Every sleeping room and every basement with habitable space needs an emergency escape and rescue opening — the "egress window." The four numbers that govern it: 5.7 square feet, 24 inches, 20 inches, and 44 inches.
Basements, habitable attics, and every sleeping room
IRC R310.1
Minimum clear opening area
5.7 sq ft (5.0 sq ft allowed for grade-floor and below-grade openings)
IRC R310.2.1
Minimum clear height
24 in.
IRC R310.2.1
Minimum clear width
20 in.
IRC R310.2.1
Maximum sill height
44 in. above the floor
IRC R310.2.2
Window wells
Minimum 9 sq ft area with 36 in. minimum horizontal dimension; wells deeper than 44 in. need a permanently affixed ladder or steps
IRC R310.2.3, R310.2.3.1
Operation
Openable from inside without keys, tools, or special knowledge; bars/grilles allowed only with compliant release
IRC R310.1.1, R310.4
Worth knowing
A 24×20 window does NOT work — 24 in. × 20 in. is only 3.3 sq ft. At the minimum height of 24 in., the width must be about 34 in. to reach 5.7 sq ft.
Basement bedroom conversions are the #1 place inspectors find missing egress — the opening is required per sleeping room, not per basement.
Replacement windows in existing openings get limited relief under R310.5/existing-building provisions, but reductions below what existed are generally not allowed.
Ladders in window wells may encroach up to 6 in. into the required well dimensions.
This guide is BuildSpec’s own summary, not code text. It cites the 2021 International Residential Code and the 2023 National Electrical Code as model standards. The IRC 2021 text itself is in the Code Library for signed-in members; BuildSpec publishes no NEC text, which is at nfpa.org. Neither is an adoption record: your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.