Where Tempered Glass Is Required: Doors, Tubs, Low Windows

The model residential code calls for safety glass in what it names "hazardous locations": glass in doors, glass within 24 inches of a door with its bottom edge under 60 inches, large low window panes next to a walkway, glass in guards and railings, glass in walls around tubs, showers and pools with its bottom edge under 60 inches above the standing surface, and glass beside stairs, ramps and the bottom stair landing. That is how Boulder County, Colorado's safety glazing handout reproduces Section R308.4 of the 2021 International Residential Code (IRC) ¹. The code's term is safety glazing; tempered glass is the type most people mean when they ask.

The IRC is a model code. A state or city adopts an edition, sometimes renumbers it and may amend it, so the locally adopted edition governs your house, and your building department has the final word. California, for example, carries the same rules as Section R324.4 of its 2025 Residential Code, with a few differences in wording, as the City of Dublin's safety glazing handout shows ². This article walks through each location using those two official handouts.

What counts as safety glass

Tempered glass is glass strengthened by reheating it to just below its melting point and then cooling it suddenly; laminated glass is two or more sheets with a plastic inner layer that holds the glass if it breaks ³. Both are forms of safety glass, which the Efficient Windows Collaborative defines as glass that is less subject to breakage or splintering ³.

Boulder's handout of Section R308.1 says each pane in a hazardous location needs a manufacturer's designation that stays visible after installation and names who applied it, the glass type and the safety glazing standard; it has to be etched, fired, embossed or otherwise impossible to remove without destroying it, and a label may be used instead (Boulder handout) ¹. On tempered glass that designation is the small permanent mark you can see on the pane; for other safety glass, the handout lets the building official accept a certificate or affidavit instead ¹.

The hazardous locations, one by one

Section numbers below are the 2021 IRC's as the Boulder handout gives them; California's numbers start with R324.4 instead, per the Dublin handout ¹². The table is a summary; each section also has exceptions, some covered below.

Glass in and beside doors

Boulder's handout treats all glass in swinging, sliding and bifold doors as hazardous, with exceptions for openings too small for a 3-inch sphere to pass through and for decorative glazing (Boulder handout) ¹. A sidelite or a window close to a door is caught when its bottom edge is less than 60 inches above the floor and it sits within 24 inches of either side of the door ¹. Exceptions include an intervening wall or permanent barrier, a door into a closet or storage area 3 feet deep or less, and glass beside the fixed panel of a patio door ¹.

Here the two handouts word one rule differently. Boulder's version covers glass on a wall less than 180 degrees from the door's plane within 24 inches of the hinge side of an in-swinging door; Dublin's version of the California code says glass perpendicular to the door (Dublin handout) ¹². It is a small example of why the adopted edition, not a summary, settles a close case.

Large, low windows

A window falls under R308.4.3 only when all four conditions are true: one pane 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 is within 36 inches horizontally (Boulder handout) ¹. If any one of them is not met, this section does not apply. A protective horizontal rail 34 to 38 inches above the walking surface is one of the exceptions ¹. This is the rule that most often touches a big picture window; picture window cost covers it from that side.

Tubs, showers and pools

Glass in walls, enclosures or fences containing or next to a bathtub, shower, hot tub, spa, whirlpool, sauna, steam room or pool is hazardous when its bottom edge is less than 60 inches above any standing or walking surface, and the rule applies to each pane of an insulated unit (Boulder handout) ¹. The exception is glass more than 60 inches, measured horizontally, from the water's edge of a tub, spa or pool, or from the edge of a shower, sauna or steam room ¹. A bathroom window beside or above a tub is the common case in a replacement job.

Stairs, ramps and landings

Glass whose bottom edge is less than 36 inches above the walking surface of a stairway, a landing or a ramp is hazardous, unless a rail at 34 to 38 inches protects it or it sits 36 inches or more away horizontally (Boulder handout) ¹. At the bottom of a stairway, glass less than 36 inches above the landing and within a 60-inch horizontal arc of the bottom tread nosing is hazardous too, unless a guard protects it and the glass is more than 18 inches from the guard ¹.

Does a replacement window have to meet this?

Boulder's handout says new windows and window replacements must comply (Boulder handout) ¹. Dublin's handout says a permit is needed even to replace windows in kind, and not when only the glass is replaced (Dublin handout) ². Other places draw the permit line elsewhere; do you need a permit to replace windows shows how cities differ.

In practice, an old window with ordinary glass may need safety glass when it is replaced, if it sits in one of the locations in Boulder's handout of R308.4 ¹. Bedroom windows bring their own rules for size and sill height, covered in egress window requirements.

What to ask before you sign

Walk the house with a tape measure first. For each window being replaced, note:

• How far the glass sits from any door, and how high its bottom edge is.
• Whether a tub, shower or stair is nearby, and how far.
• For large panes, the bottom and top edge heights and whether a walkway runs within about 3 feet.

Then ask each installer:

• Which code edition does the building department here enforce, and does it change any of these rules?
• Which of my windows will get safety glass, and is that priced in the quote, line by line?
• Who pulls the permit and books the inspection?
• Is the installer licensed where your state licenses this work? The state pages, such as California and Oregon, link the lookups.

Glass choice also affects price and energy performance; see window glass replacement cost and low-E glass explained. For the whole project, window replacement cost and how to compare window quotes cover the rest. When you have your list, you can compare quotes from window installers.

About these figures

• ¹ Official record: Boulder County, Colorado publication B-30 reproducing Sections R308.1 and R308.4 of the 2021 International Residential Code: labeling, doors (3-inch sphere), glass next to doors (60 and 24 inches, 3-foot closets), windows (9 square feet, 18 and 36 inches, 34 to 38 inch rail), guards, wet surfaces (60 inches), stairs and ramps (36 inches) and bottom landings (60 and 36 inches), and the note that replacements must comply, checked October 26, 2026.
• ² Official record: City of Dublin, California handout on Section R324 of the 2025 California Residential Code: the same hazardous locations, the perpendicular-glass wording beside in-swinging doors, and its permit notes for replacement windows and glass-only work, checked October 26, 2026.
• ³ Official record: Efficient Windows Collaborative glossary definitions of tempered, laminated and safety glass, checked October 26, 2026.