6.3.2 Air-termination systems for buildings with flat roofs

Flat roofs require a dimensionally stable and durable air-termination system. For flat roofs, the mesh method is generally used, whereby a meshed air-termination network is installed on the roof covering. The selection of the mesh size depends on the applicable protection class and the specifications in Table 4.1.3. Figure 6.2.1.3.1 shows a typical flat roof situation with an air-termination network installed.

Structure and design of an air-termination network
The air-termination network is spread across the roof covering and mechanically fastened to the roof edges, parapet and other support points. The mesh shape should be selected so that all roof structures to be protected are within the protection zone.
Air-termination conductors must be electrically conductive and connected to the parapet as an intrinsic component of the air-termination system. Thermally induced changes in the length of the parapet materials must be taken into account and the segments must be connected to each other using sliding plates.
The materials used in the air-termination network and air-termination conductors must be corrosion-resistant and electrically conductive, and must be able to withstand the mechanical stresses caused by wind and temperature cycles.

Protection of roof superstructures
Roof-mounted structures such as domelights, photovoltaic modules and fans must be protected by the air-termination network or additional local measures. How these superstructures are handled and classified is covered in chapter 6.3.7.
Figure 6.3.2.1 illustrates the practical combination of a mesh with air-termination rods for a local extension of the protection zone around exposed components.
If melting of the material in the parapet area is unacceptable, an additional active air-termination system is required, e.g. air-termination tips designed according to the rolling sphere method; see Figure 6.3.2.2.