jw_shade

I am currently drawing plans for a future home build. I need to know the feasibility of a shed (lean-to, mono slope) style roof. What are the span limitations? Truss designs available? In particular, I need to know what the maximum spacing between trusses would be. I'm planning a horizontal span of 32' with a 4/12 pitch and a total roof length of 64'. I'm hoping to design this single story with very open, vaulted ceilings (basically no attic). I'm assuming I will need to come up with some sort of traditional rafter/truss hybrid system? I am very new to this and I'm sure I've left out many important details. So please ask for any further information needed. And don't hesitate to tell me that my plan is not feasible. Thanks

jw_shade

anyone have any suggestions? I am new this forum but was hoping for some kind of general input

RobQuillin

You are going to want to go to your truss company of lumber supplier and have them run the engineering specs on your layout. I have seen mono trusses that were close to that size, but you will have to provide the truss company with the load points. If you use a mono truss you will have a shallower pitch on the bottom of the truss then on the top side of it. The only other way you might be able to do it is with an I-joists. They might make it that span, but again you have to have the lumber company run the engineering.

stihowhir

I might be remembering this wrong, but I believe it used to be said that the blue board acts as at least a partial vapor barrier. The pink stuff was reported to be vapor permeable. This would make a difference if moisture is an issue. The blue board also has a radiant insulating layer, which also can be useful.


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CustomBuild

http://www.ilevel.com/literature/TJ-4000.pdf
Here's a link to a popular I-joist company. It has a lot of technical data in it, but the longer you read it, the more you understand. There is a table almost all the way at the bottom of the page for roof application span limits. From the info you provided, it looks like the max span is around 31'-8". So you are right around the max for this type of rafter. It also specifies that a support beam is needed at the ridge. A ridge rafter is not sufficient. That being the case, an engineer would have to come up with something. If you choose to go with this type of roof, you will have to modify your plans to meet their specifications. I think if you shop around, you will find that trusses will be quite a bit more expensive, so it might pay to slightly modify your plans, to stick with I-Joists. There is contact info on the page also.
While an open floor plan is very attractive, I would like to point out that at the highest point, your ceiling will be around 20 or more feet tall. Depending on your area, and how high your heating costs are, you might end up paying an arm and a leg for heat. I went into a house once to change the light bulbs in a very high chandelier. I almost passed out from the heat. It was upwards of 95 degrees up there!