Myths About Metal Roofing: Heat, Wind and Lightning

Properly detailed and installed metal roofing is one of the most resilient, lasting, efficient and attractive kinds of roofing systems for commercial and institutional buildings. Yet there are plenty of questions about metal roofing, and building teams often find time in project meetings to address the most common, recurring topics and myths.

Facts vs Myths About Metal Roofing

I call these “mythbuster meetings,” because many of the questions are fabrications – concerns arising from less savvy professionals or from competitive “selling points.” Among the most prevalent untruths:

Myth about Wind Uplift

Myth: Wind uplift affects metal roofing more than other roofing types.

Reality: While the noncontinuous nature of metal roof attachments makes them susceptible to wind uplift concerns, most roofing types are prone to similar effects. ASCE/SEI calculations for wind loading and FEMA studies of storm areas have shown that properly applied metal roofing outlasts other roof assemblies during hurricanes and tornados.

Building geometry affects how well the roof survives, regardless of roof type. Engineering determines how many insulation board fasteners are needed, and the optimal and safest distances between clips for standing seam systems at corners and perimeters, where the forces are greatest. The interlocking or “active fastening” helps metal roofing pass severe wind and uplift tests including ASTM E1592, UL 580 and UL 1897, and the Miami/Dade County codes, according to a report from Stanford University.

Myth about Heat

Myth: Metal panels get hotter and have more thermal bridging because metal conducts heat so well.

Reality: Depending upon the surface finish, metal roofing can “provide enhanced energy efficiency with its solar reflectance and infrared emittance properties […] to meet the climate requirements of the building,” according to the Stanford University paper and research highlighted by the Cool Metal Roofing Coalition.

As compared to other roofing types, metal roofing tends to be highly reflective and is available with high emissivity. Insulated metal roofing panels have foam insulation that delivers R-values up to R-8.515 per inch thickness and total roof U-factors that exceed those of many other roofing types, helping projects meet strict energy code rules.

Myth about Lightning

Myth: Metal roofs are more likely to get hit by lighting than any other roof types.

Reality: That is bunk; simply untrue. You can read my detailed blog on the subject, or for serious mythbusters refer to the Metal Construction Association’s Technical Bulletin MCA13a, which gives a full and authoritative overview.

As the MCA summarizes, “Because metal roofing is an electrical conductor and a noncombustible material, the risks associated with its use and behavior during a lightning event make it the most desirable construction available.” That’s right: The best option for lightning risks.

I hope some of the above information provided insight and assurance about building with metal roofs. If you have any additional questions or concerns, submit them here to our technical experts.

Do Metal Roofs Attract Lightning Strikes?

LightningArticleBuilding owners and managers fortunate enough to have a metal roof know personally its durability, resiliency and reliability, not unlike that contributed to the U.S. Postal Service of yore:  “Neither snow nor rain nor heat nor gloom of night …”—nor fire, nor hail nor the like—will prevent it from fulfilling its function. Those natural elements conspire to knock on the good reputation of a metal roof, to no avail. But how does a metal roof hold up against a more ominous threat… lightning?

The Myth of Metal Roofs & Lightning

Metal conducts electricity, so it’s not unreasonable to have concerns about whether a metal roof is the best material with which to build a roof to avoid damage from lightning.

According to the Metal Construction Association’s technical bulletin on Lightning and Metal Roofing, the probability of a lightning strike is determined by several factors:

  1. Topography in the area of the structure: The probability of a strike is higher if a structure is situated on a mountaintop or hilltop as opposed to a field.
  2. Size and height of the subject structure. A tall building or a facility covering a large ground area is more likely to be struck than a short or small building. A tall, thin structure, such as a tower, a tree or utility pole, is also a more likely target for a lightning strike.
  3. Relative location of the structure with respect to nearby larger and taller structures. A very tall structure located near a small, short one will tend to further reduce the likelihood of a strike to the smaller one.
  4. Frequency and severity of thunderstorm activity in the geographic area of the project.

Notice there is no mention of the material from which the structure is made. In fact, the probabilities of a strike to a metal roofed structure are no more or less than any other kind of structure. The probability risk has more to do with the height and size of the structure and its surroundings than the material of which it is made.

The use of a lightning protection system, such as lightning rods, may lessen the consequence of a strike. And if lightning does strike a building, a metal roof actually can cause the energy impact to disperse evenly and uneventfully through the structure. Finally, metal roofing isn’t combustible or flammable.

Metal is Best Overall Roofing Material

Bottom line, metal is probably the best material option for roofing, and a safer source of protection for your facility , customers and employees when the inevitable storms come.

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