CodeMandatory
Guard opening limit (4-inch rule)
IRC R312.1.3Description
Required guards must not allow passage of a 4" sphere through any opening. Below 36" of stair tread, the limit is a 4-3/8" sphere.
Why this exists
Children can fall through openings larger than 4"; the sphere test prevents this.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
maxOpening | max | 4 | in |
Categories
Life safety
Source
ICCno manifest entry
International Residential Code (2024)
Section: R312.1.3
Published 2024-01-01 · last verified 2026-05-09
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Garage / dwelling fire separation · IRC R302.6
- Habitable space minimum ceiling height · IRC R305.1
- Egress window net opening dimensions · IRC R310.2
- Stair riser, tread, and headroom · IRC R311.7
- Smoke alarms required throughout dwelling · IRC R314
Last reviewed 2026-05-09.