What Is Tempered Glass? Why It Matters for Railing Systems
If you are shopping for a glass railing system, you will see the term tempered glass on virtually every product listing. But what does it actually mean, and why is it the only type of glass approved for railing applications?
How Tempered Glass Is Made
Tempered glass starts as ordinary float glass. It is heated to roughly 1,150 °F (620 °C) in a tempering oven, then rapidly cooled with high-pressure air jets — a process called quenching. This creates a surface layer of compression and an interior layer of tension, which together make the glass significantly stronger than untreated float glass.
Why Building Codes Require It
The International Building Code (IBC) and International Residential Code (IRC) classify glass railings as safety glazing. That means only tempered or laminated glass is permitted. Annealed (regular) glass is explicitly prohibited because it breaks into large, dangerous shards. Tempered glass, by contrast, fractures into small, relatively harmless cubes — dramatically reducing the risk of serious cuts.
This is the same reason tempered glass is required in shower doors, patio doors, and sidelights near entry doors. Any glass location where human impact is possible must use safety glazing. Learn more about code requirements on our building codes guide.
Tempered vs. Laminated Glass
Both qualify as safety glazing, but they behave differently:
- Tempered glass is roughly four times stronger than annealed glass of the same thickness. When it breaks, it shatters completely into small granular pieces.
- Laminated glass consists of two layers of glass bonded to an interlayer (usually PVB). When it breaks, the fragments stick to the interlayer and the panel stays in the frame.
For most residential railing applications, tempered glass is the standard choice. Laminated glass is sometimes specified for high-rise balconies or locations where a broken panel must remain in place until replaced.
How to Identify Tempered Glass
Every tempered glass panel carries a permanent etch mark — usually in one corner — that includes the manufacturer's name, the safety standard (ANSI Z97.1 or CPSC 16 CFR 1201), and the word "tempered." This mark is applied before the tempering process and cannot be removed. If a glass panel does not have this mark, it may not be tempered.
Strength and Thickness for Railings
Glass railing panels are typically 3/8" (10 mm) or 1/2" (12 mm) thick tempered glass. The required thickness depends on the panel height, the span between supports, and the applicable wind load. Our glass panels are available in both thicknesses to meet residential and commercial requirements.
FAQ
Can tempered glass be cut after tempering?
No. Tempered glass cannot be cut, drilled, or modified after the tempering process. Any alteration will cause it to shatter. All cuts and holes must be made before tempering. This is why ordering the correct size upfront is critical.
Is tempered glass more expensive than regular glass?
Tempered glass costs roughly 2–3 times more than annealed glass of the same size. However, for railing systems, tempered glass is the only code-compliant option, so the comparison is largely academic.
Can tempered glass break on its own?
Spontaneous breakage is extremely rare but can occur due to nickel sulfide inclusions — microscopic impurities trapped during manufacturing. Heat-soaked tempered glass undergoes additional testing to reduce this risk and is sometimes specified for critical applications.