Tempered glass required: sill < 18" AFF OR within 60" of tub/shower
NKBA 4th ed §4.2 Glazing, Windows & Glass PartitionsDescription
Any glazing (window or door) whose bottom edge is less than 18" above finished floor must be tempered, safety, or approved-equal material. Glazing less than 60" AFF in or adjacent to a tub/shower fixture is also tempered. Windows over a cooking surface must NOT be operable and must not have combustible window treatments within the combustible-zone clearance.
Why this exists
Trip / fall impact on low-sill glazing causes severe lacerations with annealed glass; tempered breaks into pebbles. The 18" sill threshold and 60" tub-side threshold are the safety-glass rules in IRC R308.4. The over-range exclusion prevents accidental ignition + steam-induced thermal-shock failure of operable windows.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
lowSillThreshold | max | 18 | in AFF | Bottom-edge height below which tempered glass is required |
tubShowerThreshold | max | 60 | in AFF | Tempered required within this distance from a tub/shower fixture |
Categories
Source
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
- Bathroom entry doorway · NKBA Bath 1
- Kitchen walkway and work-aisle widths · NKBA Kitchen 6
- Doorway clear width · NKBA Kitchen 1
- Door swing into work zones · NKBA Kitchen 2
- Distance between work zones · NKBA Kitchen 3
Last reviewed 2026-05-14.