Prefabricated House Roof Drainage Design

The design of roof drainage for prefabricated houses requires comprehensive consideration of key elements such as drainage methods, drainage slopes, drainage outlet arrangements, and the design of gutters and rainwater pipes. Specific design points are as follows:

1. Selection of Drainage Methods
Determine the drainage form based on building height: Buildings with an eave height of ≤10m can use unorganized drainage (free water dispersion), but attention should be paid to the issue of rainwater splashing. Buildings with an eave height of >10m or high-rise buildings must use an organized drainage system. Organized drainage collects rainwater through gutters and guides it to ground or underground drainage systems via rainwater pipes, effectively preventing rainwater from splashing and contaminating walls or affecting pedestrian safety. As a core structure, gutters need to be equipped with covers to prevent leaf blockages and have maintenance platforms reserved for easy later upkeep.

2. Control of Drainage Slopes
The roof slope should be set according to material characteristics: For rolled roofing waterproofing, the slope should be 2%-3%, and for concrete roofs, it should be 1%-2% to ensure rapid rainwater drainage. The flow length of gutters should not exceed 50 meters, and the slope should not be less than 0.003 (i.e., 3‰) to avoid water accumulation and leakage. If the gutter length exceeds the limit, additional drainage outlets or slope adjustments are required.

3. Specifications for Drainage Outlet Arrangement
The spacing between drainage outlets should not exceed 24 meters, and each catchment area should be controlled within 200 square meters. Specific parameters should refer to the "Technical Code for Roof Engineering" GB50345. The location of drainage outlets should avoid structural weak points and be equipped with filters to prevent blockages from debris.

4. Key Points of Gutter Design

• Types and Materials: Gutters are divided into internal gutters (hidden inside the eaves) and external gutters (exposed outside the eaves). Materials include galvanized iron sheets, colored aluminum alloys, stainless steel, and PVC resins, etc., which should be selected according to architectural style and durability requirements.
• Size Calculation: The net width of gutters should not be less than 200 millimeters, and their cross-sectional dimensions should be determined through the rainstorm intensity formula Q=ψ·q·F, where ψ is the runoff coefficient, q is the design rainstorm intensity, and F is the catchment area.
• Waterproofing Treatment: The waterproof layer should be constructed simultaneously with the roof, with emphasis on reinforcing the gutter joint areas. In cold regions, electric tracing cables can be laid inside gutters to prevent ice and snow accumulation and blockages.
• Structural Details:
  • Prefabricated concrete gutters require an additional rolled layer, with the waterproof layer pasted on the upper side and fixed with cement nails, and the side seams filled with sealing materials.
  • Block gutters require an additional reinforced layer to be laid, with bituminous hemp fibers and rolled materials pasted under the waterproof layer to form double protection.
  • For finished gutters, ensure the welding quality of drainage outlets, grind the welds to be flat, and fix the gutter plates to the roof panels with self-tapping screws or rivets.

5. Requirements for Rainwater Pipe Design
The diameter of rainwater pipes should not be less than 100 millimeters, and their diameters should be determined through the rainstorm intensity formula. Rainwater pipes should be installed vertically, with spacing corresponding to that of drainage outlets to avoid poor drainage.