| Crack Type | Morphology | Typical Width | Severity Index | | :--- | :--- | :--- | :--- | | | Hairline vertical/horizontal at frame edge; no displacement | < 0.5 mm | Low | | Type II (Seasonal) | Recurring straight crack; opens in winter, closes in summer | 0.5 - 1.5 mm | Moderate | | Type III (Structural) | Diagonal from corners; step-cracking in masonry; visible displacement | > 1.5 mm or tapered | High | | Type IV (Moisture) | Accompanying paint bubbling, efflorescence, or soft drywall | Variable | Critical |
Diagonal cracks propagating from the upper or lower corners of the window frame are classic indicators of differential foundation settlement or lateral wind loading. As the structural header above the window deflects or the sill settles unevenly, the rectangular opening distorts into a parallelogram, concentrating tensile stress at the corners. These cracks are typically wider at one end (e.g., 1-3 mm) and taper to a hairline. cracks around window frame
The primary causes of cracking can be categorized into four domains: | Crack Type | Morphology | Typical Width