Replies

1. 
   Piffin | Jan 14, 2003 06:20am | #1

   I take my information where they sell me the glulams, LVLs and TJIs for something simple like this. They have the software to figure it.

   You are missing information here, so I will assume for theoretical purposes of discussion. 30 feet is either the length of the ridge or the total span of both rafters. IF I assumed it was both, you have an area 30' x 30' The ridge beam will support half of that load. Next you need to know the load requirements for the local jurisdiction. West VA might see a lot of snow so let's assume fifty pounds live load and ten pounds dead load for a total of sixty pounds per square foot. OK 60# times 900 sq ft = 54000 pounds or maybe 27 tons that it might be called on to support.

   Now, how much deflection do you want to allow? The fun has just started...

   .

   Excellence is its own reward!

1. 
   wvjack | Jan 14, 2003 01:43pm | #2

   My understanding is that the deflection will be L360

1. 
   BossHog | Jan 14, 2003 03:45pm | #3

   L/360 may be the MAX deflection allowable by code. But is that how much you actually WANT ???

   With a 30' span, and L/360 max live load deflection (and L/240 total) your allowable live load deflection is exactly one inch, and total load deflection is 1.5 inches.

   Actually, most roofs are only required to be designed for L/240 live and L/180 dead. (L/180 would allow 2" of deflection) So this is something you need to ask about, particularly since it's apparently such a long span. (I don't really know what a "cross-gable roof" is)

   Piffin is right - Go to a local lumberyard or truss supplier - They should be able to design whatever kind of beam you need, or know who can. And they'll be familiar with local codes and loading requirements.Marriage is the mourning after the knot before.