In the case of sloping roof surfaces, rainwater is drained to the external gutters and then into the rainwater downpipes. Gutters and downpipes are defined in DIN 18460, 18461 and 18469 with regard to their terms, masses and properties. A distinction is made in particular between suspended gutters and concealed gutters (standgutters).
In terms of geometry, gutters can have semi-circular or box-shaped cross-sections and are made of metal or plastic. The rainwater downpipes are also standardised with a round or square diameter.
measuring the necessary cross-sections and diameters, the "rain output" (r) is used, which indicates the maximum amount of rain in litres per sec/ha of roof floor area. For calculations, the rule of thumb r=300l/(s*ha) can be used for non-critical design situations for curtain gutters.
For the final dimensioning, however, the runoff coefficient (DIN 1986 T2) must be taken into account.
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