For example, walls sheathed exclusively with rigid foam panels need lateral bracing to resist wind loads. Wind Basics Wind delivers a horizontal load to a structure as it flows against, around and over a building's surface. Friction slows wind speed and reduces loads. Actual loads depend on the shape and height of the building, smoothness of its surface, and lay of the land around the home. Windward roofs experience either positive or negative forces depending on steepness of the roof pitch.
Wind forces are additive.
A 40 mph wind may deliver a 4.1 psf force, but you don't simply multiply the surface area of the windward wall times the force. You must combine all forces acting on all surfaces. This calculation is complicated by serious design issues and the magic numbers required to solve the puzzle are best understood by structural designers and engineers. Unbraced wall studs act in a similar way when they are racked by wind loads. Structural sheathing and diagonal braces installed in walls parallel to the wind flow, transmit lateral wind loads down to the foundation.