Metal roofs and lightning

Q: We are building a log home with a metal (Galvalume) roof in a hilly area, but not at the top of the hill. With the metal roof, should we be more concerned about lightning? Should we install lightning rods, or should the house merely be grounded?

Richard Veith, Rockaway, NJ

A: Rex Cauldwell, a master plumber and electrician from Copper Hill, Virginia, replies: Metal roofs are safe for houses in high-lightning areas. I live in such an area and installed a standing-seam metal roof without hesitation. I don’t recommend lightning rods because they tend to attract lightning.

Grounding your metal roof is optional, although few people bother to do so. Grounding a metal roof has no effect on the lightning itself, but grounding the roof will stop the electromagnetic lines of force (generated by the lightning) from entering the building through the roof and developing damaging voltage spikes in the house.

If your building is the tallest object around, I recommend installing a 1-in. galvanized pipe taller than the building and a good distance away, and then ground it well. In many cases, this pipe can be strapped to a tree. Otherwise, the pipe will have to be secured in place with guy wires.

From Fine Homebuilding 120, pp. 18 January 1, 1999