Safety glazing: tempered or laminated.

Safety glazing is glass that has passed an impact test, so that it is unlikely to cause a serious cut when a person falls against it. Two kinds cover almost every window and door. Tempered glass breaks into small blunt pieces. Laminated glass cracks and stays in the opening. The building code names the places where a person is likely to hit the glass, and it requires safety glazing there. It calls them hazardous locations.

Tempered glass.

Tempered glass is ordinary glass that has been heated and then cooled fast. The surfaces end up in compression and the core in tension. Two things follow from that:

• It is several times stronger than ordinary annealed glass of the same thickness.
• When it does break, the stored stress releases at once. The whole pane turns into small granules with no long sharp edges.

Worth knowing:

• It cannot be cut or drilled after tempering. Sizes, holes and notches are final before the glass goes into the furnace.
• Once broken, it falls out of the opening. It will not keep out rain or people until it is replaced.
• The heat treatment leaves a slight waviness that can show in reflections on a large facade.
• Very rarely, a tiny inclusion in the glass makes a tempered pane break with no impact at all. Heat-soak testing at the factory reduces that risk.

Heat-strengthened glass is a different product. It is stronger than annealed glass, but it breaks into large pieces. On its own it does not count as safety glazing.

Laminated glass.

Laminated glass is two or more sheets of glass bonded to a plastic interlayer under heat and pressure. When it breaks, the pieces stay stuck to the interlayer. The pane cracks like a car windshield and stays in the frame.

• It keeps the opening closed after breakage, which matters for guards, for overhead glass and for security.
• The interlayer damps vibration, so laminated glass also reduces noise. The highest certified sound rating in the Vistaza range, STC 47 and OITC 40, belongs to a Vi6 casement with a triple make-up that has laminated panes inside and out.
• It costs more than tempered glass. Laminated units are usually thicker and heavier too, so the hinges have to be sized for them.
• The exposed edges should be kept out of standing water, which can cloud the interlayer over time.

An acoustic laminate is chosen for sound. Whether a given make-up also counts as safety glazing depends on its impact test and its mark. Ask.

Side by side.

	Tempered	Laminated
How it breaks	Small blunt granules	Cracks, and stays in one piece
After it breaks	The opening is empty	The opening stays closed
Strength before breaking	High	About that of the glass it is made from
Sound	No gain	Better
Weight and cost	Lower	Higher
Typical uses	Doors, sidelights, low glass, wet areas	Guards, overhead glass, security, acoustic units

The two can be combined. A laminate made from tempered sheets is common in guards.

Where the code asks for it.

In the International Building Code the rules are in Section 2406, in the glass and glazing chapter. Safety glazing has to pass one of two impact test standards, CPSC 16 CFR 1201 or ANSI Z97.1. The hazardous locations, in plain words:

• Glass in doors. Swinging, sliding and folding doors, whether the panel moves or not. On a residential floor this means every terrace door and sliding door.
• Glass next to a door. A pane close beside a door, with its lower edge below head height. The code gives this as within 24 inches of the door and less than 60 inches above the floor.
• Large, low panes. A window pane that is all four of these: larger than 9 square feet, lower edge less than 18 inches above the floor, upper edge more than 36 inches above the floor, and a walking surface within 36 inches. Floor-to-ceiling glass usually qualifies.
• Guards and railings. Glass used as a guard, or as an infill panel in one.
• Wet areas. Glass near bathtubs, showers, saunas, hot tubs and pools, where the lower edge is less than 60 inches above the standing surface. A bathroom window over a tub is the usual case.
• Stairs, ramps and landings. Glass beside them, or facing the bottom of a stair, with its lower edge less than 60 inches above the walking surface.

Each location has exceptions. The dimensions above are those of Section 2406.4 in the 2024 IBC and in the 2022 New York City Building Code. The edition that your jurisdiction has adopted governs, along with any local amendments.

Traditional wired glass is still found in older buildings. Current codes treat it like any other glass: it has to pass the impact test before it can go in a hazardous location.

The mark in the corner.

Every pane of safety glazing carries a permanent mark, usually etched in one corner. It names the maker and the standard that the glass meets. Inspectors look for it. In an insulating glass unit, check which pane carries the mark. A hazardous location that can be reached from both sides may need safety glass on both faces.

No mark in the corner means it is not safety glazing, whatever the order said.

A checklist for the window schedule.

1. Mark every hazardous location on the elevations and plans before glass is priced. Low sills, glass beside doors and bathroom windows are the ones most often missed.
2. For each one, decide tempered or laminated. Ask what should happen after a breakage. If the opening has to stay closed, use laminated.
3. Say which panes of the unit are safety glass: inner, outer or both.
4. On sound-rated elevations, settle the acoustic make-up first. Then confirm whether that make-up is also rated as safety glazing.
5. Carry the glass type for each opening onto the shop drawings, so that it is approved together with the window.
6. On replacement work, do not assume the old glass met today's rules. Check each opening against the current code.

To match glass to energy and sound targets, use find your glass. To have the glass settled opening by opening, send the plans.