used for flat or low-pitched roofs in post-and-beamconstruction. Single tongue-and-groove decking innominal 2 by 6 and 2 by 8 sizes is available with theV-joint pattern only.Decking comes in nominal widths of 4 to 12 inchesand in nominal thicknesses of 2 to 4 inches. Three- and4-inch roof decking is available in random lengths of 6to 20 feet or longer (odd and even).Laminated decking is also available in severaldifferent species of softwood lumber: Idaho white pine,inland red cedar, Idaho white fir, ponderosa pine,Douglas fir, larch, and yellow pine. Because of thelaminating feature, this material may have a facing ofone wood species and back and interior laminations ofdifferent woods. It is also available with all laminationsof the same species. For all types of decking, make surethe material is the correct thickness for the span bychecking the manufacturer’s recommendations. Specialload requirements may reduce the allowable spans.Roof decking can serve both as an interior ceiling finishand as a base for roofing. Heat loss is greatly reducedby adding fiberboard or other rigid insulation over thewood decking.INSTALLATION.— Roof decking applied to a flatroof should be installed with the tongue away from theworker. Roof decking applied to a sloping roof shouldbe installed with the tongue up. The butt ends of thepieces are bevel cut at approximately a 2° angle (fig.3-4). This provides a bevel cut from the face to the backto ensure a tight face butt joint when the decking is laidin a random-length pattern. If there are three or moresupports for the decking, a controlled random layingpattern (shown in figure 3-5) can be used. This is aneconomical pattern because it makes use ofrandom-plank lengths, but the following rules must beobserved:Stagger the end joints in adjacent planks aswidely as possible and not less than 2 feet.Separate the joints in the same general line by atleast two courses.Minimize joints in the middle one-third of allspans.Make each plank bear on at least one support.Minimize the joints in the end span.The ability of the decking to support specific loadsdepends on the support spacing, plank thickness, andspan arrangement. Although two-span continuouslayout offers structural efficiency, use of random-lengthFigure 3-4.-Ends of roof decking cut at a 2° angle.Figure 3-5.-Plank decking span arrangements.planks is the most economical. Random-length doubletongue-and-groove decking is used when there are threeor more spans. It is not intended for use over singlespans, and it is not recommended for use over doublespans (see figure 3-5).NAILING.— Fasten decking with common nailstwice as long as the nominal plank thickness. For widths6 inches or less, toenail once and face-nail once at eachsupport. For widths over 6 inches, toenail once andface-nail twice. Decking 3 and 4 inches thick must bepredrilled and toenailed with 8-inch spikes. Brightcommon nails may be used, but dipped galvanizedcommon nails have better holding power and reduce thepossibility of rust streaks. End joints not over a supportshould be side-nailed within 10 inches of each plankend. Splines are recommended on end joints of 3- and4-inch material for better alignment, appearance, andstrength.Wood FiberAll-wood fiber roof decking combines strength andinsulation advantages that make possible qualityconstruction with economy. This type of decking isweather resistant and protected against termites and rot.3-5
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