CHAPTER 3ROOF CONSTRUCTION AND TRIM CARPENTRYThe previous chapters have dealt with framingwood structures, including joists, studs, rafters, andother structural members. These constitute “roughcarpentry” and are the main supports of a wood-framestructure. (Subflooring and wall and roof sheathingstrengthen and brace the frame.)The remaining work on the structure involvesinstalling the nonstructural members. This work,referred to as “finish carpentry,” includes installing theroof covering, door and window frames, and the doorsand windows themselves. Some nonstructural membersare purely ornamental, such as casings on doors andwindows, and the moldings on cornices and insidewalls. Instillation of purely ornamental members isknown as trim carpentry.Finish carpentry is divided into exterior and interiorfinish. Exterior finish material consist of roof sheathing,exterior trim, roof coverings, outside wall covering, andexterior doors and windows. Exterior finish materialsare installed after the rough carpentry has beencompleted. Examples of interior finish materials includeall coverings applied to the rough walls, ceilings, andfloors. We will cover these topics in a later chapter.In this chapter, we’ll cover the exterior finishing ofroofs. In the next chapter, we’ll examine the exteriorfinishing of walls.ROOF SHEATHINGLUMBERRoof sheathing boards are generally No. 3 commonor better. These are typically softwoods, such as Doughsfir, redwood, hemlock, western larch, fir, and spruce. Ifyou’re covering the roof with asphalt shingles, youshould use only thoroughly seasoned wood for thesheating. Unseasoned wood will dry and shrink whichmay cause the shingles to buckle or lift along the fulllength of the sheathing board.Nominal 1-inch boards are used for both flat andpitched roofs. Where flat roofs are to be used for a deckor a balcony, thicker sheathing boards are required.Board roof sheathing, like board wall sheathing andsubflooring, can be laid either horizontally ordiagonally. Horizontal board sheathing may be closed(laid with no space between the courses) or open (laidwith space between the courses). In areas subject towind-driven snow, a solid roof deck is recommended.InstallationRoof boards used for sheathing under materialsrequiring solid, continuous support must be laid closed.This includes such applications as asphalt shingles,composition roofing, and sheet-metal roofing. Closedroof sheathing can also be used for wood shingles. Theboards are nominal 1 inch by 8 inches and may besquare-edged, dressed and matched, shiplapped, ortongue and groove. Figure 3-1 shows the installation ofboth closed and open lumber roof sheathing.LEARNING OBJECTIVE: Upon completingthis section, you should be able to identifyvarious types of roof sheathing and describetheir installation requirements.Roof sheathing covers the rafters or roof joists. Theroof sheathing is a structural element and, therefore, partof the framing. Sheathing provides a nailing base for thefinish roof covering and gives rigidity and strength tothe roof framing. Lumber and plywood roof sheathingare the most commonly used materials for pitched roofs.Plank or laminated roof decking is sometimes used instructures with exposed ceilings. Manufactured woodfiber roof decking is also adaptable to exposed ceilingapplications.Figure 3-1.-Closed and open roof sheathing.3-1
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