ASCE 7-22 · TABLE 1.5-1
How to Select Your Risk Category
Four categories ranked by hazard to human life and the consequence of failure — each one reads its design wind speed from a different return-period map.
VIOLET · CLASSIFY IN FOUR STEPS
Work the questions top to bottom
Stop at the first match. If nothing triggers III or IV, the building defaults to Category II.
Step 1 · Essential?
Must it stay operational during and after a disaster? Hospital, fire/police, EOC, 911, water treatment, shelter.
YES → CAT IVStep 2 · Hazmat?
Toxic, highly toxic, or explosive materials above IBC threshold quantities on site.
YES → CAT IIIStep 3 · Assembly > 300?
More than 300 people in one space, or a vulnerable population that cannot self-evacuate.
YES → CAT IIIStep 4 · Otherwise
Minimal-occupancy ag or temporary use drops to Cat I. Everything else is the standard default.
DEFAULT → CAT IICYAN · THE FOUR CATEGORIES
Each category reads a different speed map
Higher category → longer return-period map → higher design wind speed V → higher loads.
Category I · Low Hazard
Low hazard to human life — minimal-occupancy and storage structures.
Example: Agricultural barn, grain silo, equipment storage.
300-YEAR MRI MAPCategory II · Standard
The default. Standard occupancy with typical consequences of failure — most buildings.
Example: Homes, apartments, offices, retail, warehouses.
700-YEAR MRI MAPCategory III · Substantial
Substantial hazard — large assembly, schools, and high-consequence occupancies.
Example: Assembly >300, schools, jails, power facilities.
1,700-YEAR MRI MAPCategory IV · Essential
Essential facilities that must function for emergency response and recovery.
Example: Hospitals, fire/police, EOC, shelters, critical utilities.
3,000-YEAR MRI MAPCYAN · SIDE BY SIDE
Category, hazard, and which map you read
There is no importance factor and no fixed multiplier between categories — the category just selects the map.
| Category | Hazard to Life | Wind Speed Map (MRI) | Examples |
|---|---|---|---|
| I | Low | 300-year | Agricultural barns, silos, minor storage |
| II | Standard (default) | 700-year | Homes, offices, retail, most buildings |
| III | Substantial | 1,700-year | Assembly >300, schools, jails, power |
| IV | Essential | 3,000-year | Hospitals, fire/police, EOC, shelters |
The old wind importance factor (Iw) was eliminated in ASCE 7-10 and is absent from 7-16 and 7-22. Risk category instead points you to a different basic wind speed map; actual mph varies by site.
AMBER · AVOID THESE TRAPS
Common misclassifications
When a building contains multiple uses, classify to the highest risk category present.
School Gymnasiums
Count gym capacity. If 300+, the whole building is Category III even with small classrooms.
Church Sanctuaries
Use IBC occupant-load seating capacity, not average attendance.
Large Restaurants
A dining area over 300 occupants is a Category III assembly, not Category II.
Ag with Workers
Regular worker occupancy disqualifies Category I. Processing plants are Category II.
Outpatient Clinics
Only hospitals with emergency departments and inpatient care are Category IV; clinics are usually Category II.
College Lecture Halls
K-12 schools have special criteria; colleges are typically Category II unless assembly exceeds 300.
EMERALD · NEXT STEPS
Read the individual category pages
Each page covers thresholds, examples, and documentation for that category.