6.3.4 Air-termination systems for buildings with soft roofs

The design of a lightning protection system in accordance with protection class III generally meets the requirements for buildings with soft roofing such as thatched, straw or reed roofs. In special cases, a risk analysis in accordance with IEC 62305-2 may be necessary in order to specify the necessity and design of lightning protection.
Special installation of the air-termination system is required for soft roofs. Air-termination conductors must be installed so they are freely spanned between insulating supports to avoid direct contact with combustible roofing materials. Defined minimum distances must also be maintained in the eaves area, especially in the case of retrofitting, to ensure that these are retained even after re-roofing.
The typical distance between the down conductors is approximately 15 m for protection class III. The exact distance results from calculation of the separation distance s in accordance with IEC 62305-3, as described in chapter 7.2. For ridge conductors, spans of up to approx. 15 m should be aimed for, and for down conductors, spans of up to approx. 10 m should be aimed for without additional supports. Span stakes must be firmly connected to the roof structure, for example by means of anchor bolts and washers (cf. figures 6.3.4.1 to 6.3.4.3).