Journal

What Is Tempered Glass?.

Tempered glass is glass heat-treated in a controlled process that creates internal stresses that make it four times stronger than standard annealed glass. When it breaks, it shatters into small granular pieces rather than long sharp shards, which is why it is required by code in doors, sidelights, shower enclosures, and any glazing within 18 inches of the floor or 24 inches of a door. Also called toughened glass; the terms are interchangeable.

Updated May 31, 2026

How it works.

Glass is heated to roughly 620 degrees Celsius and then rapidly cooled by air jets across both faces. The faces cool fast and the core cools slowly, which puts the faces in compression and the core in tension. The compressed faces resist surface damage that would propagate cracks through standard glass.

Tempered glass cannot be cut, drilled, or modified after tempering; any cut releases the internal stress and shatters the entire pane. All cutting, drilling, and shaping happens before tempering.

Where it is required.

International Building Code (IBC) Section 2406 requires safety glazing (tempered or laminated) in doors, fixed panels adjacent to doors, glazing within 24 inches horizontally of a door, glazing within 18 inches of the floor on a window, shower and tub enclosures, and other locations. Local code may add to the federal requirements.

Tempered does not replace impact-rated glass for hurricane zones (laminated impact-rated glass is required there) and does not provide acoustic performance beyond standard glass. Specify tempered for safety, laminated for impact or acoustic.

Common questions.

Where do I need tempered glass?
In doors, fixed panels adjacent to doors, any glazing within 24 inches of a door horizontally, glazing within 18 inches of the floor, shower and tub enclosures, and skylights. IBC Section 2406 lists the full requirement; local code may add to it.
Is tempered glass the same as safety glass?
Tempered glass is one of two safety glass types; laminated is the other. Both meet IBC safety glazing requirements. Tempered shatters into granular pieces; laminated holds together because of the interlayer.
Can tempered glass be cut to size on site?
No. Tempered glass cannot be cut or modified after tempering. All shaping, drilling, and edge work happens at the factory before the tempering process. Order tempered glass to final dimensions.

Project in motion

Specifying glass on a project?

Glass spec ships with every Crateworks window and door. We confirm tempered, laminated, or both per opening.

Request a quoteRequest a quote