Here's what I want to do. I have a 32" opening from my dining room into my living room. I'd like to put in a set of 6' French Doors in it's place. So, I obvioulsy need to open up the opening in the wall. The wall in question runs paralell with floor joists underneath, and is perpendicular to the celing joists above. Is this a load bearing wall? THere is empty attic space above. It is stick built house w/ ceiling joists and rafters. The only thing it is supporting is the c.joists.
You still need to support the ceiling joists, so treat it as a load bearing wall and incorporate the correct size header into the structure. If the RO falls between floor joists, install blockng to the support beam in the basement.
For design purposes, you need to establish the dead and live load requirements for the attic which will bed supported by your header. So you need to check the code for your area, and/or discuss with the local code enforcement officer. They should be familiar with the attic loading. Once you have established the required load capacity for the header, you design the header and the supporting posts accordingly. As noted, you want to carry the vertical load down to the basement and support the posts on a major beam, or if necessary take the load directly down to the floor and support the posts on footers.