Wind doesn't just push - it PULLS too! Understanding positive and negative pressure is the key to hurricane-safe design.
Get accurate ASCE 7-22 positive and negative pressure calculations for your Broward County project.
Calculate Wind LoadsWind pushes INWARD
Wind PULLS outward (suction)
Here's the surprise: negative pressure (suction) often causes more damage than positive pressure! While the windward wall gets pushed at maybe +40 psf, roof corners can see -85 psf trying to rip the sheathing off.
That's why Florida's building codes focus so heavily on roof-to-wall connections and edge fasteners. The roof isn't blown OFF by wind pushing under it - it's sucked off by the vacuum on top!
| Design Consideration | Positive (+) | Negative (-) |
|---|---|---|
| Force Direction | Into building | Out of building |
| Fastener Design | Shear resistance | Pullout resistance |
| Typical Location | Windward wall | Roof, leeward, sides |
| Broward County Max | ~50 psf | ~90 psf |
Here's what many people miss: wind changes direction! During a hurricane, your "leeward" wall becomes the windward wall as the storm rotates. ASCE 7 requires checking BOTH positive AND negative pressures for every surface.
That window on the back wall? It needs to resist being pushed IN when wind hits it directly, AND resist being sucked OUT when wind creates a vacuum behind it.
Positive wind pressure is the pushing force that occurs when wind hits a surface directly, like the windward wall of a building. It pushes inward on the wall. In ASCE 7, positive pressures have a '+' sign and represent compression forces that try to push the wall into the building.
Negative wind pressure is the pulling or suction force that occurs on surfaces parallel to or away from the wind, like leeward walls, side walls, and roofs. Wind flowing over these surfaces creates a vacuum effect that pulls outward. Negative pressures have a '-' sign and represent forces trying to pull materials away from the building.
Negative (suction) pressures are often larger because wind separation and vortex formation create intense localized suction. While windward walls might see +25 psf, roof corners can see -80 psf or more. This is why roof sheathing and edge fasteners are critical in Broward County's high-wind zone.
In ASCE 7, positive pressure acts toward the surface (pushing in), while negative pressure acts away from the surface (pulling out). The pressure sign determines fastener design - positive requires shear resistance, negative requires pullout resistance. Tables show both values for each surface zone.
Broward County's 180+ mph design wind speeds create extreme pressures. Windward walls see +35 to +50 psf positive pressure. Leeward walls see -25 to -40 psf suction. Roof corners (Zone 3) can exceed -85 psf suction. Both positive AND negative pressures must be checked for each element.
Our wind load calculator provides both positive AND negative pressures for every zone on your Broward County building. Don't miss the critical suction loads!
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