Unit 48

1. Unit 48 Hip Roofs Hip Rafters • Hip Jack Rafters • Constructing Hip Roofs

2. A hip roof has four sloping sides. Four hip rafters run at a 45° angle from the exterior walls. Hip jack rafters frame the space between the hip rafters and the top of the exterior walls.

3. Side cuts are required at the ridge and tail of a hip rafter.

4. The unit run of a hip rafter is 17″, which is the 45° diagonal of a 12″ square.

5. To calculate the actual hip rafter length, one‑half the diagonal thickness of the ridge board that fits between the rafters is deducted from the theoretical length. When shortening the hip rafters, make the measurement perpendicular to the plumb line, not along the length of the roof member.

6. When laying out a hip rafter, the angles for side cuts and ridge plumb cuts are marked first.

7. The rafter table on a framing square can be used to determine the exact angle for the side cut of a hip rafter. The roof in this example has a 7″ unit rise.

8. A hip rafter overhang runs 1.42″ for every 1″ of common rafter run. In this example, the run of the common rafter is 10″. To find the run of the hip overhang, multiply 1.42″ by 10. The result is 14.2″, or 14 1/8″.

9. A framing square can be used to calculate the run of the hip rafter overhang. In this example, the run of the roof overhang is 10″.

10. Backing a hip rafter allows roof sheathing to lie in the same plane as common and jack rafters.

11. Dropping a hip rafter is faster than backing a rafter and accomplishes the same purpose.

12. When calculating lengths of hip jack rafters for layout beginning from the common rafter at the end of the ridge, the common length difference must first be determined. In this example, the roof has a 6″ unit rise and a 20′‑8″ span. The length of common rafters is 11′-6 5/8″. The hip jack rafters are spaced 24″ OC. The common length difference is 26 13/16″.

13. Hip jack rafter layout can begin from a common rafter located away from the end of the ridge board. In this example, the roof has a 5 unit rise and 23′-0″ span. The hip jack rafters are spaced 24″ OC. The common length difference is 2′-2″.

14. When calculating hip jack rafter length beginning from the corner of a building, the length of each succeeding hip jack rafter length is increased by the common length difference. In this example, the roof has a 6″ unit rise. The hip jack rafters are spaced 24″ OC. The 26 13/16″ or 2′‑2 13/16″ common length difference shown in the rafter table is the length of the first hip jack rafter placed 24″ OC from the corner of the building.

15. Hip jack rafters require a single side cut where they fasten to the hip rafter. In this example, the roof has a 4″ unit rise.

16. A hip jack rafter has plumb cuts where it fastens to the hip rafter as well as cuts at the heel and tail.

17. When calculating the theoretical ridge board length of a hip roof, subtract the total span from the total length of the building. In this example, the total span of the roof is 22′ and the total length of the building is 45′.

18. Different calculations are used when a common rafter is installed at the end of a ridge board than when a common rafter is not installed at the end.

19. When constructing a hip roof, the main framing members should be precut before construction begins.