Do Metal Roofs Attract Lightning?

Feb 19

Installing a metal roof has been found to make building owners think more about lightning and the dangers of lightning strikes. There is a perception, or at least a suspicion, that the probability of lightning striking the building will be increased by a metal roof. After all, like the materials used in lightning rods that are used to attract lightning strikes, metal is highly conductive, so is it not reasonable that the metal roof will also attract lightning?

The brief answer is, no, a metal roof won't make lightning more likely to strike, but if it happens, it can make a lightning strike less dangerous. Well, that's right, less dangerous, not more than that.

In its Technical Bulletin MCA13a, the Metal Construction Association breaks down the issue into two issues: the probability of a lightning strike at any specific location, and the consequences of that strike.

Lightning has been studied for hundreds of years, and there is good general information on how it works, but many of the details are still unknown about how it forms and where it strikes. That lack of knowledge means that it remains unpredictable in its conduct.

Lightning is a rapid discharge of static electricity from the atmosphere. There are three main types of lightning strikes: Intra Cloud (IC), discharges from a highly charged cloud area to a less charged portion within a single cloud; Cloud-to-Cloud (CC) discharges from a highly charged cloud to a less charged cloud; and Cloud-to-Ground (CG) discharges to the earth from a highly charged cloud. In terms of dangers to life and property, CG is the type that is best understood, and the type we are most concerned with.

The exact location where lightning discharges, as well as the movements of the storm, appear to be governed by geography and topography. Whether a metal roof is handy or not, when lightning is ready to discharge, it will. It is incorrect logic to assume that a metal roof similar to a lightning rod attracts lightning strikes, because lightning rods are not made to "attract" lightning. Rather, if it happens to strike the location of the building, they are made to channel lightning securely to the ground.

Lightning seeks the path of least resistance to discharge - like any electrical charge. It discharges into the earth in CG lightning, but to get there, it must move through an expanse of air. Trees and buildings are electrical conductors that are better than air. By shortening the distance that lightning has to travel by air, a tall building provides a simpler path. Consequently, it will look for the best conductor that is closest to the cloud in the general location where the lightning discharges. It is more likely to be hit by a tall tree than the short tree next to it. It is more likely to be hit by a tall or large building than a small, short one. Roof covering material, or other building structural materials, are not determining factors of where it will strike, where the building's placement and size are.

However, the consequences of the strike depend a lot on what the building is made of, and whether it has a lightning protection system or not. Through a good conductor such as copper or steel, electricity passes more easily than through a poor conductor such as wood or concrete. There is more electrical resistance in the poor conductor, which converts some of the tremendous electrical energy of the lightning into heat, potentially causing fires or explosions.

With a conductive metal roof and a conductive metal structural frame, a metal building system gives lightning a low-resistance path to the earth. With less damage than a similarly sized and located building made of higher-resistance materials, a metal building can survive a lightning strike. This outcome is rather counter-intuitive, but it's similar to the fact that you're safer inside a car - with its metal body - than standing next to the car during a lightning storm.

During a lightning strike, the real danger to human life or property depends greatly on whether or not the building is occupied, whether it is made of fuel materials, and whether it contains fuel materials. Electronic devices may be susceptible to electrical discharge and are, therefore, at risk as well. Once again, with its non-combustible steel construction, a metal building system may pose less risk than a building made of combustible materials.

A lightning protection system provides an easy path to the earth for electrical discharges, usually routing them around the outside of the structure. It consists of a metal lightning rod, at its most basic, placed so that it is the highest part of a building, and connected to metal rods buried in the earth by metal wires. (Telecommunications towers, which are usually the tallest structures in their immediate surroundings by design, are often protected by grounding them to a buried copper ring an inch or more thick, and in a circle several hundred feet across completely surrounding the tower.) A professionally designed lightning protection system may be desirable for buildings whose size and location make lightnn This could be considered another advantage of metal roofing if the presence of a metal roof raises the awareness of the need for lightning protection. Need assistance with your roof. We can help you find a Roof Company Miami - SmartLiving