technically and set out which belongs where.

Standard float glass is not used in outdoor systems. When it breaks it forms long, sharp and heavy shards that cause serious injury. The absence of a stated glass type in a quotation is therefore a warning sign in itself. There are two safety glasses usable outdoors: tempered and laminated.

Tempered glass is glass strengthened by heat treatment. Cut glass with worked edges is heated to around 600 degrees and then cooled rapidly. That rapid cooling creates compression on the glass surface and tension in its core. The result is a material roughly four to five times stronger than ordinary glass. Its resistance to thermal shock is also markedly higher.

The real safety property of tempered glass is how it breaks. When the balance of stress inside it is disturbed, the glass separates not into large shards but into small granules with blunt edges. Those granules do not cut; injury risk is far lower than with ordinary glass. But there is a critical point: when tempered glass breaks, the whole panel disintegrates at once and the granules come free. The glass no longer stays in place.

Laminated glass works on an entirely different principle. Two or more glass sheets are bonded under heat and pressure with a transparent interlayer called PVB placed between them. When the glass breaks the pieces stay bonded to that interlayer; the panel cracks but stays in place and does not fall. That is why a car windscreen forms a spider-web pattern rather than disintegrating.

This difference in behaviour directly determines where each belongs. In vertical applications - side enclosure systems - tempered glass is safe; if the glass breaks the granules fall to the ground, but that is not a hazard. In overhead applications the situation changes completely. On glass above your head - a glass roof, a canopy cover or an overhead passage - granules coming free at the moment of breakage is unacceptable.

We therefore require laminated glass in overhead applications. On a fixed glass roof, a canopy cover and any application with people beneath it, the glass must be laminated. A glass roof using only tempered glass rains granules onto the people below when it breaks. This is not a technical preference but a safety requirement; we suggest seeing in writing that overhead glass is laminated.

Combining the two is also possible and gives the highest level of safety. Tempered laminated glass is produced by bonding two already tempered sheets with PVB. It carries both the strength of tempering and the stay-in-place property of lamination. This combination is preferred on glass roofs at height, on walkable surfaces and in public spaces; it costs more, but the safety requirement justifies it.

Laminated glass is also valuable in areas with children and heavy traffic. When tempered glass breaks the panel empties completely, leaving an opening. The possibility of a child or a pet passing through that opening is a real risk, especially in balcony and terrace applications. With laminated glass the panel stays in place even when broken, so the barrier effect is preserved. We therefore suggest considering laminated glass even in vertical applications in households with children.

Thickness selection is a separate matter and relates directly to panel size. As a panel grows wider and taller, the stress created at the centre of the glass under wind load increases. Guillotine glass and sliding glass systems generally use 8 mm tempered glass, which is adequate for standard panel sizes. Very large panels, upper floors and wind-exposed façades require thicker glass or a laminated build-up.

Edge working is a detail overlooked in safety. Before tempering, the glass edges must be properly ground. Micro-cracks left at the edge create stress concentration during tempering and set the ground for spontaneous breakage later. In quality production this step is not skipped. A stated edge working method in the quotation is a sign that the maker pays attention to this detail.

There is one more phenomenon to know about tempered glass: spontaneous breakage. Nickel sulphide particles that can enter the raw material during glass production may expand over time and cause tempered glass to disintegrate with no external impact. The probability is low but not zero. A process called heat soak testing can screen out these risky panels at the production stage. This test may be requested in public spaces and overhead applications.

In applications needing thermal insulation, a double-glazed unit comes into play. In this unit there is a cavity filled with air or gas between two glass sheets, reducing heat transfer. The layers of a double-glazed unit can be tempered, laminated or a combination of both. In heated volumes such as a conservatory, insulating glass should be considered; but because weight increases, the mechanism and structure must be chosen accordingly.

Colour and coating options exist in both glass types. Smoked and bronze glass reduce light transmission and lower heat gain, while darkening the view somewhat. Solar control coated glass passes visible light while reflecting a significant part of the infrared radiation. On south-facing glass roofs these coatings do not remove the need for shading entirely, but reduce it noticeably.

In summary: tempered glass is strong and breaks into non-cutting granules, but does not stay in place. Laminated glass keeps its pieces bonded to the interlayer and the panel stays put. In vertical side enclosures tempered is sufficient; in every overhead application laminated is essential. In areas with children, laminated provides extra safety. You can review our glass systems and read about safety requirements in glass roofs in this article.

To determine which glass type and thickness suits your space, request a free site survey.

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