When to use: Estimate wind pressure on a building per ASCE 7-16. Use Components & Cladding (C&C) for roof decking, membrane, and panel fasteners (Chapter 30), or Main Wind Force Resisting System (MWFRS) for windward, leeward, and side wall pressures used to size frames, shear walls, and diaphragms (Chapter 27).
Calculate wind pressure on a building per ASCE 7-16. Components & Cladding (C&C) mode gives net uplift pressure on roof coverings and fasteners (Chapter 30). Main Wind Force Resisting System (MWFRS) mode gives net design pressures on windward, leeward, and side walls (Chapter 27) for sizing frames, shear walls, and diaphragms. Both modes share the same velocity pressure formula and internal pressure coefficient (GCpi) convention.
Velocity pressure: qz = 0.00256·Kz·Kzt·Kd·V² (psf), where Kz accounts for exposure category height effects, Kzt is the topographic factor (1.0 for flat terrain), and Kd is the wind directionality factor (0.85 for buildings). Net C&C uplift pressure: p = qh·(GCp − GCpi). The force per fastener or panel anchor F = |p|·A_trib.
Velocity pressure: qz = 0.00256·Kz·Kzt·Kd·V². Net pressure (uplift): p = qh·(GCp − GCpi) where GCp is negative (uplift) and GCpi is positive (outward internal). Roof zones: Zone 3 (corners) GCp ≈ −2.8; Zone 2 (edges) GCp ≈ −1.8; Zone 1 (field) GCp ≈ −1.0. Enclosed building internal pressure: GCpi = ±0.18.
Use when designing roof fastening patterns for metal decking, single-ply membrane roofing, photovoltaic panels, or roof cladding. Corner and edge zones require tighter fastener spacing than field zones due to higher GCp magnitudes. Tributary area per fastener determines the design pull-out force, which is compared to the fastener withdrawal capacity from the manufacturer or code tables.
MWFRS (Main Wind Force Resisting System) is the assembly of structural elements — moment frames, braced frames, shear walls, and diaphragms — that carries wind load from the building envelope down to the foundation. MWFRS pressures act simultaneously over an entire wall or roof surface and are used to compute total base shear, overturning moment, and story forces. C&C pressures, by contrast, are higher-magnitude localized pressures near edges, corners, and ridges that size individual elements (purlins, girts, cladding panels, fasteners) which see peak suction over a small tributary area but never see the whole building loaded at once. The two procedures use different pressure coefficients (Cp for MWFRS vs GCp for C&C) precisely because they answer different structural questions: "how much total lateral load must the frame resist?" versus "how much local suction must this one panel and its fasteners survive?"
The leeward wall pressure coefficient Cp depends on the ratio of building length L (dimension parallel to the wind, i.e. depth in the wind direction) to width B (dimension perpendicular to the wind). A long, shallow building (low L/B, ≤1) develops a stronger leeward suction (Cp = −0.5) because the wake behind a short depth stays more organized and low-pressure. As L/B increases toward 2, the leeward suction weakens (Cp = −0.3) as the wake becomes more diffuse over the longer building depth. Beyond L/B = 4, Cp levels off near −0.2. Practically, this means the same wind speed produces different leeward wall design pressure depending on which face is windward — engineers must check wind acting on both principal axes of a rectangular building.
ASCE 7 Chapter 30 divides roofs into three C&C zones: Zone 1 (interior field) with the lowest uplift, Zone 2 (edges within a distance of 10% of the least building dimension from the eave) with intermediate uplift, and Zone 3 (corners) with the highest uplift coefficients. Corners and edges must always be designed with the more severe GCp values.
Kz accounts for the variation of wind speed with height and terrain roughness. Exposure B (suburban) gives lower Kz (~0.70 at 30 ft) than Exposure C (open terrain, ~0.98 at 30 ft) or Exposure D (coastal, ~1.16 at 30 ft). Values are tabulated in ASCE 7 Table 26.10-1.
GCpi is the internal pressure coefficient. For an enclosed building, GCpi = ±0.18 (positive or negative). Worst-case uplift occurs when internal pressure is outward (GCpi = +0.18) combined with external suction (negative GCp). The net effect p = qh·(GCp − GCpi) amplifies uplift when both act together.
Multiply the net uplift pressure p (psf) by the tributary area per fastener A_trib (ft²): F = |p|·A_trib (lb). For example, 80 psf uplift on a 4 ft² fastener tributary area gives F = 320 lb. This is compared to the fastener pull-out or pull-through capacity from the roof system manufacturer's approved technical literature.
MWFRS stands for Main Wind Force Resisting System — the structural system (frames, shear walls, diaphragms, and their connections) that resists the overall wind load on a building and transfers it to the foundation. MWFRS design pressures per ASCE 7-16 Chapter 27 are computed for entire wall and roof surfaces (windward, leeward, side walls) rather than small localized areas, and are used to size primary lateral-force-resisting members and compute base shear and overturning moment.
MWFRS and C&C use different pressure coefficients because they represent different loading conditions. C&C pressures use GCp values that capture brief, highly localized peak suction near roof edges and corners (magnitudes like −1.8 to −2.8) because a small cladding panel or fastener can experience that peak instantaneously. MWFRS uses lower-magnitude Cp values (+0.8 windward, −0.2 to −0.5 leeward, −0.7 side) representing the average pressure over an entire wall, since the whole surface never experiences the localized peak simultaneously. Comparing a C&C uplift number directly to an MWFRS wall pressure number is comparing two different physical quantities.
Yes, for a complete design. MWFRS analysis sizes the primary lateral system — beams, columns, braces, shear walls, and their foundation connections — using pressures on whole building surfaces. C&C analysis sizes the building envelope — roof deck, wall cladding, windows, and their fasteners — using higher localized pressures near edges and corners. A building designed only for MWFRS loads can still fail envelope elements under localized C&C suction, and vice versa; ASCE 7 requires both checks for enclosed and partially enclosed buildings.
Try our Civil & Structural Studio
More calculators, simulators, and guides for this discipline.
Structural Engineering Calculations & Practical Use Cases (Full Access)
✨ Premium ContentA zoomable interactive reader — free preview, then unlock the full set.