CodeMandatory
Bathroom ventilation
IRC R303.3Description
Bathrooms must have an openable window ≥1.5 sq ft, OR a mechanical exhaust fan rated ≥50 cfm intermittent / ≥20 cfm continuous, vented to the outside.
Why this exists
Moisture from showering causes mildew + structural damage if not removed. A vent or window is the minimum control.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
minWindowArea | min | 1.5 | sq_ft | |
minIntermittentCfm | min | 50 | cfm | |
minContinuousCfm | min | 20 | cfm |
Categories
BathroomVentilation
Applies to
- Room types: bathroom, half_bath
Source
ICCno manifest entry
International Residential Code (2024)
Section: R303.3
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
- Natural light in habitable rooms · IRC R303.1
- Carbon monoxide alarms in sleeping areas · IRC R315
- Garage HVAC duct prohibition · IRC R302.5.2
- Natural ventilation in habitable rooms · IRC R303.1 (vent)
- Whole-dwelling mechanical ventilation rate · IRC R303.4
Last reviewed 2026-05-09.