How to Waterproof Prefabricated Houses

Waterproofing for prefabricated houses requires tailored solutions based on structural types, with the core being a combination of structural measures and material sealing to achieve both water prevention and drainage.

1. Waterproofing for Prefabricated Panel Roofs

1. Panel Joint Treatment
   Prefabricated panels are typically 50 centimeters wide. When joining them, wire mesh should be used to reinforce the gaps between panels, and 5 to 8 centimeters of concrete should be poured to prevent edge cracking due to temperature changes or settlement. This step is fundamental to roof waterproofing; improper panel joint treatment can lead to subsequent waterproofing layer failure due to base layer cracking.

2. Waterproof Layer Application
   The "three-coating, two-laying" process is adopted: first, apply three coats of waterproof coating (such as JS waterproof coating or leak-stopping agent) to form the base layer, then lay two layers of waterproof membrane (such as asphalt + felt). For large areas, membranes are preferred, while coatings can enhance sealing at small areas or complex nodes. Ensure the waterproof layer covers protruding parts like parapet walls and chimneys to prevent "water channeling."

3. Drainage Optimization
   If direct waterproofing costs are too high, consider adding a roof cover (such as metal tiles or color-coated steel sheets) or pouring a cast-in-place slab to replace the original prefabricated panels, reducing leakage risks through a monolithic structure. Also, check that the roof slope meets drainage requirements (generally ≥2%) to avoid water accumulation.

2. Waterproofing for Prefabricated Buildings (e.g., Prefabricated Exterior Walls)

1. Design Philosophy
   Follow the principle of "diverting water is better than blocking it, and draining is better than waterproofing" by setting drainage paths to direct infiltrated water outdoors, rather than relying solely on material barriers. For example, pressure-relief cavities are reserved at joints of prefabricated wall panels, allowing a small amount of infiltrated water to flow along the cavities to drainage pipes for discharge.

2. Joint Treatment

   • Cast-in-place Exterior Hanging (PCF Panels): A drainage cavity is set on the exterior side and sealed with weather-resistant silicone, while the interior side relies on the self-waterproofing of cast-in-place concrete. Regularly check for cavity blockages to prevent water backup.
   • Externally Hung Prefabricated Wall Panels: A three-tier waterproofing system is used: weather-resistant silicone on the exterior, a pressure-relief cavity in the middle, and rubber waterstops on the interior. At cross joints, additional polyurethane waterproof coating is applied, and drainage pipes are installed every three floors to ensure timely water discharge.

3. General Precautions

1. Combination of Structure and Materials
   Due to the numerous joints in prefabricated structures, structural measures like tongue-and-groove joints and pressure-relief cavities should be used to reduce water infiltration paths, while materials such as rubber waterstops and weather-resistant sealants should seal key nodes. For example, the perimeter of door and window openings should be filled with waterproof mortar and reinforced with exterior-mounted waterproof membranes.

2. Construction Integrity
   The roof waterproof layer should be applied continuously to avoid localized repairs causing "water channeling." For example, the junction between the parapet wall and the roof should be rounded and coated with waterproofing extending at least 30 centimeters up the wall.

The specific solution should be selected based on the house type (e.g., bungalow, multi-story prefabricated building) and budget. For complex projects, it is advisable to entrust a professional waterproofing team for design and construction.