What is ASCE 7?
ASCE 7, "Minimum Design Loads and Associated Criteria for Buildings and Other Structures," is the authoritative standard published by the American Society of Civil Engineers (ASCE) that provides requirements for determining structural loads on buildings and other structures. This standard is referenced by all major U.S. building codes including the International Building Code (IBC) and serves as the foundation for structural design across the United States.
The ASCE 7 standard covers multiple load types including dead loads, live loads, snow loads, rain loads, ice loads, earthquake loads, and wind loads. For wind engineering professionals, ASCE 7 Chapters 26-31 contain the comprehensive wind load provisions that govern how wind forces are calculated and applied to structures.
ASCE 7 Purpose and Scope
ASCE 7 provides minimum load requirements for the design of buildings and other structures that are subject to building code requirements. The standard is developed through a consensus process by committees of experts in structural engineering, wind engineering, and related fields, and is updated periodically to reflect the latest research, wind speed data, and best practices.
Current ASCE 7 Editions
ASCE 7 is updated approximately every 6 years. The three most commonly used editions in current practice are:
ASCE 7-22 (2022 Edition)
Status: Latest edition, adopted in the 2024 International Building Code (IBC)
ASCE 7-22 represents the most current wind load provisions and includes significant updates to wind speed maps, risk categories, and design procedures. This edition reflects the latest research in wind engineering and incorporates lessons learned from recent hurricane events. Many jurisdictions are in the process of adopting ASCE 7-22 as their governing standard.
ASCE 7-16 (2016 Edition)
Status: Widely adopted nationwide, referenced in 2018 and 2021 IBC
ASCE 7-16 is currently the most widely used edition across the United States. Most state and local building codes reference ASCE 7-16, making it the de facto standard for wind load calculations in practice today. This edition introduced significant changes to wind speed maps, converting from fastest-mile to 3-second gust wind speeds and updating wind speeds based on modern hurricane data.
ASCE 7-10 (2010 Edition)
Status: Legacy edition, still used in some jurisdictions, referenced in 2012 and 2015 IBC
ASCE 7-10 is considered a legacy edition but is still referenced by some jurisdictions that have not yet adopted newer building codes. Understanding ASCE 7-10 provisions remains important for retrofit projects, additions to existing buildings designed under older codes, and work in jurisdictions with older code adoptions.
Key Wind Load Chapters in ASCE 7
Wind load provisions in ASCE 7 span multiple chapters, each addressing specific aspects of wind engineering:
Chapter 26: Wind Loads - General Requirements
Chapter 26 establishes the fundamental framework for wind load determination:
- Basic Wind Speed (V): Determination from wind speed maps based on Risk Category and location
- Wind Directionality Factor (Kd): Accounts for reduced probability of maximum wind from any direction
- Exposure Categories: Classification of terrain (B, C, or D) based on surface roughness
- Topographic Effects (Kzt): Multiplier for hills, ridges, and escarpments
- Gust Effect Factor (G or Gf): Accounts for dynamic amplification due to wind gusts
- Enclosure Classification: Open, partially enclosed, or enclosed buildings
- Internal Pressure Coefficient (GCpi): ±0.18 for enclosed, ±0.55 for partially enclosed
Chapter 27: Wind Loads on Buildings - MWFRS (Directional Procedure)
The Directional Procedure is the most versatile method for calculating MWFRS wind loads:
- Applicable to buildings of all heights
- Accounts for wind directionality effects
- Uses external pressure coefficients (Cp) based on building geometry
- Requires analysis of wind from multiple directions
- Most commonly used procedure in professional practice
Chapter 28: Wind Loads on Buildings - MWFRS (Envelope Procedure)
Simplified procedure for low-rise buildings:
- Limited to buildings with mean roof height ≤ 60 feet
- Simple diaphragm buildings as defined in ASCE 7
- Provides conservative load envelope without directional analysis
- Faster calculations but typically higher design loads
- Popular for residential and light commercial construction
Chapter 29: Wind Loads on Building Appurtenances and Other Structures
Covers non-building structures and equipment:
- Rooftop equipment and appurtenances
- Solid freestanding walls and signs
- Chimneys, tanks, and open buildings
- Lattice frameworks and trussed towers
Chapter 30: Wind Loads - Components and Cladding
Dedicated procedures for C&C elements:
- Part 1: Low-rise buildings (h ≤ 60 ft) - simplified method
- Part 2: Low-rise buildings (h ≤ 60 ft) - alternate procedure
- Part 3: Buildings with h > 60 ft
- Part 4: Buildings with h ≤ 160 ft (simplified)
- External pressure coefficients (GCp) varying with effective wind area
- Zone-specific pressures (corner, edge, interior)
Chapter 31: Wind Tunnel Procedure
Advanced analysis method for complex buildings:
- Required for buildings with unusual geometry or dynamic characteristics
- Flexible structures where analytical methods don't apply
- Buildings in complex terrain or urban environments
- Can provide more economical designs for large/complex projects
- Requires specialized wind tunnel facilities and expertise
Major Changes Between ASCE 7 Editions
ASCE 7-22 Key Changes from 7-16
- Updated Wind Speed Maps: Revised based on latest meteorological data and hurricane research
- Risk Category Updates: Modifications to Risk Category definitions and wind speed factors
- Revised C&C Provisions: Updated pressure coefficients and effective wind area criteria
- Enhanced Topographic Provisions: Clarifications on Kzt application and calculations
- Appendix D Updates: Revised approximate fundamental period equations
- Commentary Enhancements: Expanded explanations and design examples
ASCE 7-16 Key Changes from 7-10
- Wind Speed Conversion: Changed from strength-level (ASD) to ultimate wind speeds (LRFD)
- Risk Category Based Wind Speeds: Different basic wind speeds for Risk Categories II, III, and IV
- 3-Second Gust Wind Speeds: All wind speeds now based on 3-second gust (previously included fastest-mile)
- Updated Wind Maps: New wind speed contours based on updated hurricane database
- Increased Wind Speeds: Many coastal areas saw 10-15 mph increases in design wind speeds
- Simplified C&C Provisions: Reorganized Chapter 30 for clarity
- Kd Simplification: Wind directionality factor simplified to 0.85 for most buildings
ASCE 7-10 Key Features (Historical Context)
- Used 3-second gust wind speeds for most applications
- Also included fastest-mile wind speed maps (legacy)
- Single basic wind speed for all Risk Categories (with importance factors)
- Conservative approach to MWFRS and C&C calculations
- Established modern framework still used in current editions
Understanding Wind Speed Maps
Wind speed maps are fundamental to ASCE 7 wind load calculations. These maps provide basic wind speeds based on meteorological data, hurricane modeling, and statistical analysis of extreme wind events.
ASCE 7-16 and 7-22 Wind Speed Maps
- 3-Second Gust Wind Speeds: Peak 3-second gust at 33 feet above ground in Exposure C
- Risk Category Specific: Separate maps for Risk Categories II, III, and IV
- Ultimate Wind Speeds: Unfactored wind speeds for use with LRFD load combinations
- Return Periods: 300-year for Risk Category II, 700-year for III, 1700-year for IV
- Special Wind Regions: Areas requiring site-specific analysis due to local wind phenomena
How to Determine Basic Wind Speed
- Identify building location (address, latitude/longitude)
- Determine Risk Category based on occupancy and use
- Select appropriate wind speed map for your Risk Category
- Find location on map and read wind speed contour
- Check for Special Wind Regions requiring additional analysis
- Verify with local jurisdiction for any locally adopted wind speeds
Important Note: Local Amendments
Many jurisdictions adopt ASCE 7 with local amendments. Some states and cities specify different wind speeds than shown on ASCE 7 maps, particularly in coastal high-wind regions. Always verify the governing wind speed with your local building department before finalizing calculations.
Risk Categories in ASCE 7
Risk Categories classify buildings based on their use and the consequences of failure. Wind loads increase with higher Risk Categories to provide additional safety for critical facilities.
| Risk Category | Building Type | Wind Speed MRI | Examples |
|---|---|---|---|
| I | Low Hazard to Human Life | 300 years | Agricultural facilities, minor storage buildings |
| II | Standard Occupancy | 300 years | Residential, office, retail, warehouses |
| III | Substantial Hazard | 700 years | Schools, jails, assembly >300, power plants |
| IV | Essential Facilities | 1700 years | Hospitals, fire/police stations, emergency shelters |
Load Combinations with Wind Loads
ASCE 7 Chapter 2 provides load combinations for structural design. Wind loads must be combined with other loads using appropriate load factors:
Strength Design (LRFD) Load Combinations
- 1.2D + 1.0W + L + 0.5(Lr or S or R)
- 0.9D + 1.0W (for uplift and overturning)
Allowable Stress Design (ASD) Load Combinations
- D + 0.6W
- 0.6D + 0.6W (for uplift and overturning)
Where: D = Dead Load, W = Wind Load, L = Live Load, Lr = Roof Live Load, S = Snow Load, R = Rain Load
Commonly Used ASCE 7 Wind Load Parameters
Velocity Pressure Exposure Coefficient (Kz or Kh)
Varies with height and exposure category. Accounts for increase in wind speed with elevation above ground and the effect of terrain roughness.
Topographic Factor (Kzt)
Multiplier to account for speed-up effects over hills, ridges, and escarpments. Can significantly increase design pressures (1.0 to 1.5+). Often overlooked but critical for hilltop construction.
Gust Effect Factor (G)
For rigid structures (fundamental frequency ≥ 1 Hz): G = 0.85. For flexible structures, detailed calculation required per ASCE 7 Section 26.11.
Enclosure Classification
- Enclosed Buildings: GCpi = ±0.18
- Partially Enclosed Buildings: GCpi = ±0.55 (significantly higher pressures)
- Open Buildings: Special provisions apply
ASCE 7 Compliance and Code Requirements
Using the correct edition of ASCE 7 is critical for code compliance:
- Check Building Code Adoption: Verify which edition of IBC (and thus ASCE 7) your jurisdiction has adopted
- State Amendments: Many states modify IBC/ASCE 7 with state-specific requirements
- Local Amendments: Cities and counties may have additional modifications
- Permit Submittals: Calculations must reference the adopted code edition
- PE Seal Requirements: Most jurisdictions require professional engineer seal for wind load calculations
Best Practice: Verify Before You Calculate
Before starting any wind load analysis, contact the local building department to confirm:
- Which edition of ASCE 7 is adopted
- Whether state or local amendments apply
- If site-specific wind speeds are required
- PE seal and submittal requirements
Resources for ASCE 7 Standards
Obtaining ASCE 7 Publications
- ASCE 7 Standard: Available for purchase from ASCE (asce.org)
- Commentary: Detailed explanations and design examples included with standard
- ASCE 7 Hazard Tool: Online tool for determining site-specific wind speeds and seismic parameters
- Wind Load Calculator Software: Professional software automates ASCE 7 calculations
Professional Development
- ASCE continuing education courses on wind load provisions
- State PE board seminars on code updates
- Wind engineering conferences and workshops
- Online training and webinars on ASCE 7 procedures
Conclusion
ASCE 7 serves as the authoritative standard for wind load determination in the United States. Understanding the provisions across different editions—particularly ASCE 7-22, 7-16, and 7-10—is essential for structural engineers, architects, and building officials. The standard's comprehensive approach to wind load calculation, from basic wind speed determination through detailed MWFRS and C&C analysis, ensures structural safety and code compliance.
As ASCE 7 continues to evolve with new editions incorporating the latest research and meteorological data, professionals must stay current with changes and understand how different editions affect design requirements. Professional wind load calculator software that supports multiple ASCE 7 editions streamlines compliance while ensuring accurate, reliable results for projects nationwide.