Adding a Bathroom to a Prefabricated Slab House

Adding a bathroom to a prefabricated slab house requires strict adherence to structural safety and waterproofing standards. The specific steps and precautions are as follows:

I. Floor Slab Reinforcement and Structural Safety

The load-bearing capacity of prefabricated slabs is limited, so reinforcing the floor slab is crucial when adding a new bathroom. A reinforcement plan must be determined through professional structural calculations, with common methods including:

1. Steel Mesh Reinforcement: Add horizontal and vertical steel mesh beneath the floor slab, fixed with chemical anchors or planted rebars to form a composite load-bearing structure.
2. Interlayer Panel Reinforcement: Lay high-strength fiber-reinforced panels (such as carbon fiber panels) or lightweight concrete interlayers to distribute the load to the surrounding load-bearing walls.
3. Upturned Beam Method: Pour concrete upturned beams on the prefabricated slab, with the beam ends supported on the load-bearing walls. Build partition walls on the beams to reduce direct pressure. Key Points: The reinforcement plan must comply with the "Building Structural Load Code". A structural engineer must conduct an on-site assessment before construction. Unauthorized drilling or removal of load-bearing components is strictly prohibited.

II. Wall Construction and Material Selection

1. Lightweight Materials: Prioritize lightweight bricks (density ≤ 800kg/m³) or aerated concrete blocks, with wall thickness not exceeding 120mm to reduce pressure on the floor slab.
2. Tie-in Treatment: At the junction of new and old walls, lay steel wire mesh (mesh size ≤ 10mm × 10mm) with a width of not less than 300mm to prevent crack propagation.
3. Lightweight Partition Wall Alternatives: If space is limited, use light steel keel gypsum board partition walls filled with sound insulation cotton, with a concrete waterstop at the bottom for moisture resistance.

III. Waterproofing and Drainage Systems

1. Waterproof Layer Construction:
   • Base Layer Treatment: After cleaning the prefabricated slab surface, apply a penetrating crystalline waterproof coating to form a crystalline sealing layer.
   • Waterproof Layer Structure: Sequentially lay a 1.5mm thick polyurethane waterproof coating (applied in two cross-coated layers) and a 20mm thick cement mortar protective layer.
   • Water Test: After the waterproof layer is completed, seal the floor drain, fill with water to a height of ≥ 20mm, and maintain for 72 hours without leakage to pass the test.
2. Drainage Pipe Design:
   • Sewage Pipe Diameter: Toilet sewage pipes ≥ 110mm, floor drain and washbasin drainage pipes ≥ 50mm to avoid blockages.
   • Long-Distance Drainage: If the bathroom is far from the main sewage pipe, install a sewage lift pump (such as the Shenglida 3 model), which must have automatic start-stop and anti-backflow functions.

IV. Ventilation and Equipment Selection

1. Forced Ventilation: Windowless bathrooms must be equipped with a silent exhaust fan (power ≤ 30W, noise ≤ 40dB) with an exhaust volume of ≥ 100m³/h. The exhaust outlet must be fitted with a check valve.
2. Equipment Layout: Rationally plan the movement paths of the toilet, shower area, and washbasin. The wall height should be determined according to the equipment type (e.g., shower area ≥ 2.2m, toilet area ≥ 2.0m).

V. Compliance and Safety Tips

1. Approval Process: Before construction, submit structural safety certificates to the property management and housing construction departments. Reinforcement procedures must be completed for any modifications to load-bearing walls.
2. Professional Construction: Must be carried out by a qualified team, with a focus on monitoring floor slab drilling (diameter ≤ 50mm) and rebar welding quality.
3. Long-Term Maintenance: Inspect the waterproof layer every 5 years and replace the seals of the sewage lift pump every 2 years to ensure system reliability.

Core Principle: Prioritize structural safety, emphasize both waterproofing and drainage, and combine compliant construction with long-term maintenance.