A system is disclosed for retaining a concrete to form a foundation of a structure. The system includes side walls that receives and retain the concrete and a bracket assembly that retains the side walls. The side walls include a first side wall and a second side wall, at least one of the first and second side walls is comprised of a component having an interior cavity. The bracket assembly includes reinforcement posts and a separator bar. The separator bar has a plurality of apertures disposed along its length. The apertures include a first set and a second set. The first set and the second set of apertures are sized to retain the reinforcement posts at locations corresponding to nominal widths of the component and building materials that comprise the components to form a cross section of the foundation approximating one of a rectangle, a trapezoid or combinations thereof.