Determine the Correct ASCE 7 Risk Category for Your Building
Selecting the correct risk category is one of the most important decisions in structural design. The risk category determines the importance factor, mean recurrence interval for wind speeds, and ultimately the design loads for your building.
Risk categories are assigned based on the consequences of failure and the building's use and occupancy. Use this guide to navigate ASCE 7 Table 1.5-1 and IBC requirements to determine your building's classification.
Does the building need to remain operational during and after disasters to protect public health and safety?
Does the building contain toxic, highly toxic, or explosive materials in quantities exceeding IBC threshold limits?
Can more than 300 people congregate in a single room or area within the building?
Does the building house vulnerable populations unable to evacuate without assistance?
Is the building used exclusively for agricultural storage or temporary use with no regular human occupancy?
If none of the above criteria apply, the building is classified as standard occupancy.
| Building Type | Occupancy Threshold | Risk Category | Notes |
|---|---|---|---|
| Assembly Buildings | 300+ in one area | III | Count largest single space only |
| Elementary Schools | 250+ capacity | III | Check gymnasium/cafeteria capacity |
| Daycare Centers | 500+ children | III | Vulnerable population criteria |
| Nursing Homes | Any occupancy | III | Cannot self-evacuate |
| Hospitals (non-emergency) | 50+ resident patients | III | Includes surgery/ICU |
| Jails & Prisons | Any occupancy | III or IV | IV if essential to public safety |
| Power Plants | N/A | IV | Essential facility designation |
| Fire/Police Stations | N/A | IV | Emergency response facilities |
| Agricultural Buildings | Minimal occupancy | I | Must have low hazard to life |
Mistake: "It's just a school, so Risk Category II."
Correct: Count gym capacity. If 300+, entire building is Risk Category III even if classrooms are small.
Mistake: "Small congregation, must be Risk II."
Correct: Count sanctuary seating capacity using IBC occupant load factors, not average attendance.
Mistake: "Restaurants are commercial, Risk II."
Correct: If dining area exceeds 300 occupants, classify as Risk Category III assembly.
Mistake: "It's a farm building, automatic Risk I."
Correct: Regular worker occupancy disqualifies it from Risk I. Processing plants are Risk II.
Mistake: "Medical facility = Risk Category IV."
Correct: Only hospitals with emergency departments and inpatient care are Risk IV. Clinics are usually Risk II.
Mistake: "Educational building = higher category."
Correct: K-12 schools have special criteria. Colleges are typically Risk II unless assembly areas exceed 300.
When a building contains multiple occupancy types, classify based on the highest risk category present. Example: Office building with ground-floor restaurant (350 capacity) = entire building is Risk Category III.
Consider potential future occupancy changes. Designing shell buildings for future tenant fit-out may warrant designing to a higher risk category to avoid costly retrofits.
Additions must meet current code requirements. If adding assembly space that exceeds 300 occupants, the entire building (including existing) may need reclassification.
Many jurisdictions modify ASCE 7 risk category criteria. Always verify local building code amendments and consult with the authority having jurisdiction (AHJ).
| Question | Risk I | Risk II | Risk III | Risk IV |
|---|---|---|---|---|
| Must operate post-disaster? | No | No | No | Yes |
| Assembly > 300 people? | No | No | Yes | N/A |
| Contains hazmat? | No | No | Yes | N/A |
| Vulnerable populations? | No | No | Yes | N/A |
| Regular occupancy? | Minimal | Yes | Yes | Yes |
| Importance Factor | 0.87 | 1.00 | 1.15 | 1.15 |
Single-family homes: Risk II
Apartments/Condos: Risk II
Dormitories: Risk II (unless >300 assembly)
Assisted Living: Risk III
Office buildings: Risk II
Retail stores: Risk II
Shopping malls: Risk II (check food courts)
Hotels: Risk II (check ballrooms)
K-12 schools: Usually Risk III
Colleges/Universities: Risk II (unless large assembly)
Daycare (<500): Risk II
Daycare (500+): Risk III
Churches (<300): Risk II
Churches (300+): Risk III
Theaters: Usually Risk III
Sports arenas: Risk III
Warehouses: Risk II
Manufacturing: Risk II
Chemical plants: Risk III (hazmat)
Ag storage: Risk I (if minimal occupancy)
Hospitals (emergency dept): Risk IV
Outpatient clinics: Risk II
Nursing homes: Risk III
Medical offices: Risk II
When submitting for building permits, clearly document the risk category designation:
Yes, owners can elect to design to a higher risk category for enhanced protection. This is common for buildings that may have future use changes or when owners want additional safety margins. Document this decision clearly on construction documents.
ASCE 7 Table 1.5-1 states "more than 300." If your calculated occupancy is exactly 300, the building technically qualifies as Risk Category II. However, consider designing to Risk Category III if there's any uncertainty in occupant load calculations or potential for future increases.
Yes. Change of occupancy requires building department approval and potential structural re-evaluation. Converting Risk Category II to Risk Category III (e.g., office to church) typically requires structural upgrades to meet higher wind load requirements.
Use IBC Section 1004 and Table 1004.5 to calculate occupant loads. Divide the net floor area by the occupant load factor for the specific use. For assembly spaces without fixed seating, this is typically 5-15 square feet per person depending on the type of assembly use.
Yes. Intentional misclassification constitutes professional misconduct and code violation. If discovered during plan review, expect project delays. If discovered after construction, expensive retrofits may be required. Always err on the side of caution and consult with the building official when uncertain.
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