Fig. 79. - Plan of Hip and Valley Roof.
In Fig. 79 is represented the plan of a hip and valley roof. This form of a roof is frequently termed broken-back hip and valley, because the main hips are intersected by the common rafters of the gables from one side and the valley rafters from the other. This breaks the line of the hip, hence the origin of the term broken-back. In Fig. 79 let A B, B C, D E and E F represent the line and run of the four main hips. It will be seen that C B is the only hip line which is not broken by a common rafter or a jack from the gables. The main hip line A B is broken at H by the common rafter on the front gable which joins it, as shown by the dotted line G H. If A was the bottom terminus of the hip it would cause several of the common rafters on the left side of the front gable to be cut in two, making more jacks and more work, while weakening the general construction of the roof. In framing, the hip should stop against the ridge of the front gable at H. The hip line D E is broken at I by a jack on the left gable, shown by dotted line I J. In framing, the hip should stop against the ridge of the left gable at I. The hip line F E is broken at K by the intersection of the valley rafter L K. For a scientific job of framing the valley rafter a b on the front side of right gable should extend to the ridge of the rear gable, as it is the nearest place of support, and the hip rafter E F should stop at c against the valley a b. The line B C is the run of the only hip rafter which forms an unbroken line.
From B square down the rise of the hip to M, and connect M with C for the length of the hip rafter. A bevel set at M will give the down bevel and at C the bottom bevel. The method of obtaining the lengths of the hip rafters, which are termed broken back, will be plainly illustrated in other diagrams.
Before proceeding further, however, the reader should be reminded of the fact that on one-half pitch roofs the run of a hip or valley is the length of a corresponding common rafter, hence the dotted line D I shows the length of the common rafter on the left gable for a roof of one-half pitch. If the roof was some other pitch - say one-third, for example - then the length of the common rafter for this gable could be shown by setting off the run and rise, as indicated by d e J.
Fig. 80.-Front Elevation of Roof Plan Shown in Fig. 79.
Proceed in like manner with the gables, and also with the main common rafter. Fortunately, there is always an easy way of doing work, and we will now proceed with the method that makes all roof framing easy. Referring to Fig. 80, first draw a horizontal line, A B, representing the front plate, and set off on this line the location or starting points of all hips and gables shown on the front of plan as C D E. Now, C E represents the starting points of two of the main hips, and also the span of the building having the longest common rafter, F being the center of the span. From F set off the length of the common rafter perpendicularly, as shown by the dotted line F G. Connect G with C and E for the length and position of the main hips. Set off the length of the common rafter on the right gable B H, and draw the ridge line H I; then I E is the length and position of the right gable valley rafter. Set off the length of common rafter on the left-hand gable A J and draw the ridge line J K; then K C is the length and position of the left-gable valley. Connect K D for the front-gable valley. Space and draw the rafters as shown, which will give the length and cut of every jack in the front elevation, including those which cut from the broken hip K G to the valley K D. The line K G is also the length of the broken hip, which stops against the ridge of the left gable. A bevel set in any of the angles where the jacks join a hip or valley will give bevel across the back. The plumb cut is the same as that of the common rafter. C L shows the length of the common rafter on the front gable.
In Fig. 81 is shown the right elevation of the roof plan, A B representing the length of plate line, C D E F the starting points of the hips and valleys on the right side of plan, while C and F are the starting points of the main hips. From C and F set off the run of the main common rafter as C N and F O. From N and O set off the length of the main common rafter, as shown by the dotted lines N G and O P. Connect G and P, which is the ridge of the main roof. Connect G C and F P for the main hips. Set off the length of the common rafter on the rear gable B H and draw the ridge line H I. Set off the length of the common rafter on the front gable A J and draw the ridge line J K. From the center of the right gable set off the length of the common rafter, as shown by the dotted line L M. Draw the valley from D through the point M, continuing it to the ridge line or rear gable, which is the nearest place of support. Then D R is the length of the valley rafter on the front side of the right gable. Connect M E for the valley on the back side of the right gable. C G is the main hip, which is full length.
Fig. 81. - Right Elevation of Roof Plan Shown in Fig. 79.
C K is the front gable valley, and the jacks are cut from the ridge line J K to the valley C K, also from the plate C D to the main hip C G, and from the ridge G P to the valley D M. The main hip P F is broken at I, but extends to the valley rafter D R for a proper place of support. Jacks are cut from the ridge line I H and the valley line M R to the valley M E, as shown. The dotted portion of the hip line P F shows that if the hip was put in full length it would necessitate cutting two common rafters and two jacks on the rear gable, which would make additional work and have a tendency to weaken the roof. Thus the length of every rafter in the right elevation of the plan has been shown, and as the bevels are the same as indicated in Figs. 79 and 80 further explanation is unnecessary.