Cracks in the Roof of Prefabricated Panel Houses

Cracks in the roof of prefabricated panel houses need to be comprehensively evaluated and addressed based on their type, characteristics, and degree of danger.

Types and Characteristics of Cracks

1. Shrinkage Cracks: These occur during the production of prefabricated panels when the cement hydration reaction causes volume shrinkage. When the shrinkage stress exceeds the tensile strength of the concrete, cracks form. These cracks are fine, with widths mostly ranging from 0.05 to 0.2 millimeters, evenly distributed, and generally have a minor impact on structural safety.
2. Temperature Cracks: Changes in ambient temperature cause the prefabricated panels to expand and contract. When the temperature stress becomes excessive under structural constraints, cracks appear. These are commonly found on the top floor of houses, often distributed in a regular diagonal or horizontal pattern. They may be more pronounced in winter and generally do not affect structural safety but can lead to water leakage issues.
3. Settlement Cracks: When slight uneven settlement occurs in the house foundation, cracks may form in the prefabricated panels. These cracks are generally wider, may extend from the bottom to the top of the panel, and exhibit a certain directional pattern related to the direction of settlement, having a significant impact on structural safety.

Criteria for Dangerous Cracks

According to the "Technical Guidelines for Structural Safety Inspection of Self-built Houses," cracks in prefabricated panels exceeding 1 millimeter require vigilance. The location of the crack is also a key factor in assessing the degree of danger. Stress cracks, such as horizontal cracks that appear when the roof sags, should be noted even if they are only 0.8 millimeters wide. If a crack extends from the roof to two-thirds of the wall height or is exactly on a load-bearing beam, the danger factor doubles. If the crack continues to lengthen and widen, even if it has not reached 1 millimeter, a professional organization should be consulted for inspection.

Crack Treatment

1. Fine Cracks: Cracks as thin as hair can be directly sealed with glue to prevent water penetration and further expansion.
2. Medium Cracks: Special adhesive should be injected, which takes 72 hours to dry. During construction, attention should be paid to panel joint treatment. When installing prefabricated panels, a 10 - 15 millimeter thick mortar layer should be applied to enhance structural stability.
3. Severe Cracks: If the cracks are wide or continue to expand, potentially involving structural safety issues, the use of the relevant area should be immediately stopped, and a professional organization should be contacted for structural safety assessment and repair.