Rafter tables are commonly imprinted on the steel square (carpenter square, rafter square, framing square). I've revised it a bit to include angles of the side cuts for hip and valley and the jack rafters.
For info on how to use these tables see Rafter Tables on the Framing Square.
The angles shown are to be used with the popular compound miter or cutoff saws.
The common rafter is one of a series of lineal structures extending from the fascia of the overhang to the top of an exterior wall to the ridge board of a roof. The angle given for a common rafter is called the plumb cut, since the ends are vertical or plumb. The plumb cut on a common rafter is at the ridge, the bird's mouth on the wall and at the fascia.
|Roof Pitch:||Length per Foot of Run||Angle of Plumb Cut in Degrees|
|2 in 12||12.16||9 1/2|
|3 in 12||12.37||14|
|4 in 12||12.65||18 1/2|
|5 in 12||13.00||22 1/2|
|6 in 12||13.42||26 1/2|
|7 in 12||13.89||30 1/4|
|8 in 12||14.42||33 3/4|
|9 in 12||15.00||37|
|10 in 12||15.62||39 3/4|
|11 in 12||16.28||42 1/2|
|12 in 12||16.97||45|
The hip rafter is the structural board which forms the hip at an outside corner of the roof and is installed between 2 common rafters at the ridge. The valley rafter is the structural board which forms the valley at an inside corner of the roof. Both the hip and valley rafters form a 45 degree angle, compounded with the slope of the roof. The angle or plumb cut for a hip or valley rafter, given in our table, is taken from the rafter square based on the slope of the roof and diagonal. If the common rafter has a slope of 5" in 12", the hip or valley rafter has a slope of 5" in 17". 17" is the diagonal of a 12" square. The compound angle for the hip or valley rafter is the plumb cut, given in the table, and the degree on each side of this cut, on both ends, as In the table.
|Roof Pitch in Inches||Length per Foot of Run||Angle of Side Cut in Degrees||Angle of Plumb Cut in Degrees|
|2 in 12||17.09||44.9||6.7|
|3 in 12||17.23||44.6||10|
|4 in 12||17.44||44.2||13.2|
|5 in 12||17.69||43.8||16.4|
|6 in 12||18.00||43.3||19.4|
|7 in 12||18.36||42.7||22.4|
|8 in 12||18.76||42.2||25.2|
|9 in 12||19.21||41.5||27.9|
|10 in 12||19.70||40.7||30.5|
|11 in 12||20.22||40||32.9|
|12 in 12||20.78||37.1||35.2|
There are two types of jack rafters: the hip jack and the valley jack. The hip jack is a short rafter that spans from the wall plate to a hip rafter. The valley jack goes from a valley rafter to the roof ridge. Each jack rafter has the same side cut and plumb cut on the hip or valley rafter and the same angle as the common rafter at the ridge or fascia. The side cut is the angle given in the table, the plumb cut is the same angle as in the table for the hip or valley rafter.
|Roof Pitch in Inches||Difference in Length on 16" Centers||Difference in Length on 24" Centers||Angle of Side Cut in Degrees|
|2 in 12||16 1/4||24 5/16||44.6|
|3 in 12||16 1/2||24 3/4||44.1|
|4 in 12||16 7/8||25 3/16||43.5|
|5 in 12||17 5/16||26||42.7|
|6 in 12||17 7/8||26 7/8||41.9|
|7 in 12||18 1/2||27 7/8||40.8|
|8 in 12||19 1/4||28 7/8||39.8|
|9 in 12||20||30||38.7|
|10 in 12||20 7/8||31 1/4||37.4|
|11 in 12||21 3/4||32 5/8||36.5|
|12 in 12||22 5/8||34||35.9|
Dave(Ask Dave) (About Dave)
Hi, I'm Dave Osborne. With over 50 years experience as a journeyman carpenter, foreman and contractor in heavy construction I enjoyed working with apprentices and sharing the tricks of the trade that others shared with me. Now I get emails from Members all over the world and we include many of my answers in our Free Monthly Newsletters. Some of my answers include drawings and instructions specific to a project, but may also answer your questions. I use correct construction terminology, so you can confidently inform your building supply dealers or contractors exactly what you need.
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