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detail B

detail A

evaluation: BLIDS – SIEMENS
I = 20400 A residential building

Figure 5.1.4.1 Types of metal roofs, e.g. roofs Figure 5.1.4.2 Example of damage: Sheet metal
with round standing seam

IEC 62305-3 (EN 62305-3) lightning protection standard clear-
ly illustrates the risk for metal roofs. Where an external light- rolling sphere
with a radius acc.
ning protection system is required, the metal sheets must have to class of LPS
the minimum values stated in Table 5.1.1.5. air-termination tip
The thicknesses t are not relevant for roofing materials. Metal
sheets with a thickness t’ may only be used as a natural air-
termination system if puncture, overheating and melting is ac-
cepted. The owner of the structure must agree to accept this
type of roof damage since the roof will no longer be rainproof.

If the owner does not accept damage to the roof in the event
of a lightning strike, a separate air-termination system must
be installed on a metal roof so that the rolling sphere (radius
r according to the class of LPS) does not touch the metal roof
(Figure 5.1.4.3). Figure 5.1.4.3 Air-termination system on a metal roof – Protection
against puncture
In this case, an air-termination system with many air-termina-
tion tips is recommended. Suitable for all classes of LPS
Distance of the Height of the air-
The heights of air-termination tips in Table 5.1.4.1 have prov- horizontal conductors termination tip *)
en effective in practice, regardless of the class of LPS.
3 m 0.15 m
When fixing the conductors and air-termination tips, no holes 4 m 0.25 m
may be drilled into the metal roof. A number of conductor hold- 5 m 0.35 m
ers is available for the different types of metal roofs (round
standing seam, standing seam, trapezoidal). Figure 5.1.4.4a 6 m 0.45 m
shows adequate conductors for a metal roof with round stand- *) recommended values
ing seam. If conductor holders with lightning current carrying
clamp are used, an air-termination tip can be directly fixed. Table 5.1.4.1 Lightning protection for metal roofs – Height of the
air-termination tips
It must be observed that e.g. on a trapezoidal roof the con-
ductor in the conductor holder located at the highest point Figure 5.1.4.5 shows a conductor holder with fixed conduc-
of the roof must be fixed, whereas the conductors in all other tor routing and an air-termination tip on a trapezoidal roof.
conductor holders must be routed loosely due to the length To reliably prevent the ingress of moisture, the conductor hold-
compensation resulting from the changes in temperature er must be hooked into the fixing screw above the cover plate
(Figure 5.1.4.4b). for the drill hole.

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