A: Not required. Ventilation in bathrooms must be from window or fan, your choice:
- Window: If you install a window in the bathroom, it must be at least 3 sq. feet area. This window need only be half-openable. Or,
- Fan: Installing a bathroom fan obviates the need to install a window. The bathroom fan should pull out at least 50 cubic feet per minute (cfm). And because windows provide light as well as ventilation, if you go the fan-only route you do need to install artificial lighting.
Section R303 of the International Residential Code discusses light and ventilation regulations.