Do you need a lightning rod on a metal roof?
Lightning is among the leading cause of deaths related to weather. Additionally, it causes an average of 22,600 fires per year in the US alone.
Apart from deaths from the resulting fire, it also damages property with an estimated worth of 451 million per year. Therefore, it is important to take preventive measures.
There are a lot of myths about installing a lightning rod on a metal roof. Some people believe that they are safe without it, while others are unsure. In this article, I will debunk all the myths and explain everything you need to know.
Do you need a lightning rod on a metal roof?
Yes, you need to install a lightning rod on a metal roof. Although metal roofs do not attract lightning, they don’t prevent it from striking the building.
There is a misconception that associates lightning strikes with roofing materials. The fact is all of them have equal chances. You still need a lightning protection system to mitigate the dangers of a strike.
Can lightning damage a metal roof?
Metal roofs are the most used in lightning-prone regions because they hold the largest fire-resistance rating.
They do not combust like other roofing materials when lightning strikes. Materials such as asphalt and wood have a higher probability of igniting and causing a fire. Therefore, lightning cannot damage a metal roof directly.
If the metal roof does not have a properly installed earth connection, lightning may force its energy to the housing electrical system in search of an earth connection. If the building catches fire or cracks due to shockwaves, the metal roof will be damaged.
What happens when lightning strikes a metal roof?
Metal roofs are good conductors of heat and electricity. In case of a lightning strike, the metal roof will conduct the current to a ground connection.
If there is no ground connection, it can force its way through the conductive metals holding the roof to the ground.
Metal roofs do not pose high fire threats like other types of roofing materials that are ignitable. Lightning also produces extreme heat. The metal roof loses the heat quickly through conduction and radiation to the air.
Factors that influence lightning strikes
Metal roofs do not attract lightning. However, it can strike based on the following factors.
Building height
Lightning strikes the highest points in an environment. Hence it can strike the tallest building if it’s taller than other structures in the zone.
Topography
Buildings in high places such as hills have a higher probability of getting struck than buildings in low areas.
Roof surface area
Large roof surface areas on tall buildings are more prone to lightning strikes. This is because they provide a large target hence increasing the chances.
Regions
Some regions are more prone to lightning strikes compared to others. For example, Lake Maracaibo in Venezuela is the most struck place by lightning in the world.
It receives an average of 28 strikes per minute, lasting up to 10 hours for 140-160 nights per year. Conversely, the Arctic and Antarctic regions receive 0.1-1 strikes per square kilometer yearly.
Thunderstorm-prone regions are also highly affected. This is because thunderstorms are accompanied by lightning.
The United States alone experiences an average of 100,000 thunderstorms per year. Elements such as lightning, hail, and greater winds determine the severity of a storm.
Consequences of Lightning on metal-roofed building
Power surge damage
Lightning can channel its energy through the building’s wiring system, searching for a ground connection.
Many connected electronics will be damaged from the power surge if this happens. For example, computers, TV, home theatre, Ac system, and kitchen appliances are all vulnerable to power surge damage.
Lightning Fire
Metal roofs will not cause a fire because they do not combust on lightning strikes.
But if the building does not feature a lightning protection system (LPS), other materials can cause a fire. For example, when it channels high voltage to the wiring system causing electric devices to cause an explosive fire.
Alternatively, if the underlying structure is made of combustible material, it may cause fire due to the extreme heat temperatures.
If this fire is not contained, it can spread fast and torch the whole building down. Metal roofs are not guaranteed protection from lightning fires.
Shock wave damage
Lightning can cause an explosive shock wave. If your house is in close range to the shockwave, then it may cause the concrete to fracture.
Most Shockwaves feature highly destructive forces that can weaken concrete walls, chimneys, stone, and cinderblock. The fractured materials are very dangerous.
Components of a lightning protection system
A lightning rod alone is not enough to protect your building against lightning strikes. It takes a full lightning protection system to do the job.
A rod is just a small part of the system. It acts as the termination point while the rest of the system is responsible for containing the energy and channeling it to the ground.
Lightning rods are made of conductive materials such as copper and aluminum. However, cooper is the most commonly used material in creating an LPS.
Although the metal roof will conduct lightning, it has to be connected to the ground with the help of a lightning protection system. Metal roofs do not carry current because their thickness, in most cases, is not enough to guarantee a lightning path.
But when you use an LPS, it protects roofs, structural components, communication devices, electrical circuits
The LPS components are mostly made from low resistance materials such as copper and aluminum to provide a safe passage to the ground. A lightning rod must be accompanied by a ground network which consists of the following components.
- Conductors- These can include structural members.
- Interconnecting components- These areConnectors and fittings that complete the system make sure there is reliable continuity.
- Bonding- It reduces potential differences caused by lightning.
- Ground rod- It directs the lightning deep into the earth.
- Surge Protective devices- Filters the intrusion of lightning and equalizes the grounded system’s potential during a lightning event.
LPS safety standards
National Fire Protection Association has set safety standards for installing an LPS. These standards feature design requirements, risk and application control measures.
In addition, these standards have to be followed regardless of the roofing materials. Here are some examples of the LPS installation guidelines from the NFPA and LPI.
- The air terminals should not exceed 20 feet along the perimeter
- You should not place the air terminals of roof edges, outside corners, and ridge ends of flat roofs.
- You need to attach an air terminal on chimneys structural projections like chimneys, air conditioning units, finials, decorative spires, dormers, or any other equipment on the rooftop.
- The metallic equipment on the rooftop also needs to be integrated with the LPS. These are equipment such as railings, vent fans, skylights, metal framing, and antennas.
The rooftop elements are integrated into the LPS following different criteria characterized by their location or composition.
For example, metallic elements thicker than 3/16 inches should be integrated via a bonding procedure. However, most of the elements placed on the rooftop do not exceed 3/16 inches.
Therefore, you should employ conductors and air terminals for such objects. Ignoring the rooftop projections, pitch, and metal equipment will lead to an under-protected roof.
How to install a lightning rod on a metal roof?
You should install an LPS following the NFPA guidelines discussed above. Additionally, you need to be careful to avoid abrading the panel surfaces. If you live in a high wind area, you have to give the rod attachment more attention.
There are no special requirements for high wind areas. It’s upon you to make sure it doesn’t get blown away.
Resting the lightning rod on the metal roof cover is unwise since it can cause abrasion because of the wind movements. The Federal Emergency Management Agency has provided a guideline for standing the lightning arrester.
It should be installed on the panel. FEMA also recommends LPS installers use premade clips on the roof. After anchoring the clips, you can now anchor the air terminal plates and then the panel clips.
Do metal roofs require grounding?
There is no requirement from the National Fire Protection Association to have metal roofs grounded. Metal roofs have equal chances of getting struck by lightning as other materials. You need to install an LPS for maximum protection.
In the event of lightning, the metal roof will ground the current via the rest of the structure without causing danger to the occupants.
NFPA recommends using PVC pipes for electrical wires inside the building for advanced safety. Ignoring these guidelines poses a serious risk.
More Benefits of a metal roofing
Durability
If installed correctly, metal roofs are resilient to harsh conditions such as strong winds. Additionally, they do not require constant repairs like other roofs. However, it is important to inspect them regularly.
Note that durability depends on the type of product that you choose. Some are more impact-resistant than others.
Longevity
Metal roofs can last up to 70 years with little or no maintenance. Other materials, such as the traditional asphalt, last 20-30 years.
Energy efficiency
Metal roofs reduce house cooling costs by reflecting infrared and UV rays from the sun.
These rays are responsible for producing heat. Metal roofs can reduce up to 40% of cooling costs in summer. Conversely, if constructed with a four-inch strapping system,
Lightweight
Metal is one of the lightest roofing materials. It weighs up to 3 pounds per square foot depending on the material and thickness. In comparison, clay or concrete tile can weigh up to 10 pounds per square foot.
The supporting structure of heavy roofing material such as clay tiles will consume many resources to make strong structures. Lightweight roofing materials will cut some structural engineering costs.
Safety
Metal roofing is one of the safest, especially in harsh weather conditions. They have a class A fire-resistant rating.
This means embers, lightning, and flying sparks cannot set them on fire. However, it is important to note that some underlying materials such as wood can ignite in intense heat. This affects the overall C-rating of the roofing.
Environmental friendly
All metal roofs are recyclable. Besides, most manufacturers use up to 95% recycled materials to produce their products. Metal roofs can be resealed to extend their lifespan.
This means they do not have to be replaced entirely. Since metal is in high demand, it doesn’t end as a landfill easily.
Boosts a home value
Apart from the harsh environmental protection, metal roofs also boost home value. Even though they are expensive to install, the value may increase up to 6%, sealing your costs.
Disadvantages of metal roofing
High initial costs
Metal roofs have a high initial cost. Although there is cheaper metal roofing, they are usually low quality.
This is one of the setbacks people face as they build their new homes. However, they save money in the long run because they don’t require frequent repairs.
Color inconsistency
Metal roofs can fade over time depending on the quality of paint, climatic conditions, and materials.
In addition, they are highly susceptible to staining. When you replace some parts of the roofs, you can easily note the difference in color consistency. Even if you repaint the metal roofs, a fresh one can still see the difference.
Noise
Metal roofing can be noisy in heavy hailstorms or rainfall. When objects fall on a metal roof, they produce loud sounds compared to other materials such as wood shakes and asphalt. Modern installation methods can mitigate this by adding insulation.
Final Thoughts
Most people think that metal roofs offer full protection against lightning strikes. But the truth is metal roofs only prevent the building from catching fire easily.
But when the lightning forces its way into the electrical system of the house, then it can cause huge damage.
If materials underneath the metal roof are combustible, it affects the roofing fire protection C-rating. Only a Lightning protection system can offer maximum protection from the effects of lightning strikes.