Solid sawn lumber is used in many aspects of today's house construction. While 2x4 and 2x6 lumber is used almost exclusively for wall framing, it is still common in floor construction, but less so as roof framing.
Methods of Wood Construction
In platform construction, the floors and walls are built in sequential fashion, typically beginning with the first floor deck, which sits on the foundation. Floor joists are sheathed with sub-flooring, such as plywood or oriented strand board. Once the deck is sheathed, the walls are constructed on the "platform" and "tipped" into place. Wall sheathing may be attached to the stud prior to tipping the segment. Hence, the name "platform" derived from floor upon which exterior walls and interior partitions are constructed. The process continues with the installation of floor joists and decking on top of the walls, until the upper most wall is secured prior to placement of the roof framing.