Velocity Pressure Exposure Coefficient Kz (ASCE 7-22 §26.10)
The ASCE 7 velocity-pressure exposure coefficient Kz at a height and exposure category, instead of a flat 30 ft value.
Example
You enter
- Exposure category C
- Height above ground z (ft; mean roof height for Kh) 50
You get
- Exposure coefficient Kz 1.088
Checked against published worked examples from: ASCE 7-22 §26.10.1 (reproduces the repo's 30 ft stub).
Details, formula, and sources
ScopeASCE 7-22 §26.10.1 Kz = 2.41 (z/zg)^(2/alpha) for 15 ft <= z <= zg (held at the z = 15 ft value below), with the 7-22 Table 26.11-1 constants (B 7.5/3280 ft, C 9.8/2460 ft, D 11.5/1935 ft). It scales qz = 0.00256 Kz Kzt Ke V^2, so it rises with height and a smoother exposure. At 30 ft it returns 0.69/0.98/1.17 (B/C/D), within 0.01 of the hard-coded stub, but a 50 ft eave in Exposure C is 1.09, about 11% more pressure. Use Kz at each height for the windward wall, Kh (at mean roof height) for leeward/side/roof and all C&C. The engineer of record governs.
Formula or tableKz = 2.41 (z/zg)^(2/alpha) for 15 ft <= z <= zg; Kz = 2.41 (15/zg)^(2/alpha) for z < 15 ft. ASCE 7-22 Table 26.11-1: B alpha 7.5 zg 3280, C 9.8/2460, D 11.5/1935.
Source and editionThe ASCE 7-22 §26.10.1 velocity pressure exposure coefficient Kz (Table 26.10-1), with the revised Table 26.11-1 terrain exposure constants (alpha, zg), by name.
Free accessASCE 7 is available through the ASCE Library at ascelibrary.org; the §26.10 exposure-coefficient equation and the Table 26.11-1 constants are public. The height z is the user's own building dimension.
What governsEstimate. AHJ and licensed professional govern.
API field namesexposure, z_ft, kz
- Exposure coefficient Kz = 2.41 (z/zg)^(2/alpha), held at the z = 15 ft value below 15 ftASCE 7-22 Table 26.10-1
- Exposure constants B alpha 7.5 zg 3280 ft; C 9.8/2460; D 11.5/1935 (7-16: 7.0/1200, 9.5/900, 11.5/700 with 2.01)ASCE 7-22 Table 26.11-1
- Use Kz per height z for windward, Kh (mean roof height) for leeward/side/roof and all C&CASCE 7 Ch. 27/30