Natural light in habitable rooms
IRC R303.1Description
Habitable rooms must have aggregate glazing area of not less than 8% of the floor area, with at least half of that area operable for ventilation (4% of floor area).
Why this exists
Glazing rules ensure habitable rooms get daylight (vitamin D, circadian rhythm, mood) and have a path for natural ventilation. The 8% / 4% rule is the floor below which the room reads as a closet, not a habitable space.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
minGlazingRatio | min | 0.08 | ratio | Minimum glazing area / floor area (8%). |
minOperableRatio | min | 0.04 | ratio | Minimum operable area / floor area (4%). |
Categories
Applies to
- Room types: living_room, dining_room, kitchen, family_room, bedroom, master_bedroom, office, bonus_room, recreation
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.
Plan symbols this applies to
These plan symbols invoke this directive when placed on a floor plan. Click any to see where it's drawn and what other rules apply to it.
Related directives
- 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)
- Bathroom ventilation · IRC R303.3
- Whole-dwelling mechanical ventilation rate · IRC R303.4
Last reviewed 2026-05-09.