When is a guardrail required?
A guard is required wherever a walking surface — a deck, balcony, landing, or the open side of a stair — is more than 30 inches above the floor or grade below, measured within 36 inches horizontally (IRC §R312.1.1, IBC §1015.2). Below that 30-inch threshold a guard isn't required by code, though it can still be a good idea.
Source: 2021 IRC §R312.1.1 · IBC §1015.2 · Verify against your AHJ and the adopted code edition.
The trigger is a drop of more than 30 inches. A guard is required at the open side of any walking surface — deck, balcony, landing, ramp, or stair — where it sits more than 30 inches above the floor or grade below (IRC §R312.1.1, IBC §1015.2).
Two details matter:
- The 30 inches is measured to the surface below at any point within 36 inches horizontally — so a deck near a downslope can trip the rule even if the deck boards are lower than 30 inches at the edge.
- It applies to the open side of stairs too, not just flat surfaces.
Once a guard is required, its height and opening limits kick in — see how tall a guardrail needs to be and the maximum gap between balusters.
Work it out: the guardrail calculator shows the cited heights and lays out compliant baluster spacing once you know a guard is needed.
Sources
- ICC — International Codes (IRC / IBC) — 2021 IRC §R312.1.1 / IBC §1015.2