The attic needs an emergency overflow

Due to its design, an attic creates a kind of tub on a flat roof. Heavy rain or heavy snowdrifts can accumulate an amount of water that overloads the normal drainage system. In these moments, the emergency overflow takes over so that there is no standing water and roof damage.

The normal drainage must be supplemented

In earlier times, a few holes were drilled in parapets through which the water was drained in the form of spouts. This random principle harbors the risk that the waterproofing of the parapet will decompose and that backwater and puddles will form on the roof in the event of heavy rain or high levels of meltwater.

  • Also read - A parapet usually needs a cover plate
  • Also read - A parapet needs a statically correctly calculated cover
  • Also read - Construction of the parapet

The DIN 1986-100 and DIN EN 12056-3 standards now make emergency drainage for flat roofs mandatory. In principle, drainage in the structure of the parapet to the outside must continue to be considered. Water drains placed inside are no longer built and planned. The following two construction variants are possible:

1. One or more gullies in the attic take in water and direct it horizontally through inclined pipes through a penetration through the parapet.

2. One or more "holes " in the attic at the lowest point of the roof (sloping or sloping valley) offer the running water the drainage path to the downpipe or spout.

With both variants, the draining water can be collected and recycled. The normal drainage capacity is calculated based on the roof area and the average annual rainfall at the construction site.

Thunderstorms and thunderstorms lead in exceptional cases to an extreme increase in the amount of water that collects on a roof with a border. In this case, the emergency drainage forms the "silent capacity reserve".

Limit weight load from standing water

In addition to the formation of puddles and damage due to waterlogging, the emergency drainage must also be installed because of the potential weight load from standing water. For every ten centimeters of water level, one hundred kilograms weigh on one square meter of roof area. The emergency drainage must start automatically and at the latest when the water level is too high, which is statically calculated during planning.

Tips & Tricks Tests have shown that rectangular drains and spouts offer a much higher water flow rate than round pipes. Choose a rectangular shape for your emergency overflow to take advantage of this additional effect.