other types and requires more time and labor toconstruct.ShedThe shed roof, or lean-to, is a roof having only oneslope, or pitch. It is used where large buildings areframed under one roof, where hasty or temporaryconstruction is needed, and where sheds or additions areerected. The roof is held up by walls or posts where onewall or the posts on one side are at a higher level thanthose on the opposite side.FRAMING TERMSKnowing the basic vocabulary is a necessary part ofyour work as a Builder. In the following section, we’llcover some of the more common roof and rafter termsyou’ll need. Roof framing terms are related to the partsof a triangle.RoofFeatures associated with basic roof framing termsare shown in figure 2-2. Refer to the figure as you studythe terms discussed in the next paragraphs.Span is the horizontal distance between the outsidetop plates, or the base of two abutting right triangles.Unit of run is a fixed unit of measure, always 12inches for the common rafter. Any measurement in ahorizontal direction is expressed as run and is alwaysmeasured on a level plane. Unit of span is also fixed,twice the unit of run, or 24 inches. Unit of rise is thedistance the rafter rises per foot of run (unit of run).Total run is equal to half the span, or the base ofone of the right triangles. Total rise is the verticaldistance from the top plate to the top of the ridge, or thealtitude of the triangle.Pitch is the ratio of unit of rise to the unit of span.It describes the slope of a roof. Pitch is expressed as afraction, such as 1/4 or 1/2 pitch. The term “pitch” isgradually being replaced by the term “cut.” Cut is theangle that the roof surface makes with a horizontalplane. This angle is usually expressed as a fraction inwhich the numerator equals the unit of rise and thedenominator equals the unit of run (12 inches), such as6/1 2 or 8/12. This can also be expressed in inches perfoot; for example, a 6- or 8-inch cut per foot. Here, theunit of run (12 inches) is understood. Pitch can beconverted to cut by using the following formula: unit ofspan (24 in.) x pitch = unit of rise. For example,Figure 2-2.—Roof framing terms.1/8 pitch is given, so 24 x 1/8 equals 3, or unit of risein inches. If the unit of rise in inches is 3, then the cut isthe unit of rise and the unit of run (12 inches), or 3/12.Line length is the hyptenuse of the triangle whosebase equals the total run and whose altitude equals thetotal rise. The distance is measured along the rafter fromthe outside edge of the top plate to the centerline of theridge. Bridge measure is the hypotenuse of the trianglewith the unit of run for the base and unit of rise for thealtitude.2-2

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