I’m stumped. I need some advice as to how to frame a valley rafter that is the transition point of a 6 in 12 gable to a 6 in 12 hip roof in which the seat cut terminates at a fourty – five degree corner. I need info regarding backing cuts, etc. because the interior is cathedral. I know I can figure it out if I dub around with it long enough but I’d like to know if there is a mathamatical formula to use to make it a less time consuming process and to help me understand the geometry nuances better. any help from you folks out there would be appreciated. Thanks, Steve.
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Steve,
The backing angle can be found one way by using the Tan-¹(Sin(Hip Angle).
For your 6/12 roof.
19.47° (Hip Angle)
Tan-¹(Sin(19.47) = 18.43° (Backing Bevel for Bottom of Valley)
You said the valley seatcut terminates at a 45° corner. In my drawing is your roof somethiung like the left side 45° corner or a regular 90° corner like the right side?
Hi, thanks for you're reply, To answear you're question: the corner the valley dies on resembles the one on the left in you're drawing.
Hey Joe, nice drawing. I was trying to visualize the roof as described, and having a hard time. It still sounds to me like all he needed was the seat-cut and backing angles for an irregular 135 degrees valley, and the hip/gable stuff was just a diversion.
Huck,If it's like he says where the valley sits on the 45° corner the valley is still a regular valley running at 45° and the backing angle is still 18.43° and the other four marked in green on the drawing are hips running at 67.5° if all three sides are equal and the one hip next to the supporting valley would have hip to valley jacks nailed to them with the bottom of the hip/valley jack planing into the backing bevel on the bottom of the supporting valley.Even if the drawing on the right side is changed to match the left side the gable valleys are still running at 45° becasue everything is the same pitch.
Joe Carola
Gentelmen Thanks for you're intrest. I should add, or clarify that the hip from the hip roof is seated on the ridge of the gable roof and both are on plane with eachother therefore that junction is the center of my valley rafter which will terminate on the 45 degree corner, so if I'm not mistaken, on the gable side of valley my plumb cut should be a 6-12 and cheek cut should be a 22.5, on the hip side - same plumb and cheek but with a backing of something like 18.43 degrees.
Steve,
Is the situation similar to the upper left of this drawing http://pic9.picturetrail.com/VOL293/2163851/7154567/92953903.jpg
and then the pic?
http://pic9.picturetrail.com/VOL293/2163851/7273486/97535256.jpg
you can resize the pic in IE
The missing valley in the atattached jpeg is the one in question.
Looking at your picture, then the valley is a 6-13 if that corner is 45° (or 135) depending on where you are looking.
I edited this once, because I thought I had it all wrong.
6-13 hip backing (or valley)
tan-1(6/13)=24.78°
tan-1((sin24.78)*(tan22.5))= 9.847°
I'm pretty sure that's right, but . . . .
hopefully Joe C will give you the right answer :-)
Edited 5/22/2005 11:37 am ET by TIMUHLER
Edited 5/22/2005 11:44 am ET by TIMUHLER
Thanks for you're input, I believe the info you and Joe have given me is all I need.