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Figure 5.1.7.1 Green roof Figure 5.1.7.2 Air-termination system on a Figure 5.1.7.3 Conductor routing above the
green roof cover layer

If a meshed air-termination system is used, the IEC 62305-3 According to the state of the art of lightning protection tech-
(EN 62305-3) lightning protection standard requires a mesh nology, such roof-mounted structures are protected against
size which depends on the relevant class of LPS (see chapter direct lightning strikes by means of separately mounted air-
5.1.1, Table 5.1.1.3). An air-termination conductor installed termination systems. This prevents partial lightning currents
inside the cover layer is difficult to inspect after some years from entering the building where they would interfere with or
because the air-termination tips or studs are overgrown and even destroy sensitive electrical / electronic equipment.
no longer recognisable and frequently damaged during main-
tenance work. Moreover, air-termination conductors installed In the past, these roof-mounted structures were directly con-
inside the cover layer are susceptible to corrosion. Conduc- nected so that parts of the lightning current were conducted
tors of air-termination meshes installed evenly on top of the into the building. Later, roof-mounted structures were indirect-
cover layer are easier to inspect even if they are overgrown ly connected via a spark gap. This meant that direct lightning
and the air-termination system can be elevated by means of strikes to the roof-mounted structure could still flow through
air-termination tips and rods and thus “grow” with the plants the “internal conductor” although the spark gap should not
on the roof. Air-termination systems can be designed in differ- reach the sparkover voltage in the event of a more remote
ent ways. A meshed air-termination network with a mesh size lightning strike to the building. This voltage of approximately
of 5 m x 5 m (class of LPS I) up to a maximum mesh size of 4 kV was almost always reached and thus partial lightning
15 m x 15 m (class of LPS III) is typically installed on the roof currents were also injected into the building via the electrical
surface, regardless of the height of the building. The mesh is to cable, for example, which led to interference with the electrical
be preferably installed on the external edges of the roof and on or electronic installations.
any metal structures serving as air-termination system.
Stainless steel (V4A, e.g. material No. AISI/ASTM 316 Ti) has The only way of preventing that these currents are injected
proven to be a good wire material for air-termination systems into the building is to use isolated air-termination systems
on green roofs. which ensure that the separation distance s is maintained.
Aluminium wires must not be used for installing conductors in
the cover layer (in the earth substrate or granulate) (Figures Figure 5.1.8.1 shows partial lightning currents entering the
5.1.7.1 to 5.1.7.3). structure.

The different roof-mounted structures can be protected by
5.1.8 Isolated air-termination systems various types of isolated air- termination systems.
Roof-mounted structures such as air-conditioning and cool-
ing systems, e.g. for mainframes, are frequently installed on Air-termination rods
the roofs of large office and industrial buildings. These roof- Small roof-mounted structures (e.g. small fans) can be protect-
mounted systems must be treated like antennas, electrically ed by individual air-termination rods or a combination of sev-
controlled domelights, advertising signs with integrated light- eral air-termination rods. Air-termination rods up to a height
ing and all other protruding roof-mounted structures because of 2.0 m can be fixed by means of one or two concrete bases
they typically have a conductive connection into the building, piled on top of each other (e.g. Part No. 102 010) so that they
e.g. via electrical lines or ducts. are isolated (Figure 5.1.8.2).

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