Many more recently built homes particularly splits and ranch style homes utilize scissor trusses for the vaulted attic structure. In the home inspection process I often run into small cracks in the drywall at the ceiling/wall joint or across the ridge of the ceiling. Generally these are not a concern, they are typically caused by what is called truss lift or truss spread. Drywall is not flexible. It tends to crack when pressure is applied to it. These cracks occur when the framing in the wall expands and contracts with seasonal changes. In the winter time cold temperatures will cause all materials to shrink. In addition winters in MN have very low humidity levels which dries out the wood and causes shrinkage. When the bottom cord of the truss is nestled in warm attic insulation it can cause differential shrinking which deforms the truss slightly causes the drywall to crack.
The newer lumber is derived from faster growing trees vs. lumber from the past. The result of a faster growing tree is larger growth rings which can lead to more shrinkage. Ever notice how framing in older houses is so much heavier and dense than todays 2x4s. It is because the wood took much longer to mature back then and growth rings are very close together. Hence less shrinkage. There is a way to combat this on interior walls that butt up to ceilings. The Moe-Tie is a piece of metal that is fastened to the vertical interior wall and not connected to the truss above. The ceiling drywall is installed and fastened to the Moe-Tie on the wall instead of the truss. It is then screwed into the truss 16″ or so back away from the wall allowing the drywall to flex. Here is a great article that has some visual aids to explain these ties.
Repairs can be attempted on these cracks but most times they will come back with the season changes. An expansion joint could be installed or repairing the crack with joint compound like Durabond 90 and Beadex Joint Tape may stop smaller cracks from forming again. I have heard in some cases a paintable silicone or latex caulking can be applied to the crack, smoothed and painted. This may allow some flexing.
If you see these types of cracks don’t worry your house is not going to fall down. This issue is a result of the truss design and very common in homes with vaulted ceilings.