Section 1604.5/Risk Category
IBC 1604.5 and Table 1604.5 classify buildings into Risk Categories I through IV based on occupancy and use, which determines wind speed, seismic importance, snow load, and flood design requirements.
Table 1604.5 assigns every building to one of four Risk Categories. Risk Category I: low hazard to human life (agricultural, minor storage, temporary). Risk Category II: standard occupancy (offices, residences, retail, most commercial). Risk Category III: substantial risk to human life (buildings with 300+ people in one area, schools with 250+ occupants, colleges with 500+, healthcare not in Category IV, jails, power stations). Risk Category IV: essential facilities (hospitals, fire stations, police stations, emergency shelters, air traffic control). The Risk Category determines the wind speed map used, the seismic importance factor, the snow load importance factor, and the flood design requirements.
Why this section exists
Not all buildings carry the same consequences of failure. The Risk Category system scales the design loads and detailing requirements to match the consequences. Essential facilities (Category IV) use the highest wind speeds, the most restrictive seismic detailing, and the highest snow and flood loads because they must remain operational after a design-level event. The Risk Category is the single most important classification decision on a project because it cascades through every structural design parameter.
What plan reviewers look for
Plan reviewers check the structural general notes for the Risk Category and verify it matches the building's use per Table 1604.5. They confirm the Risk Category is consistent across all design parameters. They check for mixed-use buildings where different occupancies may place the building in a higher Risk Category than the primary use.