Page 319 - 2018_IRC

WALL CONSTRUCTION

TABLE R608.7(1B)—continued
UNREDUCED LENGTH, UR, OF SOLID WALL REQUIRED IN EACH EXTERIOR ENDWALL
FOR WIND PERPENDICULAR TO RIDGE FIRST STORY OF TWO STORY a, c, d, e, f, g
UNREDUCED LENGTH, UR, OF SOLID WALL REQUIRED IN ENDWALLS FOR WIND PERPENDICULAR TO RIDGE
(feet)
SIDEWALL ENDWALL ROOF Basic Wind Speed (mph) Exposure
LENGTH LENGTH SLOPE 115B 120B 130B 140B 150B 160B
(feet) (feet)
— — 110C 119C 127C 136C Minimum b
— — — 110D 117D 125D
< 1:12 9.87 10.74 12.61 14.62 16.79 19.10 10.10
5:12 13.71 14.93 17.52 20.32 23.33 26.54 10.87
15
7:12 15.08 16.42 19.27 22.35 25.66 29.20 11.22
12:12 18.67 20.33 23.86 27.67 31.77 36.14 12.19
< 1:12 9.87 10.74 12.61 14.62 16.79 19.10 10.30
5:12 13.71 14.93 17.52 20.32 23.33 26.54 11.85
30
7:12 17.44 18.99 22.29 25.85 29.67 33.76 12.54
12:12 24.62 26.81 31.46 36.49 41.89 47.66 14.48
60
< 1:12 10.27 11.18 13.12 15.21 17.47 19.87 10.50
5:12 14.26 15.52 18.22 21.13 24.26 27.60 12.82
45
7:12 20.21 22.01 25.83 29.95 34.39 39.12 13.86
12:12 31.20 33.97 39.87 46.23 53.07 60.39 16.76
< 1:12 10.64 11.59 13.60 15.77 18.11 20.60 10.70
5:12 14.77 16.09 18.88 21.90 25.14 28.60 13.79
60
7:12 23.05 25.09 29.45 34.15 39.21 44.61 15.18
12:12 37.97 41.34 48.52 56.27 64.60 73.49 19.05
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 pound force per linear foot = 0.146 kN/m, 1 pound per square foot = 47.88 Pa.
a. Tabulated lengths were derived by calculating design wind pressures in accordance with Figure 28.4-1 of ASCE 7 for a building with a mean roof height of 35
feet, topographic factor, K equal to 1.0, and Risk Category II. For wind perpendicular to the ridge, the effects of a 2-foot overhang on each endwall are
zt,
included. The design pressures were used to calculate forces to be resisted by solid wall segments in each endwall. The forces to be resisted by each wall line
were then divided by the default design strength of 840 pounds per linear foot of length to determine the unreduced length, UR, of solid wall length required
in each endwall. The actual mean roof height of the building shall not exceed the least horizontal dimension of the building.
b. Tabulated lengths in the “minimum” column are based on the requirement of Section 28.4.4 of ASCE 7 that the main windforce-resisting system be designed
for a minimum pressure of 1016 psf multiplied by the wall area of the building and 8 psf multiplied by the roof area of the building projected onto a vertical
plane normal to the assumed wind direction. Tabulated lengths in shaded cells are less than the “minimum” value. Where the minimum controls, it is
permitted to be reduced in accordance with Notes c, d and e. See Section R608.7.1.1.
c. For buildings with a mean roof height of less than 35 feet, tabulated lengths are permitted to be reduced by multiplying by the appropriate factor, R , from
1
Table R608.7(2). The reduced length shall be not less than the “minimum” value shown in the table.
d. Tabulated lengths for “one story or top story of two story” are based on a floor-to-ceiling height of 10 feet. Tabulated lengths for “first story of two story” are
based on floor-to-ceiling heights of 10 feet each for the first and second story. For floor-to-ceiling heights less than assumed, use the lengths in this table or
Table R608.7(1A) or (1C), or multiply the value in the table by the reduction factor, R , from Table R608.7(3).
2
e. Tabulated lengths are based on the default design shear strength of 840 pounds per linear foot of solid wall segment. The tabulated lengths are permitted to be
reduced by multiplying by the applicable reduction factor for design strength, R 3 , from Table R608.7(4).
f. The reduction factors, R , R and R , in Tables R608.7(2), R608.7(3), and R608.7(4), respectively, are permitted to be compounded, subject to the limitations
2
3
1
of Note b. However, the minimum number and minimum length of solid wall segments in each wall line shall comply with Sections R608.7.1 and R608.7.2.1,
respectively.
g. For intermediate values of sidewall length, endwall length, roof slope and basic wind speed, use the next higher value, or determine by interpolation.

294 2018 INTERNATIONAL RESIDENTIAL CODE ®
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