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Categories
From ASCE 7 26.2 and Table 26.13-1, the Enclosure categories are based relations between total opening area in any one wall Ao , the area of the wall with opening Ag. the area of openings in all other walls Aoi, the area of the walls in the other surfaces Agi .
Enclosed: Ao < 0.01 Ag and Ao < 4 sq ft.
Partially Enclosed: Ao > 1.1 Aoi, and Ao > 4 sq ft or 0.01 Ag and Ao / Agi < 0.2 Aoi / A
Partially Open: Not enclosed, partially enclosed, or Open, which is defined by each wall having Ao > 0.8 Ag
Open Buildings
Special procedures for Open buildings have not been implemented and Shearwalls does not allow input of the Open enclosure category. It was determined that the effort to implement of the provisions for these buildings in ASCE 7 Figures 27.3.4 to 27.3-7 was not merited given the low prevalence of such structures designed with wood shear walls. These may be implemented in a future version of the program.
Estimation
The program estimates the enclosure category of the building using the design code equations and the building geometry. Because it cannot account for skylights or hip ends, you can override the enclosure category. If your enclosure category is different from the one calculated by the program, you are warned when loads are generated.
Total Surface Area
The total surface area is that of the exterior walls and the roofs. In estimating the roof area, a hip roof is approximated by one in which the hips were gable ends, so a slight inaccuracy is introduced. Overhangs are not included in the roof area.
Opening
Openings are doors and windows input in the Opening Input Form. The program has no way of including skylights in this calculation.
Definition of a Wall
One could interpret a "wall" as an entire building face, or any small jog in the building. ASCE 7 refers to "a wall that receives positive external pressure" Therefore, each face of the building (North, South, East, West) is considered an external wall, i.e. there are four walls per structure for this purpose.