Tempered or laminated glass: which to use in each opening and how to measure it

Not every glass opening accepts the same type of pane. The CTE-DB-SUA (Spanish Building Code, Safety in Use and Accessibility) sets out the cases where single glass is outright prohibited, and confusing it with tempered or laminated isn't just a technical mistake: it is a regulatory breach.

When single glass isn't an option

Single or monolithic glass is prohibited by regulation on low surfaces exposed to impact: glass doors, areas near the floor and balustrades. In those cases tempered or laminated glass is needed, never monolithic.

• Tempered glass: heated and cooled abruptly at the factory, which multiplies its mechanical strength and makes it break into small non-sharp fragments. It is mandatory in glass doors, shower screens, balustrades and any glass surface less than 90 cm from the floor. Important: once tempered, the piece can't be cut or drilled — any size or opening has to be decided before the process.
• Laminated glass: two or more panes bonded by an interlayer (butyral/PVB). If it breaks, the fragments stay stuck to the interlayer instead of falling loose, which besides safety against falls from height makes break-in access harder — usual on ground floors and shop windows.

On glass balustrades, under safety regulations for heights, it is always tempered or laminated, never single glass: it is one of the applications where monolithic glass is expressly ruled out because of the fall risk if it breaks.

How the area of a made-to-measure piece is calculated

All pieces of glass, mirror or screen are calculated the same way: width × height of each piece, multiplied by the number of units.

Example: a fixed shower screen of 80×200 cm: (80/100) × (200/100) = 1.6 m² per unit. This is the same calculation the PresupuestoYa calculator applies automatically for the Glazier trade.

Double glazing: how far it's worth increasing the cavity

The composition of double glazing is stated as glass/cavity/glass in mm — for example 4/12/4. A larger cavity improves thermal insulation up to a point, but beyond 16-20 mm the additional benefit is small compared with the extra cost: it's not always worth going up to the widest cavity available.

Details that change the final result

• Shower screen: always in tempered glass, never monolithic, because of the proximity to water and impact risk. Check the tray is square before ordering it — an out-of-square tray leaves a visible gap at the edge.
• Mirror in a damp area: always protect the bottom edge from standing moisture (with a profile or silicone), because it is the point where the silver layer on the back starts to oxidise soonest.
• Decorative/acid-etched glass: it is a treatment over the whole surface; if the client wants only one translucent area and the rest clear, screen printing or vinyl is needed, not a uniform acid etch.

Frequently asked questions

Can I use single glass in an interior door? Not if it is less than 90 cm from the floor or exposed to impact: regulations require tempered or laminated in those cases.

Can tempered glass be drilled after it's made? No. Once tempered, the piece doesn't allow cuts or drilling — any opening or size must be decided before the tempering process.

What air cavity do I choose for double glazing? 12-16 mm is usually the optimum; above 16-20 mm the additional thermal benefit no longer justifies the extra cost so much.

Conclusion

Getting single, tempered and laminated glass right is not an aesthetic preference: it is a regulatory obligation depending on the location of the opening. Calculating the exact area per piece and deciding the composition before ordering the tempering avoids mistakes that, once the piece is made, can no longer be corrected.