Install a reliable flat roof drainage in an attic

It is due to the design and nature of the matter that an attic forms a kind of tub on a roof. This circumferential barrier for the water drainage must be through a professionally dimensioned flat roof drainage. There are several construction forms to choose from in the implementation;.

On the inner roof surface or in the side edge of the roof

A parapet as a circumferential roof border creates a kind of basin or tub in which rain and melt water collects. In order to divert it, the following two drainage routes are generally possible:

1. External drainage
2. An internal drainage

Discharges leading to the outside run through the roof border, i.e. the structure of the parapet laterally and horizontally to the outside. These openings have always been installed as emergency overflows in the parapet with additional internal drainage. The lateral pipes usually lead through the attic wall and end with sufficient drip distance to the facade below as a beak drainage or in downpipes.

Roof gullies take in the water

The flat roof with a parapet always has a slope of one to two percent. The drainage system must take this into account. Generally speaking, there must be greater drainage capacity on the side where the water flows.

With an outside drainage, the flow is obvious. With internal drainage, roof gullies take in the water. In addition to a linear slope, you can also work with recesses around the drainage hole.

Two physical discharge models

The following two types of installation are used for drainage on a flat roof:

Gravity drainage

In the case of gravity drainage, "oversized " pipe cross-sections are installed. They are calculated in such a way that they do not fill up to more than a third even with peak loads. This guarantees an effective and rapid drainage.

Pressure drainage

Pressure drainage uses gravity to create a negative pressure. The roof gullies are led horizontally in collecting pipes to a downpipe with a small cross-section. There the water rushes up to the mouth of the downpipe in the underground pipe of the house. The widening there causes a brief backflow effect when the system is filled, which leads to a kind of "plugging". This falls in one swing into the resulting negative pressure at the mouth. This increases the flow rate of the water.

Tips & Tricks For the installation of a pressure drain you need a minimum roof height in order to be able to generate sufficient negative pressure.