Do Metal Roofs Attract Lightning? The Facts for North Carolina Homes

Metal roofs do not attract lightning. The National Weather Service lists the idea that structures with metal attract lightning as a myth and states plainly that the presence of metal makes absolutely no difference on where lightning strikes. The Metal Construction Association reaches the same conclusion in its technical bulletin on lightning, stating that metal roofing does not in any way increase the risk of a strike.

The myth makes intuitive sense, because metal conducts electricity well. But lightning does not go looking for conductors from miles away. A lightning channel forms in the storm and steps toward the ground in a branching path; only in the final moments does it connect with something on the ground, and what it connects with is mostly a matter of what sticks up highest and closest.

So a metal roof on a one-story ranch among tall pines is no more likely to be struck than an asphalt roof on the same house. A tall, isolated house on a hilltop is more likely to be struck than its neighbors, whatever it is roofed with.

Height, pointed shape and isolation decide where lightning strikes. The National Weather Service names those three as the dominant factors. Lightning tends to hit the tallest object in an area, especially one that stands alone or comes to a point: a tree in an open field, a church steeple, a radio tower, a chimney or a lone house on a ridge.

In North Carolina, that often means the tall loblolly and longleaf pines around a house are more likely targets than the roof. A strike to a nearby tree can still send current through the ground or jump to the house, which is one reason trees overhanging a roof are worth trimming.

Your own exposure depends on the setting. Homes on hilltops in the western Piedmont, on open farmland in the Coastal Plain, on lakefront lots with open water around them and on the barrier islands with few tall trees stand out more than homes in a wooded Cary subdivision. If your house is the tallest thing around, think about lightning protection whatever roof you choose.

If lightning hits a metal roof, the metal conducts the current across its surface instead of the roof material catching fire, and the current then looks for the easiest path to ground. That path may be through gutters and downspouts, through wiring, plumbing or gas lines inside the house, or across to a nearby tree. The Metal Construction Association bulletin notes that the roof material generally performs as a noncombustible material in a lightning event, which reduces the fuel available at the strike point.

What the metal roof does not do on its own is route that current safely. The bulletin warns that a building's electrical ground is not designed to handle the enormous current of a lightning strike, and it says a complete lightning protection system, with air terminals connected to a proper grounding source, is what does that job. Without one, a strike can still damage electronics, wiring and appliances in any house.

For fire performance generally: when installed with two layers of GAF VersaShield® underlayment over a 15/32-inch plywood deck, the Interlock roof assembly can achieve a Class A fire rating (ASTM E108 / UL 790). No roof is fireproof, and fire ratings describe fire from outside, not lightning current inside the walls.

A house with a metal roof is as safe during a thunderstorm as any other house, provided you follow the usual indoor lightning precautions. The National Weather Service says a house is a safe place to be during a thunderstorm as long as you avoid anything that conducts electricity. That means staying off corded phones, away from plumbing, out of the shower or bath, and away from electrical appliances, wiring, computers and TV cables during the storm.

The roof material does not change that advice. Lightning current can enter any house through utility lines, plumbing or the structure, whether the roof is metal, asphalt, tile or slate. The NWS also advises staying away from windows during storms, both because wind can throw debris through them and because, rarely, lightning can enter older homes through gaps in window frames.

Outside, the advice is simple: when thunder roars, go indoors. Lightning can strike miles from the storm itself, and the NWS office in Raleigh notes it can reach up to 25 miles from the parent thunderstorm. Porches with metal roofs are not shelters; get inside a fully enclosed building.

Most homes do not need a lightning protection system, but some benefit from one regardless of roofing. Consider one if your house:

• stands on a hilltop, ridge or open lot and is the tallest structure nearby;
• sits on a lake or open water with few taller objects around;
• has had a strike or nearby strike before;
• holds equipment or records that would be costly to lose to a surge.

The Metal Construction Association recommends that systems be designed and installed in accordance with NFPA 780, the national standard for lightning protection, and it cites UL 96A and LPI-175 as installation references. Lightning protection is specialized work done by certified lightning protection installers, not by roofers, though the roofer and the installer need to coordinate where air terminals and conductors attach so roof penetrations are sealed properly.

Whole-house surge protection at the electrical panel is a separate, smaller step that helps protect electronics and appliances from surges coming in on utility lines. A licensed electrician can advise on it.

A metal roof does not make lightning damage worse, and in some ways it limits it. Lightning damage to houses usually comes from three things: fire where the strike ignites combustible material, structural damage where the current explodes moisture in wood or masonry, and electrical damage as the current travels through wiring and plumbing. A metal roof does not add fuel at the strike point, which addresses the first. The second and third depend on the path the current takes through the house, which a lightning protection system controls and the roof material does not.

After any strike, have the roof and attic checked even if you see no fire. Look for scorch marks, damaged flashing, split framing and damaged vents, and have an electrician check the electrical system. Document everything with photos for your insurer; see roof insurance claims in NC and roof leaks after a thunderstorm for what to do next.

If a roofer tells you a metal roof will draw lightning to your house, the National Weather Service disagrees, and so does the industry that builds metal roofs.

Lightning should not steer you toward or away from a metal roof. The material does not change your strike risk, and a metal roof does not burn at a strike point. Base the decision on the things that do differ by material in North Carolina: wind resistance, salt air near the coast, summer heat, weight, upkeep, cost and how long you plan to own the house.

If lightning is a genuine concern because of where your house sits, address it directly with a lightning protection system designed to NFPA 780 and installed by a qualified installer. That protects the house whatever the roof.

Metal Roof NC, an authorized Interlock aluminum roofing dealer, can coordinate with your lightning protection installer on attachment and flashing details when a system is added at the same time as a new roof. For more on the roofing side, see aluminum roofing, are aluminum shingles good for North Carolina and hurricane-resistant roofing.