Figure 6-23.-Most common types of pitched roofs.numerator is the UNIT RISE and thedenominator is the UNIT SPAN. By commonpractice, unit run is always given as 12. See theroof pitch diagram in figure 6-24. Expressed inequation form,Suppose that a roof rises 8 units for every12 units of run—meaning that unit rise is 8 andunit run is 12. Since the unit span is 24, the pitchof the roof is 8/24, or 1/3. This value is alsoindicated in the center view of the roof pitchdiagram in figure 6-24.On construction drawings, the pitch of a roofis indicated by a small ROOF TRIANGLE likethe one in the upper view of figure 6-24. Thetriangle is drawn to scale so that the length of thehorizontal side equals thealways 12), and the lengthequals the unit rise.unit run (which isof the vertical sideFigure 6-24.-Roof pitch diagram.Rafter LayoutRAFTERS are framing members that supporta roof. They do for the roof what joists do forthe floor and what the studs do for the wall. Theyare generally inclined members spaced from 16to 48 in, apart that vary in size, depending on theirlength and the distance they are spaced.The tops of the inclined rafters are fastenedin one of the various common ways, which isdetermined by the type of roof. The bottoms ofthe rafters rest on the plate member, whichprovides a connecting link between the wall andthe roof and is really a functional part of both.6-21
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