Abstract: An improved railway car body structure is described. One of the features of the box car is that the longitudinal side walls are formed by a plurality of spaced apart vertical side posts which are hat-shaped in cross-section and define a bottom wall portion, opposed side walls and opposed end flanges extending in a common plane. Horizontal structural stiffeners are secured between the vertical side posts. The stiffeners define a recessed wall portion aligned with a recessed formation formed in the opposed end flanges of the vertical side posts. Ferrous sheet members are secured to the side wall and also to the end frames by welds disposed in the recess wall portion of the stiffeners and recessed formation of the vertical posts to form flush, unobstructed, inner side and end walls of the railway car. A new roof structure is also described and incorporates improved skylight designs.