Figure 2-30.—Equal-pitch hip roof framing diagram.HIPMost hip roofs are equal pitch. This means the angleof slope on the roof end or ends is the same as the angleof slope on the sides. Unequal-pitch hip roofs do exist,but they are quite rare. They also require special layoutmethods. The unit length rafter table on the framingsquare applies only to equal-pitch hip roofs. The nextparagraphs discuss an equal-pitch hip roof.The length of a hip rafter, like the length of acommon rafter, is calculated on the basis of bridgemeasure multiplied by the total run (half span). Any ofthe methods previously described for a common raftermay be used, although some of the dimensions for a hiprafter are different.Figure 2-30 shows part of a roof framing diagramfor an equal-pitch hip roof. A roof framing diagrammay be included among the working drawings; if not,you should lay one out for yourself. Determine whatscale will be used, and lay out all framing membersto scale. Lay the building lines out first. You can findthe span and the length of the building on the workingdrawings. Then, draw a horizontal line along thecenter of the span.In an equal-pitch hip roof framing diagram, the linesindicating the hip rafters (AF, AG, BI, and BK in figure2-30) form 45° angles with the building lines. Drawthese lines at 45°, as shown. The points where they meetthe center line are the theoretical ends of the ridge piece.The ridge-end common rafters AC, AD, AE, BH, BJ,and BL join the ridge at the same points.A line indicating a rafter in the roof framing diagramis equal in length to the total run of the rafter itrepresents. You can see from the diagram that the totalrun of a hip rafter (represented by lines AF-AG-BI-BK)is the hypotenuse of a right triangle with the altitude andbase equal to the total run of a common rafter. You knowthe total run of a common rafter: It is one-half the span,or one-half the width of the building. Knowing this, youcan find the total run of a hip rafter by applying thePythagorean theorem.Let’s suppose, for example, that the span of thebuilding is 30 feet. Then, one-half the span, which is thesame as the total run of a common rafter, is 15 feet.Applying the Pythagorean theorem, the total run of a hiprafter is:What is the total rise? Since a hip rafter joins theridge at the same height as a common rafter, the totalrise for a hip rafter is the same as the total rise for acommon rafter. You know how to figure the total rise ofa common rafter. Assume that this roof has a unit of runof 12 and a unit of rise of 8. Since the total run of acommon rafter in the roof is 15 feet, the total rise ofcommon rafter is the value of x in the proportionalequation 12:8::15:x, or 10 feet.2-20

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