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TOPIC: Lightning

Metal Roofs and Lightening

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Hi. This isn't an expert question, but I just wanted to say that I installed a metal roof on my home two and a half years ago and I couldn't be happier with it. My wife was a little resistant to the idea, she had the same perceptions that a lot of people had when I told them I was getting a metal roof put on the house. She thought that it would be loud and noisy, and because we get a lot of spring and summer thunderstorms here in Missouri, she also thought it would attract lightening. We've had some pretty brutal storms here in the last couple of years, but there's no noise difference. And as far as lightening, I'm not sure why exactly (I think it has something to do with the sheathing they put underneath it that acts as a ground) but we had a tree in our yard sheared by a lightening strike, and as much lightening as we get here, it's never hit the roof. And, we're no longer picking shingles up from the yard after a big storm. Like I said, we're very happy with it, and I'm glad we went with one.
Guest User

3/27/2001
Does a metal roof need bonding to ground and is it more likely to attract a lightning strike. What test have been carried out to show that lighning is not a problem?
Guest User

4/5/2001
I haven't read much about the lightning issue. Are there any added hazards having a metal roof? Is it grounded in any way?
Guest User

5/7/2001
Here is information from my company's Technical Bulletin on metal roofing and lightning: PROBLEM When a metal roof is installed on a building, it seems to heighten the awareness of lightning. There is still much that is not known about lightning but most experts agree that a path of ionization begins from a cloud and extends earthward. This path of ionization establishes a route for a lightning strike. The dramatic part of the strike occurs when electrons race upward from earth to sky along this route, resulting in the characteristic flash of light. Resistance to the flow of this electricity will generate heat energy and can cause explosions and fire. CAUSE The main factor with where lightning strikes is location. High topographic areas are most prone. Additionally, the lightning will strike the highest object in that area. For that reason, lightning often strikes trees, power poles, silos, antennas, and other towers. In wide open spaces, if a human is present, they will be the highest object and might be struck. In years past, when plumbing vents protruding from the roofs of buildings were metal, there was risk that, due to their height, they'd be struck and that energy would be transferred into the home's plumbing system. ANALYSIS Although metal conducts electricity, lightning is not drawn to it. If it does become charged by a strike, the energy is grounded out safely through the structure. Although it is unusual for lightning to strike a building, the consequences of such a strike depends upon several things. The consequences will be worst if the building is constructed of combustible materials or if it has flammable or explosive contents. SOLUTION Because metal roofing is a noncombustible material, the low risk associated with its use in the event of lightning makes it a very desirable roofing option. However, regardless of roof type, there are some installations where lightning protection might be desirable.
Todd Miller
Isaiah Industries, Inc.

5/15/2001