A common non-structural cause is the "drywall butt joint" positioned directly over the window edge. If drywall sheets are hung without proper staggering, the natural seam may align with the frame. Without adequate tape and compound reinforcement, this seam cracks inevitably. Additionally, insufficient shimming or over-tightening of fasteners can pre-stress the frame, inducing immediate cracking after initial occupancy.
An Analysis of the Etiology, Diagnostic Classification, and Remediation of Cracks around Window Frames in Residential Buildings cracks around window frame
Immediate engineering assessment is required. The window is a symptom, not the cause. Remediation may involve under-pinning the foundation, installing steel mullions, or rebuilding the header. After structural repair, the window must be re-shimmed and re-fastened before finishing. A common non-structural cause is the "drywall butt