Roof Drainage Design Information

• Gutter Design:
  • The water volume of the gutter is related to the diameter and number of downspouts.
  • The inner diameter of the downspout should not be less than 75mm, and the maximum catchment area for one downspout should be less than 200㎡.
• Drainage Outlet Setting:
  • The distance from the rainwater flowing to the drainage outlet is generally not more than 30m.
  • The setting of the drainage outlet also determines the division of the slope-finding area. When the slope-finding length of the roof is long, additional drainage outlets and internal drainage pipes can be added.
• Drainage Slope:
  • The structural slope for flat roofs should not be less than 3%, and the material slope should preferably be 2%.
  • The single-slope span greater than 9m should be provided with structural slope, with a slope not less than 3%.
  • The longitudinal slope of the gutter and eaves gutter should not be less than 1%, and the water drop difference at the gutter bottom should not exceed 200mm.
• Downspout Layout:
  • Downspouts should be arranged at the shady corners next to the balcony outer side or the air-conditioner shelf for easy maintenance.
  • The rainwater on the podium roof of high-rise buildings should be drained separately, and the balcony rainwater system should be set separately.

• Siphonic Roof Rainwater Drainage System:
  • Applicable to large roofs in areas with high rainstorm intensity.
  • Utilizes the height of the building roof and the potential energy of rainwater to create a siphonic effect, allowing rapid drainage of roof rainwater through pipe diameter changes and the formation of negative pressure in the pipeline.
• Green Roof Drainage System:
  • Green roofs require a dedicated drainage layer, such as a ceramic particle drainage layer or a special water storage and drainage layer.
  • The drainage layer should have good water retention and air permeability while meeting drainage requirements.

• Construction Key Points:
  • Strictly follow the design drawings and construction specifications during construction.
  • Ensure that the drainage facilities are installed securely, connected tightly, and without leakage.
  • Conduct a comprehensive inspection of the drainage system to ensure smooth drainage.
• Maintenance Requirements:
  • Regularly clean and maintain the drainage system to prevent clogging.
  • Check if the drainage slope has changed and adjust if necessary.
  • Repair or replace damaged drainage facilities in a timely manner.

minimum roof pitch for rain

The determination of the minimum roof pitch generally hinges on the roofing material utilized and the prevalent climatic conditions of the region. For a broad spectrum of materials, a minimum pitch of 2:12 is typically necessary to guarantee sufficient water drainage. Nevertheless, this standard may fluctuate depending on various factors, such as the quantity of precipitation or snowfall your area experiences.

Roof Pitch to Angle Chart