Within a year of purchasing our new home the drywall ceiling started to separate from the wall. This occurs in most of the second floor (two story house) and the interior walls only. Two spots are the worst separating as much as 1/2 inch with the other ceiling joints cracking with minor separation. The ceiling separates from the wall in the winter and comes back together in the spring until the next winter. This is the third winter in our new home and it has happened every year. The builder (large national name) has had multiple people look at it. One of them suspected that the roof trusses were not secured properly. Does any one know what could be causing this?