Cracks in the Roof of Prefabricated Houses

There are several main reasons for cracks appearing in the roofs of prefabricated houses:

Renovation of Prefabricated Panels in Old Houses

In the renovation of old houses, prefabricated panels are a relatively common building material. These panels have gaps in the middle during manufacturing, which gives them a certain degree of inherent instability. Over long-term use, factors such as temperature changes, building settlement, and external forces can cause the connection points between the prefabricated panels to loosen and experience stress changes, leading to cracking on the roof. Such cracks are usually caused by the structural characteristics of the prefabricated panels themselves and their long service life, making them a relatively common issue in old houses.

Prefabricated Cast-in-Place Roofs in Rural Self-Built Houses

• Rapid Shrinkage: In rural self-built houses, the use of prefabricated cast-in-place roofs is quite common. After concrete is poured onto the roof, it goes through a setting period, also known as the shrinkage period, during which curing is required. When the weather is hot, the moisture on the surface of the concrete evaporates more quickly, causing the internal moisture of the concrete to be lost too fast and thus accelerating the setting speed of the concrete. At this time, the air bubbles inside the concrete cannot be squeezed out in a timely manner. Over time, these air bubbles gradually burst, exerting an expanding force on the concrete and eventually forming cracks.
• Unsatisfactory Rebar Placement: Rebar plays a crucial tensile role in concrete, enhancing its overall strength and stability. However, if the rebar is not placed properly during construction, such as adding rebar haphazardly or not arranging it according to design requirements, it can alter the overall tensile force distribution within the concrete. During the shrinkage and setting of the concrete, due to inconsistent tensile forces, different parts will experience different stresses, resulting in cracks. Even small components like the electrical boxes for adding lights in the middle of the house can potentially change the tensile force distribution of the concrete and lead to cracks.

Assembly Construction Techniques in New Houses

Taking the 3D steel truss floor panel assembly construction technique used in the Shangchengfu community in Liangshan County as an example, cracks usually appear at the splicing positions of the prefabricated bottom formwork panels. This is because during the splicing process, stress changes occur between the prefabricated bottom formwork panels, and the bonding strength between the panels may not meet the expected standards. When affected by external forces or temperature changes, regular fine cracks are likely to appear. However, such cracking generally only occurs on the bottom formwork panels, which serve as auxiliary structures, and not on the load-bearing parts of the house. Therefore, the safety of the main structure of the house is usually not affected.