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Egress Window Requirements — Size, Sill Height & Window Wells

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.

Requirement	Model Code Standard	Section
Where required	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.

Sections cite the 2021 International Residential Code and 2023 National Electrical Code as model standards. This is BuildSpec’s own summary — not ICC or NFPA text; read the authoritative language at codes.iccsafe.org. Your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.

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