I have seen several homes each winter season with the phenomenon called Truss Uplift. This is often very disconcerting to the home owner, however, it is not something that is to be feared. Essentially, what is seen in the home is gaps between the top floor ceilings and the interior walls. These gaps can be as much as two inches in extreme cases. More often that not it is much smaller than that. This phenomenon is often mistaken for settling of the floors which, in turn, lowers the walls from the ceilings. Truss Uplift is exactly the opposite in that the ceiling is actually lifting off the walls.
Trusses, unlike previous building techniques where rafters and ceiling joists were manually crafted, are pre-engineered and pre-fabricated. Engineered trusses are lighter but considerably stronger than their predecessor and are held together with a fastener called gusset plates. When a home is built by modern building standards there is a considerable amount of insulation that is blown into the attic. This covers the bottom chord of the trusses and, in turn, the bottom chord remains dry and warm. The same modern building standards have us creating greater ventilation in the attic leaving the top chords in a cold and often moist (Humid), environment. The cold and moist air causes the top chords to expand while the bottom chords are shrinking due to warm and dry air that they lay in. This causes the bottom chord of the trusses to arch upwards thereby lifting the ceiling off the interior walls.
Although this phenomenon is not aesthetically pleasing there is nothing to be concerned about. It does not cause any structural problems with the home and it will stop occurring when the warmer temperatures arrive. There is no resolution to the problem so calling a contractor in will not help. This is one phenomenon that, unfortunately, you will need to live with. There are methods to minimizing this problem during the construction phase. Once the home is built, however, there are few solutions to hiding the gaps. Some quick tips can be found here. This is only one of many sites that can provide ideas.
Truss Uplift is not always the cause of gaps between walls and ceilings but if it is the cause of yours you can rest assured your home is still safe and sound.