What are standard installation steps for installing lightning protection systems on metal roofs?
A lightning protection system employs highly conductive materials to provide a low-resistance path to safely ground lightning’s dangerous and destructive electricity. LPS materials and components must be listed and specifically manufactured for lightning protection. A safety standard-compliant system provides proven and effective grounding to dissipate lightning’s harmful electrical discharge via a grounding “network.” The standard installation steps include:
- Strike termination devices (air terminals or lightning rods)
- Conductors (which can include qualified conductive structural members)
- Interconnecting components and fittings required to complete the LPS
- Bonding to reduce potential differences created by the lightning current
- Grounding electrodes (ground rods, plates or conductors) installed to direct the lightning current into the earth
- Surge protective devices (SPD’s installed at every service entrance to filter the intrusion of lightning from utility lines and further equalize potential between grounded systems during lightning events)
How are lightning protection systems connected and attached to metal construction and roofs?
The national safety standard for LPS (NFPA 780) provides specified guidelines for components, equipment placement and installation methods for roofs, including requirements for metallic appurtenances such as skylights, vent fans, AC units, protruding metal roof framing and railings. More often than not, these structural metal elements need to be incorporated into the LPS. How elements are incorporated into the LPS also depends on their composition and roof location. (Example: 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.) LPS attachments are also required for rooftop projections such as chimneys, turrets, dormers, decorative spikes and finials. Since a majority of rooftop equipment does not meet the 3/16 requirement, strike termination devices 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.
What are some common lightning protection installation errors seen on metal roofs?
Lightning protection is a specialized trade that is governed by industry safety standards. Design and installation is typically not within the scope of expertise held by roofers or general contractors, which is why LPI-certified experts should install LPS to eliminate errors and ensure standard compliance. Common LPS installation errors made by unqualified trades can include:
- Omitting bonding required for metal bodies, vents and other rooftop equipment
- Conductor incorrectly connected to grounding terminations with no transition above grade
- Improper number and/or location of required conductor or downlead runs
- Improper spacing (strike termination devices) and/or use of nonstandard products like ESE, DAS or CTS devices
- Selection of unsuitable LPS components and materials for the metal roof (specialized contractors know how to avoid potential corrosion created by dissimilar metals)
- Use of inappropriate metals or compounds that advance corrosion and thus decrease the life of the LPS or metal roofUse of LPS roof sealants and adhesives that do not meet roofing requirements for compatibility or compliance with roof manufacturer warranties
- Lack of advance LPS planning and job coordination to include installation provisions for component placement, raceways or down conductor coursing
- Improper spacing or ground terminals (noncompliance with minimum distance and soil depth requirements, i.e. ground rods installed too close to the foundation or above grade
- Utilities not interconnected to the LPS (a safety standard requirement for common bonding of grounded systems)
- Surge protection devices omitted or SPD’s installed which are not UL-rated for lightning protection
What are some additional LPS quality assurance guidelines that are important to follow for metal roofs?
Integration and maintenance of LPS for metal roof systems is often underestimated. Roofing contractors, project designers and building owners can expect the best results when their LPS designs and plans adhere to the following:
- An up-to-date LPS specification from a trusted industry authority such as LPI to outline details for materials, methods and workmanship. LPI provides these quality resources and industry specifications for LPS guidance, including information for re-roofing projects.
- Reference to the nationally recognized safety standards for LPS in your construction documents. (LPI and NFPA 780 are trusted authoritative sources for LPS design, component application and installation methods.)
- Contracting with a certified LPI Master Installer/Designer (MID) to ensure compliance with nationally recognized safety standards. Working with a certified LPI MID is similar to using a RCI certified roofing consultant to assure maintenance of the highest quality for the entire roof area of the building envelope.
- A third-party close-out inspection by LPI-IP is a must for quality assurance and certification. The LPI-IP provides several inspection options, including: LPI-IP Master Installation, LPI-IP Reconditioned Master Installation and LPI-IP Limited Scope to accommodate a variety of project needs.
Assessing the need for lightning protection typically involves comparing the expected lightning frequency with the tolerable lightning risk—which means weighing the lightning probability against its consequence to life and environment. Critical structures and facilities like hospitals, emergency operations centers, police and fire stations, nursing homes, schools, data centers and server buildings are routinely equipped with LPS since they cannot afford to experience a lightning loss or “tolerate” the risk. When designed and installed by a LPI-certified specialist, LPS can meet the needs for safety, technology and design for all structures–including those with metal roofing and components.
Reader note: a condensed version of this article has been published in the April, 2020 edition of Metal Construction News Magazine.