Section 405 Underground Buildings
The provisions of Sections 405.2 through 405.9 apply to building spaces having a floor level used for human occupancy more than 30 feet (9144 mm) below the finished floor of the lowest level of exit discharge.
Exceptions: The provisions of Section 405 are not applicable to the following buildings or portions of buildings:
- One- and two-family dwellings, sprinklered in accordance with Section 903.3.1.3.
- Parking garages provided with automatic sprinkler systems in compliance with Section 405.3.
- Fixed guideway transit systems.
- Grandstands, bleachers, stadiums, arenas and similar facilities.
- Where the lowest story is the only story that would qualify the building as an underground building and has an area not greater than 1,500 square feet (139 m2) and has an occupant load less than 10.
- Pumping stations and other similar mechanical spaces intended only for limited periodic use by service or maintenance personnel.
A building having a floor level more than 60 feet (18 288 mm) below the finished floor of the lowest level of exit discharge shall be divided into not fewer than two compartments of approximately equal size. Such compartmentation shall extend through the highest level of exit discharge serving the underground portions of the building and all levels below.