Hip roof

[Shed Guy]

Ok as by my name you can figure that I build sheds for a living, since I usally build three a day I don't have time to mess around! So I cut "EVERYTHING" in the shop and bring it to the job site and wack it together! My pet peev is jack rafters,, everthing I cut ie:commons, hips, ridge beam fits bang on, even the legnth of my jacks are bang on the only problem is that I can't seem to get a perfect fit of my jacks to the hip ex: 10x12 shed 5/12 pitch, I cut the commons at a 5/12 the hips at a 5/17 but what angle is the jack suposed to be? I cut a 45* cheek cut but 5/12 and 5/17 do not fit nice against the hip! I see on my framing square "SIDE CUT LEGNTH OF JACK RAFTER" IS 11.06 so I tried 5/11.06 and it seemed to fit rather well but is that the right way to read the square? For example on a 6/12 pitch under "SIDE CUT LEGNTH OF JACK RAFTER" it is 10.75 so on a 6/12 should I use 6/10.75 as my jack angle??? Would apreciate some help if anyone can thanks.

[TSJHD1]

Side cut info on a framing square is useless info. If the roof is regular, i.e. same pitch all around, the jack ANGLE is the same as commons. The BEVEL is 45 degrees. It's that simple.

The problem you may be having could be due to pre-cutting in the shop. Here's what I mean: I am just now finishing up a hip roof and have noticed my bevels on my LVL are hitting @ their short-points, leaving the long points somewhat open. All these rafters were cut well ahead of time. What I believe has happened is the material took on some moisture, which caused swelling similar to a 45 degree mitre swelling the short points together, but leaving the long points open. Maybe this is what's happening in your case.

Tom

[Joe Carola]

Ok as by my name you can figure that I build sheds for a living, since I usally build three a day I don't have time to mess around! So I cut "EVERYTHING" in the shop and bring it to the job site and wack it together! My pet peev is jack rafters,, everthing I cut ie:commons, hips, ridge beam fits bang on, even the legnth of my jacks are bang on the only problem is that I can't seem to get a perfect fit of my jacks to the hip ex: 10x12 shed 5/12 pitch, I cut the commons at a 5/12 the hips at a 5/17 but what angle is the jack suposed to be? I cut a 45* cheek cut but 5/12 and 5/17 do not fit nice against the hip! I see on my framing square "SIDE CUT LEGNTH OF JACK RAFTER" IS 11.06 so I tried 5/11.06 and it seemed to fit rather well but is that the right way to read the square? For example on a 6/12 pitch under "SIDE CUT LEGNTH OF JACK RAFTER" it is 10.75 so on a 6/12 should I use 6/10.75 as my jack angle??? Would apreciate some help if anyone can thanks.

Forget the side cuts on your framing square as Tom already said. That mark would only be used to mark the TOP EDGE (1-1/2" side of the 2x) jack rafter as a guide for a handsaw. Your not using a handsaw.

Your framing square is set at 5/17 for the Hip Pllumbcut, 5/12 for the Common Plumbcut, and 5/12 for the Jack Rafter Plumbcut with your saw set at 45° when cutting ther Jack Rafter Plumbcut. Is this what your doing in my first drawing?

Are you holding the framing square 11-1/16"/12 like the Side Cut says to mark the PLUMBCUT for the Jack rafter in my second drawing?

[Joe Bartok]

Shed Guy, I'm with Tom: The info on a framing square is good only for regular Hips/Valleys where the pitches are equal. To answer your question:

For example on a 6/12 pitch under "SIDE CUT LEGNTH OF JACK RAFTER" it is 10.75 so on a 6/12 should I use 6/10.75 as my jack angle??? Would apreciate some help if anyone can thanks.

You would use 10.75/12.
The Jack Rafter Side Cut Angle is arctan(10.75/12) = 41.85504°
Another way of looking at the Jack Rafter Side Cut Rise/Jack Rafter Side Cut Run ratio is:
Common Rafter Run/Common Rafter Length
For example, if the Common Rafter Run = 12, the Common Rafter Length = 13.41641
The Jack Rafter Side Cut Angle is arctan(12/13.41641) = 41.81031°
The above examples are true only for regular Hip rafters where equal pitches meet at a 90° plan angle.

Not everyone likes my methods, but I prefer to calculate the angles. Here's a link to some
Roof Framing Angle Formulas. The formulas work for irregular pitches and plan angles.