Abstract: Structural members for building systems include plastic base members having side flanges connected by a central web. For use at floor level at the perimeter of the building, a base member includes a series of openings spaced longitudinally along one flange to receive tubular members that span the building interior. Base members for use inwardly of the building perimeter include aligned openings in both flanges to permit the tubular members to extend through. Upright members also include side flanges and a central connecting web. Further inner flanges integral with the connecting web are spaced slightly from the side flanges and define slots running along the length of the member to receive edges of panels forming opposite surfaces of a wall. The inner flanges are shorter in length than the side flanges so that the upper ends of the upright members can receive a spanning element that runs from one upright member to the next.