Calculation of the Effective Roof Area

The effective roof area is entered as the "Area (A) in m²" in the drainage calculation.

In accordance with DIN 1986-100 14.2.4.1, the effective roof area is defined as the roof area projected in plan.

Roof area calculation for a parapet roof

Practical tip: If rainwater flows onto the roof area from a surrounding parapet, for example, the area of the parapet must also be taken into account when determining the effective roof area.

Effective facade area

During planning it must be checked whether wind-driven rain on facades affects the rainwater discharge into the drainage system. If wind action has to be considered, the effective area shall be calculated in accordance with DIN EN 12056-3:2001-01, 4.3, Table 3.

In that case, 50% of the vertical facade area is taken into account as additional necessary discharge on the roof area located below.