Platform construction is the most widely used method in North America. In this method the floor and walls are assembled separately.When the floor is constructed it provides a platform for workers to construct walls and roof respectively. Studs are one storey high, so walls can be assembled on the sub-floor in sections and erected one storey at a time. This allows builders to use prefabricated or engineered lumber units such as roof truss’s or floor I-joist. Also,the bottom and top plates of walls act as fire stops at floors and ceiling’s and nailing support for exterior sheathing and interior drywall.