Metal Roofs and Lightning: What Actually Decides a Strike

Somebody asks me this on most estimates, usually a little embarrassed, because they suspect the answer and want to hear it from someone who has been on a lot of roofs. The answer is no, a metal roof does not attract lightning. Here is why, and here is what actually happens if a house is struck, because that part matters more.

What decides where lightning strikes

Lightning is looking for the shortest path from the cloud to the ground. What decides that path is height, shape, and location: the tallest thing in the area, a pointed shape, a hilltop, an open field. The National Weather Service says this plainly in its lightning myths material, and the Metal Roofing Alliance says the same. The material of a roof does not enter into it. A metal roof is not grounded, it is not taller than the trees and utility poles around it, and it is not a better target than the asphalt roof next door.

Your house's odds of being struck are set by where it sits and what is near it. The roof you choose does not move them.

What happens if it is struck

This is the part that should shape your thinking. If lightning hits a house, the energy has to go somewhere, and a roof material that burns gives it somewhere to start a fire. Wood shake and asphalt can ignite from a strike.

A metal roof does the opposite. Steel conducts, so a strike spreads across the panel instead of concentrating at a point, and steel does not burn, so there is no fuel at the point of contact. The Metal Roofing Alliance's consumer material puts it simply: if lightning does strike, metal safely disperses energy instead of igniting. A metal roof does not reduce your chance of a strike. It reduces what a strike can do.

Lightning protection is a separate system

A metal roof is not a lightning protection system, and nobody should sell it to you as one. A real lightning protection system is air terminals, conductors, and ground rods designed to carry a strike to earth around the structure. It is installed by a specialty contractor, it is rare on houses, and it is common on barns, churches, and tall buildings in open country.

If your home is the tallest thing on a hill with no trees and you want that protection, it is its own project and it works with any roof. On a standing seam roof the conductors can clamp to the seams without penetrating the panel, which is a small point in metal's favor for that install. It is not a reason to choose the roof.

Where the myth comes from

Two places, I think. One is the sensible instinct that metal conducts electricity, which is true and has nothing to do with whether it draws a strike. The other is the old lightning rod, a metal spike on the roof, which people remember as "metal on the roof attracts lightning." The rod does not attract lightning either. It gives a strike that was already coming a safe path down.

What I would tell you

Take lightning off the list of reasons for or against a metal roof. It does not change your odds. It does make the outcome of a strike better than it would be on a combustible roof, which is a small real benefit you get along with the roof. The decision should rest on the things that actually vary from house to house: how long you plan to stay, what the roof geometry allows, and what you are willing to pay per year of protection.

If you want the longer version of how fire reaches a roof here and what a Class A rating does and does not cover, the fire article has it.

Now you have the facts, and the question can stop being embarrassing.