Your roof is not only a weather barrier, it is a work platform for other trades, including lightning-protection installers. Understanding a few basics about lightning protection will simplify job-site coordination and lead to more successful projects.Lightning protection systems (LPS) are increasingly being used to enhance building resilience to natural disasters. More architects are specifying them because climate change is increasing the frequency of lightning strikes, and the growing use of electronic devices in buildings make them vulnerable to lightning surges.
Lightning protection installers are among the first trades on a job site and one of the last to leave; grounding may have to be installed simultaneously with foundations and final connections cannot be made until all building systems are in place.
The Maryville, Mo.-based Lightning Protection Institute (LPI) has certification programs for journeymen and master installers. An advanced Master Installer/Designer certificate is also available; it is crucial because project architects typically delegate design authority to the lightning protection contractor. The installer/designer must then meet stringent standards issued by the Quincy, Mass.-based National Fire Protection Association; Northbrook, Ill.-based UL LLC; and LPI.
Most of an LPS is below roof level. The most obvious above-roof components are air terminals, formerly called lightning rods. They must be located at the highest points on a roof. Depending on the building’s size and configuration, additional air terminals are required around the roof perimeter at intervals not exceeding 20 feet, within the field of the roof, on rooftop equipment and as dictated by the standards. Air terminals can be as slender as 3/8-inch diameter and as short as 10-inches tall; larger ones can be used for decorative purposes or to meet special requirements. While most air terminals now have blunt tips, pointed ones are still encountered and can be a hazard to the unwary.
Air terminals are interconnected by conductors—typically multi-strand cables that can safely carry up to 3 million volts of lightning to ground. Conductors must also be used to bond rooftop equipment and metal components to ground. In most buildings, through-roof penetrations are required so the down conductors can be run inside the structure; the penetrations can be sealed with typical flashing details. If conductors are exposed to view, they should be located in the least conspicuous locations and follow the building’s architectural lines.
Every wire entering the building must have a surge-protective device on it, and these are sometimes mounted above the roof. A variety of mounting devices, connectors, fasten- ers and adhesives are also required. All LPS components should be listed by UL specifically for lightning protection.
LPS components are typically cop- per or aluminum. To prevent galvanic action with roofing and flashings, copper components should be used with copper roofing and aluminum components with steel or aluminum roofing.
Before getting on the job, the roofer, LPS installer, and general contractor should agree on project schedule and roof access, as well as review proposed locations of lightning protection components. Penetrations, especially, should be located and marked prior to roofing so they can be found afterward.
The roofing manufacturer should be consulted for its recommendations. Adhesives, for example, must be compatible with the roofing, and some manufacturers require an extra layer of membrane under attachment points.
For added assurance, the building owner should have UL or LPI Inspection Service inspect the job and certify the LPS was properly installed.