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ASCE 7-22 Wind — MWFRS Wall & Roof Pressures (Directional Procedure)

Chapter 27 Part 1, Eq. 27.3-1: p = q·K_d·G·C_p − q_i·K_d·(GC_pi). In ASCE 7-22 K_d appears once, in both terms of the pressure equation, and not in q. Windward pressures use q_z up the height; leeward and side walls use q_h. Both signs of internal pressure are reported.

Site & Building

V mph

Exposure

K_zt

Mean roof height h ft

Windward step ft

L — dimension parallel to wind ft

B — dimension normal to wind ft

Enclosure (Table 26.13-1)

K_d (Table 26.6-1)

G — gust-effect factor

0.85 for rigid buildings (fundamental frequency ≥ 1 Hz, §26.11.1). Flexible buildings need G_f (§26.11.5) — not computed here.

Roof

Roof slope θ °

Wind direction

Area for the −1.3 reduction (Fig. 27.3-1 Note b) ft²

Results

q_h · L/B · C_p leeward—

Leeward wall p (+GC_pi / −GC_pi)—

Side walls p (+GC_pi / −GC_pi)—

Roof

h/L · interpolation weight · RF—

Positive = toward the surface. The internal pressure cancels in the net horizontal (windward − leeward) value, which is what the MWFRS resists. §27.1.5 minimum: 16 psf on the wall area (and 8 psf on the projected roof area).

Tornado check (v549)ASCE 7-22 §26.1.1: Risk Category III and IV buildings in the tornado-prone region must also be checked for tornado loads (Chapter 32), and the larger effect governs — tornado roof uplift can exceed the wind value by about 40 % (FEMA/NIST Tulsa example). Use the ASCE 7-22 Tornado Loads tool. ASCE 7-22 also introduced new basic wind speed maps (e.g. lower values along much of the North Atlantic coast, higher along parts of Texas and the Florida panhandle — FEMA Highlights of Significant Changes to the ASCE 7-22 Wind Provisions, 2022).

Eq. 27.3-1p = q·K_d·G·C_p − q_i·K_d·(GC_pi); q = q_z windward, q_h leeward/side; q_i = q_h (for partially enclosed buildings the positive internal pressure may use q_z at the highest opening — q_h is conservative)

Fig. 27.3-1Windward C_p = 0.8; leeward −0.5 (L/B ≤ 1), −0.3 (2), −0.2 (≥ 4), linear between; side walls −0.7

VerifyStructSuite ASCE 7-22 Chapter 27 example (V = 100 mph, Exposure C, q_h = 23.45 psf): leeward C_p −0.5 → −12.06 / −4.88 psf; C_p −0.4 → −10.36 / −3.19; windward z = 25 ft → 10.32 / 17.50 psf — all reproduced exactly in the regression test.

Fig. 27.3-1 roofθ < 10° or wind parallel to the ridge — h/L ≤ 0.5: −0.9 (0–h/2), −0.9 (h/2–h), −0.5 (h–2h), −0.3 (> 2h); h/L ≥ 1.0: −1.3·RF (0–h/2), −0.7 (> h/2); second value −0.18 everywhere; linear between h/L = 0.5 and 1.0. RF (Note b, only on −1.3): 1.0 (≤ 100 ft²), 0.9 (250), 0.8 (≥ 1,000), linear.

Fig. 27.3-1 slopedWind normal to the ridge, θ ≥ 10°: windward slope suction and pressure values by θ (10–60°) and h/L (≤ 0.25, 0.5, ≥ 1.0), interpolated linearly between values of the same sign only; leeward slope −0.3 to −0.7. Unchanged since ASCE 7-10 — confirmed by reproducing the ASCE 7-22 StructSuite example (θ 26.6°, h/L 0.69: −0.33 / +0.15 windward, −0.6 leeward; pressures −9.21 / −1.07 / +6.10 and −13.75 psf).

Verify roofSame StructSuite example, wind parallel to the ridge, 0–11 ft strip (C_p −0.9 / −0.18): −18.84 / −11.66 and −6.64 / +0.54 psf — reproduced exactly.

ScopeWalls and all roof slopes (zones for θ < 10° or wind parallel to the ridge; slope table for θ ≥ 10° normal to the ridge); rigid buildings. NOT included: the Figure 27.3-8 load cases (torsion), parapets, overhangs and flexible-building G_f.

Preliminary calculation tool. Final design requires the full text of the referenced standard (see the sources on this page) and review by a licensed PE.