ASCE 7-22 · TABLE 1.5-1 · RISK CATEGORY III
Risk Category III — a substantial hazard to human life
High-occupancy and high-consequence structures designed from the 1,700-year wind map — a longer return period than standard buildings, with no importance-factor multiplier.
DEFINITION
Failure here would harm many people
Risk Category III covers buildings whose collapse poses a substantial hazard to human life — large assembly spaces, vulnerable occupants who cannot self-evacuate, and facilities whose loss would affect the public.
The classification comes from ASCE 7-22 Table 1.5-1. The Risk Category does not scale loads by a factor — it selects which basic wind speed map you read the design speed from. Category III uses the 1,700-year mean recurrence interval (MRI) map, giving higher design speeds than the standard 700-year map.
WHAT QUALIFIES
The structures that land in Category III
Use the largest single assembly space — not total building population — when testing the occupant thresholds.
Assembly Occupancies
Theaters, halls and venues where a crowd gathers in one space.
>300 IN ONE AREASchools (K–12)
Buildings with a gym, auditorium or cafeteria that seats a large crowd.
LARGE ASSEMBLY SPACEHouses of Worship
Sanctuaries with a congregation capacity in the assembly range.
>300 SEATSDay-Care Facilities
Large centers caring for children who depend on adults to evacuate.
CAPACITY >500Jails & Detention
Occupants are not free to evacuate and rely on staff in an emergency.
RESTRICTED EGRESSPower, Water & Hazmat
Power-generating, water/sewage treatment, and facilities with hazardous materials whose release could threaten the public.
PUBLIC CONSEQUENCETHE RISK LADDER
Where III sits, and which map it reads
A higher Risk Category points you at a longer-return-period map — higher design wind speed, higher loads. There is no fixed multiplier between rungs.
Category I
Low hazard to life — minor agricultural and storage structures.
300-YR MRI MAPCategory II
Standard occupancy — homes, offices, retail, most buildings.
700-YR MRI MAPCategory III — you are here
Substantial hazard — large assembly, schools, jails, power and water.
1,700-YR MRI MAPCategory IV
Essential facilities — hospitals, fire/police, EOCs, shelters.
3,000-YR MRI MAPIII vs II vs IV
Higher than II, below IV
Modern ASCE 7 (7-10, 7-16, 7-22) has no wind importance factor — the old Iw multiplier was eliminated. Instead, the Risk Category chooses the map. Category III reads from a longer-return-period (1,700-year) map than Category II's 700-year map, so its design wind speeds and resulting loads are higher. Category IV's essential facilities go further still, using the 3,000-year map. The exact wind speed depends entirely on your project's location — there is no single number that converts one category to another.
NEXT STEPS
Confirm your category, then run the numbers
Verify the classification against ASCE 7-22 Table 1.5-1, then read your design wind speed from the correct map.