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I have a semi-circular great room to cover with a conical roof. The engineering call for 1 3/4″ x 14″ LVL’s 24′ o.c. radiating from a circular wall above. The span is about 24 feet and the pitch is 3 in 12. The center of the circle is 8 feet beyond the end of the radians/rafters so there will be some space to hang the rafters on a “bent”, built-up 1×12 ledger. Other than laying out these “spokes” in a perfectly spaced pattern I don’t think I’ll have too much trouble framing the roof. I’ve been losing sleep over the way the 1/2″ ply or OSB is going to lay down over these rafters especially as it gets closer to the center of the circle. Any ideas?
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Replies
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Steve- I use a product called " wiggle wood". Its plywood that has all the grain running in the same direction. It comes in 1/4" thickness and I build up layers to give a good nailing base. The smallest radius it will bend is 8".
*b WBA At Your ServiceKen, I didn't think bending ply was an exterior rated sheathing. Am I wrong about this ?
*Tim - I don't know if it had an exterior rating. However I've used it from everything from bell cast roofs to concrete forming without any delamination or breakdown.Does it matter if its covered with felt and shingles anyway?
*b WBA At Your ServiceKen, I looked at a sheet that I have in my basement and it is definitely not an exterior product. It is a 3 ply material with the inner ply probably around 1/32". This is definitely not a structural rated sheathing. I can't believe we're even talking about the same product. You could never use this stuff for roof sheathing and not fall through during installation. You always want to use exterior plywood for roof sheathing. Over the years, the plywood can definitely get damp during very rainy periods which can cause certain delamination of non-exterior glues. The roof described here has only a 3" pitch. I would think that 1/2" CDX would work, 3/8" double layer worst case scenario.
*I agree that a double layer of 3/8 ply would work well. If the bend gets too severe (as it would on a steeper pitch) you can use 3/4" board sheathing ripped to a truncated triangle shape and nailed parallel to the rafters. Of course you also need to put in blocking between the rafters in this case.
*a couple layers of 1/4" ply with ice and water shield should work
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I have a semi-circular great room to cover with a conical roof. The engineering call for 1 3/4" x 14" LVL's 24' o.c. radiating from a circular wall above. The span is about 24 feet and the pitch is 3 in 12. The center of the circle is 8 feet beyond the end of the radians/rafters so there will be some space to hang the rafters on a "bent", built-up 1x12 ledger. Other than laying out these "spokes" in a perfectly spaced pattern I don't think I'll have too much trouble framing the roof. I've been losing sleep over the way the 1/2" ply or OSB is going to lay down over these rafters especially as it gets closer to the center of the circle. Any ideas?