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Exposure Category C

Open Terrain
Wind Flows Free

Flat fields and open country let wind travel unobstructed. Watch how this affects your Miami-Dade wind load calculations.

Exposure C: Open Terrain
0.98
Kz at 30 ft
Unobstructed Wind Flow
0 ft
Open Fetch
2,600+ ft

Wide Open Spaces

Picture yourself standing in an open field west of Miami. There are no tall buildings, no dense forests - just flat land stretching to the horizon. A strong breeze hits you with its full force.

That's Exposure Category C. When wind blows across open terrain, nothing slows it down significantly. Low obstructions like fences, small structures, and scattered trees are too short (under 30 feet) to create meaningful wind reduction.

In Miami-Dade, you'll find Exposure C conditions in agricultural areas, golf courses, airports, and transitional zones between urban and coastal areas.

Flat Open Country
Grasslands, farmland, wide clearings
Scattered Obstructions
Objects less than 30 ft tall
Airport Zones
Runways and surrounding clear areas
B
Urban/Suburban
Kz = 0.70
C
Open Terrain
Kz = 0.98
D
Coastal
Kz = 1.09

The Middle Ground

Exposure C sits right between urban (B) and coastal (D). At 30 feet height, Exposure C gives you Kz = 0.98 - that's 40% higher than Exposure B's 0.70, but about 10% lower than Exposure D's 1.09.

Think of it as the default exposure. ASCE 7 actually says to use Exposure C unless you can definitively prove Exposure B or D applies. It's the conservative middle choice.

For many inland Miami-Dade properties that aren't densely urban but also aren't right on the coast, Exposure C is the appropriate choice.

Height Makes a Difference

Even in open terrain, wind speed increases as you go higher. Near the ground, friction from grass and soil slows the wind slightly. But at 100 feet up? The wind is roaring at nearly full speed.

This is why tall buildings in Exposure C areas experience much higher wind loads at their tops than at their bases. The Kz factor captures this effect - it grows from 0.85 at 15 feet to 1.27 at 100 feet.

For a single-story building, you might use Kz around 0.85. For a 10-story building's upper floors, you'd use Kz values over 1.2 - that's a 40% increase in wind pressure!

15 ft
30 ft
60 ft
100 ft
150 ft

Frequently Asked Questions

What is Exposure Category C? +
Exposure Category C applies to open terrain with scattered obstructions having heights generally less than 30 feet. This includes flat, open country, grasslands, areas around airports, and regions with sparse development.
Where is Exposure C used in Miami-Dade? +
Exposure C is used in Miami-Dade's inland areas that are flat and open, such as agricultural zones in the western parts of the county, open fields, golf courses, and areas transitioning from urban to rural settings.
What are the Kz values for Exposure C? +
Exposure C Kz values at typical heights are: 0.85 at 15 ft, 0.98 at 30 ft, 1.13 at 60 ft, and 1.27 at 100 ft. These represent the velocity pressure exposure coefficient that accounts for how wind speed changes with height in open terrain.
How much higher are wind loads in Exposure C vs B? +
At 30 feet height, Exposure C has Kz = 0.98 compared to Exposure B's Kz = 0.70. This means Exposure C has approximately 40% higher velocity pressure than Exposure B at the same height and wind speed, resulting in significantly higher wind loads.

Calculate Your Exposure C Wind Loads

Our calculator automatically applies the correct Kz values for Exposure C at every height. Get ASCE 7-22 compliant wind load calculations for your Miami-Dade project.

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