Occupied Roofs: Lightning Protection Systems

February 26, 2021

Lightning protection systems
safeguard structures from one of
the most violent forces of nature.
While the principles of lightning
protection were established more
than 250 years ago by Benjamin
Franklin, the design and installation of lightning
protection systems continue to evolve in
response to advances in science and changes
in architectural design, construction materials,
and building technology.1 One area of ongoing
innovation is lightning protection systems for
occupied roofs.
Rooftop terraces and gardens have become
some of the most sought-after amenities in urban
buildings. Tenants and condominium owners
pay a premium for these design features and
expect high-quality detailing and construction
that does not distract from the views the rooftops
provide. Anything installed on an occupied roof
must also be robust enough to withstand damage,
unintentional or otherwise, from people
coming in contact with rooftop equipment.
Lightning protection systems can satisfy
these expectations, as demonstrated by several
recently constructed buildings in downtown
Chicago, Illinois. These case study projects
illustrate innovative approaches to integrating
lightning protection into roofing, parapets,
and railings while still complying with North
American standards.
Lightning protection is a specialized building
system that must be integrated with electrical,
structural, mechanical, and enclosure
design and construction. The following guidelines
will help building enclosure consultants
to coordinate their work with other building
Codes: A lightning protection system should
comply with the latest requirements of the North
American consensus standards, including:
• NFPA 780 – Standard for the Installation
of Lightning Protection Systems,
• LPI 175–Standard of Practice for the
Design–Installation–Inspection of
Lightning Protection Systems,
• UL 96–Lightning Protection
• UL 96A – Installation Requirements for
Lightning Protection Systems, and
• In Canada: CSA B72 – Installation Code
for Lightning Protection Systems.3
Risk Assessment: Best practice requires
building design professionals to conduct
a lightning risk assessment to ensure public
health, safety, and welfare. NFPA 780 contains
a simplified risk assessment methodology that
can be completed in as little as 15 minutes
using free, online apps such as www.bit.ly/
LightningRisk; performing an assessment does
not require specialized knowledge or training.
Building enclosure consultants can best serve
their clients (and limit their own liability) by
determining whether this risk assessment has
been addressed by the client or other members
of the client’s design team and, if necessary,
discussing with the client who might be best
qualified to do the assessment.
System: Rooftop air terminals, informally
called lightning rods, are the most visible element
of a lightning protection system, yet they
are only one part of a complete system. A system
also includes a network of lightning conductors
extending down a building to connect
to ground electrodes embedded in the earth
outside the structure’s foundations, bonding
connections to metal objects on and within
the structure, and surge protection devices on
incoming power and data lines (Figure 1).
Air terminals are not highly visible when
viewed from the ground; they can be as small
as 3/8-in. diameter, rise as little as 10 in. above
surrounding construction, and be set back up
to 24 in. from the building perimeter.4
Still, some designers would prefer that air
terminals not be seen up close by someone on
a terrace. For them, a strike termination device
can be used instead of a conventional lightning
rod. A strike termination device can be any
permanent part of a structure made from metal
at least 3/16-in. thick (0.064-in. thick for handrails)
and made electrically continuous with
the lightning protection system. Railings, shade
structures, decorative items, and other metal
fabrications can be used in lieu of air terminals
to meet design requirements.5
Air terminals or strike termination devices
must be located around a roof perimeter and at
high points of a structure as determined by a
“rolling sphere” analysis. The electrical charges
capable of causing damage by lightning usually
strike within a 150-ft. radius and are modeled
8 • IIBEC Interface February 2021
as if a 300-ft.-diameter sphere is rolled across a
building’s surface; wherever the sphere touches
the building is a location where lightning can
attach to the building.6
Design: Most lightning protection systems
can be specified by requiring compliance with
North American consensus standards and then
delegating the actual design to individuals
holding Lightning Protection Institute (LPI)
certification, based on rigorous examination,
as a Master Installer/Designer or Master Installer.
When practical, the lightning protection professional
should be consulted early in the design process
to help assure the lightning protection system
will meet the project’s aesthetic requirements, be
affordable, and provide reliable protection.
Installation and Certification: Installation
should also be entrusted to firms employing
LPI-certified professionals. Lightning protection
systems are not in the bailiwick of
most building code officials, so third-party
inspection and certification by the Lightning
Protection Institute–Inspection Program (LPIIP)
should be used for quality assurance; LPI-IP
is the industry’s most comprehensive inspection
program. Inspection and certification programs
are also available for reroofing of or
modifications to existing buildings.7
Renelle on the River, a luxury condominum
building at 403 N. Wabash Ave. in Chicago,
uses railings as strike termination devices
around its rooftop terrace, giving visitors
unimpaired views of the Chicago River and the
city’s skyline. The top rail of the parapet’s aluminum
glazing system contains an extra-thick
February 2021 IIBEC Interface • 9
Figure 1. Lightning protection requires a complete system that provides multiple paths to safely
conduct lightning to ground. Credit: East Coast Lightning Equipment, Inc.
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channel sized to meet the metal thickness requirements for strike termination devices.
The channel is made electrically continuous with steel balusters concealed inside
the parapet’s framing members. The base of the balusters is attached to lightning
protection conductor cables that lead to through-structure penetration devices and,
from there, into the ground. In occupied roof areas, the connections and conductors
are located beneath raised paving panels (Figures 2 and 3).
The NEMA (Chicago) at 1200 S. Indiana Ave. has commanding views of Grant
Park. To honor the views, its architects specified railings as strike termination devices
around the pool deck. The railings were installed on the inside face of the building’s
extra-wide parapet, placing them more than 24 in. from the face of the building. This
required air terminals to be installed on the parapet coping to satisfy a rolling sphere
analysis (Figures 4 and 5).
In this instance, the visual impact of the air terminals is minor,
because the air terminals are outside the glass railing and below
the common sight lines for views of the park. Lightning conductor
cables connect the air terminals and the bottom of the balusters
to through-structure penetration devices that connect with
the rest of the lightning protection system. The conductors and
through-structure penetration devices are concealed among the
foliage in planter beds around the terrace.
Figure 2. Views from the Renelle
terrace are not inhibited by the
lightning protection system. Photo
courtesy of Belgravia Group.
Figure 3. The glazed parapet railing
system was specially detailed and
installed to serve as a strike termination
device. The cable trailing off to the left
connects to a through-roof penetration
and other rooftop lightning protection
components. Photo courtesy of East
Coast Lightning Equipment, Inc.
Figure 4. NEMA building pool deck and terrace.
Photo courtesy of Crescent Heights.
Figure 5. The geometry of the building and the physics of
lightning strikes required air terminals on the parapet cap in
addition to a metal railing used as a strike termination device.
Photo courtesy of East Coast Lightning Equipment, Inc.
10 • IIBEC Interface February 2021
Instead of trying to minimize the
appearance of the lightning protection
system at the nearby Paragon building
(1326 S. Michigan Ave.), the architect
exalts the air terminals, making them
a proud part of the tall wind screen.
Aluminum air terminals are
bolted to the tops of aluminum stanchions
that, in turn, conduct lightning
to beneath the elevated concrete
roof pavers. There, lightning conductor
cables connect the stanchions
to throughstructure
that connect
to down conductors
the building
(Figures 6, 7,
and 8).
Figure 6. Aluminum air terminals
are mounted to the top of the
windscreen baluster to extend the
vertical lines of the building. Photo
courtesy of East Coast Lightning
Equipment, Inc.
Figure 7. The metal
balusters conduct
lightning to beneath
the deck pavers
where they connect to
lightning conductor
cables leading
to through-roof
penetration devices.
Photo courtesy of
East Coast Lightning
Equipment, Inc.
Figure 8. The balusters
and slender air
terminals blend into
downtown Chicago’s
skyline. ©Solomon
Cordwell Buenz /
©Dave Burk
one third page.indd 1 9/11/2020 11:18:54 AM
February 2021 IIBEC Interface • 11
The richly appointed One Bennett Park (451 E. Grand Ave.) utilizes
several creative techniques to incorporate rooftop lightning protection
components into the building’s architectural features.
Classically shaped, cast-bronze air terminals are used around a terrace
located on a two-story-high podium. Viewed from the terrace, the air terminals
are partially screened by foliage, and the masonry parapet is drilled
so that conductor cables can run, out of sight, into the planters. However,
the air terminals are visible from the street and are mounted on limestone
pedestals aligned with the building’s fenestration (Figures 9 and 10).
Terraces at upper levels utilize ornate metal railings, wind screens,
and pergolas as strike termination devices (Figure 11).
Many tall buildings have building maintenance units (BMUs) or
other roof-mounted devices for raising and lowering window-washing
and exterior-maintenance crews. As these machines move from one
location to another, they can bump into and damage air terminals. The
potential for damage can be minimized by installing air terminals on
spring adapters that will flex upon impact (Figure 12).
The 155 N. Wacker building also has an extensive “green roof” that
12 • IIBEC Interface February 2021
Figure 9. The decorative air terminals are barely noticeable through the
planter foliage. Photo courtesy of East Coast Lightning Equipment, Inc.
Figure 11. The metal balcony and frames of the windscreens and
pergola are made electrically continuous with the lightning protection
system and used as strike termination devices. Credit: Peter Aaron/
Otto for Robert A.M. Stern Architects
Figure 10. The ornamental cast-bronze air terminals are
stylistically appropriate for the cladding’s classical limestone
detailing. Photo courtesy of East Coast Lightning Equipment, Inc.
required lightning protection system conductor cables to be installed beneath
the rooftop plantings (Figure 13).
More than a quarter of work-related lightning fatalities occur during
roofing and construction activities. While lightning protection systems protect
people inside buildings, they do not protect anyone on the roof. Building
enclosure consultants should communicate to their clients and instruct their
February 2021 IIBEC Interface • 13
Figure 12. Air terminals should be mounted on springs at
locations vulnerable to damage by building maintenance
units (shown), window washing, or other activities. Photo
courtesy of East Coast Lightning Equipment, Inc.
Figure 13. Rooftop conductors and throughstructure
penetration devices can be coordinated
with plantings and pavers on green roofs. Photo
courtesy of East Coast Lightning Equipment, Inc.
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own personnel working in the field that, as
the National Weather Service advises, “When
thunder roars, go indoors.”8
The Lightning Protection Institute and
its members provide guidance and support to
assure best practices for lightning protection
systems. See www.lightning.com.
The authors thank HLP Systems, Inc. for
arranging access to rooftops.
A previous version of this article appeared
in Building Enclosure, Winter 2020.
1. See, for example, Norman L. Fowler.
“A Brief History of Lightning
Protection.” Minutes of the Twenty-Fifth
Explosives Safety Seminar, Volume III.
August, 1992. Department of Defense
Explosives Safety Board. https://apps.
2. To learn more about the basics of lightning
protection, see www.lightning.org
and ecle.biz.
3. North American standards do not recognize
the overblown claims for early
streamer emission or charge dissipation
systems; an article explaining concerns
about these non-recognized systems is
at bit.ly/nonconventional_systems.
4. Some photos in articles have been
retouched to make the air terminals
more visible.
5. For more about strike termination
devices, see bit.ly/
6. See bit.ly/rolling-sphere for an animation
of rolling sphere technique for
determining placement of air terminals.
7. Information on inspection and building
certifications programs is at lpi-ip.com.
8. OSHA Fact Sheet. “Lightning Safety
When Working Outdoors.” www.weather.
Jennifer Morgan is
a co-owner of East
Coast Lightning
Equipment. She can
be reached via ecle.
Jennifer Morgan
Michael Chusid, RA,
FCSI, is an expert in
building products
and can be reached
via www.chusid.
Michael Chusid,
14 • IIBEC Interface February 2021
Billerica Memorial High School’s designers, Perkins&Will, of
Boston, Massachusetts, set out to create a space where students and
their teachers could see things in a different way. The target of LEED
AP Silver Certification is evident in the many windows and glass claddings,
which also serve to lend an airy, open feeling to the building by
channeling sunlight into the building’s interior. The educators’ desire
to integrate subjects and literally break down walls is reflected in the
multi-story “town centers,” featuring labs and universal classrooms,
which flank open, flexible spaces.
Carbon-conscious detailing included the use of Forest Stewardship Council-certified
spruce timber, and a “high-performance insulated envelope (with attention to thermal
The history of the town of Billerica as a mill town was also considered and integrated
into the design in the shape of traditional materials like brick, which is corbeled to create the
perception of movement as the angle of the light from the sun changes over the course of the
day. Ash ceilings in the tall, open area top a bright, cheerful space.
The introduction to the project on the Perkins&Will website notes, “It’s a concept we’ve
called reflection with direction—honoring the past, aiming for the future—and it’s woven
throughout the fabric of the new building’s architecture, detailing, and branding. The school
demonstrates how simplicity gives rise to depth, and how we, collectively, can be re-made.”
Watch a short video about the new school and its effect on and integration with the
community of Billerica at this link: https://vimeo.com/388506358.
— Architectural Record, Perkins&Will
1. Broome, Beth. 2021. “Billerica Memorial High School by Perkins&Will.”
Architectural Record. https://www.architecturalrecord.com/articles/14937-billerica-
memorial-high-school-by-perkinswill (accessed 1/4/2021)
Billerica Memorial High School
Photos from perkinswill.com are
© Chuck Choi.