structural ridge beam size

huangyhg

structural ridge beam size
i am building a home in west virginia. the design is cross gabled,i.e., the center section has a perpendicular section on each side. the center section is a 6/12 pitch.  i am using 2x12 rafters on a 45 foot ridge beam. the dl=15psf, ll=40psf.  what size ridge beam(lvl?glulam?microlam?) do i need?  thanks
jack
you present your question as if it is simple, but it is not.  the liability of doing engineering over the internet makes it unwise to give you a beam size but here are some of the things to consider.
1.  if you design the ridge beam as a "true ridge beam it will take 1/2 of the entire roof load.  if there are no interior posts it becomes a very large ridge beam with a 45 ft span.  the purpose for putting in a heavy ridge beam is to take out the horizontal component from having opposed rafters meeting at the ridge that tend to push the walls out when they are loaded.  
2. the valley rafters and cross ridge beam for the gables also put large concentrated loads at the center so that the load on your ridg beam is not uniform.  
3.  for a 45 ft long ridge beam with no interior supports the end column become very critical because of the long columns and high loads.
4.  the connections of the ridge to the columns can become critical looking at uplift from wind especially if you have long overhangs or wings at your gables.
in short, hiring a local licensed engineer to ensure that your largest investment "your house" does not come crashing down around your knees in the first really heavy snow or wind is a small price compared to the risk.  there are many simple wrong answers to simple looking complex problems.
yup.  well said!
i think you have something incorrect.  
for exasmple  
if you are talking a true ridge beam spanning 45' if the width is only 10'
you would need 5- 1.75"x18" deep microlams
it is possible to design a wood truss ridge beam for this purpose. submit design/load criteria to a local truss manufacturer for design and load calcs, then design your end bearing. i have used wood truss ridges with spans to 65' with no problem.