Cracks in the Roof of Prefabricated Houses

Cracks in the roof of prefabricated houses need to be addressed in a targeted manner based on their causes and degree of danger.

Causes of Cracks

• Process Issues: When using prefabricated construction techniques, the joints of the prefabricated bottom formwork panels are prone to regular fine cracks due to stress changes and insufficient bonding strength.
• Material Characteristics:
  • Shrinkage Cracks: These occur when the volume shrinks due to cement hydration reactions. When the shrinkage stress exceeds the tensile strength of the concrete, fine cracks (with widths ranging from 0.05 to 0.2 millimeters) form uniformly.
  • Temperature Cracks: Changes in ambient temperature cause the prefabricated panels to expand and contract. Excessive temperature stress under structural constraints leads to the formation of these cracks, which are commonly found on the top floor, often slanting or horizontally distributed, and are more pronounced in winter.
  • Settlement Cracks: These are caused by slight uneven settlement of the house foundation. The cracks are relatively wide and may extend from the bottom of the panel to the top, with their direction related to the direction of settlement.

Assessing the Degree of Danger

• Crack Width: According to the Technical Guidelines for Structural Safety Inspection of Self-built Houses, cracks exceeding 1 millimeter require vigilance (1 millimeter is twice the thickness of a bank card); stress cracks (such as horizontal cracks when the roof is sagging) exceeding 0.8 millimeters also warrant attention.
• Crack Location: If the crack extends from the roof to two-thirds of the wall height or is located on a load-bearing beam, the danger factor doubles.
• Development: If the crack continues to lengthen and widen, even if it does not reach 1 millimeter, a professional inspection is necessary; if the crack width exceeds 0.3 millimeters, continues to develop, or is accompanied by abnormalities such as house tilting, it may indicate a structural problem and requires timely inspection and assessment.

Treatment Methods

• Fine Cracks: Cracks as thin as hair can be directly sealed with glue.
• Medium Cracks: Special adhesive needs to be injected, and it takes 72 hours to dry.
• Construction Points: When installing prefabricated panels, the treatment of panel joints is crucial. A 10 to 15-millimeter-thick mortar layer should be applied to ensure bonding strength and reduce the risk of cracks.