Roof drainage

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Overflowing gutter
Instead of using a downpipe, rainwater can also be drained away using a rain drainage chain .

A roof drainage is a technical system for draining rainwater from roofs . A basic distinction is made between external and internal roof drainage. External systems consist of a rain gutter , accessories and a downpipe . It is used to avoid moisture penetration into the exterior or basement wall, impairment or contamination by spray or dripping water and to secure traffic routes against hazards emanating from precipitation or ice. It feeds the rainwater into the public drainage network , a rainwater harvesting system or rainwater infiltration . Internal roof drainage systems consist of gullies and downpipes, whereby the gullies can be connected via an internal gutter (trough).


Since July 2001, roof drainage systems have had to be examined for their adequate dimensioning using a hydraulic calculation.

For economic reasons and to ensure self-cleaning ability, only a medium rain event is used as a basis. According to DIN 1986-100, this is the local five-minute rainfall , which statistically falls once every five years and is measured in l / (s * ha).

Further influencing factors are the connected roof area, whereby the precipitation area projected into the floor plan is used, the runoff coefficient of roof areas (depending on the roof slope and the time delay between rainwater discharge and actual runoff) as well as influences from the channel length, channel angle, leaf catcher baskets and downpipe distortions that help reduce the Discharge capacity (see DIN 1986-100).

A drainage system is to be considered in the planning as a complete system from the rainwater catchment area via gutters and drains, the underground pipes to the sewer connection or the infiltration system.


The requirements, design, dimensioning and calculation bases are regulated in the following guidelines:

  • DIN EN 12 056-3 Gravity drainage systems inside buildings, Part 3 - Roof drainage, planning and dimensioning
  • DIN 1986-100 drainage systems for buildings and land, part 100 - Additional provisions to DIN EN 752 and DIN EN 12 056
  • DIN EN 612 hanging gutters and rainwater downpipes made of sheet metal; Terms, classification and requirements
  • DIN EN 1462 gutter bracket for hanging gutters; Requirements and testing
  • VDI 3806 Roof drainage with pressure flow > This guideline was withdrawn in 2009-01 and has been incorporated into DIN 1986-100.


  • Guidelines for the execution of metal roofs - external wall cladding and building plumbing work - technical rules for the plumbing trade from the Central Association of Sanitary, Heating, Air Conditioning.

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Wiktionary: Roof drainage  - explanations of meanings, word origins, synonyms, translations