What are the guidelines indicating the need for lightning rods on a house?

Dear Tom,
I do not have lightning rods on my house, but there have been a few strikes to houses in my area in the last couple of years. What are the guidelines indicating the need for lightning rods on a house?
James Waggoner,
Des Moines, Iowa
Dear James,
The risk of a lightning strike to a house varies with the location of the structure. An assessment of the threat to any given structure involves at least five criteria: The type of structure, its construction, location, surrounding topography and the local lightning frequency. In addition to the house itself, it is recommended that any tree near the house and taller than the house be protected against lightning because trees do not offer protection. In fact, they can create a “side flash” of lightning to the house.
Much information is available on house lightning protection, and a good place to start is with the Lightning Protection Institute.

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