Modular Stairs. Instead of a one-piece stringer, an Ascendings modular staircase has individual CNC-machined aluminum "risers." Since the risers and treads are predrilled, installation entails little more than fastening eight bolts per step and takes only three to eight hours, says the maker. Treads can be made of wood, metal, lightweight concrete, or glass. A complete staircase costs between $3,000 and $4,000 per step, depending on the finish options. Ascendings, 812/342-0809, ascendings.com.