R311.4 Vertical egress. Egress from habitable levels
including habitable attics and basements not provided with an
egress door in accordance with Section R311.2 shall be by ramp
in accordance with Section R311.8 or a stairway in accordance
with Section R311.7.
EXCEPTION:
Stairs or ladders within an individual dwelling unit used for access to areas of 200 square feet (18.6 m2) or less, and not
containing the primary bathroom or kitchen.