Metal Roofs and Lightning: Myth and Fact

Many homeowners worry that a metal roof will draw lightning. Research summarised by the Metal Construction Association (MCA) indicates that roofing material does not meaningfully change the probability of a strike. A metal roof neither attracts lightning nor protects a building from it.

What determines strike risk

• Height and size of the building relative to its surroundings.
• Terrain: hilltops and open ground are more exposed.
• Nearby taller objects such as trees, towers and other buildings.
• Local frequency and severity of thunderstorms.

If lightning does strike

Metal is electrically conductive and noncombustible. The MCA notes that a conductive path lets the strike's energy pass with little resistive heating, reducing the chance of fire or explosion, and that noncombustible roofing lowers fire risk compared with combustible coverings. A metal roof is not, however, a lightning protection system.

Lightning protection

Where protection is needed, for example on tall or isolated buildings, a properly designed lightning protection system (LPS) with air terminals, down conductors and earthing should be installed. In the United States, NFPA 780 covers the materials and installation of such systems; other countries have equivalent national or IEC-based standards. Metal roofing can be incorporated into an LPS design when a qualified designer specifies it.

Bottom line

Choosing metal neither raises nor lowers the chance of a strike, and its noncombustible nature can be an advantage if a strike occurs.

Common sources of confusion

Lightning rods are metal, which leads some people to assume that metal draws strikes. In fact, lightning protection systems work by giving a strike that would occur anyway a controlled, low-resistance path to earth. A metal roof without such a system does not change where lightning strikes.