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• The 2015 Edition Wood Frame Construction Manual for One- and Two-Family Dwellings as referenced by the 2015 International Building Code and the 2015 International Residential Code served as the primary guide for design considerations.
• For wind loads specifically, ASCE 7-10 Minimum Design Loads for Buildings and Other Structures was consulted. ASCE 7-10 Figure 26.5-1A classifies the state of Tennessee as an area with a basic wind gust of 115 miles per hour based on a 700 year return. Additionally, to maintain general applicability to DADU’s placed in any property configuration, the maximum exposure factor was utilized. That produced a value of 20.37psf due to the wind load.
• As advised from the local industry professional, the design of lateral load resistance on this scale of project is purely based on wind loads as they are much more significant than the applicable seismic loads in this area. Using a standard 10 foot high exterior wall with a proposed width of 22 feet yields a total load of 4,500 pounds. With a square building, that load would be symmetrically shared along both adjacent, perpendicular exterior walls. Therefore, each exterior wall would need to resist 2,250 pounds of lateral load.
• The Oriented Strand Board (OSB) sheathing would be the primary component to resist the shear forced on the structure. The linear horizontal sum of continuous vertical sections of sheathing on an elevation would constitute the total width of the applicable shear wall for each elevation. Per the professional’s guidance, each portion of shear wall tallied must also exceed a 3 foot minimum to be counted towards the sum. For analysis, the side of the building with the least horizontal width available to resist shear formed the basis of calculations.
• In this instance, that side was the front of the building, a 22 foot wide wall, with a three foot doorway and a total window width of 5 feet. Neglecting a one foot section of wall between two windows left a total of 12 feet to act as a shear wall. The available shear wall is shaded in the appended figure.
• With 12 feet of shear wall to resist 2,250 pounds of lateral force, the OSB sheathing must be able to resist 188 pounds of force per linear foot. Utilizing the commonly accepted industry standard of 15/32 sheathing fastened with 8 penny nails at 6 inch on center edge nailing would suffice.
• With that combination, based on LP Building products specifications, the shear wall would be able to resist 280 pounds per linear foot, well above the required 188 pounds. For a building of these dimensions, the 2015 International Residential Code Table 4.3A deems this panel and fastener pattern acceptable.
• Vertical stud spacing again followed a traditional industry practice with 2 inch by 4 inch vertical studs spaced at 16 inches on center. International Residential Code provides this standard as an acceptable configuration for a 2 story residential building with a roof assembly. This information is displayed in IRC 2015 Table R602.3[5].
• The American Wood Council (AWC) assumed residential floor live loads in this setting to range from 30-40psf. Additionally, the AWC assumed dead loads to range from 10-20psf. To preserve general applicability, the greater end of both ranges was selected. However, assuming the smaller dead load value would not alter the product selection in the end based on the range that the span covers. Using Trus Joist product specification chart, 4-inch TJI 230 Joists spaced at 16 inches on center would be adequate to cover the 22-foot span.