I moved into a newly built house less than a year ago and the door between the Master Bedroom and Master Bathroom will not close. When we moved in last year, the door would close; but the gap narrowed at the top of the jam from the hinge side of the jam to the knob side of the jam. Now the top of the door hits the top of the jam ~8" from the knob side of the jam. The vertical sides of the jam are level, but the top and bottom have a bubble whose leading edge is slightly outside the marks. Two possible contributing factors are that the house is suspended over a crawl space and that there are no support, cinder block piers under the Master Bedroom (~16' span from outside wall to double cinder blocked piers supporting the other wall) and that just inside the bathroom door is a Jaccuzzi bath. The builder must have recognized the additional weight of the bath and placed a single cinder block pier in the crawl space very near the bath. The underside of the floor joist adjacent to the pier (and possibly directly under the door frame) has the same/similar bubble location as the top/bottom of the door jam. With the cooler weather we have used bath more and this also seems to possibly have contributed to the door not closing. I have my opinions as to how to fix the problem, but I'd like another perspective.

QUESTION: With the limited information given above, what should I/builder do to rectify the problem and not just shave a portion off the door to resolve one of the symptoms?

Is the builder still willing to warranty your home at this point? If so just tell him to make the necessary repairs, it isn't you job to figure out a fix for his error. If not in warranty try getting a bottle jack and some shoring under that joist. Jack it up a small amount to see if you can get rid of the bow, then shim between the cinder blocks and the joist.