5.1.3 Air-termination systems for buildings
with flat roofs
The mesh method is used to design an air-termination system
for buildings with flat roofs (Figure 5.1.3.1). A meshed airtermination
network with a mesh size according to the class of
LPS is arranged on the roofing (Table 5.1.1.3).
Figure 5.1.3.2 illustrates the practical application of the
meshed air-termination system in combination with air-termination
rods to protect the structures mounted on the roof,
e.g. domelights, photovoltaic modules or fans. Chapter 5.1.8
shows how to deal with these roof-mounted structures.
Roof conductor holders on flat roofs are laid at intervals of approximately
1 m. The air-termination conductors are connected
to the roof parapet which is used as a natural component of
the air-termination system. As the temperature changes, so
does the length of the materials used for the roof parapet.
Therefore, the individual segments must be equipped with
“slide sheets”.
If the roof parapet is used as an air-termination system, these
individual segments must be permanently interconnected so
as to be electrically conductive without restricting their ability
to expand. This can be achieved by means of bridging braids,
brackets or cables (Figure 5.1.3.3).
The changes in length resulting from changes in temperature
must also be taken into account for air-termination conductors
and down conductors (see chapter 5.4.1).
A lightning strike to the roof parapet can melt the material
used. If this is not acceptable, an additional air-termination
system, e.g. with air-termination tips, must be installed using
the rolling sphere method (Figure 5.1.3.4).
Conductor holders for flat roofs, homogeneously
welded
Under wind conditions, roof sheetings can horizontally move
across the roof surface if they are not properly fixed /laid on
the surface. To ensure that conductor holders for air-termination
systems are not displaced on the smooth surface, the
air-termination conductor must be fixed. Conventional roof