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¨ If the roof is made of non-flammable material, the con-
ductors of the air-termination system can be installed on
the surface of the structure (e.g. gable or flat roof). Non-
flammable building materials are commonly used. The com-
ponents of the external lightning protection system can
therefore be mounted directly on the structure (Figures
5.1.1.18 and 5.1.1.19).
¨ If the roof is made of highly flammable material (class
B 3 building material, see Supplement 1 of the German
DIN EN 62305-3 standard) e.g. thatched roofs, the distance
Figure 5.1.1.17 Protection of small-sized roof-mounted structures between the flammable parts of the roof and the air-termi-
against direct lightning strikes by means of air- nation rods, air-termination conductors or air-termination
termination rods
meshes of the air-termination system must not be less
than 0.4 m. Highly flammable parts of the structure to be
protected must not be in direct contact with parts of the
external lightning protection system. Neither may they be
located under the roofing, which can be punctured in the
event of a lightning strike (see also chapter 5.1.5 Thatched
roofs).

Isolated air-termination systems protect the complete struc-
ture against a direct lightning strike by means of air-termina-
tion rods, air-termination masts or masts with cables spanned
over them. When installing the air-termination systems, the
separation distance s from the building must be maintained
(Figures 5.1.1.20 and 5.1.1.21).
Figure 5.1.1.18 Gable roof with conductor holder Isolated air-termination systems are frequently used when the
roof is covered with flammable material (e.g. thatched roof) or
also for systems located in hazardous areas (e.g. tanks) (see
also chapter 5.1.5 “Air-termination system for buildings with
thatched roofs”).

A further method of designing isolated air-termination systems
is to use electrically insulating materials such as GRP (glass-

s separation distance acc. to IEC 62305-3 (EN 62305-3)
α protective angle acc. to Table 5.1.1.4

α α
s s
Figure 5.1.1.19 Flat roof with air-termination rods and conductor air- air-
holders: Protection of the domelights termination termination
mast mast
protected
¨ Isolated structure
¨ Non-isolated
The two types can be combined. reference plane
Figure 5.1.1.20 Isolated external lightning protection system with
The air-termination systems of a non-isolated external light- two separate air-termination masts according to
ning protection system of a structure can be installed in the the protective angle method: Projection on a
following ways: vertical surface

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