What are building envelope wind loads?

Building envelope wind loads are the localized peak pressures acting on the walls, roof, windows, doors and cladding that enclose a structure. Per ASCE 7 Chapter 30, every envelope piece is designed as Components and Cladding (C&C), which captures the sharp suction at edges and corners rather than the averaged pressures used to size the main frame (MWFRS).

Why are C&C envelope pressures higher than MWFRS pressures?

MWFRS sizes the building frame from pressures averaged over large areas, while Components and Cladding sizes each envelope element for the sharp, localized peaks where wind separates at corners and edges. Because those local suction peaks are far higher than the area-averaged values, C&C pressures on walls, roof corners and openings run higher than MWFRS pressures.

How does a broken window change wind pressure inside a building?

A single breached opening can reclassify a building from Enclosed to Partially Enclosed, raising the internal pressure coefficient GCpi from about plus or minus 0.18 to plus or minus 0.55 (roughly triple). Wind pressurizes the interior and pushes outward on every wall and the roof, which is why impact glazing and shutters that keep the envelope sealed matter so much.

How is velocity pressure calculated for building envelope loads?

Velocity pressure at roof height uses qh = 0.00256 x Kz x Kzt x Kd x Ke x V squared, where Kz is the exposure coefficient, Kzt the topographic factor, Ke the ground elevation factor and V the basic wind speed. For buildings the directionality factor Kd is 0.85. The result feeds the C&C pressure for each envelope zone.

What is the difference between enclosed, partially enclosed, and open buildings?

Enclosure class sets the internal pressure GCpi. An enclosed building is sealed with no dominant opening (GCpi plus or minus 0.18). A partially enclosed building has a dominant opening that pressurizes the interior (GCpi plus or minus 0.55). An open building, such as a canopy or carport, has walls at least 80 percent open with no trapped internal pressure (GCpi 0.00).

ASCE 7-22 · COMPONENTS & CLADDING

Building Envelope Wind Loads

Walls, roof, windows, doors and cladding form the envelope — every piece designed as Components & Cladding (C&C), where localized peak pressures rule.

−1.4WALL CORNER GCp (ZONE 5 @10 SF)

−3.2ROOF CORNER GCp (ZONE 3 @10 SF)

~3×INTERNAL PRESSURE IF BREACHED

0.85Kd · DIRECTIONALITY FACTOR

Calculate Envelope Pressures C&C vs MWFRS

FIG 30.3-1 / 30.3-2A · PRESSURE MAP

Where the envelope feels the worst suction

Wind separates at corners and edges. Roof corners and wall corners draw the highest negative (outward) GCp — openings sit right in the path.

Velocity pressure at roof height: q_h = 0.00256 K_z K_zt K_d K_e V², with K_d = 0.85 for buildings.

TABLE 26.13-1 · INTERNAL PRESSURE GCpi

Enclosure class sets the internal pressure

How tight the envelope is decides GC_pi — the pressure pushing on the inside of every wall, roof and opening.

Enclosed

Sealed envelope, no dominant opening. The baseline condition.

GCpi ±0.18

Partially Enclosed

A dominant opening lets wind pressurize the interior — far higher GC_pi.

GCpi ±0.55

Open

Walls 80%+ open (canopies, carports). No trapped internal pressure.

GCpi 0.00

One broken window can triple internal pressure

A breached opening can shift a building from Enclosed (±0.18) to Partially Enclosed (±0.55) — roughly 3× the internal pressure. That is exactly why opening protection (impact glazing, shutters) matters: it keeps the envelope sealed under storm debris.

ASCE 7-22 · CHAPTER 30

The envelope is designed as Components & Cladding

MWFRS sizes the frame from averaged pressures. C&C sizes each envelope piece for the sharp, localized peaks at edges and corners — which is why C&C pressures run higher.

Wall GCp · Fig 30.3-1

Field Zone 4 −1.1, corner Zone 5 −1.4, positive +1.0 (all @10 sq ft). Suction usually controls.

@10 SQ FT

Roof Corner GCp · Fig 30.3-2A

Roof Zone 3 corners reach −3.2 @10 sq ft — the most demanding suction on the whole envelope.

ZONE 3

THE FOUR ENVELOPE SYSTEMS

Every element carries a C&C pressure

Each must resist both inward and outward design pressure for its zone.

RUN THE NUMBERS

Calculate envelope pressures by zone

Get zone-by-zone C&C pressures for walls, roof and openings — organized for product selection and specification.

Try Wind Load Calculator Compare C&C vs MWFRS

KEEP READING

Building Envelope Wind Loads

Where the envelope feels the worst suction

Enclosure class sets the internal pressure

Enclosed

Partially Enclosed

Open

One broken window can triple internal pressure

The envelope is designed as Components & Cladding

Wall GCp · Fig 30.3-1

Roof Corner GCp · Fig 30.3-2A

Every element carries a C&C pressure

Walls

Roof

Windows & Doors

Cladding & Soffit

Calculate envelope pressures by zone

Related guides

C&C vs MWFRS

Window & Door Pressure

Roof Wind Uplift