Answers

Usually cracks in wallboard or ceilings indicate movement or settling in the structure. This is not uncommon in new home construction as footings and foundations cure and the moisture content stabilizes in the framing. It can also be caused by frost heaving in colder climates during freeze / thaw cycles. If your builder won't address it, hire a structural engineer. An engineer should be able to identify what is causing the movement to occur. Good Luck!

this is very common in new homes.  I would work with the builder first.  That is the easiest way to correct the problem.  They are in the buiness of building home and need good referrals  I would try the builder again and you would be surprised at the outcome with a softer approach. 

Philip Anderson

Berkeley Ca