Subfloor

3. 4. 5. 6. Figure 1-32.—Types of framing anchors. Place the outside pieces between the inside trimmers. Drive three 16d nails through the trimmers into the headers. Mark the position of the tail joists on the headers (the tail joists should follow the regular joist layout). Fasten the tail joists to the outside headers with three 16d nails driven through the headers into the ends of the tail joists. Double the header. Drive three 16d nails through the trimmer joists into the ends of the doubled header pieces. Nail the doubled header pieces to each other with 16d nails staggered 16 inches OC. Double the trimmer joists and fasten them together with 16d nails staggered 16 inches OC. A pair of joists, called trimmers, is placed at each side of the opening. These trimmers support the headers. The headers should be doubled if the span is more than 4 feet. Nails supporting the ends of the headers are driven through the trimmer joists into the ends of the header pieces. Tail joists (cripple joists) run from the header to a supporting wall or girder. Nails are driven through the header into the ends of the tail joist. Various metal anchors, such as those shown in figure 1-32, are also used to strengthen framed floor openings. Crowns Most joists have a crown (a bow shape) on one side. Each joist should be sighted before being nailed in place to make certain the crown is turned up. The joist will later settle from the weight of the floor and straighten out. Caution should be exercised when sighting the board for the crown. Some crowns are too large and cannot be turned up for use as a joist. SUBFLOOR The subfloor, also known as rough flooring, is nailed to the top of the floor frame. It strengthens the entire floor unit and serves as a base for the finish floor. The walls of the building are laid out, framed, and raised into place on top of the subfloor. Panel products, such as plywood, are used for subflooring. Plywood is less labor intensive than board lumber. Plywood is the oldest type of panel product. It is still the most widely used subfloor material in residential and other light-framed construction. Other types of material available for use as subflooring include nonveneered (reconstituted wood) panels, such as structural particleboard, waferboard, oriented strandboard, and compositeboard. Plywood is available in many grades to meet abroad range of end uses. All interior grades are also available with fully waterproof adhesive identical with that used in exterior plywood. This type is useful where prolonged moisture is a hazard. Examples are underlayments, subfloors adjacent to plumbing fixtures, and roof sheathing that may be exposed for long periods during construction. Under normal conditions and for sheathing used on walls, standard sheathing grades are satisfactory. Plywood suitable for the subfloor, such as standard sheathing, structural I and II, and C-C exterior grades, has a panel identification index marking on each sheet. 1-16