tables. Let’s suppose that the common rafter unit of riseis 8. In that case, the unit length of a valley rafter is 18.76.The total run of the longer valley rafter between theshorter rafter tie-in and the rafter plate is the hypotenuseof a right triangle with the altitude and base equal toone-half of the span of the addition. Suppose theaddition is 20 feet wide. Then, the total run is:Figure 2-60.-Intersection ridge and valley rafter locationlayout.The locations of additional ridge and valley rafterscan be determined as indicated in figure 2-60. In anequal-span situation (views A and B), the valley rafterlocations on the main-roof ridge lie alongside theaddition ridge location. In view A, the distance betweenthe end of the main-roof ridge and the addition ridgelocation is equal to A plus distance B, distance B beingone-half the span of the addition. In view B, the distancebetween the line length end of the main-roof ridge andthe addition ridge location is the same as distance A. Inboth cases, the line length of the addition ridge is equalto one-half the span of the addition, plus the length ofthe addition sidewall rafter plate.Figure 2-60, view C, shows an unequal-spansituation. If framing is by the long and short valley raftermethod, the distance from the end of the main-roof ridgeto the upper end of the longer valley rafter is equal todistance A plus distance B, distance B being one-half thespan of the main roof. To determine the location of theinboard valley rafter, first calculate the unit length of thelonger valley rafter, or obtain it from the unit length rafterYou know that the valley rafter is 18.76 units longfor every 16.97 units of run. The length of rafter for14.14 feet of run must therefore be the value of inthe proportional equation 16.97:18.76::14.14:x, or15.63 feet. The location mark for the inboard end of theshorter valley rafter on the longer valley rafter, then, willbe 15.63 feet, or 15 feet 7 9/16 inches, from the heelplumb cut line on the longer valley rafter. The length ofthe additional ridge will be equal to one-half the span ofthe addition, plus the length of the additional sidewalltop plate, minus a shortening allowance one-half the 45°thickness of the longer valley rafter.If framing is by the suspended ridge method, thedistance between the suspension point on the main-roofand the end of the main-roof ridge is equal to distanceA plus distance C. Distance C is one-half the span of theaddition. The distance between the point where theinboard ends of the valley rafters (both short in thismethod of framing) tie into the addition ridge and theoutboard end of the ridge is equal to one-half the spanof the addition, plus the length of the additional ridge(which is equal to one-half of the span of the main roof),plus the length of the addition sidewall rafter plate.Roof Frame ErectionRoof framing should be done from a scaffold withplanking not less than 4 feet below the level of themain-roof ridge. The usual type of roof scaffold consistsof diagonally braced two-legged horses, spaced about10 feet apart and extending the full length of the ridge.If the building has an addition, as much as possibleof the main roof is framed before the addition framingis started. Cripples and jack rafters are usually left outuntil after the headers, hip rafters, valley rafters, andridges to which they will be framed have been installed.For a gable roof, the two pairs of gable-end rafters andthe ridge are usually erected first.Two crewmembers, one at each end of the scaffold,hold the ridge in position. Another crewmember sets thegable-end rafters in place and toenails them at the rafterplate with 8d nails, one on each side of a rafter. Beforewe proceed any further, see table 2-1 as to the type and2-36

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