Why do we get a 15% discount? Because the worst wind can't hit ALL walls at once. Watch the wind rose spin!
Get accurate ASCE 7-22 wind load calculations with correct Kd factors for your Broward County project.
Calculate Wind LoadsApplied to all enclosed buildings in Broward County
Imagine standing outside during a hurricane. The wind isn't always blowing from the same direction - it shifts, gusts, and rotates. Over the course of a storm, your north wall gets hammered for a while, then the wind shifts and the east wall takes over.
Broward County's design wind speed is 180+ mph - but that's the maximum from ANY direction. If we designed every single wall for 180 mph hitting it head-on, we'd be massively over-designing. The probability of 180 mph hitting the north wall at the exact same moment it hits the south wall? Essentially zero.
Wind speed data shows preferred directions. In South Florida, easterly trade winds dominate normal weather, but hurricanes can come from any direction. ASCE 7's Kd factor of 0.85 represents a 15% reduction that's statistically justified based on decades of wind research.
You don't calculate Kd - you look it up. For enclosed buildings: Kd = 0.85. For round tanks: 0.95. For chimneys: 0.95. It's already factored into our wind load calculations at WindLoad.co!
| Structure Type | Kd Factor |
|---|---|
| Buildings (Enclosed, Partially Enclosed, Open) | 0.85 |
| Arched Roofs | 0.85 |
| Chimneys, Tanks, Similar Structures (Square) | 0.90 |
| Chimneys, Tanks, Similar Structures (Round) | 0.95 |
| Solid Freestanding Signs | 0.85 |
| Open Signs and Lattice Frameworks | 0.85 |
| Trussed Towers | 0.85 |
Kd is a reduction factor that accounts for the probability that maximum wind speeds won't occur from every direction simultaneously. Since wind has preferred directions and buildings have multiple faces, it's statistically unlikely that the worst wind will hit every wall at its maximum. For most buildings, Kd = 0.85.
ASCE 7 allows Kd because the design wind speed is based on the maximum from ANY direction. But a building has multiple orientations - North, South, East, West walls. The probability of the absolute maximum wind hitting all walls simultaneously is very low, so a 0.85 reduction factor is statistically justified.
For enclosed and partially enclosed buildings in Broward County (Risk Category II, III, IV), Kd = 0.85. For open buildings and other structures like chimneys, tanks, and signs, Kd ranges from 0.85 to 0.95 depending on the structure type per ASCE 7-22 Table 26.6-1.
Kd is multiplied into the velocity pressure qz formula: qz = 0.00256 x Kz x Kzt x Kd x Ke x V squared. It reduces the overall wind pressure by about 15% for typical buildings. This reduction applies to both MWFRS and C&C calculations.
No. ASCE 7 requires using the tabulated Kd values which already account for directional probability. Using wind data from a specific direction would require additional statistical analysis and is not permitted under the standard simplified procedures. The 0.85 value is calibrated for the directional procedure.
Our calculator automatically applies the correct directionality factor for your building type. Accurate ASCE 7-22 calculations for Broward County in seconds.
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