How much window area do I need for natural light and ventilation in a room?
Glazing must be at least 8% of floor area for light, and openable area at least 4% for ventilation (IRC R303.1).
Habitable rooms must have an aggregate glazing (glass) area of not less than 8 percent of the room's floor area to provide natural light.
For natural ventilation, the minimum openable area to the outdoors must be at least 4 percent of the floor area being ventilated, through windows, doors, louvers, or other approved openings.
These window requirements can be waived where approved artificial light and a mechanical ventilation system are provided instead, as set out in the exceptions to this section.
Verified against
Related answers
- What is the minimum floor area for a habitable room? — IRC §R304.1
- What is the minimum width or dimension for a habitable room? — IRC §R304.2
- What is the minimum ceiling height for a habitable room? — IRC §R305.1
- What is the minimum basement ceiling height, and can beams or ducts hang lower? — IRC §R305.1.1
- Does a basement or basement bedroom need an egress window? — IRC §R310.1
- When does glass next to a door have to be tempered safety glazing? — IRC §R308.4.2
- Does glass around a bathtub or shower have to be tempered? — IRC §R308.4.5
- How high does a window sill have to be above the floor to meet fall-protection rules? — IRC §R312.2.1
Need this scoped to your jurisdiction?
Adopted edition and local amendments vary by city and county. Ask Donnie checks your jurisdiction and cites the exact adopted section.
Ask Donnie →General information based on the International Residential Code (a model code). This is AI assistance to verify — not legal advice. Confirm the adopted edition and any local amendments with your local building department (AHJ) and a licensed professional before you build.