Does a bathroom need a window, or is an exhaust fan enough?
A bathroom needs 3 sq ft of glazing with half openable, or a mechanical exhaust fan vented outdoors at 50 cfm intermittent / 20 cfm continuous (IRC R303.3).
Bathrooms and similar rooms must have an aggregate glazing area of at least 3 square feet (0.3 m²), at least half of which is openable.
A window is not required where artificial light and a local exhaust fan are provided instead. The exhaust must discharge directly to the outdoors, not into an attic or crawl space.
Under the mechanical provisions (Section M1507), the bathroom exhaust rate is 50 cfm for intermittent operation or 20 cfm for continuous operation.
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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.