Chapter 3 Roof Construction and Trim Carpentry

CHAPTER 3 ROOF CONSTRUCTION AND TRIM CARPENTRY The previous chapters have dealt with framing wood structures, including joists, studs, rafters, and other structural members. These constitute “rough carpentry” and are the main supports of a wood-frame structure. (Subflooring and wall and roof sheathing strengthen and brace the frame.) The remaining work on the structure involves installing the nonstructural members. This work, referred to as “finish carpentry,” includes installing the roof covering, door and window frames, and the doors and windows themselves. Some nonstructural members are purely ornamental, such as casings on doors and windows, and the moldings on cornices and inside walls. Instillation of purely ornamental members is known as trim carpentry. Finish carpentry is divided into exterior and interior finish. Exterior finish material consist of roof sheathing, exterior trim, roof coverings, outside wall covering, and exterior doors and windows. Exterior finish materials are installed after the rough carpentry has been completed. Examples of interior finish materials include all coverings applied to the rough walls, ceilings, and floors. We will cover these topics in a later chapter. In this chapter, we’ll cover the exterior finishing of roofs. In the next chapter, we’ll examine the exterior finishing of walls. ROOF SHEATHING LUMBER Roof sheathing boards are generally No. 3 common or better. These are typically softwoods, such as Doughs fir, redwood, hemlock, western larch, fir, and spruce. If you’re covering the roof with asphalt shingles, you should use only thoroughly seasoned wood for the sheating. Unseasoned wood will dry and shrink which may cause the shingles to buckle or lift along the full length of the sheathing board. Nominal 1-inch boards are used for both flat and pitched roofs. Where flat roofs are to be used for a deck or a balcony, thicker sheathing boards are required. Board roof sheathing, like board wall sheathing and subflooring, can be laid either horizontally or diagonally. Horizontal board sheathing may be closed (laid with no space between the courses) or open (laid with space between the courses). In areas subject to wind-driven snow, a solid roof deck is recommended. Installation Roof boards used for sheathing under materials requiring solid, continuous support must be laid closed. This includes such applications as asphalt shingles, composition roofing, and sheet-metal roofing. Closed roof sheathing can also be used for wood shingles. The boards are nominal 1 inch by 8 inches and may be square-edged, dressed and matched, shiplapped, or tongue and groove. Figure 3-1 shows the installation of both closed and open lumber roof sheathing. LEARNING OBJECTIVE: Upon completing this section, you should be able to identify various types of roof sheathing and describe their installation requirements. Roof sheathing covers the rafters or roof joists. The roof sheathing is a structural element and, therefore, part of the framing. Sheathing provides a nailing base for the finish roof covering and gives rigidity and strength to the roof framing. Lumber and plywood roof sheathing are the most commonly used materials for pitched roofs. Plank or laminated roof decking is sometimes used in structures with exposed ceilings. Manufactured wood fiber roof decking is also adaptable to exposed ceiling applications. Figure 3-1.-Closed and open roof sheathing. 3-1