Can Old Houses with Prefabricated Slabs Add Floors

Old houses with prefabricated slabs can have additional floors added, but specific conditions must be met and strict compliance with standardized procedures is required.

I. Structural Prerequisites and Safety Inspections

1. Support Structure Requirements: Adding floors must be based on columns, beams, and cantilever beams as support foundations to ensure a clear load transfer path. If the original building lacks a complete frame structure, adding floors may lead to partial collapse.
2. Necessity of Professional Inspections: Before adding floors, a professional team must be commissioned to conduct a comprehensive inspection of the original prefabricated slabs, focusing on identifying defects such as cracks, steel bar corrosion, and concrete carbonation. If the floor slab has structural damage, it must be repaired or reinforced first.

II. Construction Specifications and Material Requirements

1. Interface Treatment:
   • If concrete is poured directly, an electric pickaxe must be used to chisel out a groove 12 centimeters wide and 10 centimeters high on the top of the prefabricated slab to ensure reliable embedding of the newly added steel bars with the wall;
   • The surface of the original floor slab must be chiseled into a rough finish and fully moistened, and pure cement paste must be applied as an interface agent to enhance the bond strength between the new and old concrete.
2. Steel Bar Configuration:
   • The steel bars for adding floors should be welded or tied to the original prefabricated slab steel bars. It is recommended to use Grade III deformed steel bars laid out in a grid with a spacing of 150 millimeters;
   • For hidden beam sections, 16-millimeter thick steel bars must be used to ensure local bending resistance.
3. Concrete Performance:
   • C30 grade concrete must be selected, as its compressive strength can meet the load requirements after adding floors;
   • After pouring, the concrete must be immediately covered with plastic film for moisture retention and curing for more than 15 days to prevent cracking.

III. Key Restrictions

1. Prohibited Scenarios for Adding Floors:
   • If there are through cracks in the walls or the foundation depth is less than 1.2 meters, adding floors is strictly prohibited;
   • If the original building was not designed with seismic structural measures or the joints of the prefabricated slabs were not properly treated, the risk is extremely high.
2. Load Calculation: The bearing capacity of the original prefabricated slab must be verified through structural calculations. The total load after adding floors (including live loads) must not exceed 80% of the original design value.

IV. Legal and Approval Requirements
The floor addition project must be submitted to the local planning department for approval, and a construction project planning permit must be obtained before construction can commence. Unauthorized floor addition without approval is considered illegal construction and may face penalties such as forced demolition and fines.

Summary: Adding floors to prefabricated slab houses must prioritize structural safety and achieve a balance between safety and compliance through professional inspections, standardized construction, and legal approvals.