hey burleymike, the LVL will carry the load easily: 2 LVL, 2"x12' nominal, glued and triangle nailed 12' o.c. BUT, there are more options.
there are two places the built up LVL beam can be installed; the obvious is BELOW the ceiling joists at the center of the joist run. the less obvious is ABOVE the joists.
to mount ABOVE the joists, you need a hole in the gable end to feed the beam thru. and you will be most comfortable if you begin the jacking process noted in the next papagraph to assure that the ceiling won't give way while you are in the attic. of course, blocking and end posts are mandatory to transfer the load all the way to the foundation.
after the beam is set, the ceiling can be jacked up until the top of the joists contact the bottom of the new beam using wooden t-posts and typical auto floor jacks. to minimize drywall damage, take the entire ceiling up (a little at a time) evenly. then crawl into the attic, sweep the insul back away from center, and attach steel straps to the side of each joist over the top of the beam and back down the to the other side forming an upside down "u". the steel banding strap material used by lumber yards for bundling loads is just great for this use; it's cheap or free and you can air nail right thru it into the joists. two spikes on each side yields a shear strenght of 1200 lbs. drive a shim on top between the strap and the beam to tighten the joint. sweep the insul back into place as you back out. remove the jacks and job is done w/ NO loss of head room.
to mount BELOW the ceiling joists at the center of the joist run, snap a line on the ceiling to mark one side of the beam. prepare your beam pockets and end posts.
a few inches away from the beam location, set your t-posts and jacks. take the entire ceiling up (a little at a time) evenly and a little HIGHER than where the top of the beam will be (use a tight string end to end to gage this) before you set the beam. run three or four screws through the drywall into each joist exactly where the beam will impact the drywall, keep the screws flush and, bingo, NO drywall compression will be possible at beam impact. set the beam and pull the jacks out nice and easy
now, all this misses the more simple solution; it's called a King Post. assuming the rafters are also on 24" centers, you jack the ceiling up like noted above until it is flat end to end on the center run. crawl into the attic armed w/ 2x4s precut to be nailed beside EACH joist reaching straight up to beside the rafter above at or very near the ridge. perfect geometric plumb and straight are not important for function in the cure. use at least 4 spikes (16 penny nails) in each joist and each rafter (1200 lbs shear). this cure structurally converts the rafter/joist system into an elementary truss consisting of two triangles. it will work, it's cheap, it will take less time to build.
