In this paper allowable axial stresses of restrained tapered roof girders are developed. They are particularly useful to determine the allowable stress in the interaction equation for frames consisting of segmented tapered sections because the roof girders are generally supported adequately in the lateral direction by purlins. This study has concentrated on the in plane design of roof girders when the overall column instability above the strong axis governs the design. Because of the complexity of the problems due to the many parameters@ the effective length factors are presented in the form of curves for both cases of sidesway permitted and sidesway prevented. Illustrative examples of using these allowable stress curves are also presented.