NASCLA · Code numbers · Episode 5

Stairs and Guards, Measured

1:41

The transcript is below. The full episode plays in the EstatePass CT dashboard.

Chapters

0:00The step
0:35The stair
0:49Handrail
0:54Guard
1:21Recap

In short

Under the 2021 International Building Code, stair risers are 7 inches maximum and 4 minimum, and rectangular treads are at least 11 inches deep. Stairs are at least 44 inches wide, or 36 when serving fewer than 50 people, with 80 inches of headroom. Handrails sit 34 to 38 inches above the nosings. Guards are required where the drop is more than 30 inches within 36 inches of the edge, are at least 42 inches high, and must not pass a 4-inch sphere. The residential code's 7¾-inch riser and 10-inch tread do not apply to commercial stairs.

Riser 7 in max, 4 in min; tread 11 in min.
Width 44 in (36 under 50 people); headroom 80 in.
Handrail 34–38 in; guard 42 in where the drop is over 30 in.
No opening in a guard may pass a 4 in sphere.

Transcript

0:00The step

Commercial stairs are built to a short list of numbers. The exam asks for them exactly, and the numbers for houses make tempting wrong answers. Start with one step. Under the building code, a riser is at most 7 inches, and at least 4. The tread is at least 11 inches deep. The residential code allows a 7 and three-quarter inch riser and a 10 inch tread. On a commercial question, those are the traps.

0:35The stair

Now the whole stair. It is at least 44 inches wide, or 36 when it serves fewer than 50 people. And it needs at least 80 inches of headroom above the line of the nosings.

0:49Handrail

Handrails sit between 34 and 38 inches above the nosings.

0:54Guard

Pause. A guard is required on a commercial stair. How high must it be? 42 inches, measured from the walking surface, or from the nosings on a stair. A guard is required where the drop is more than 30 inches, within 36 inches of the open edge. And no opening in it may let a 4 inch sphere pass through.

1:21Recap

7 and 11 for the step, 44 wide, 80 overhead, 34 to 38 for the handrail, 42 for the guard. Next: markup and margin. Subscribe so you catch it.

Sources

2021 IBC 1011.2, 1011.3 and 1011.5.2
2021 IBC 1014.2 and 1015.2–1015.4
2021 IRC R311.7.5

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