ASCE 7-22 · TABLE 1.5-1 · RISK CATEGORY I
Risk Category I — the lowest design wind loads in ASCE 7
Buildings that pose a low hazard to human life on failure — barns, minor storage, certain temporary structures. They read wind speed from the 300-year MRI map, the lowest of the four ASCE 7 maps.
ASCE 7-22 · TABLE 1.5-1
What qualifies as Risk Category I
Low hazard to human life: minimal or no human occupancy, and failure would not endanger the public.
Agricultural Barns
Livestock barns, hay and equipment barns, pole barns — limited occupancy, low life-safety consequence.
LOW HAZARDMinor Storage & Silos
Grain silos, bulk material and equipment storage not occupied during extreme weather events.
UNOCCUPIEDTemporary Structures
Construction trailers, portable and temporary buildings not intended for permanent occupancy.
TEMPORARYASCE 7-16 / 7-22 · MEAN RECURRENCE INTERVAL
Risk Category sets the wind speed map, not a multiplier
There is no wind importance factor in ASCE 7-16 or 7-22. A higher risk category simply points you to a map with a longer return period — and therefore a higher design wind speed. Risk Category I sits at the bottom.
| Risk Category | MRI Map | Relative Design Speed | Typical Use |
|---|---|---|---|
| I — low hazard | 300-year | Lowest | Ag barns, minor storage, temporary |
| II — standard | 700-year | Higher | Homes, offices, retail, most buildings |
| III — substantial hazard | 1,700-year | Higher still | Large assembly, schools, jails, power |
| IV — essential | 3,000-year | Highest | Hospitals, fire/police, shelters, EOCs |
Longer return period → higher mapped wind speed → higher loads. The exact mph for each map varies by location — you read it from the corresponding ASCE 7 figure for your site. No fixed ratio links one category to the next.
WHAT THIS MEANS FOR DESIGN
Lower map — but the load is still fully calculated
Risk Category I does not skip the analysis. You read V from the 300-year map, then run the same velocity-pressure procedure as any other building.
Read V from the 300-yr map
Risk Category I uses the lowest-speed ASCE 7 map. The mph depends on your site.
300-YR MRISame velocity-pressure path
Apply Kz, Kzt and Kd just like any building — directionality Kd = 0.85 for MWFRS and C&C.
Kd = 0.85Internal pressure still applies
Enclosure governs GCpi — enclosed buildings use ±0.18. The reduced map is the only relief.
GCpi ±0.18CAUTION · WHEN RISK CATEGORY I DOES NOT APPLY
Agricultural use alone does not qualify
If failure could endanger people or the public, the building moves up to Risk Category II or higher — even on a farm.
Regular Human Occupancy
Milking parlors, processing plants with workers, or farm offices staffed daily.
NOT RC IPublic Visitors
Farm stands, corn mazes, petting zoos and agritourism open to the public.
NOT RC IHazardous Materials
Toxic, highly toxic or explosive storage whose release could endanger the public.
NOT RC IEducational Facilities
School farms and university or vocational research buildings with student occupancy.
NOT RC IIf there is any chance of future conversion to occupied use, design to Risk Category II from the start to avoid a later structural re-evaluation.
NEXT STEP
Confirm the category, then run the numbers
Verify your building's risk category, then calculate the wind loads with professional ASCE 7 software.