Buildings shall have solid walls in each exterior endwall line (the side of a building that is parallel to the span of the roof or floor framing) and sidewall line (the side of a building that is perpendicular to the span of the roof or floor framing) to resist lateral in-plane wind forces. The site-appropriate basic wind speed and exposure category shall be used in Tables R608.7(1A) through (1C) to determine the unreduced total length, *UR*, of solid wall required in each exterior endwall line and sidewall line. For buildings with a mean roof height of less than 35 feet (10 668 mm), the unreduced values determined from Tables R608.7(1A) though (1C) are permitted to be reduced by multiplying by the applicable factor, *R*_{1}, from Table R608.7(2); however, reduced values shall be not less than the minimum values in Tables R608.7(1A) through (1C). Where the floor-to-ceiling height of a story is less than 10 feet (3048 mm), the unreduced values determined from Tables R608.7(1A) through (C), including minimum values, are permitted to be reduced by multiplying by the applicable factor, *R*_{2}, from Table R608.7(3). To account for different design strengths than assumed in determining the values in Tables R608.7(1A) through (1C), the unreduced lengths determined from Tables R608.7(1A) through (1C), including minimum values, are permitted to be reduced by multiplying by the applicable factor, *R*_{3}, from Table R608.7(4). The reductions permitted by Tables R608.7(2), R608.7(3) and R608.7(4) are cumulative.

The total length of solid wall segments, *TL*, in a wall line that comply with the minimum length requirements of Section R608.7.2.1 [see Figure R608.7(1)] shall be equal to or greater than the product of the unreduced length of solid wall from Tables R608.7(1A) through (1C), *UR* and the applicable reduction factors, if any, from Tables R608.7(2), R608.7(3) and R608.7(4) as indicated by Equation R6-1.

(Equation R6-1)

where:

*TL* = Total length of solid wall segments in a wall line that comply with Section R608.7.2.1 [see Figure R608.7(1)].

*R*_{1} = 1.0 or reduction factor for mean roof height from Table R608.7(2).

*R*_{2} = 1.0 or reduction factor for floor-to-ceiling wall height from Table R608.7(3).

*R*_{3} = 1.0 or reduction factor for design strength from Table R608.7(4).

*UR* = Unreduced length of solid wall from Tables R608.7(1A) through (1C).

The total length of solid wall in a wall line, *TL*, shall be not less than that provided by two solid wall segments complying with the minimum length requirements of Section R608.7.2.1.

To facilitate determining the required wall thickness, wall type, number and grade of vertical bars at each end of each solid wall segment, and whether shear reinforcement is required, use of Equation R6-2 is permitted.

(Equation R6-2)

After determining the maximum permitted value of the reduction factor for design strength, *R*_{3}, in accordance with Equation R6-2, select a wall type from Table R608.7(4) with *R*_{3} less than or equal to the value calculated.