Table 3-4.-Plank Decking Estimating Factortraditional designs have considerable y more. Much of theboards are to be used, multiply the total roof area by1.16. To determine the total number of board feetneeded, add 5 percent for trim and waste.Plywood SheathingTo determine how much plywood will be needed,find the total roof area to be covered and divide by 32(the number of square feet in one 4-by 8-foot sheet ofplywood). This gives you the number of sheets requiredto cover the area. Be sure to add 5 percent for a trim andwaste allowance.Decking or PlankingTo estimate plank decking, first determine the areato be covered, then refer to the chart in table 3-4. In theleft column, find the size planking to be applied. Forexample, if 2- by 6-inch material is selected, the factoris 2.40. Multiply the area to be covered by this factorand add a 5 percent trim and waste allowance.Wood Fiber Roof DeckingTo estimate the amount of weed fiber deckingrequired, first find the total roof area to be covered. Forevery 100 square feet of area, you will need 6.25 panels,2 by 8 feet in size. So, divide the roof area by 100 andmultiply by 6.25. Using our previous example with aroof area of 2,310 square feet, you will need 145 panels.EXTERIOR TRIMLEARNING OBJECTIVE: Upon completingthis section, you should be able to identify thetypes of cornices and material used in theirconstruction.Exterior trim includes door and window trim,cornice trim, facia boards and soffits, and rake orgable-end trim. Contemporary designs with simplecornices and moldings contain little of this material;exterior trim, in the form of finish lumber and moldings,is cut and fitted on the job. Other materials orassemblies, such as shutters, louvers, railings, and posts,are shop fabricated and arrive on the job ready to befastened in place.The properties desired in materials used for exteriortrim are good painting and weathering characteristics,easy working qualities, and maximum freedom fromwarp. Decay resistance is desirable where materials mayabsorb moisture. Heartwood from cedar, cypress, andredwood has high decay resistance. Less durable speciescan be treated to make them decay resistant. Manymanufacturers pre-dip materials, such as siding,window sash, door and window frames, and trim, witha water-repellent preservative. On-the-job dipping ofend joints or miters cut at the building site isrecommended when resistance to water entry andincreased protection are desired.Rust-resistant trim fastenings, whether nails orscrews, are preferred wherever they may be in contactwith weather. These include galvanized, stainless steel,or aluminum fastenings. When a natural finish is used,nails should be stainless steel or aluminum to preventstaining and discoloration. Cement-coated nails are notrust-resistant.Siding and trim are normally fastened in place witha standard siding nail, which has a small flathead.However, finish or casing nails might also be used forsome purposes. Most of the trim along the shingle line,such as at gable ends and cornices, is installed beforethe roof shingles are applied.The roof overhangs (eaves) are the portions of theroof that project past the sidewalls of the building. Thecornice is the area beneath the overhangs. The upwardslopes of the gable ends are called rakes. Several basicdesigns are used for finishing off the roof overhangs andcornices. Most of these designs come under the categoryof open cornice or closed cornice. They not only add tothe attractiveness of a building but also help protect thesidewalls of the building from rain and snow. Wideoverhangs also shade windows from the hot summersun.Cornice work includes the installation of thelookout ledger, lookouts, plancier (soffit), ventilationscreens, fascia, frieze, and the moldings at and belowthe eaves, and along the sloping sides of the gable end(rake). The ornamental parts of a cornice are calledcornice trim and consist mainly of molding; the moldingrunning up the side of the rakes of a gable roof is calledgable cornice trim. Besides the main roof, the additionsand dormers may have cornices and cornice trim.3-8
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