Metal roofing is the easiest and most affordable way of roof covering for a single-family house. Such a covering has a long service life, is easy to assemble and corrosion- resistant. Such materials as zinc, zinc- titanium, steel, aluminum or copper can be used. It is widely believed that a metal roof does not need lightning protection, because it acts as an air terminal. But is it really so?
According to paragraph 2.11 of the AD 34.21.122-87 on buildings and structures with metal roofs, the rood should be used as air terminal. But point 22.214.171.124 of the IS 153 imposes a delimitation on a roof thickness depending on the type of metal, that is why it is necessary to consider this information when performing lightning protection. Let's study this on an example of our Expert project.
Question: It is necessary to calculate lightning protection for a hangar. The room is made of a semi-circular galvanized steel sheet 1.8 mm thick, ribbed design, there is no thermal insulation or carcass under the sheet. Galvanized sheet is mounted on reinforced concrete walls 3.3 m high. Can in this case the sheet of curved galvanized steel serve both as a roof and lightning rod?
Answer: In accordance with paragraph 126.96.36.199 of the IS 153 a roof 0,5 mm thick can be used as a lightning rod. At the sheet thickness from 0.5 mm to 4 mm it can be used, but with the proviso that the roof should not be necessarily protected from damage and there is no risk of ignition of flammable materials under it. If the roof is necessary to protect against burn-through and damage, then you need to use iron 4 mm thick.
In this example, if the roof must be protected from burn-through, it cannot be used as a lightning rod, but rod lightning rods mounted on it should be used. At the highest point of the building a lightning arrester in the form of a rod 0,5 - 1,5 meters is installed. The higher the air terminal is, the wider is the safety zone. A down conductor in the form of a steel wire is attached to the lightning rod, it is lowered from the roof of the wall and is connected to the grounding device.
If all the conductive elements are safely connected together, and there are no flammable materials under the roof, the metal roof can be used as a lightning rod. Did you face an unanswerable question? Write to the ZANDZ Technical Center and we will answer you.