MWFRS vs components and cladding: why wind design isn't one pressure for the whole building

Main Wind-Force Resisting System (MWFRS) pressures are what size a building's overall lateral system — its braced frames, shear walls or moment frames, and the foundation resisting the total overturning moment and base shear those pressures generate. These pressures are calculated as an averaged effect over a relatively large tributary area, a whole wall face or a large zone of one, because what matters for the global structure is the total accumulated force, not a highly localized peak.

Components and cladding: the same wind, a genuinely different design case

A single cladding panel, window, or roof fastener doesn't care about the building's total overturning moment — it only cares about the peak, momentary, highly localized pressure spike it might experience right where it sits, especially near corners, eaves and ridges, where wind flow separation creates sharp local suction peaks well above the broader average MWFRS pressure at that same wall. Components and cladding (C&C) design uses its own separate, generally higher-magnitude pressure coefficients, calibrated specifically for small tributary areas and these local peak-suction zones — using an MWFRS-level pressure to size cladding or its fasteners would genuinely understate the load a small, edge-located element can see.

Wind Load Calculator computes MWFRS along-wind pressures on the windward and leeward walls only — a number correctly scaled for sizing the building's overall lateral system, but not the right pressure to hand a cladding or fastener design check, which is a distinct, smaller-tributary-area calculation the tool deliberately doesn't attempt. Side-wall and roof MWFRS pressures, and frictional wind forces along a building's length, are similarly out of scope — the tool is explicit that it covers the along-wind windward/leeward MWFRS case specifically, not a full envelope of every wind design check a real building needs (see the related tool below).