Your question can not be answered without more details of the truss design, loads, deflection requirements, etc.<br>
The manufacturers of prefab roof trusses publish span and load capacity information for their trusses. I suggest that you contact the manufacturers.<br>
Open web 2x4 trusses can accomodate substantial spans however load, truss depth, and sevicability issues must be addressed, as well as material species and grade, before design can be made.
I would not go over 45ft witha flat bottom truss. A scissor truss can span that far too, but much will depend on the pitch of both the roof and ceiling. The two people are correct in not wanting to make a decision without knowing the specifics. When I worked in the truss industry, I had problems with long span trusses 45 ft or more. But with the right lumber and proper bracing anything can be done.<br>
What i,m trying to do is build a small block house 29' x 44'. A typical house with a 4/12 grade. plywood shealting with asphalt singles. I need to do is , span 29 feet so I can have a large great room. But the floor plan could not be develope till I can figure out the roof system. This is only a general thinking question, the final product will be done by the roof trusses engineers
wood trusses @ 24" o.c. w/ 2X4's (or 2X6) top & bottom chords & diagonals should span these ranges (~30 ft) that you are talking about with no problem. i am assuming ~ 16 psf dead & 16 psf live load. i live in florida & this is standard for the industry. obviously, as usual, the connections are critical. also need to consider uplift from winds etc. i assumed a slope ~ 5/12.. in florida these are 'pre engineered' by amny different manufacturers.<br>
just analyse axial loads as a truss and be sure to add in local bending effects on top & bottom chords.<br>
If you live anywhere north of the Mason-Dixon line you will have live load (SNOW+1/2WIND) greater than 16psf.<br>
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Check your applicable Code book, they all have snow and wind loads. SBCCI has a map of the code areas at their website. BOCA does also but it's in the "Members Only" section.
Trying to design your own trusses is pretty much a waste of time, unless youre going to build them yourself. Prefab truss manufacturers will provide sealed designs as part of the service, and have some fairly sophisticated software to determine wind and snow loads over the roof system. The standard for lightweight trusses is ANSI TPI 1- 1995, and any fabricator has to conform to this.
