6.4.4.1 Material requirements for down conductors

Down conductors are primarily mounted directly onto the building (without separation distance). The reason for installing them directly onto the structure is the temperature rise in the event of lightning striking the lightning protection system.
If the wall is made of flame-resistant or normally inflammable material, the down conductors may be installed directly on or in the wall.
Owing to the specifications in the building regulations of the German federal states, highly combustible materials are generally not used.
This means that down conductors can usually be mounted directly on the building.

Wood with a density greater than 400 kg/m² and a thickness greater than 2 mm is considered to be normally inflammable. Thus, the down conductor can be directly mounted on wooden poles, for example.
If the wall is made of highly combustible material, the down conductors can be directly installed on the surface of the wall provided that the temperature rise when lightning currents flow through them is not dangerous.