ASCE 7-22 Main Wind Force Resisting System Wind Load Changes

Open the ASCE 7-22 velocity pressure equation and the first thing you notice is what's missing: Kd. It didn't disappear — it moved down into the individual pressure equations, where it now sits explicitly. Same value, new address.

That's the 7-16-to-7-22 transition for the Main Wind Force Resisting System (MWFRS) in miniature. From a distance it looks quiet — the framework is intact, and for ordinary buildings the numbers barely move. Up close, the wind chapters shifted in ways that don't announce themselves. Kd changed homes. Kz was recalibrated for the first time since 1995. Two simplified methods were deleted outright. The partially open classification rule flipped for one narrow case. Tornado loads became a live requirement for Risk Category III and IV buildings. And elevated buildings got a procedure with no ancestor in any prior edition. A few of these shift the numbers; others change which methods the standard offers at all. Here's what each one says, and how to apply it.

Not all jurisdictions have adopted ASCE 7-22 — verify the edition in force in your jurisdiction before applying these provisions. The same edition-basis shifts run through the other 7-22 load chapters too: the snow load provisions moved to a strength-level map basis, and the rain load provisions added a ponding term.

ASCE 7-22 vs. 7-16 MWFRS Wind Load Changes at a Glance

ASCE 7-22 changes five MWFRS wind-load provisions from 7-16: Kd's position in the pressure equations, the Kz terrain constants, two deleted simplified methods, a new tornado-load requirement for Risk Category III/IV buildings, and a new elevated-buildings procedure. A few of these change the resulting pressures; two remove methods from the standard entirely.

Kd Directionality Factor: Where It Moved in ASCE 7-22

The wind directionality factor Kd has been pulled out of the velocity pressure equation and written explicitly into each individual pressure equation instead. It's one of the more visible structural changes in ASCE 7-22 Chapter 26 — worth getting straight first, since every pressure downstream depends on it.

The before and after, side by side:

Kd is gone from the velocity pressure and now appears explicitly in ASCE 7-22 Equations (27.3-1) through (27.3-3) for the directional procedure and Equation (28.3-1) for the envelope procedure. The design pressure equation shows the other half of the move — in 7-16 Kd was already baked into qz and absent here; 7-22 carries it explicitly:

The Kd value itself did not change. ASCE 7-22 Table 26.6-1 is identical to 7-16, and Kd = 0.85 for buildings remains the operative value. For a single-shape building, the end result of the full calculation is numerically identical whether Kd was applied in the velocity pressure step or the design pressure step — 0.00256 × 0.85 × Kz × Kzt × Ke × V² produces the same number either way.

The reason is physical correctness, not arithmetic. Per the Commentary (C26.10.2), Kd depends on both the wind climate's directionality and the building's shape, so it belongs in each pressure and force equation rather than in a single velocity pressure applied to every element. For a building that combines shapes — an enclosed building with an attached open canopy, say — the 7-22 approach lets each pressure equation use the Kd appropriate to that element, instead of forcing one value everywhere.

The bookkeeping rule is simple: under 7-22, Kd belongs in each pressure equation and nowhere else. Carried in both qz and the pressure equation, it gets counted twice — 0.85² ≈ 0.72 rather than 0.85 — and the resulting pressures come out about 15% low.

Kz Recalibration in ASCE 7-22: First Update Since 1995

The terrain constants behind every Kz value — α (power law exponent) and zg (gradient height) in Table 26.11-1 — were recalibrated in ASCE 7-22, the first change since 1995.

Both feed directly into the Kz formula itself, given as a note under Table 26.10-1:

The recalibration follows newer boundary-layer research: Harris and Deaves (1981)^[1] and Zilitinkevich and Esau (2002)^[2] put storm boundary layers at 6,700–13,000 ft — far above the 1,200 ft zg Exposure B carried from ASCE 7-95 through 7-16. Per Commentary C26.7, the new zg values follow wind speed profiles shown to be reasonably accurate up to 3,280 ft, and the power law exponents were recalibrated against the Harris and Deaves (1981) and Kelly et al. (2019)^[3] profile models.

Part 2 Simplified Methods: Deleted in ASCE 7-22

Chapter 27 Part 2 and Chapter 28 Part 2 let you skip the full analytical procedure: pick the table for building height and exposure, read off a design pressure. ASCE 7-22 deletes both, with no replacement.

ASCE 7-16 Chapter 27 Part 2 covered enclosed simple diaphragm buildings up to h ≤ 160 ft. ASCE 7-16 Chapter 28 Part 2 covered the tabular envelope method for low-rise buildings up to h ≤ 60 ft. ASCE 7-22 doesn't offer a simplified alternative in either chapter, at any height.

The Commentary (ASCE 7-22 Commentary C26.1.2) states the rationale plainly: "The Wind Load Subcommittee evaluated the need for the tabular methods and concluded that ASCE 7 should generally not tabulate calculated design pressures for specific buildings and that the tabular methods belong in a guide or other resource." The committee's position: ASCE 7 is a standard, not a design handbook, and pre-computed pressure tables for specific configurations don't belong in it — regardless of how often engineers reached for them.

ASCE 7-22 dropped the Part structure along with the methods themselves — Chapters 27 and 28 no longer carry Part 1 / Part 2 headings at all, so a 7-22 citation to "Chapter 27 Part 1" has nothing to point at. MWFRS design now runs through what remains of each chapter: the analytical directional procedure in Chapter 27, or the analytical envelope procedure in Chapter 28. The directional procedure develops pressures using wind-direction-specific external pressure coefficients Cp; the envelope procedure instead uses the (GCpf) coefficients of Figure 28.3-1, which Commentary C28.3 describes as "pseudo" loading conditions — values derived from wind tunnel work at the University of Western Ontario by rotating the model through a full 360°, chosen so they envelop the governing structural actions independent of wind direction rather than being assembled from the directional Cp values. Wind tunnel testing per Chapter 31 remains available outside those chapters' applicability limits.

The distinction is procedural first: whatever the two approaches gave for a given building, the table isn't in the standard anymore, so the analytical route is the only one you can cite. If your practice leaned on Part 2 for routine low-rise or mid-rise work, budget for a full analytical calculation on every project going forward, not just the ones that used to fall outside the old height limits.

ASCE 7-22 Tornado Loads for Risk Category III/IV Buildings (Chapter 32)

Chapter 32 is new in its entirety in ASCE 7-22 — no 7-16 counterpart exists for any of it. Section 26.1.1 adds the trigger: Risk Category III and IV buildings and other structures must also be designed for tornado loads per Chapter 32, "as applicable." For the buildings it reaches — schools, hospitals, emergency facilities, and other Risk Category III/IV occupancies — this isn't a bolt-on load case. Section 32.1.1 requires designing for the greater of the Chapter 32 tornado loads or the Chapter 26–31 wind loads, combined per Chapter 2.

Chapter 32 is a structural load case, not storm shelter design — the standard says so explicitly. The Section 32.1.1 User Note states that a building designed for tornado loads exclusively under Chapter 32 cannot be designated a storm shelter; the parallel User Note at Section 26.1.1 says the same of a building designed for wind loads exclusively under Chapter 26. Storm shelters and safe rooms are a separate, higher-hazard track: ICC 500, the ICC/NSSA Standard for the Design and Construction of Storm Shelters^[4], and FEMA P-361^[5] (whose "safe room" criteria meet or exceed ICC 500's) both design to a deterministic 130–250 mph tornado speed map and require the shelter envelope to resist a 15 lb sawn-lumber 2×4 missile at 53 to 100 mph, depending on the shelter design wind speed and whether the surface is vertical or horizontal (100 mph on walls, 67 mph on roofs in the 250 mph zone) — protection levels well above the probabilistic, 1,700- to 3,000-year-return-period tornado speeds behind Chapter 32. The two tracks aren't mutually exclusive on the same project: the IBC separately mandates ICC 500-compliant shelters for certain critical facilities sited in the 250 mph zone of ICC 500 Figure 304.2(1) — 911 call stations, emergency operations centers, and fire, rescue, ambulance, and police stations (IBC Section 423.4), and Group E occupancies with an occupant load of 50 or more, subject to exceptions (IBC Section 423.5) — regardless of whether Chapter 32 applies. Note that the trigger for those shelter mandates is the ICC 500 speed map, not the Figure 1609.5 tornado-prone region above. Where that IBC shelter mandate is in play, the building still carries the Chapter 26–32 loads described in this section in addition to, not instead of, the ICC 500 shelter criteria. In short: Chapter 32 sets the tornado load the building's structure must survive; ICC 500 and FEMA P-361 set a separate, stricter standard for whether occupants can shelter inside it.

Applicability runs through two gates. First, Risk Category: only III and IV are in scope; I and II never trigger Chapter 32. Second, location: the building has to sit in the tornado-prone region defined by Figure 32.1-1 (reproduced in the 2024 IBC as Figure 1609.5^[6]). Outside that region, or below Risk Category III, Chapter 32 doesn't apply — no exemption check needed.

Inside the tornado-prone region, Section 32.5.2 exempts most buildings anyway. The tornado speed VT (read from Figures 32.5-1 or 32.5-2, based on Risk Category and the building's effective plan area) is compared against the basic wind speed V:

Use the exposure that produces the greatest wind loads for any direction at the site. If VT stays under 60 mph, or under the exposure-based fraction of V, tornado design isn't required — either one exempts on its own, even for a Risk Category III/IV building inside the mapped region.

Run your own numbers through the three gates:

Where Chapter 32 is required, budget for it as a real scope item: it has its own directionality factor, exposure coefficients, gust effects, and internal pressure coefficients running parallel to (and distinct from) Chapter 26's.

ASCE 7-22 Elevated Buildings Wind Load Provision (Section 27.3.1.1)

Among the new provisions in ASCE 7-22 Chapters 27 and 28, Section 27.3.1.1 stands out: it establishes explicit wind load procedures for buildings elevated on structural elements — stilts, columns, piers — where wind can pass beneath the structure. This section has no counterpart in ASCE 7-16 or any prior edition.

Applicability is gated by the "elevated building" definition in Section 26.2 and by geometric limits within Section 27.3.1.1 that decide whether the support elements can be treated as isolated lateral-load members rather than a fully enclosed base story. The provision has three subsections:

Section 27.3.1.1.1 — Loads on the elevated building itself. The elevated building above the base level is treated as a standard enclosed, partially enclosed, or partially open building using the directional procedure of Section 27.3.1. This is conceptually the same calculation you'd run for any building — the elevated condition affects how the elements below are handled, not the treatment of the building envelope above.

Section 27.3.1.1.2 — Lateral loads on structural elements below the elevated building. The columns, piers, and other supporting elements below the elevated floor receive lateral loads based on a net force coefficient Cf = 1.3 applied to their vertical projected area. The velocity pressure for this calculation is evaluated at an intermediate height:

where:

• $z$ = intermediate velocity-pressure height (ft)
• $h_B$ = bottom-of-floor height above grade (ft)
• $h$ = mean roof height (ft)

It's not arbitrary — the Commentary (C27.3.1.1) ties it to the wind stagnation point sitting near 60% of building height rather than at the top, so the intermediate height better represents the loading on the supports.

Section 27.3.1.1.3 — External loads on the bottom horizontal surface. Pressure on the underside of the elevated floor uses the flat/low-slope roof pressure coefficients from Figure 27.3-1. The basis is compelling: wind tunnel testing by Kim et al. (2020)^[7] at Florida International University found that C&C loads on the bottom surface of elevated low-rise buildings rival the roof C&C loads. Before 7-22 there was no standard method for them — designs either ignored them or leaned on judgment with no code anchor.

Who this provision affects directly: coastal elevated structures, beach houses on piers, and any building on an open substructure in a wind-governed jurisdiction. For those project types, Section 27.3.1.1 is now required, not optional.

Worked Example: Coastal Beach House on Piers

Design parameters:

• Location: coastal North Carolina
• Occupancy: single-family residence — Risk Category II
• $h_B$ = 10 ft (bottom-of-floor height above grade); $h$ = 22 ft (mean roof height)
• Exposure D, flat terrain (Kzt = 1.0), sea level (Ke = 1.0), V = 130 mph
• Rigid building, gust effect factor G = 0.85 (Section 26.11.1)
• Six supporting columns, each 1.0 ft wide × 10.0 ft tall (Af = 10 ft²)
• Plan dimension parallel to the wind direction considered, L = 40 ft

Scope: the two subsections with no 7-16 equivalent — column lateral load (§27.3.1.1.2) and bottom-surface pressure (§27.3.1.1.3). Not covered: the elevated building's own envelope loads (§27.3.1.1.1, same directional procedure as any building) or a complete design — see the checklist after the results.

Solving for:

These forms are assembled, not quoted. Neither subsection states an equation — each specifies coefficients and the velocity-pressure height and leaves you to build the expression. The bottom-surface form follows Equation (27.3-1) with the internal-pressure term dropped, consistent with the subsection's "external loads" title; a space that's enclosed or partially enclosed below the floor still needs internal pressure considered. The column force follows the Chapter 29 force equation, Equation (29.4-1), which carries a gust effect factor G that §27.3.1.1.2 does not mention. G is omitted here, which is conservative by roughly 18% — carrying it would give 418 lb per column instead of 497. Worth deciding deliberately rather than inheriting.

where:

• $F$ = lateral force on one supporting column (lb)
• $p$ = pressure on the bottom horizontal surface of the elevated floor (psf)
• $q_z$ = velocity pressure at the intermediate height $z$ (psf)
• $K_d$ = wind directionality factor = 0.85 (Table 26.6-1)
• $C_f$ = net force coefficient on the column's projected area = 1.3 (§27.3.1.1.2)
• $A_f$ = projected area of one column (ft²)
• $G$ = gust effect factor (§26.11.1)
• $C_p$ = external pressure coefficient for the bottom surface, from Figure 27.3-1

Both need qz first, evaluated at the intermediate height z:

Kz is computed here from the Table 26.10-1 Note 1 formula to show the recalibrated 2.41 in use. Table 26.10-1 itself tabulates 1.03 for Exposure D at 0–15 ft, and §26.10.1 makes the table the governing path — the 0.01 difference carries through to qz = 44.6 psf and F = 492 lb per column.

Column lateral load, with Cf = 1.3 on the projected column area (not Cp — see below):

Cf, not Cp. §27.3.1.1.2 uses the net force coefficient on the column's projected area — not the Figure 27.3-1 wall/roof Cp that governs the envelope above in §27.3.1.1.1. Same provision, same figure set, easy to cross the two since there's no 7-16 habit to fall back on.

Applying F. F acts horizontally, parallel to the wind direction under consideration. Since qz is evaluated at one height for the whole substructure rather than varying with elevation, it's reasonable to idealize F as a uniform pressure over each column's height for member design. Sum F across all six columns for the substructure's share of base shear — 497 lb × 6 ≈ 3.0 kip — then add that to the elevated building's own lateral loads from §27.3.1.1.1. Per §27.3.1.1, the overall MWFRS lateral load is the combined effect of both sections, not the substructure force alone.

Bottom-surface pressure, using the same qz with the Figure 27.3-1 flat-roof zone coefficients ($h$ = $h_B$ = 10 ft, $h/L$ = 10/40 = 0.25, which falls in the figure's $h/L\le 0.5$ branch → windward zone $C_p$ = -0.9):

One reading, flagged as such. §27.3.1.1.3 directs that h be taken as the height of the top of the supporting elements "used to define the distance from the windward edge," and Commentary C27.3.1.1 confines the substitution the same way — to the calculation of zone limits. Neither says whether that substituted h also governs the h/L ratio that selects the coefficient branch. This example applies it to both, which is the reading consistent with the Commentary's stated intent of limiting the extent of higher edge loads on short elevations. Using the true mean roof height in the ratio instead gives h/L = 22/40 = 0.55, interpolating to Cp ≈ −0.94, and changes the zone map itself. Worth resolving with your AHJ on a real project.

Sign flips. On this surface a negative Cp pushes down, not up — and §27.3.1.1.3 states this outright rather than leaving it to inference: negative roof pressure coefficients denote downward loading on the bottom floor assembly, positive ones upward. Note that the h/2-to-h zone carries the same −0.9 as the leading zone; only h-to-2h (−0.5) and beyond-2h (−0.3) step down. Figure 27.3-1 also lists a −0.18 companion value for each of these zones, and both conditions have to be checked — at −0.18 the pressure here is −5.9 psf, which can govern once combined with the other loads.

Summary of Results

This was two of the three subsections, for one wind direction. A complete elevated-building design still has to address, at minimum:

1. The elevated building's own envelope loads (§27.3.1.1.1) — the standard directional-procedure calculation from Section 27.3.1, using the Kd and Kz treatment from earlier in this article
2. Bottom-surface pressure at the remaining zones — h/2 to h repeats the −0.9 of the leading zone; h to 2h (−0.5) and beyond 2h (−0.3) reduce. Each zone also carries a −0.18 alternate in Figure 27.3-1 that has to be checked alongside it
3. Overturning and foundation uplift, combining the column lateral loads with the bottom-surface vertical pressure — Section 27.3.1.1 does not let the bottom-surface load offset overturning from the lateral loads
4. Wind from other principal directions, since h/L and the governing zone shift with the direction considered
5. Flood and breakaway-wall provisions, where the site also falls in a coastal flood zone — ASCE 24 and the applicable building code, not Chapter 27, govern any enclosure below the elevated floor in that case

Meeting the Section 26.2 definition of "elevated" isn't on its own enough to put you in Section 27.3.1.1. The building also has to clear both geometric limits in that section — the blocked-plan-area limit that scales with L/B (50% below 2.5, down to 30% at 5.0), and the requirement that the vertical projected area of the elements plus any enclosed space stay at or under 75% of the area swept by the element height and the building width above. Miss either one and that wind direction reverts to Section 27.3.1 with the substructure treated as solid and unopened. Both limits are evaluated per wind direction, so the same building can qualify one way and not another. Where it does apply, it's three separate calculations with no 7-16 equivalent to work from — a provision that starts from a blank page, without a prior-edition habit to fall back on.

Quick Hits: Other ASCE 7-22 Wind Chapter Changes

A few more provisions worth knowing about. None of these change how you set up a calculation the way Kd, Kz, or the deleted methods do — they're narrower corrections, clarifications, or optional paths.

The Bottom Line

The 7-16-to-7-22 MWFRS transition rewards starting in one place and working outward. Begin at the velocity pressure equation: Kd comes out of qz and goes into each pressure equation, and Kz comes from ASCE 7-22 Table 26.10-1 or the updated Table 26.11-1 constants. Then pick up the two provisions with no 7-16 counterpart: the Risk Category III/IV tornado check via Figure 32.1-1, and — for any building on an elevated substructure — the three-part procedure in Section 27.3.1.1. That covers most of where the two editions diverge, in both numbers and method. If you'd rather have that edition logic handled consistently across wind, snow, rain, seismic, dead, and live loads, that's what Prose is built to do.

Related Resources

• ASCE 7-22 Snow Load Changes — the strength-level ground snow maps, Ct grid, and W2 drift parameter that shifted in 7-22
• Rain Load Calculation per ASCE 7 — static head, hydraulic head, ponding, and the SDSL changes in 7-22
• Replace your wind load spreadsheets — why edition-specific load development belongs in a tool that cites its own work

If you read this provision differently or have run into it applied another way on a real project, reach out — support@prose-eng.com. I'm a practicing engineer, not an infallible one.