Conversion of Prefabricated Slab Houses to Cast-in-Place Slab Houses

Prefabricated slab houses can be converted to cast-in-place slab houses, but comprehensive evaluation and cautious implementation are required.

I. Necessity of Conversion
Houses built in the 1980s-1990s and earlier often used prefabricated hollow or perforated slabs, which suffer from poor integrity, insufficient load-bearing capacity, and weak earthquake resistance. Cast-in-place slabs, with their high overall stiffness, strong continuity, good earthquake resilience, and excellent waterproofing, are the preferred renovation solution recommended by structural engineers, especially for scenarios requiring enhanced structural safety or improved functionality.

II. Key Steps Before Conversion

1. Professional Structural Assessment:

   • Commission a qualified testing agency to conduct a comprehensive inspection of the house, including concrete strength, steel reinforcement corrosion, slab joint conditions, wall verticality, and foundation settlement.
   • Focus on checking whether the lap length of the prefabricated slab ends on the wall (beam) is ≥80mm and whether there are severe cracks or exposed reinforcement at the slab bottom.
   • Recalculate the floor load based on the post-renovation usage function, review the load-bearing capacity of the existing walls, columns, and foundations, and assess whether simultaneous reinforcement is needed.

2. Conversion Path Selection:

   • Retain Prefabricated Slab + Add Composite Layer: Pour a cast-in-place layer directly onto the original prefabricated slab, minimizing damage and suitable for houses with good structural conditions.
   • Rebuild After Removing Prefabricated Slabs:
     • Remove Prefabricated Slabs: Clear the floor to ensure no residual structures affect subsequent construction.
     • Install Formwork: The formwork must have a flat surface and serve as the support system for the cast-in-place layer.
     • Reinforcement Binding: The reinforcement must be inserted and welded to the walls and columns to ensure structural integrity.
     • Pour Concrete: Remove the formwork after the concrete dries naturally to complete the floor construction.

III. Limitations of Conversion

1. Cost and Duration: Conversion involves structural assessment, reinforcement design, construction, and material costs, making it relatively expensive; the construction period is longer, requiring coordination of construction sequences to minimize impacts on occupancy.
2. House Disturbance: Removing prefabricated slabs may cause vibrations to walls and beams, necessitating temporary support measures to prevent structural instability.
3. Technical Feasibility: The feasibility of conversion must be assessed based on the actual condition of the house (e.g., foundation settlement, wall damage) to avoid structural damage due to increased loads.

IV. Decision-Making Recommendations
Before conversion, comprehensively consider the building's current condition, budget, and technical conditions, prioritizing safety over cost-effectiveness. If the house has severe structural defects or requires significant functional upgrades, conversion is highly valuable; if only local repairs are needed or the budget is limited, other reinforcement methods (e.g., carbon fiber cloth reinforcement, adding structural columns) can be considered.