Double round roof valley framing
Hey guys here’s one for you to chew on. Recently picked up a set of plans for a second stry addition. no problem but all the roof trusses/rafters are to be radiused glu-lams. Not to difficult yet,BUT, there is a radiused dormer as well. Two radiused roofs at ninety degree angles. How do you build the valley other than “Keep cuttin’ on ‘er till she fits!” method.
There is mention on the plans of a compound radiused Glu-lam for a valley rafter. How do they build that thing?
jim
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I recently built a bell shaped roof- double radius with 4 hips. First on the floor I drew out the common rafters on a graph using 6 " square blocks . for the hips I the made a grid of blocks 6"vertical x 8½"horizontal - I then could plot the curves to cross the verticl graph lines at the same heights as the commons. For the horizontal intersections I measured the distance in oneach block on the common, multiplied it by 1.41 and transfered it to the hip graph, the freehanding the curves was easy and accurate. From these 2 graphs it is also easy then to figure out where to cut the jack rafters. The only hard part was beveling the hip rafters- as the angle of bevel constantly changes throughout the curves.
I'm impressed.
I'd love to try one of those one day. Mind if I use some of your ideas?
Take a lot of pictures of the framing and the finished product. I want to do one of these really bad.
There is a section in Will Holladay's new book about cutting ellipses and arches. The "hip" or "valley", depending on your perspective, but "valley" in your case, where two intersecting barrels meet is an ellipse. I'll email you an article that will describe it better than I can. Also go to amazon and check out George Collins book on the subject. I can't remember the name. It is something about circular joinery.
The hardest part is if you have different radii for the two roofs. You have to figure the total run of the valley, and the total run (all of this is in plan) of the commons and express this as a ratio. The valley run/ common run. If the radii were the same you could express this as 17/12.
Brisketbean does this kind of work. His website is http://www.grandentries.com
You can see in some of his pictures that the valleys in the groin vaults are elliptical. I'm assuming you know how to lay out an ellipse. If it was me, I think what I would do is frame everything you can up to the valley and then figure out where the two roofs would touch at the top and the bottom. I would measure the height off the wall plates to the top point and I would measure from the intersection at the bottom to the plumb down point of the top intersecting poitn and then you have the semi-major axis of the ellipse and the semi-minor. Semi-major meaning the horizontal number you find and the semi-minor being the height. You can then lay out the valley.
I'm on the right track with this, but someone has to help me out.
I hope this helps. For info on ellipses check out the thread ellipse here in breaktime.
I had a question about this same thing awhile ago. It was more of an academic question because I didn't have anything like this to frame. I can't remember the answer.