Walkout basement: do you still need egress windows?

A Wisconsin homeowner-to-be asked on Reddit's r/Homebuilding whether a walkout basement planned as an entertainment room, with a yard door and two windows, needs egress windows. Under Section R310 of the International Residential Code, every basement needs at least one operable emergency escape and rescue opening, and every basement sleeping room needs its own. A side-hinged or sliding door can serve as that opening; only a door below the adjacent ground needs a bulkhead enclosure. A walkout door at grade covers the rec room.

Wisconsin builds one- and two-family homes to its own Uniform Dwelling Code, chapters SPS 320 to 325, rather than the IRC. Under SPS 321.03(5), a basement needs one exit: a door to the exterior or a stairway to the floor above. A basement used for sleeping needs two, as far apart as practical and not reached from the same stairway. The second can be an exterior door, another stairway, a stair to a garage with its own exit door, or an egress window in every bedroom. The interior stair plus the walkout door meets that test.

A Wisconsin exit window needs a net clear opening of at least 20 by 24 inches nominal, its bottom no more than 60 inches above the floor (with a platform when higher than 46 inches), and, below grade, an areaway reaching 36 inches out from the wall. The IRC asks for 5.7 square feet of net clear opening (5 square feet at or below grade), 24 inches of height, 20 inches of width, a sill no higher than 44 inches and a 9-square-foot well, with a ladder if it is deeper than 44 inches.

Light rules can also drive window size. The IRC asks for glazing equal to 8% of a habitable room's floor area, with exceptions for rooms with mechanical ventilation and artificial light; Wisconsin's SPS 321.05 exempts basement habitable rooms other than bedrooms. Settle with the inspector how each room is labeled on the plans before ordering windows. A bedroom added later brings in Wisconsin's two-exit rule and needs its own escape opening under the IRC.