How tall does a guardrail need to be?
Residential guards must be at least 36 inches high (2021 IRC §R312.1.2); in most commercial buildings the minimum is 42 inches (2021 IBC §1015.3). A guard is required wherever a walking surface, including stairs and landings, is more than 30 inches above the floor or grade below.
Source: 2021 IRC §R312.1.2 · IBC §1015.3 · Verify against your AHJ and the adopted code edition.
A guard protects the open side of a walking surface from a fall. Two numbers cover most jobs:
- Residential: 36 inches minimum — 2021 IRC §R312.1.2.
- Commercial: 42 inches minimum — 2021 IBC §1015.3.
When is a guard required? Wherever a walking surface is more than 30 inches above the floor or grade below, measured within 36 inches horizontally (IRC §R312.1.1 / IBC §1015.2). That threshold applies to decks, landings, and the open sides of stairs alike.
The stair exception: on the open side of a stair, a residential guard may be measured 34 inches from the nosing line rather than 36 — and where the top of the guard doubles as the handrail, it lives in the 34–38 inch handrail band.
Editions and local amendments differ (these are the 2021 I-Codes), and openings in the guard have their own limits — see the maximum gap between balusters.
Work it out: the guardrail calculator shows the cited guard heights for residential and commercial and lays out even, compliant baluster spacing.
Sources
- ICC — International Codes (IRC / IBC) — 2021 IRC §R312.1 / 2021 IBC §1015