What is the components and cladding (C&C) wind load formula in ASCE 7?

The net C&C design pressure is p = qh x (GCp - GCpi). Here qh is the velocity pressure at mean roof height, GCp is the external coefficient from the zone and effective wind area figures, and GCpi is the internal coefficient. You combine them at whichever sign produces the worst (largest) pressure on the element.

How do I calculate velocity pressure qh for C&C?

Use qh = 0.00256 x Kh x Kzt x Kd x Ke x V squared, evaluated at mean roof height. Kh is the velocity pressure exposure coefficient, Kzt is the topographic factor (1.0 on flat ground), Kd is the directionality factor (0.85 for buildings), Ke is the ground elevation factor, and V is the basic wind speed in mph.

What are the C&C wall and roof zones?

Walls use Zone 4 (interior field) and Zone 5 (corners). Flat roofs use Zone 1 (interior), Zone 2 (edge), and Zone 3 (corner). Corners and edges see the highest suction, so Zone 5 walls and Zone 3 roof corners govern fastener and cladding design. Coefficients come from ASCE 7-22 Figures 30.3-1 and 30.3-2A.

What is effective wind area and why does it matter?

Effective wind area determines which point on the GCp curve you read. Coefficients are largest on the smallest areas, so a single corner fastener at about 10 sqft sees a much higher GCp magnitude than a 500 sqft panel. That is why corner clips and fasteners need tighter spacing than large field panels.

What internal pressure coefficient (GCpi) do I use?

GCpi depends on enclosure classification: enclosed buildings use plus or minus 0.18, partially enclosed buildings use plus or minus 0.55, and open buildings use 0.00. You apply the sign that worsens the net pressure, so for governing suction on an enclosed building you add +0.18 to the negative external coefficient.

ASCE 7-22 · CHAPTER 30 · COMPONENTS & CLADDING

Components & Cladding wind pressure, decoded

C&C are the elements that take wind directly — cladding, windows, doors, roof panels, and their fasteners. Small areas at corners see the highest suction.

p = q_h(GC_p−GC_pi)C&C DESIGN PRESSURE

5WALL + ROOF ZONES

−3.2PEAK ROOF CORNER GC_p @10 SQFT

2002SERVING ENGINEERS SINCE

ZONE MAP

Where the pressure concentrates

Walls use Zones 4 (interior) and 5 (corner). Flat roofs use Zones 1 (interior), 2 (edge), and 3 (corner). Corners and edges govern.

THE C&C PRESSURE EQUATION

One formula, two signs

Net design pressure combines an external coefficient with the internal coefficient, taken at whichever sign is worst.

p = q_h × (GC_p − GC_pi)

p

Net design pressure on the element (psf), perpendicular to the surface.

psf

q_h

Velocity pressure at mean roof height h.

0.00256 K_hK_ztK_dK_eV²

GC_p

External coefficient by zone and effective wind area (figures 30.3-1 / 30.3-2).

EXTERNAL

GC_pi

Internal coefficient: enclosed ±0.18, partially enclosed ±0.55.

INTERNAL

VERIFIED GC_p ANCHORS · ASCE 7-22

Zones & GC_p coefficients

Coefficients shrink as effective wind area grows. Walls per Fig 30.3-1; flat roofs per Fig 30.3-2A.

Surface / Zone	GC_p @ 10 sqft	GC_p @ 500 sqft	Figure
Wall Zone 4 — interior (suction)	−1.1	−0.8	30.3-1
Wall Zone 5 — corner (suction)	−1.4	−0.8	30.3-1
Wall — positive (inward)	+1.0	+0.7	30.3-1
Flat roof Zone 1 — interior	−1.7	−1.0	30.3-2A
Flat roof Zone 2 — edge	−2.3	−1.4	30.3-2A
Flat roof Zone 3 — corner	−3.2	−1.4	30.3-2A

EFFECTIVE WIND AREA

Smaller area, bigger pressure

Effective wind area sets which point on the GC_p curve you read. Peak suction lands on the smallest elements, so a single corner fastener sees far more pressure per square foot than a large panel. This is why corner clips and fasteners need tighter spacing.

10 sqft

Fasteners & clips — highest GC_p magnitude.

PEAK

100 sqft

Windows & single panels — intermediate.

MID

500 sqft

Large panels & spans — lowest GC_p.

LOW

WORKED EXAMPLE · ONE CONSISTENT RESULT

A corner window, end to end

Enclosed building, Exposure C, V = 150 mph, mean roof height h = 30 ft, flat terrain. Wall corner Zone 5, effective wind area 10 sqft.

Step	Value
K_h at 30 ft, Exposure C	0.98
K_zt (flat) · K_d · K_e	1.0 · 0.85 · 1.0
q_h = 0.00256 × 0.98 × 1.0 × 0.85 × 1.0 × 150²	48.0 psf
GC_p — Wall Zone 5 @ 10 sqft	−1.4
GC_pi — enclosed (worst suction)	+0.18
p = 48.0 × (−1.4 − 0.18)	−75.8 psf

Negative = outward suction. The window and its anchors must resist 75.8 psf pulling away from the wall.

RUN IT AUTOMATICALLY

Let the calculator handle every zone

WindLoadCalc applies effective wind area, GC_p, and zone-by-zone pressures for each C&C component — enter a ZIP and go.

Open WindLoadCalc View Calculators

KEEP READING

Components & Cladding wind pressure, decoded

Where the pressure concentrates

One formula, two signs

p

q_h

GC_p

GC_pi

Zones & GC_p coefficients

Smaller area, bigger pressure

10 sqft

100 sqft

500 sqft

A corner window, end to end

Let the calculator handle every zone

Related guides

C&C vs MWFRS

Roof Wind Uplift

Window & Door Pressure

Components & Cladding wind pressure, decoded

Where the pressure concentrates

One formula, two signs

p

qh

GCp

GCpi

Zones & GCp coefficients

Smaller area, bigger pressure

10 sqft

100 sqft

500 sqft

A corner window, end to end

Let the calculator handle every zone

Related guides

C&C vs MWFRS

Roof Wind Uplift

Window & Door Pressure

q_h

GC_p

GC_pi

Zones & GC_p coefficients