Do Metal Roofs Attract Lightning?

In a word, no. I know, it seems counter-intuitive that a large metal object such as a roof would not attract lightning. But to understand this fact, one needs a better knowledge of what lightning is and how it behaves.

Lightning is a rapid discharge of static electricity in the atmosphere. There are three major types of lightning strike:

  1. Intra Cloud, discharges inside a single cloud, from a highly-charged area of the cloud to a less-charged portion
  2. Cloud-to-Cloud discharges from a highly-charged cloud to a less-charged cloud
  3. Cloud-to-Ground discharges from a highly-charged cloud to the earth.

The Cloud-to-Ground type is the type that is best understood, and the type we are most concerned with in terms of dangers to us.

A metal roof, according to The Metal Construction Association, does not make lightning more likely to strike, but it may make a lightning strike LESS dangerous if it occurs. How can that be? Since metal is highly conductive, doesn’t it stand to reason that the metal roof will attract lightning, too?

Actually, the exact location where lightning strikes appears to be governed by geography and topography, as well as the movements of the storm. When lightning is ready to discharge, it does so, whether there is a metal roof handy or not. Lightning seeks the path of least resistance to discharge.

In Cloud-to-Ground lightning, it’s discharging into the earth, but it has to move through an expanse of air to get there. Trees and buildings are better electrical conductors than air. A tall or large building is more likely to be hit than a small, short one. But the real factor that determines WHERE lightning will hit is the location, not what material it is made with.

A metal building system, with a conductive metal roof and a conductive metal structural frame, gives lightning a low-resistance path to the earth. A metal building may survive a lightning strike with less damage than a similarly sized and located building made of higher-resistance materials. This result is rather counter-intuitive, but it is similar to the fact that during a lightning storm you are safer inside a car – with its metal body – than you are standing next to the car.

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