ASCE 7-22 · EXPOSURE CATEGORY C

Exposure C — open terrain, the baseline exposure

Flat open country, grasslands, and most coastlines outside D. Scattered obstructions under 30 ft. This is the default exposure that ASCE 7 wind-speed maps are built on.

0.85Kₒ AT ≤15 FT
15 ftzₘₐₙ (MIN HEIGHT)
+40%VS EXPOSURE B AT 30 FT
2002TRUSTED SINCE

WHAT IT LOOKS LIKE

Open, flat, minimal obstruction

Wind reaches the structure with little to slow it — only scattered low features under 30 ft tall.

h Open country · scattered obstructions < 30 ft

TERRAIN CONSTANTS · TABLE 26.11-1

The numbers that define Exposure C

15 ftzₘₐₙ MINIMUM HEIGHT
9.8α (3-SEC GUST)
2460 ftzₘ GRADIENT HEIGHT

Because zmin = 15 ft, Kz holds at 0.85 for every height at or below 15 ft.

TABLE 26.10-1 · VELOCITY PRESSURE COEFFICIENT

Kz for Exposure C by height

Verified ASCE 7-22 values. Pressure scales with Kz, so it climbs steadily with height.

Height z (ft)Kₒ (Exposure C)
0–150.85
200.90
250.94
300.98
401.04
501.09
601.13
801.21
1001.26
1201.31
1601.39
2001.44

SITE TYPES

When to use Exposure C

Open, flat terrain with only scattered low obstructions — and the default when B or D can't be clearly established.

Agricultural Land

Crop fields, pasture, and farmland with scattered low farm buildings.

OPEN COUNTRY

Grasslands & Plains

Prairie, meadow, rangeland, and open fields with native grasses.

FLAT TERRAIN

Airfields

Runways, taxiways, and open grounds away from building clusters.

EXPOSED

Rural Residential

Isolated houses on large lots and farmhouses surrounded by fields.

WIDELY SPACED

Undeveloped Land

Cleared lots, vacant land, and freshly cleared construction sites.

NO LANDSCAPING

The Default Choice

When B or D can't be clearly established, C is the conservative default.

BASELINE

HOW C COMPARES · AT 30 FT

Between suburban B and coastal D

At 30 ft, the velocity-pressure coefficient tells the whole story.

ExposureKₒ at 30 ftRelative to C
B (suburban)0.70C is +40% higher than B
C (open terrain)0.98baseline
D (coastal)1.16D is +18% higher than C

Exposure B (Suburban)

Closely-spaced obstructions lower the pressure — Kz = 0.70 at 30 ft.

LOWER LOADS

Exposure D (Coastal)

Smooth water fetch raises the pressure — Kz = 1.16 at 30 ft.

HIGHER LOADS

CALCULATE IT

Exposure C wind loads, computed instantly

WindLoadCalc.com applies the correct Kz coefficients for open terrain across every ASCE 7-22 height — no manual table lookup.

Calculate Exposure C Loads Exposure Selection Guide

KEEP EXPLORING

Related exposure & wind-speed resources

Exposure B (Suburban)

Urban and suburban areas with closely-spaced obstructions.

EXPOSURE

Exposure D (Coastal)

Coastal areas and the highest wind pressures.

EXPOSURE

Exposure Selection Guide

How to determine the correct exposure category.

GUIDE

Transition Zones

Where exposure categories change across a site.

EXPOSURE

ASCE 7-22 Wind Speed Maps

MRI-based maps and changes from ASCE 7-16.

MAPS

3-Second Gust

The 3-second gust parameter behind every map value.

WIND SPEED