Two-story house with roof trusses.

What's happening: Seasonal truss uplift. Roof trusses expand/contract with humidity changes more than the 2×4 interior partitions. In winter (dry), trusses shrink upward, pulling away from the ceiling drywall and creating the gap. In summer (humid), they swell back down, closing the gap.

The real fix:

1. Stop mudding the gap. It will always crack again.

1. Install resilient channel or hat channel perpendicular to the trusses at the ceiling edge, allowing the drywall to float independently of truss movement.

1. OR use flexible trim: Remove the existing drywall edge, install a flexible PVC or vinyl trim strip that can compress/expand with movement.

1. Best solution: Install truss uplift clips (like USG's "Truss Uplift Clip") where the drywall attaches to the trusses. These allow 1/4" vertical movement while maintaining the ceiling connection.

Code note: This isn't a structural issue requiring a licensed engineer, but if you're modifying ceiling assemblies, ensure any new fasteners into trusses follow manufacturer spacing requirements (typically 16" o.c. for drywall).

The key is accommodating movement rather than fighting it. Any rigid connection (mud, screws alone) will fail repeatedly.

What's Happening: Truss Uplift (Arching) Your roof trusses are bowing upward in winter. The bottom chord stays warm and dry (buried in attic insulation), while the top chords are cold and absorb moisture, causing them to expand. This differential movement forces the bottom chord to lift—often ¼" to ¾" at the center span. Since interior partition walls are nailed to the truss bottom chord, the ceiling (attached to the wall) tears away, creating the gap. Mudding it only masks the symptom; the truss will lift again next winter, cracking the repair.

The Real Fix: Decouple the Ceiling from the Truss at Partitions Do not nail the ceiling drywall to the truss bottom chord within 16"–24" of interior partition walls.

Implementation (New Work or Retrofit):

1. Remove fasteners: Cut drywall screws/nails securing the ceiling to the truss bottom chord for the first 24" out from the partition wall.
2. Install Truss Clips (e.g., Simpson LTC, USP LTC): Fasten clips to the top plate of the partition wall (into studs). The clip's vertical leg has a slot allowing the truss chord to move up/down independently.
3. Re-fasten ceiling: Screw the ceiling drywall to the clip's horizontal leg (or use 1x3 backing on the wall top plate screwed to the clip).
4. Float the corner: Tape the joint with paper tape and setting-type compound. Use a "floating corner" technique (no tape on the wall, or use a vinyl corner bead with a tear-away flange) to allow slight seasonal flex without cracking.

Code Reference: IRC R802.10.2 / IBC 2303.4.5 require trusses to be installed per design drawings. Truss manufacturers (TPI/WTCA) universally require bottom chord lateral restraint only at bearing points, not at interior partitions. Nailing partitions to chords violates the engineering.

Critical Check: Verify the partition walls are non-bearing. If they carry roof/floor load, they must stay tight to the truss; uplift indicates a structural defect (undersized truss, missing bearing, or wall settlement) requiring an engineer.

Cost: ~$2–$3/clip. One-time fix. Stop mudding.