ASCE 7-22: What the Standard Requires for Wind Loads, and Where CFD Fits

ASCE 7-22 is now the load standard behind the 2024 International Building Code and the 2023 Florida Building Code, and it changed more about wind design than most engineers expect: the simplified wind methods are gone, the directionality factor moved, and tornado loads became a separate chapter. CFD has not changed status. It is still not a code-listed procedure for design wind loads, and the ASCE 7-22 commentary requires peer review and a verification and validation study for any CFD-based wind load estimate.

What is ASCE 7?

ASCE 7 is the US standard that sets the minimum design loads a building or other structure must resist. Its full title is Minimum Design Loads and Associated Criteria for Buildings and Other Structures, published by the American Society of Civil Engineers (ASCE) and its Structural Engineering Institute (SEI), which is why it is also cited as ASCE/SEI 7.

The standard covers dead, live, soil, flood, tsunami, snow, rain, atmospheric ice, seismic, wind, tornado and fire loads, plus the load combinations used to design against them. It applies to both the primary structure (beams, columns, lateral systems) and secondary elements such as cladding and roof coverings.

Every building is assigned a Risk Category from I to IV based on the consequence of failure. Risk Category I covers low-hazard structures such as agricultural buildings, Category II covers most ordinary buildings, Category III covers buildings with large occupancies such as schools and assembly halls, and Category IV covers essential facilities such as hospitals and fire stations. The Risk Category sets the return period of the design wind speed, snow load and seismic demand the building must meet.

Since the 2022 edition, site hazard values must come from ASCE’s digital geodatabases, accessed through the ASCE Hazard Tool, instead of being read from printed maps.

ASCE 7 editions and which one applies

The edition you design to is the one referenced by the building code your jurisdiction has adopted. ASCE 7 is not law on its own; it becomes enforceable when a building code adopts it by reference.

ASCE has issued three supplements and an errata to ASCE 7-22, so check that your copy is current. The next edition, ASCE 7-28, is in development.

Many jurisdictions still enforce the 2018 or 2021 IBC, which means ASCE 7-16 remains in daily use. Confirm the adopted edition with the authority having jurisdiction before you start the load calculation, because coefficients and equations differ between editions.

How code compliance works under ASCE 7

ASCE 7 sets a minimum, and the engineer of record is responsible for deciding whether that minimum is enough. Engineering codes exist to make a structure safe for its intended use, and they share one approach: they codify proven practice into requirements an engineer can apply and an official can check.

The standard’s analytical wind procedures are calibrated on a limited family of regular building shapes and site conditions. When a building departs from that family, the code does not extend its tables; it directs the engineer to the wind tunnel procedure or to recognized literature. The engineer still has to judge whether effects outside the code’s assumptions, such as wake buffeting from a neighboring tower or resonance in a flexible structure (the failure mode behind the Tacoma Narrows Bridge collapse), could govern the design.

Design engineers, reviewers, project managers, contractors and fabricators all work within this framework, so every party needs to know which edition applies and which procedure was used.

ASCE 7 wind load chapters at a glance

Wind loads in ASCE 7-22 are spread across seven chapters. Chapter 26 holds the inputs every procedure uses, Chapters 27 to 30 hold the analytical procedures, Chapter 31 holds the wind tunnel procedure, and Chapter 32 holds the new tornado provisions.

The 2024 IBC, Section 1609.1.1, requires wind loads on every building or structure to be determined in accordance with Chapters 26 to 30 of ASCE 7. For the step-by-step calculation of velocity pressure and design pressure, with a worked example, see our guide to wind load analysis.

Which ASCE 7 wind procedure applies to your building

The procedure depends on building height, shape, structural response and site. The original version of this article described a “simplified method”; ASCE 7-22 removed the simplified methods from Chapters 27, 28 and 30, so the choice is now between the three procedures below.

Envelope Procedure (Chapter 28): low-rise buildings

The Envelope Procedure applies to low-rise buildings, defined in ASCE 7 as enclosed or partially enclosed buildings with a mean roof height of 60 ft or less that does not exceed the building’s least horizontal dimension. It uses pseudo-pressure coefficients that envelope the worst case across all wind directions, so it gives conservative MWFRS loads without a direction-by-direction check.

In ASCE 7-16, Chapter 28 had a Part 2 for simple diaphragm buildings. ASCE 7-22 deleted it, leaving only the detailed method.

Directional Procedure (Chapter 27): buildings of all heights

The Directional Procedure applies to enclosed, partially enclosed and open buildings of any height with a regular shape. It evaluates wind pressure direction by direction using external pressure coefficients, and it separates rigid buildings (fundamental natural frequency of 1 Hz or more) from flexible buildings (below 1 Hz). Flexible buildings need a gust effect factor that accounts for resonant amplification in the along-wind direction.

The procedure does not cover buildings whose response is governed by across-wind loading, vortex shedding, or aeroelastic instability such as galloping or flutter. It also does not cover sites where channeling or buffeting in the wake of upwind obstructions warrants special consideration. Those cases go to Chapter 31.

Wind Tunnel Procedure (Chapter 31) and ASCE 49

The Wind Tunnel Procedure is required for buildings outside the scope of the analytical procedures and permitted for any building. A scale model of the building and its surroundings is tested in a boundary layer wind tunnel that reproduces the atmospheric boundary layer, and pressures, forces and structural response are measured for each wind direction.

Test conditions are governed by ASCE/SEI 49-21, Wind Tunnel Testing for Buildings and Other Structures. Chapter 31 also sets lower limits on how far wind tunnel loads can fall below the analytical procedures, so a tunnel study can reduce design loads but not without bound.

Typical triggers for a wind tunnel study are irregular or twisted geometry, slender towers susceptible to across-wind response or vortex-induced vibration, long-span roofs and bridges, and dense urban sites where neighboring buildings shield or amplify the wind.

What changed in ASCE 7-22 wind provisions

The ASCE 7-22 wind changes that most often affect a design are the removal of the simplified methods and the relocation of the directionality factor. The full list of significant changes versus ASCE 7-16:

• Simplified methods deleted. Part 2 of Chapters 27 and 28 (simple diaphragm buildings) and Parts 2 and 4 of Chapter 30 were removed.
• Directionality factor moved. K_d is no longer in the velocity pressure equation; it now appears in the individual pressure and force equations in Chapters 26 to 30.
• Basic wind speed maps revised in hurricane regions. Speeds decreased along the North Atlantic coast and in coastal Louisiana, Mississippi and Alabama, and increased along coastal Texas (roughly 10 mph) and the Florida panhandle and Big Bend.
• Exposure coefficients revised. K_z and K_h values in Table 26.10-1 and the terrain exposure constants in Table 26.11-1 changed, and the topographic factor K_zt criteria in Section 26.8 were adjusted.
• Wind-borne debris region redefined. The one-mile criterion now applies where an Exposure D condition exists upwind of the water line.
• C&C roof zones simplified. Gable and hip roofs with slopes between 7° and 45° now use three pressure zones, with coefficients generally lower or unchanged.
• New provisions. Tornado loads (Chapter 32), ground-mounted solar panels (Section 29.4.5), roof pavers (Section 30.12), attached canopies on buildings taller than 60 ft (Section 30.9), and elevated buildings (Section 27.3.1.1).

The tornado provisions apply to Risk Category III and IV buildings in the tornado-prone region of the US. They target tornadoes up to roughly EF2 intensity; protection against stronger tornadoes still requires a storm shelter designed to ICC 500.

Can CFD be used for ASCE 7 wind loads?

Not as a standalone code procedure. ASCE 7-22 lists the Directional, Envelope and Wind Tunnel Procedures for design wind loads, and CFD is not among them. The ASCE 7-22 commentary to Chapter 31 states that any use of CFD to estimate MWFRS, C&C or other structures’ wind loads requires peer review and a verification and validation (V&V) study.

The ASCE/SEI Prestandard for Performance-Based Wind Design (Version 1.1, 2023) takes the same position for performance-based design. Its Section 5.3.1 names wind tunnel testing as the only approach consistent with reliable application of performance-based design principles for determining local pressures and global loads.

In practice this means:

• CFD results alone are not a code-compliant substitute for a Chapter 27 to 30 calculation or a Chapter 31 wind tunnel study.
• CFD used to support design loads needs a documented V&V study and independent peer review, and acceptance is at the discretion of the authority having jurisdiction and the engineer of record.
• CFD has no such restriction when it is used to inform design decisions, compare options, or study effects the code does not address, such as pedestrian-level wind.

The position of CFD in the standard is set by committee consensus on validation evidence. Research groups and standards bodies continue to publish CFD best-practice guidelines and validation benchmarks for wind engineering, and SimScale publishes its own validation cases against wind tunnel data (see below). Until a future edition adds a computational procedure, treat CFD as a design tool that sits upstream of the code calculation and the tunnel test.

Where CFD adds value on an ASCE 7 project

CFD is most useful at the stage where the code coefficients are least reliable and the design is still open to change. A simulation returns pressure, velocity and force over the whole domain, for any number of wind directions and geometries, before the design is fixed and before a tunnel slot is booked.

Effect of surrounding buildings on wind flow

ASCE 7 accounts for terrain through exposure categories and for hills and escarpments through the topographic factor, but it does not model specific neighboring buildings. A CFD model of the building in its real urban context shows where neighbors shield the facade, where they speed up flow through gaps, and where the building sits in the wake of an upwind tower. These are the site conditions that push a project out of the analytical procedures and into Chapter 31, so identifying them early tells you whether a wind tunnel study will be needed.

Flow separation, vortex shedding and across-wind response

Sharp corners, setbacks and abrupt changes in section cause the flow to separate and shed vortices. On slender towers, vortex shedding at a frequency close to a structural mode produces across-wind oscillation, which the analytical procedures exclude. A transient CFD simulation resolves the separated flow and the unsteady pressures it produces, so designers can test corner modifications, tapering or openings for their effect on shedding before the tunnel test confirms the chosen option.

Fluid-structure interaction

A fluid-structure interaction analysis couples the flow solution with the structural deformation, so the effect of the structure’s flexibility on the wind loads it experiences is included. It is used to study aeroelastic effects such as galloping and flutter on flexible structures, cable-supported elements and lightweight roofs.

Preparation for wind tunnel testing

Wind tunnel tests are expensive and slow to reschedule, so the planning has to be right the first time. A virtual wind tunnel run on the design geometry shows where pressure gradients are steepest (and therefore where taps are needed), which surrounding buildings must be included in the proximity model, and which wind directions are likely to govern. Running both a full-scale and a model-scale simulation also helps with the correlation and scaling of the physical measurements.

Pedestrian wind comfort

Wind problems at street level are often discovered only after a building is completed, when corner speed-up, downwash and channeling make entrances, plazas and terraces uncomfortable or unsafe. ASCE 7 does not address pedestrian-level wind, and many planning authorities require a wind microclimate assessment in its own right. A CFD study evaluated against criteria such as Lawson identifies these areas in the design phase, when a canopy, podium or landscaping change is still cheap. See what pedestrian wind comfort is for the full method.

How close CFD results sit to wind tunnel data

Validation against wind tunnel measurements is what makes CFD results usable in design, and what any peer reviewer will ask for first. SimScale publishes its validation cases openly:

• The CAARC facade pressure validation compares mean pressure coefficients on the standard CAARC tall building against wind tunnel data. SimScale’s lattice Boltzmann (LBM) solver with IDDES turbulence modeling matched the windward facade closely and predicted the leeward facade better than previously published LES results.
• The mean surface pressure validation for a building with balconies tests facade detail at a scale where code coefficients do not apply.
• The pedestrian wind comfort validation study compares the velocity field against wind tunnel and field measurements.

Run CFD alongside your ASCE 7 workflow with SimScale

SimScale runs wind simulations in a web browser, with the compute in the cloud, so wind studies can run at the concept stage instead of being reserved for a specialist at the end of the design. The transient LBM solver handles full urban models and multi-direction wind analyses, and the SimScale API lets teams build wind studies into their own design tools. Thornton Tomasetti did this with an in-house digital wind tunnel app that runs from Rhino, so designers who are not CFD specialists can check wind loading, facade pressures and pedestrian comfort while the massing is still changing.

A typical workflow on an ASCE 7 project uses CFD to compare massing and facade options, identify the governing directions and site effects, and decide whether a Chapter 31 study is needed. The code calculation or the wind tunnel study then provides the loads that go into the submittal.

Frequently asked questions

References

1. ASCE/SEI 7-22, Minimum Design Loads and Associated Criteria for Buildings and Other Structures. American Society of Civil Engineers, 2021.
2. ASCE/SEI 49-21, Wind Tunnel Testing for Buildings and Other Structures. American Society of Civil Engineers, 2021.
3. ASCE/SEI, Prestandard for Performance-Based Wind Design, Version 1.1. American Society of Civil Engineers, 2023.
4. FEMA, Highlights of Significant Changes to the Wind Load Provisions of ASCE 7-22, fact sheet, 2022.
5. International Code Council, 2024 International Building Code, Section 1609.