Truss uplift! What are those cracks in my ceiling?
A home inspector may observe during a home inspection a crack in the corner of an interior ceiling made of drywall. The crack may be at the top of the wall, and it may appear very thin or narrow (a hairline crack).
Now, if there is a roof structure above this ceiling, the ceiling drywall may be attached/fastened to the ceiling joist (the boards that are above the drywall ceiling to which the drywall is attached). If that roof structure is made of trusses, then the cracking of the drywall may be caused by the trusses -- in what is referred to as "truss uplift." Truss uplift is NOT a major structural defect. Truss uplift occurs when the bottom chord of a roof truss bends upward and separates or cracks the interior drywall or plaster at the corner.
Truss uplift may occur when the truss is moving due to moisture conditions, temperature changes, or wind. In certain conditions, the bottom chord of the trusses may lift up ("uplift"), and that move upward may cause cracks to appear on the drywall below the truss. When a truss lifts up, the center of the bottom truss chord may lift up. The ceiling drywall is attached to the truss chords that move. In certain locations, the truss lifts up in the hot summer and creates a crack. Then in the cold winter, the truss settles back and closes the crack.
The solution may be that a contractor attaches the ceiling drywall without any fasteners into the bottom truss chord near the ceiling corner. This provides flexibility in the drywall at the corner. There are also clips and truss backing angles that can be installed. The key is to connect the drywall on the ceiling and the wall together while avoiding nailing or screwing them to the bottom of the trusses near the ceiling corner.