How NFPA 101 is structured, and what this covers. NFPA 101 carries TWO chapters for every occupancy, one headed New and one headed Existing. What selects between them is the occupancy, not the age of the building. A change of occupancy inside a hundred-year-old building creates a new occupancy and is judged by the new chapter, which is generally the more demanding of the two. A building carrying on in the use it was approved for is an existing occupancy. Get that wrong and every threshold below it is wrong.

This page answers from the new occupancy chapters only — NFPA 101 (2021) Chapters 12 through 42 and IBC §907.2.1 through §907.2.13. It does not cover the paired existing occupancy chapters, or special-condition sections like atriums, covered malls, high-piled storage, aircraft hangars, or underground/windowless buildings (IBC §907.2.14–23). The CodeGreen Tools app carries both chapters and will ask you which applies. Both codes have many more exceptions and edge cases than fit in a two-input form — treat this as a starting point for which section to go read, not a final determination. This tool is a planning aid, not a substitute for a code review by a licensed design professional or your authority having jurisdiction, and requirements vary by code edition and local amendments.