How to Prefabricate the Roof of an 8x6-Meter Span House

The prefabrication of the roof for an 8×6-meter span house requires systematic planning in terms of selection, construction, and safety design. The specific plan is as follows:

I. Selection and Parameter Design of Prefabricated Panels

1. Span Adaptation: For the 6-meter direction, select C30 concrete prefabricated hollow panels with spans of 3.6m, 3.9m, or 4.2m, and meet the total span requirements through splicing. The bearing length at the panel end should be ≥120mm to ensure support stability.
2. Load-Bearing Capacity and Reinforcement:
   • Select Grade II panels (load-bearing capacity of 2.0kN/m²) with a concrete compressive strength of ≥30MPa.
   • Longitudinal reinforcement should use HRB400E grade Φ10mm @150mm, and distribution reinforcement should use HPB300 grade φ6mm @200mm. Reinforcement within 300mm of the panel end should be densified to φ10mm @100mm to enhance local crack resistance.

II. Construction Process and Key Steps

1. Base Layer Treatment:
   • Clean the roof base layer and remove any ineffective waterproof layers. Ensure a flatness deviation of ≤5mm/2m and a drainage slope of ≥2% (corresponding to a height difference of 0.3~0.6 meters for a 6-meter span). Level with cement mortar.
2. Laying of Prefabricated Panels:
   • Dry Laying Method: Set brick piers or prefabricated blocks (height of 100~200mm) at the supports. Lay the prefabricated panels to form an elevated layer, which provides good thermal insulation but requires stable support points.
   • Wet Laying Method: Lay a 20~30mm thick layer of cement mortar on the base layer, press in the prefabricated panels, and adjust the flatness. The height difference between adjacent panels should be ≤3mm, offering strong integrity but slightly poorer thermal insulation.
3. Panel Joint Treatment:
   • The panel joints should be 20~50mm wide and filled with C35 fine aggregate concrete (mixed with a micro-expansion agent). For the wet laying method, joint filling should be done after the mortar reaches the required strength.

III. Structural Safety and Drainage Design

1. Seismic Resistance and Load:
   • Design for seismic resistance at a magnitude of 7 degrees, with a roof live load of 2.0kN/m². Since the prefabricated panels are not integrally connected to the walls, reinforcement should be densified to enhance local stability and prevent cracks caused by foundation settlement.
2. Drainage System:
   • Adopt an organized drainage system with an eaves gutter width of 300mm and a slope of 5%. The height of the roof ridge for a double-pitched roof should be calculated as span × slope ÷ 2 (e.g., for a slope of 15%30%, the roof ridge height for a 6-meter span would be 0.450.9 meters).

IV. Material and Equipment Preparation

1. Auxiliary Materials:
   • Waterproof Layer: 3mm thick SBS modified asphalt membrane (heat resistance ≥90℃, low-temperature flexibility with no cracks at -20℃).
   • Thermal Insulation Layer: 100mm thick extruded polystyrene board (thermal conductivity ≤0.030W/(m·K)).
   • Protective Layer: 40mm thick C20 fine aggregate concrete (with φ4mm @150mm×150mm steel reinforcement mesh inside).
2. Construction Equipment: Equip with a 5-ton truck crane, level gauge, vibrating rod (φ30mm), etc. Construction can only commence when the strength of the roof ring beam reaches at least 75% of the design value.

Precautions: Regularly inspect the stability of panel joints and supports, control construction loads not to exceed the design value (0.5~2.0kN/㎡), and it is recommended to consult a structural engineer before construction.