When Building Codes Require Tempered Glass in Windows

Building codes require safety glazing, usually tempered or laminated glass that has passed an impact test, wherever people are likely to walk into or fall against glass. That covers glass in and beside doors, around tubs and showers, next to stairs and landings, and large panes that come close to the floor. The rules sit in Section R324 of the 2024 International Residential Code (IRC), Section R308 in the 2021 edition, and replacement glass in those spots has to meet them as well.

What counts as safety glass

Safety glazing is defined by test performance, not by a glass type alone. The IRC (R324.3.1) requires glazing in hazardous locations to pass the impact test in the Consumer Product Safety Commission’s standard, 16 CFR Part 1201. Glazing that is not in a door or in an enclosure for a tub, shower, hot tub, whirlpool, sauna or steam room may instead be tested to the ANSI Z97.1 standard.

The federal standard defines the two common types:

• Tempered glass is specially heat-treated or chemically treated glass that cannot be cut, drilled, ground or polished after treatment without breaking. When highly tempered glass breaks at any point, the whole piece breaks into small particles.
• Laminated glass is two or more pieces of glass bonded to one or more layers of resilient plastic.

The federal rule itself applies to glass in doors, storm doors, sliding patio doors, and bathtub and shower doors and enclosures. Windows next to doors, tubs and stairs are covered by the building code, which adopts the same test.

One practical consequence follows from the definition: tempered glass cannot be cut to fit on site. It has to be ordered as tempered, in the finished size.

The seven hazardous locations

The 2024 IRC lists seven locations in Section R324.4. Glass in any of them must be safety glazing unless an exception applies.

1. In doors (R324.4.1). All fixed and operable glass panels of swinging, sliding and bifold doors. Exceptions: openings too small for a 3-inch sphere to pass through, and decorative glazing.
2. Beside doors (R324.4.2). Glass whose bottom exposed edge is less than 60 inches above the floor and that is either within 24 inches of either side of the closed door, in the same plane, or on a wall at less than 180 degrees to the door and within 24 inches of the hinge side of an in-swinging door. Exceptions include decorative glazing, glass behind an intervening wall or permanent barrier, and glass next to the fixed panel of a patio door. Glass beside the door of a closet or storage area 3 feet deep or less is judged by the window rule below instead.
3. Large, low windows (R324.4.3). A pane is hazardous when all four conditions hold: it is larger than 9 square feet, its bottom edge is less than 18 inches above the floor, its top edge is more than 36 inches above the floor, and a walking surface lies within 36 inches of it horizontally. A protective horizontal rail at 34 to 38 inches, strong enough for a 50-pound-per-foot load and at least 1.5 inches tall, is one exception.
4. Guards and railings (R324.4.4). Glass in guards and railings is always a hazardous location, whatever its size or height.
5. Wet areas (R324.4.5). Glass in walls, enclosures or fences around tubs, showers, hot tubs, spas, whirlpools, saunas, steam rooms and pools, when its bottom exposed edge is less than 60 inches above a standing or walking surface. The rule applies to each pane of a multi-pane unit. Glass more than 60 inches horizontally from the water’s edge, or from the edge of a shower, sauna or steam room, is exempt.
6. Stairs and ramps (R324.4.6). Glass whose bottom exposed edge is less than 36 inches above the walking surface of stairs, ramps and their landings. Exceptions: a qualifying rail at 34 to 38 inches, or glass 36 inches or more away horizontally.
7. Bottom stair landing (R324.4.7). Glass less than 36 inches above the landing and within a 60-inch horizontal arc of the bottom tread nosing. It is exempt when protected by a guard and set more than 18 inches behind it.

An example from a bathroom: if a window’s bottom edge is under 60 inches above the tub floor and it sits within 60 inches of the tub’s edge, every pane in it needs safety glazing.

How to tell whether a pane is already safety glass

Look for a permanent mark or label on the glass. Section R324.1 requires each pane in a hazardous location to carry a manufacturer’s designation that states who applied it, the type of glass, and the safety glazing standard it meets. It must stay visible after installation.

• Permanent marks. The designation must be acid-etched, sandblasted, ceramic-fired, laser-etched, embossed, or of a type that cannot be removed without being destroyed. The code also permits a label in place of the manufacturer’s designation.
• Alternatives for glass other than tempered. The building official may accept a certificate, affidavit or other evidence instead of the mark.
• Small-pane assemblies. In units made of panes no larger than 1 square foot each, at least one pane must carry the full designation, and the others must be labeled “CPSC 16 CFR 1201” or “ANSI Z97.1.”

A pane in a hazardous location with no mark or label cannot be confirmed as safety glass by looking at it. Treat it as unverified until someone who can test or document it says otherwise.

Replacing glass or windows in these locations

Replacement work does not get a pass. The 2024 International Existing Building Code says replacement glazing in hazardous locations must meet the safety glazing requirements of the building or residential code (Section 402.1). The exception covers glass block walls, louvered windows and jalousies repaired with like materials. For windows, Section 505.1 adds that installing or replacing windows must meet the requirements for new installations.

ENERGY STAR’s storm window guidance flags the same issue for add-on storm windows: state or local codes may require safety glass in accident-prone locations such as near stairs.

Manufactured homes follow a separate federal list in HUD’s construction standards (24 CFR 3280.113). One example of the difference: HUD’s rule reaches glass within 12 inches of a door’s edge, where the IRC uses 24 inches.

When to bring in a professional, and what to ask

A window or glass contractor should identify hazardous locations before ordering, because tempered units are made to size and cannot be altered afterward. Measure first, then ask:

• Which openings in this quote fall into a hazardous location under the code edition the building department enforces, R324 or R308?
• Will those units be ordered as tempered or as laminated glass, and will each pane carry a permanent safety-glazing mark?
• For bathroom windows near a tub or shower: is every pane in the insulating unit safety glass, as R324.4.5 requires?
• For windows beside doors and along stairs: what are the measured heights of the bottom edges and the horizontal distances?
• Does the permit inspection check the marks, and who pulls the permit?

Ask for the answers on the quote, opening by opening. A mark that is missing on delivery day is far easier to deal with before installation than after.