CodeMandatory
Habitable rooms need exterior windows
LGT-WINDOW-AREA-01Description
Habitable rooms must have window area of at least 8% of floor area, of which at least 4% must be openable for ventilation.
Why this exists
Habitable rooms need natural light and ventilation per IRC R303 — at least 8% of the floor area in glazing.
Categories
DaylightVentilation
Source
ICCno manifest entry
International Residential Code (2024)
Section: R303.1
Published 2026-05-09 · last verified 2026-05-09
Solver enforcement
The constraint solver runs check function lgt-window-area-01 as a hard constraint — layouts that fail are rejected outright.
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)
- Bathroom ventilation · IRC R303.3
Last reviewed 2026-05-09.