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The method of determining external pressure coefficients CpCg for low-rise structures from ASCE 7 Figure 28.3-1 assumes symmetric, rectangular structures. They are based on boundary layer wind tunnel studies of buildings of that shape, verified against full scale measurements. As relatively few low-rise structures have such a regular shape, Shearwalls extends this method to buildings with multiple blocks and/or eccentric ridge lines.
Intersecting Blocks - Walls
The area of exterior walls beneath a sloped roof are considered to "have" the slope of the roof for the purpose of Case A (transverse) load generation, which depends on roof angle. If there is a hip end in the Case B (longitudinal) direction, and side panel Case A coefficients are used on the wall beneath the hip end, they are the same as the rest of the building face formed by the side panel of the other block.
Intersecting Blocks - Roofs
A hip end panel in the same plane as a side panel on another block has the co-efficient from the same load case as the side panel, so it is equivalent to the situation where the side panel from one block forms the roof on the entire face and the other block joins that block without forming a hip end.
Eccentric Ridge Lines
The coefficients used on the side roof panels and the walls below the panels are based on the angle of each roof panel. This applies to each roof on a structure with multiple blocks.
End zones
End zones are created wherever the corner of a block is an exterior corner of the structure. End zones are not created where two blocks join each other forming either a straight wall and roof, or an interior corner.
Basis for Height-to-Width Limit Design Setting
Low-rise structures must have mean roof height less than least-horizontal dimension, and in the absence of guidance in the ASCE 7, the Design Setting Apply height to-width ratio is used to specify whether this limit is to be applied to each block or to the structure as a whole.