Building codes require tempered glass, or an equivalent safety glazing like laminated glass, in any location where a person could reasonably walk into, fall against, or slip onto a glass surface. In a typical home that means every pane in a door, the glass around showers and tubs, large windows close to the floor, panels flanking entryways, glass near stairs and landings, and overhead installations like skylights. The specific triggers come from the International Residential Code (IRC), which most jurisdictions adopt, combined with a federal impact-test standard at 16 CFR Part 1201.1eCFR. 16 CFR Part 1201 – Safety Standard for Architectural Glazing Materials
Each location below carries its own measurements. If your project touches any of them, the glass has to be tempered (or laminated) and permanently marked to prove it.
Doors and the Glass Around Them
Every pane of glass inside a door is a hazardous location under the IRC. That covers swinging doors, sliding patio doors, bifold doors, storm doors, and combination doors, and it applies no matter how small the pane is. Walking into a door happens at full stride, often with hands full, and the resulting lacerations are the single most common architectural glass injury.
Sliding glass patio doors sit at the top of the federal standard’s performance scale. Every pane must pass a 400 foot-pound impact test under Category II.1eCFR. 16 CFR Part 1201 – Safety Standard for Architectural Glazing Materials Smaller door panes under 9 square feet can meet the lighter Category I threshold of 150 foot-pounds. Two narrow carve-outs exist: decorative glass where no piece could pass a 3-inch sphere, and leaded or carved glass thick and textured enough that it cannot produce dangerous shards.
Glass next to a door is treated almost as strictly. The IRC calls any pane within a 24-inch arc of either vertical edge of a closed door a hazardous location when the bottom edge of the glass is less than 60 inches above the floor.2International Code Council. 2021 O’Fallon Building Code – Chapter 24 Glass and Glazing That picks up sidelights, low transoms, and decorative glass flanking a front entry. The 24 inches is measured as an arc that wraps slightly around the frame, not a straight horizontal line, which is why a sidelight that looks safely offset still often needs tempering.
Showers, Tubs, and Wet-Area Walls
Glass enclosing a shower, bathtub, sauna, hot tub, or steam room must be safety glazing whenever its bottom edge is less than 60 inches above the standing surface. Wet floors, soap, and bare skin give the highest injury risk in a house, so these enclosures also fall under Category II and must survive the full 400 foot-pound impact test.1eCFR. 16 CFR Part 1201 – Safety Standard for Architectural Glazing Materials
The 60-inch rule extends past the enclosure itself. Any glass set into a wall around the wet area triggers the same requirement if its bottom edge sits below that line. A small decorative window beside a soaking tub counts, even though it has nothing to do with the tub surround.
Frameless shower doors carry a related practical point. Without a frame to stiffen the panel, the glass itself has to resist flexing, so industry practice calls for a minimum of 3/8-inch tempered glass, with 1/2-inch preferred on larger openings. Framed doors can run thinner, typically 3/16 or 1/4 inch, because the frame carries much of the load.
Windows: The Four-Factor Test
Most windows do not need tempered glass. The IRC uses a four-part test, and all four conditions must apply to the same pane before safety glazing kicks in:
- The exposed area of the single pane exceeds 9 square feet.
- The bottom edge of the glass sits less than 18 inches above the floor.
- The top edge sits more than 36 inches above the floor.
- A walking surface runs within 36 inches, measured horizontally, of the glass.
The combination is aimed at large, low picture windows that a person could mistake for an opening and walk straight into. Miss any one factor and standard glass is allowed. A 4-square-foot bathroom window fails the size test and does not need tempering regardless of how low it sits. A tall, narrow sidelight near a hallway can hit all four and need tempering even though it looks modest.
Stairs, Landings, and Ramps
Falls on stairs carry more energy than slips on a flat floor, so the code draws a tighter zone around glass near elevation changes. Glass next to a stairway, landing, or ramp is a hazardous location when it sits within 36 inches horizontally of the walking surface and its bottom edge is less than 36 inches above that walking surface.3International Code Council. 2012 IRC Significant Changes – Glazing Adjacent Stairs and Ramps
Earlier editions of the code used a 60-inch vertical threshold, and jurisdictions that have not adopted recent IRC versions sometimes still enforce it. The newer 36-inch number was chosen to line up with guard-height rules, on the reasoning that glass above that height is already behind a railing or wall.
One exception: if a protective rail runs on the accessible side between 34 and 38 inches above the floor, and the rail can take a 50-pound-per-linear-foot horizontal load without touching the glass, the pane itself does not need to be safety glazing. The rail acts as the crash barrier.
Glass that functions as the guard or railing is treated differently again. Because the glass is the only thing stopping a fall, it must be safety glazing regardless of size or position.
Skylights and Overhead Glazing
Tempered glass overhead creates a problem the code has to solve: when it breaks, the small granular cubes fall. The general rule for overhead tempered panels is a broken-glass retention screen below the glass, strong enough to hold twice the pane’s weight, made of noncombustible material, and installed within 4 inches of the glazing.
Residential skylights get an exception from the screen requirement when the tempered glass is used as single glazing, or as both panes of an insulating unit, provided each pane is 16 square feet or smaller, the highest point of the glass is 12 feet or less above any walking surface, and the glass is no thicker than 3/16 inch. Beyond those limits a screen is required, or the builder has to switch to laminated glass, which holds its fragments to the plastic interlayer when it breaks. Overhead is one of the few residential spots where laminated has a clear practical edge over tempered.
Impact Categories to Specify When Ordering
The federal standard splits safety glazing into two performance categories, and they are not interchangeable:
- Category I meets a 150 foot-pound impact test. It covers storm doors, combination doors, and standard doors where no single pane is larger than 9 square feet.
- Category II meets a 400 foot-pound impact test. It is required for shower and tub enclosures, sliding patio doors, and any door with a pane larger than 9 square feet.
Testing uses a weighted leather bag swung into the pane from a calibrated height; the glass either does not break or breaks without producing dangerous shards.1eCFR. 16 CFR Part 1201 – Safety Standard for Architectural Glazing Materials Installing Category I where Category II is called for is a code violation even though both are technically safety glass. If you are ordering replacement glass, specify the category the location requires.
How to Tell If a Pane Is Already Tempered
Every piece of safety glass must carry a permanent identification mark, often called a “bug,” etched or stamped into a corner. The federal standard defines a permanent label as one that would be destroyed by any attempt to remove it, and lists sandblasting, acid etching, hot-stamping, and destructible polyester labels as acceptable methods.1eCFR. 16 CFR Part 1201 – Safety Standard for Architectural Glazing Materials The mark names the manufacturer and the safety standard the pane meets.
Once a pane is installed, tempered glass is visually identical to standard glass. The etch is the only quick way to confirm it. Building inspectors routinely reject installations where the mark is missing or illegible, which in practice means the pane gets replaced. If you are buying replacement glass or evaluating existing installations, look for the bug in a corner of each pane.
What Tempered Glass Does Not Cover
Tempered glass is not fire-rated. It has no fire-resistance rating and will fail under sustained heat exposure. Tempering improves thermal shock resistance, but that is measured in temperature swings the glass can survive without cracking, not in hours of fire containment. Where codes call for fire-rated glazing, such as fire-separation walls or stairwell enclosures in commercial buildings, tempered glass alone will not satisfy the requirement. Those assemblies need specialty products like fire-rated ceramic glass or intumescent-interlayer laminated glass rated for 20 minutes to 3 hours depending on the wall assembly. Treating “safety glazing” and “fire-rated glazing” as the same thing is an expensive mistake because the entire assembly has to come out and go back in.
What Tempered Glass Costs
Tempered glass generally runs 20 to 50 percent more than standard plate glass of the same size, which works out to roughly $2 to $9 extra per square foot for a typical residential pane. The premium reflects the extra manufacturing step and the fact that every pane has to be cut to final size before tempering, since tempered glass cannot be cut or drilled afterward without shattering.
Retrofitting existing windows or shower enclosures to meet the code adds labor, and in most jurisdictions it requires a building permit. Permit fees for window replacement vary, commonly falling somewhere between $50 and $600 depending on the scope and local fee schedule. The cheapest path is to specify tempered glass from the start of a bathroom remodel or window replacement, rather than finding out at the inspection stage that panes need to come back out.