Floor Joists

Figure 1-16.—Header joist. placed in sections. Solid girders must be measured and cut so that the ends fall over the center of a post. Built-up girders should be placed so their outside joints fall over the posts (fig. 1-13). FLOOR JOISTS In platform framing, one end of the floor joist rests directly on the sill plate of the exterior foundation wall or on the top plate of a framed outside wall. The bearing should be at least 1 1/2 inches. The opposite end of the joist laps over or butts into an interior girder or wall. The size of joist material (2 by 6, 2 by 10, 2 by 12, and so forth) must be chosen with consideration for the span and the amount of load to be carried. The foundation plan usually specifies the joist size, the spacing between joists, and what direction the joists should travel. The usual spacing of floor joists is 16 inches OC. Floor joists are supported and held in position over exterior walls by header joists or by solid blocking between the joists. The header-joist system is used most often. Header Header joists run along the outside walls. Three 16d nails are driven through the header joists into the ends of the common joists, as shown in figure 1-16. The header and joists are toenailed to the sill with 16d nails. The header joists prevent the common joists from Figure 1-17.—Lapped joists. rolling or tipping. They also help support the wall above and fill in the spaces between the common joists. Lapped Joists are often lapped over a girder running down the center of a building. The lapped ends of the joists may also be supported by an interior foundation or framed wall. It is standard procedure to lap joists the full width of the girder or wall. The minimum lap should be 4 inches. Figure 1-17 shows lapped joists resting on a steel girder. A 2- by 4-inch plate has been bolted to the top of a steel beam. The joists are toenailed into the plate. Solid blocking may be installed between the lapped ends after all the joists have been nailed down. Another system is to put in the blocks at the time the joists are placed. Double Joists should be doubled under partitions running in the same direction as the joists. Some walls have water pipes, vent stacks, or heating ducts coming up from the basement or the floor below. Place bridging between double joists to allow space for these purposes (fig. 1-18). Cantilevered Cantilevered joists are used when a floor or balcony of a building projects past the wall below, as shown in figure 1-19. A header piece is nailed to the ends of the 1-8