headers for basement doorways
The main purpose of the header is to transfer load from the structure above to the jack studs given that there is no stud on 16 inch centers in the middle of the doorway.
Since your structure above is a truss system that did/does not require support from below, the header is no longer necessary. I would omit a header rather than cut down the doorway height and sacrifice headroom. But adequate framing is needed at ceiling height to prevent warping of the door frame or throwing the door out of alignment due to any movement or give up there. With no header you might consider not shimming the middle of the top jamb.
On one of my projects I used a header of 2x4's and shims for cripples, for a doorway in a non-load-bearing wall; no more space.
Last edited by AllanJ; 12-15-2008 at 11:57 AM.