Do you notice cracking at the wall to ceiling intersections in your home that seem to worsen in the winter and all but disappear in the summer? Your home is likely experiencing a phenomenon known as truss lift.
Trusses are engineered assemblies made of wood or metal used to provide roof framing that transfers the roof load to the outside walls of your home. Due to easy availability and low cost, most homes use wood trusses. If you look in your attic and see many web-like triangles fastened at the joints with wood or metal plates, your home is constructed with wood trusses.
The bottom member or chord is typically surrounded by insulation keeping this piece warm while the rest of the truss is exposed to the cold attic air. This temperature disparity causes the truss parts to expand or contract at different rates resulting in movement of the truss and the attached drywall. In the summer, all parts of the truss return to the same temperature causing the drywall separations close.
This condition does not affect the structural integrity of the house in any way, it is strictly a cosmetic annoyance. The cracks can be sealed with caulking materials that will remain flexible and can be painted. Decorative trim (such as crown molding) can also be installed that is attached only to the ceiling and will move up and down as the trusses flex concealing the cracks.