Unit 49 Intersecting Roofs Intersecting Roofs with Equal Spans • Intersecting Roofs with Unequal Spans • Valley Rafters • Valley Jack Rafters • Hip-Valley Cripple Jack Rafters • Valley Cripple Jack Rafters • Constructing Intersecting Roofs
In this intersecting roof, the hip section over the garage at the right intersects with the main gable roof. An intersecting roof, also known as a combination roof, consists of two or more roof sections sloping in different directions. A valley is formed where the different sloping sections are joined. See Figure 49‑1.
For intersecting roofs with equal spans, both sections are the same width and both ridge boards are the same height. In a roof with equal spans, the total rise (height) is the same for the two ridges. See Figure 49‑2. Where the slopes of the roof meet to form a valley between the two sections, a pair of valley rafters are placed. Valley rafters extend from the inside corners formed by the two sections of the building to the corners formed by the intersecting ridges. Valley jack rafters run from the valley rafters to the ridges. Hip‑valley cripple jack rafters are placed between the valley rafter and hip rafter.
For intersecting roofs with unequal spans, the intersecting ridge board is lower on the section with the smaller span. An intersecting roof with unequal spans requires a supporting valley rafter to run from the inside corner formed by the two sections of the building to the main ridge. See Figure 49‑3. A shortened valley rafter runs from the other inside corner of the building to the supporting valley rafter. Similar to an intersecting roof with equal spans, an intersecting roof with unequal spans also requires valley jack rafters and hip‑valley cripple jack rafters. In addition, a valley cripple jack rafter is placed between the supporting valley rafter and shortened valley rafter.
Side cuts at the seat of a valley rafter must be angled back at the heel plumb cut line to allow the rafter to drop down into the inside corner of the building. The layout of a valley rafter is almost identical to the layout of a hip rafter. The unit rise measurement and 17″ measurement on a framing square provide the angles for the plumb and seat cuts. The side cut angles for valley rafters are the same as the angles for hip rafters. The only difference in layout occurs at the seat and tail of the valley rafter. Side cuts must be angled back at the heel plumb cut line to allow the valley rafter to drop down into the inside corner of the building. See Figure 49‑4.
Valley rafters require side cuts at the seat and tail of the overhang. Side cuts are also required at the tail of the overhang so that the corner formed by the valley will align with the rest of the roof overhang. See Figure 49‑5.
Valley rafters require angled side cuts at the ridge, heel, and tail. The angle of the side cuts at the heel and tail is the same as the angle where the rafter connects with the ridge board. The layout procedure for a valley rafter is shown in Figure 49‑6. Note that, unlike hip rafters, valley rafters do not require backing or dropping in an equal span roof, but they may require dropping in an unequal span roof.
An intersecting roof with unequal spans has a supporting valley rafter and a shortened valley rafter. An intersecting roof with unequal spans requires two types of valley rafters—supporting and shortened. See Figure 49‑7. A supporting valley rafter extends from the wall plate to the main ridge board and has a single side cut where it fits against the ridge board. A shortened valley rafter runs at a 90° angle to the supporting valley rafter. Shortened valley rafters have a square cut where they butt against the supporting valley rafter.
A shortened valley rafter runs at a 90° angle to the supporting valley rafter. Shortened valley rafter length is based on the run of the minor roof section. The length of a shortened valley rafter is based on the run of the narrower roof. See Figure 49‑8.
A shortened valley rafter has a square cut where it butts against the supporting valley rafter. The layout procedure for a shortened valley rafter is shown in Figure 49‑9.
Angled side cuts are required at the heel plumb line Angled side cuts are required at the heel plumb line. Angled tail cuts may also be needed. Layout of valley rafters is almost identical to the layout of hip rafters. The Hip-Val scale on the Speed® Square is used to lay out the proper angle based on the unit rise. The side cut angles for valley rafters are the same as the angles for hip rafters. The only difference in layout occurs at the seat and tail cuts of the valley rafters. Side cuts are angled back at the second heel plumb cut line to allow the valley rafter to drop down into the inside corners of the building. See Figure 49-10.
Valley jack rafter lengths can be calculated from the longest jack rafter at the inside corner of the building. In this example, the roof has a 9² unit rise and the rafter spacing is 24² OC. The chosen procedure for calculating valley jack rafter lengths depends on how the rafters are positioned on the roof. Figure 49‑11 shows the procedure to use when the valley jack rafter spacing begins from the inside corner of a building.
Valley jack rafter lengths can be calculated when spacing begins from a common rafter positioned away from the inside corner. In this example, the roof has a 9² unit rise and the rafter spacing is 24² OC. Figure 49‑12 shows the procedure to use when valley jack rafter spacing begins from a common rafter positioned away from the inside corner.
Valley jack rafter lengths can be calculated when spacing begins from the center point of intersecting ridges. In this example, the roof has a 4² unit rise and the rafter spacing is 16² OC. Figure 49‑13 shows the procedure to use when valley jack rafter spacing begins from the center point of the intersecting ridges.
A valley jack rafter has a square cut where it fits against the ridge and a side cut where it meets the valley rafter. Valley jack rafters require a square cut where they are nailed against the ridge and a side cut where they meet the valley rafter. See Figure 49‑14 for the procedure for laying out a valley jack rafter.
Framing square rafter tables may be used to calculate the length of hip‑valley cripple jack rafters. In this example, the roof has a 6² unit rise. Additional information required is the distance from the end of the main section to the intersecting roof section. This distance, shown as length A-C on the drawing, is 4¢‑0². A framing square rafter table can be used to find the lengths of hip‑valley cripple jack rafters. First, find the distance from the end of the main roof section to the intersecting roof section. Multiply the number of feet in this distance by the number on the common rafter line under the unit rise number at the top of the square. This procedure is shown in Figure 49‑15.
A hip‑valley cripple jack rafter has a plumb cut and side cut at each end. Since hip‑valley cripple jack rafters fit between the hip and the valley rafter, they require a plumb cut and side cut at each end. A layout procedure is shown in Figure 49‑16.
A valley cripple jack rafter is always twice the length of the valley jack rafter. Note that the valley cripple jack rafter and the valley jack rafter meet at the same point on the shortened valley rafter. The run of a valley cripple jack rafter is always twice the run of the valley jack rafter that it meets at the shortened valley rafter. For this reason, the length of a valley cripple jack rafter is also twice the length of that valley jack rafter. See Figure 49‑17. Spacing of valley cripple jack rafters is the same as common rafters.
The run of a valley cripple jack rafter is twice the run of the valley jack rafter that it meets at the shortened valley rafter. Side cuts on valley cripple jack rafters run in opposite directions. The angles for plumb cuts and side cuts on valley cripple jack rafters are found by using the same framing square method described for laying out other types of jack rafters. A procedure for laying out valley cripple jack rafters is shown in Figure 49‑18.
The ridge board intersecting a hip roof in which the two roof sections have unequal spans fits into the corner formed by the supporting and shortened valley rafters. After the main ridge board has been set in place, the ridge board of the intersecting portion of the roof can be erected. First, however, the correct point of intersection must be marked on the main ridge board. Methods to locate the point of intersection for three different types of intersecting roofs are shown in Figures 49‑19 and 49‑20.
To locate the center point of a ridge board intersecting a gable roof, add the distance between the end of the main roof and side of the intersecting roof to the run of the intersecting roof. The center point of a ridge board intersecting a hip roof in which the two roof sections have equal spans must be located accurately. After the main ridge board has been set in place, the ridge board of the intersecting portion of the roof can be erected. First, however, the correct point of intersection must be marked on the main ridge board. Methods to locate the point of intersection for three different types of intersecting roofs are shown in Figures 49‑19 and 49‑20.
When calculating the length of an intersecting ridge board when a gable roof intersects with the main roof, one-half the thickness of the main ridge board is subtracted from the theoretical length. Whenever possible, intersecting ridge boards should be cut to their exact lengths before they are set in place. Methods to calculate ridge board lengths for three different types of intersecting roofs are shown in Figures 49‑21, 49‑22, and 49‑23.
The procedure is shown for calculating the length of the intersecting ridge board when a hip roof intersects with the main roof and when the two sections have equal spans. Whenever possible, intersecting ridge boards should be cut to their exact lengths before they are set in place. Methods to calculate ridge board lengths for three different types of intersecting roofs are shown in Figures 49‑21, 49‑22, and 49‑23.
The procedure is shown for calculating the length of an intersecting ridge board when a gable roof intersects with the main roof and when the two sections have unequal spans. Whenever possible, intersecting ridge boards should be cut to their exact lengths before they are set in place. Methods to calculate ridge board lengths for three different types of intersecting roofs are shown in Figures 49‑21, 49‑22, and 49‑23.
When framing an intersecting roof with equal spans, the main ridge board is set at the proper height and supported with the end common rafters. In this example, both sections of the intersecting roof are gable roofs. A procedure for framing an intersecting roof with equal spans is shown in Figure 49‑24. In this example, both sections of the intersecting roof are gable roofs.
When framing an intersecting roof with unequal spans, the main ridge board is set at the proper height and supported with the hip rafters and common rafters at each end. In this example, one section of the intersecting roof is a gable roof and the other section is a hip roof. The framing procedure for an intersecting roof with unequal spans differs somewhat from the procedure for a roof with equal spans. In a roof with unequal spans, the ridge board of the smaller roof section is lower than the main ridge board. The ridge board of the smaller roof section is fastened to the intersecting point of the shortened valley rafter and the supporting valley rafter. One method for framing an intersecting roof with unequal spans is shown in Figure 49‑25.
Blind valley construction does not require valley rafters. Blind valley construction is a method of building intersecting roofs without valley rafters. See Figure 49‑26. The main roof is sheathed and the intersecting section is built on top of the sheathing.
The valley jack rafters for blind valley construction require a seat cut combined with a side cut where the rafters fasten to the 1 × 6. Boards (1 × 6s) are fastened to the top of the sheathing as a base for nailing the valley jacks. The roof section consists of common rafters and valley jack rafters. The length of the longest set of valley jack rafters is determined by subtracting the common length difference from the common rafter. The valley jack rafters require a seat cut combined with a side cut where they fasten to the 1 × 6. The layout for the valley jack rafter cuts is shown in Figure 49‑27.