Wet locations: the 60 in trigger
Under 2018 IRC R308.4.5, glazing in walls, enclosures or fences containing or facing tubs, showers, hot tubs, spas, whirlpools, saunas, steam rooms and pools is a hazardous location when its bottom exposed edge is less than 60 in (1524 mm) above any standing or walking surface.
Keep the heights apart: 36 in is the stair and landing trigger, 18 in is the R308.4.3 window condition, and 72 in is not in the section.
The 60 in horizontal exception
R308.4.5 exempts glazing more than 60 in, measured horizontally in a straight line, from the water's edge of a tub (or the edge of the shower, sauna or steam room).
Worked example: a bathroom window with its bottom edge 30 in up sits 72 in in a straight line from the tub's water's edge. 72 in is more than 60 in, so the exception applies.
The traps: the rule covers glazing near the listed fixtures, not every bathroom pane, and the 18 in window figure is no wet-location exemption.
Bottom of a stairway: 36 in and a 60 in arc
Under R308.4.7, glazing is hazardous when it is less than 36 in above the bottom landing and within a 60 in (1524 mm) horizontal arc of less than 180 degrees from the bottom tread nosing.
The arc is 60 in, not 36 in (the height trigger) and not 24 in (the R308.4.2 door distance). The 18 in figure belongs to the exception, not the arc.
The guard exception
The R308.4.7 exception applies where the glazing is protected by a guard complying with R312 and the plane of the glass is more than 18 in (457 mm) from the guard.
- A rail 24 in high matches no exception. The rail exception in R308.4.6 uses a rail 34 to 38 in high resisting 50 plf.
- A top edge below 36 in does not exempt anything; the trigger is the bottom edge below 36 in.
- A pane under 9 sq ft is a window condition under R308.4.3, not a stair exception.