Attic headroom rule — code only counts floor area under a 7-foot ceiling (IRC R305.1)

What this diagram shows

A cross-section of an attic under an 8-in-12 pitched roof explaining how much of it can legally become living space. A horizontal line is drawn at a ceiling height of 7 feet 0 inches — the minimum for a habitable room. Everything below that line, out toward the eaves, has too little headroom to count, so short knee walls are built at about the 5-foot mark to close off the unusable triangle for storage. The floor is split into three bands: the low band under 5 feet does not count as floor area at all, the sloped band between 5 and 7 feet may be used but does not count toward the minimum required area, and the tall central band at 7 feet or more is the only part that satisfies the code. The rule: at least half of the required floor area must have a ceiling of 7 feet or more, which is why a big raw attic often yields a much smaller legal room — and why adding a dormer is the usual way to grow the tall band. The sloped ceiling surface itself is roughly 1.7 times the floor area on an 8-in-12 roof, so insulation, drywall, and paint all cover more than the floor footprint.