Lightning is a flow of electrical current between the earth and the sky. The result of the electrical flow can be millions of volts and its costs can be billions of dollars of lightning-related damage annually. The risk of lightning damage and the disruption to the U.S. industry and property is continually rising. Besides property damage, a large part of the total cost is from facilities downtime and business operations interruption.
Dissipate lightning’s dangerous and destructive electricity
Photo courtesy of East Coast Lightning Equipment Inc.
Some people falsely believe that metal roofs can increase the risk of a lightning strike. Metal roofs are no more attractive to lightning than any other type of roofing material. Metal roofing materials are non-combustible, so if a metal roof does get struck by lightning; it is less likely to result in a fire than other types of roofing materials.
While a building’s structural steel will conduct lightning, it is the bonding, interconnection and grounding provided by a lighting protection system (LPS) that will dissipate lightning’s harmful electricity safely to ground. Arcing and side-flashing can occur without the continuous preferred path to ground provided by LPS. The anchoring sections of metal roofing and siding systems are not constructed to carry current because, in most situations, the thickness of the metal used is insufficient to provide a guaranteed path for lightning.
When lightning strikes, an LPS offers assurance. An effective LPS not only protects roofs, walls and other structural components from direct lightning strikes, but it also shields electrical circuits, communications, process control systems and other elements that are vulnerable to indirect strikes.
An LPS employs highly conductive materials (typically copper and aluminum materials) to provide a low-resistance path to safely ground lightning’s dangerous and destructive electricity. LPS materials and components must be UL listed and specially manufactured for lightning protection. According to the Maryville, Mo.-based Lightning Protection Institute (LPI), a safety standardcompliant system provides proven and effective grounding to dissipate lightning’s harmful electrical discharge by employing a grounding network, which must include:
- Strike termination devices (air terminals or rods)
- Conductors (which can include conductive structural members)
- Appropriate Interconnecting components such as connectors and fittings required to complete the system
- Bonding to reduce potential differences created by the lightning current
- Grounding electrodes (ground rods, plates or conductors) installed to direct the lightning current deeply into the earth
- Surge protective devices (SPDs) installed at every service entrance to filter the intrusion of lightning from utility lines and further equalize potential between grounded systems during lightning events
Photo courtesy of TLSmith Consulting Inc.
LPS Guidelines
LPS installation can be successfully completed by referring to the nationally recognized safety standards of LPI 175, NFPA 780 (from National Fire Protection Association) and UL 96A. “The science of lightning protection is keeping pace with our ever-changing technology,” says Bud VanSickle, executive director for LPI. “The newly released 2017 edition of NFPA 780 includes 12 chapters and 15 annex section to address design requirements, application and risk assessment measures for LPS.”
Below are some examples of LPS air terminal installation guidelines detailed in NFPA 780, UL 96A and LPI 175:
- Roof attachment at regular intervals not to exceed 20 feet along ridges and perimeter roof edges.
- Placement no more than 2 feet from ridge ends, roof edges and outside corners of flat roofs.
- Attachments required on rooftop appurtenances and structural projections such as chimneys, turrets, dormers, decorative spires and finials, air conditioning units and other rooftop equipment.
- Safety standards also provide guidelines regarding requirements for other metallic rooftop equipment such as skylights, vent fans, protruding metal roof framing and railings, as many times these structural elements need to be incorporated into the LPS.
How these elements should be incorporated into the LPS depends on their composition and roof location. For example, according to LPI, safety standards allow for exposed metallic objects constructed of a continuous metal thickness exceeding 3/16 of an inch need only to be interconnected to the LPS via bonding. Since a majority of rooftop equipment does not meet the 3/16-inch requirement, air terminals and conductors must be employed for proper protection. Failure to address necessary measures for roof pitch, projections and metal rooftop equipment can result in either under-protected roof areas or added construction expenses due to use of excess components.
Also, “One preferred method for attaching components to metal roof is with adhesives; this avoids unnecessary penetrations,” says Jennifer A. Morgan, secretary/treasurer at East Coast Lightning Equipment Inc., Winsted, Conn., and an officer of the Lightning Safety Alliance, Winsted. “If items are installed to fascia, they can be attached with fasteners.”
An LPS cable attached to a metal roof’s ridge cap. (Photo courtesy of East Coast Lightning Equipment Inc.)
Installing LPS
Thomas Smith, AIA, RRC, F.SEi, founder of TLSmith Consulting Inc., Rockton, Ill., stresses that an LPS be installed in a manner that does not abrade the surface of the panels; panel abrasion could lead to panel corrosion. Also, “In high-wind areas, special attention needs to be given to attachment of the LPS so that it does not blow away,” he says. “Last time I looked, UL 96A and NFPA 780 had no special requirement for high-wind areas. On most other roof systems, the LPS conductors rest on the roof covering. But this is unwise with metal because movement of the conductor, by wind or thermal, can abrade the surface of the metal panels. It is important to stand the conductor off the panels as noted by the Federal Emergency Management Agency (FEMA).”
FEMA has design guidelines to prevent LPSs from becoming disconnected from standing seam metal roofs in hurricane-prone regions. FEMA recommends that pre-manufactured, mechanically attached clips that are commonly used to attach various items to roof panels be used. After anchoring the clips to the panel ribs, the air terminal base plates and conductor connectors are anchored to the panel clips. In lieu of conductor connectors that have prongs, FEMA recommends that mechanically attached looped connectors be installed. Also, FEMA recommends in lieu of pronged splice connectors, bolted splice connectors be used because they provide a more reliable connection and prevent free ends being whipped around by wind.
In addition to wind accountability, galvanic corrosion is a serious issue when copper components are installed on metal roofs that are either manufactured from painted metal or galvanized aluminum. “A metal roof should never have copper lightning protection components installed on it unless the roof metal is copper,” says Mark S. Harger, president/CEO, Harger Lightning & Grounding, Grayslake, Ill. Also, Harger feels it is imperative that the installation contractor follow the roofing manufacturer’s requirements when it comes to attaching lightning protection components to the roof surface. “Through-roof penetrations should be kept to a minimum and be sealed by a qualified roofing contractor,” he adds.
Ground rod installation for an LPS. (Photo courtesy of Bonded Lightning Protection Systems Ltd.)
Qualified LPS Installation
Installing a highly specialized LPS for a metal roof involves a combination of science, art, craftsmanship and technological acumen. Harger believes that as long as the roofing contractor has been properly trained, a separate contractor is not necessary. “Harger Lightning & Grounding trains contractors on how to install lighting protection systems on all types of roofs, including metal roofs,” he says.
LPI has certification programs to help teach LPS installation. Those taking the exam must be members of LPI and are retested about every three years when the standards are updated. The testing programs for its Master Installer Series involve a set of five exams that include true/false, multiple choice, short answer, fill-in-the-blank and design application problems. More design problems are included with each progressive test and knowledge of NFPA 780 and LPI 175 is required to pass.
“LPI qualifies installation providers through our certification testing program, which includes a series of up-to-date exams to assure contractors are qualified to the current requirements of the standards,” says VanSickle. “Secondly, the LPI field inspection program (LPI-IP) provides independent third-party inspectors who can ensure system compliance in accordance with specified safety standards.”
