A TRUSS is an engineered structural frame that is used to span distances that are too great for single-piece members without intermediate supports. Figure 6-37 shows a roof truss or rafter truss assembly. Chords and webs are connected to one another by GUSSET PLATESmetal

plates or plywood pieces that are nailed, glued, or bolted in place. The load that the roof must carry is the important factor to be considered in selecting the type of truss. These loads may con-sist of the roof itself, forces caused by wind, and the weight of snowfall or ice.

Some of the most common types of light wood trusses are shown in figure 6-38. The W-truss (fig. 6-38, view A) is perhaps the most widely used. It uses four web members assembled in the

Figure 6-38.-Light wood trusses: A. W-type; B. King post; C. Scissors.

shape of the letter W instead of a center post. The KING POST truss is the simplest type of structure. It consists of an upper and lower chord with a vertical center post (fig. 6-38, view B). The SCISSORS truss (fig. 6-38, view C) is used for structures with sloped ceiling room, such as a vaulted ceiling.

Perhaps the best way to define building finish is to say that it comprises those nonstructural parts of the building. The finish is divided into EXTERIOR finish (located principally on the outside of the structure) and INTERIOR finish (located inside). The work involved in the installation of nonstructural members on the structure is called FINISH CARPENTRY.

The principal items of the exterior finish are the ROOF SHEATHING and COVERING, EXTERIOR TRIM, and WALL SHEATHING. The order in which these items are erected may vary slightly, although in some cases two or more items may be installed at the same time. 

Normally, roof sheathing is installed as soon as possible to allow work inside a structure to progress during inclement weather.