Roof-Mounted Solar: ROI and Best Practices

Solar PV

THE USE OF solar pv in building design is sharply
on the rise. When considering adding rooftop
solar, knowing what information is needed up
front, planning the solar PV system design for
optimal power production, and utilizing quality
materials to secure the system for its lifetime
are essential. But what information is needed to
make an informed decision?

First, it’s important to understand why
mounting solar to a metal roof rather than
alternative roof types can make the most sense.
Today’s trends lean toward evaluating the
long-term costs of owning and maintaining a
roof. For owners and designers, environmental
aspects of the industry—pre- and
postconstruction—have become the primary
focus in the life cycle of a roof’s materials.
Additionally, concerns over landfills becoming
overburdened with former building components
discarded due to shortsighted, budget-conscious
building objectives are driving the focus on
more sustainable roofing materials and their
“cradle-to-grave” carbon footprint.
Metal roofing is known for its durability,
environmental sustainability, variant styles, and
versatility. The life-cycle costs and environmental
appeal of metal offer several advantages over
current life-cycle trends. As a result, metal is
experiencing a surge in popularity for both
commercial and residential applications because
the maintenance requirements and life-cycle
ownership costs are substantially lower than
those of the alternatives.
SERVICE LIFE
In the commercial/industrial market sector,
a field/lab study published by the Metal
Construction Association indicates that the
Roof-Mounted Solar:
ROI and Best Practices
Feature
By Rob Haddock and Mark Gies service life of (standing seam) coated steel is
in the range of 70 years. Based upon empirical
data, several domestic producers of 55% AlZn
steel have recently raised no-cost warranted
material performance up to 60 years, equaling
the assumed building service life as described
in LEED version 4. Additionally, because of the
negligible maintenance afforded by properly
installed metal roofs, owners are not faced with
costly roof upkeep, patching, and repair.
With few exceptions, nonmetal commercial
roofing systems generally expire after 15 to
20 years. They not only have more intensive
maintenance requirements year over year, but also
inevitable replacement. This results in an acute
(“whole building”) life-cycle cost disadvantage
compared to standing seam metal roofing, which
is documented to have a service life approaching
70 years and minimal maintenance requirements.
SUSTAINABILITY
The growing demand for durable and
environmentally friendly construction materials
with reduced maintenance and longer service
lives often can lead commercial designers and
owners to metal roofing. It is attractive, highly
©2025 International Institute of Building Enclosure Consultants (IIBEC)
Interface articles may cite trade, brand,
or product names to specify or describe
adequately materials, experimental
procedures, and/or equipment. In no
case does such identification imply
recommendation or endorsement by
the International Institute of Building
Enclosure Consultants (IIBEC).
Modern Steel Construction (EAF statistics,
May 2023)
This paper was presented at the 2024 IIBEC
International Convention and Trade Show.
Powerful Percentages
How does domestically produced hot-rolled
structural steel stack up sustainability-wise?
• 93% recycled content
• 98% recycling rate
• 95% of US production is represented
by facility-specific environmental
product declarations (EPD)
• 75% is produced via electric arc furnace
(scrap-based)
28 • IIBEC Interface January 2025
reflective, long-lasting, weather-resistant, and
easy to maintain.
Metal roofing is a sustainable material
because of its extended service life, low
production consumption of natural resources,
zero-petroleum byproducts, and recyclable
economic prudence.
At nearly an 98% recycling rate, steel is one
of the most-recycled construction materials
available, second only to copper. This is
important to building owners and designers
conscious of both environmental and economic
efficacies. Old metal roofs rarely end up in
landfills, thus preserving landfill space and
helping to protect the environment.
Metal roofing is also resistant to fire,
weather, and climate conditions due to
its sturdy and inert composition. It is
noncombustible, adds no fuel, and will not
ignite during a wildfire or lightning strike,
which may help save on insurance premiums.
Metal is impervious to ultraviolet
degradation. Premium factory finishes of
polyvinylidene fluoride paint films offer up
to 40-year warranties against excessive fade,
chalk, and film integrity. Further, because
metal panels have structural characteristics,
they can be designed to resist virtually
any wind speed, including a Category 5
hurricane.
THE METAL ROOF, A PERFECT
PLATFORM FOR SOLAR PV
Today, building owners are adding grid-tied
solar photovoltaic (PV) sources to augment
the power required to run their facilities. The
financial prospect of PV makes sense, turning
cash positive in three to seven years and
providing power for decades thereafter.
With the increasing use of solar on commercial
buildings, metal roofing has become a driver for
roof type selection in many cases.
The service life of solar PV is between 28 and
37 years, with an average of 32.5 years, according
to Wiser, Bolinger, and Seel. Most alternative
roofing systems expire long before the life of the
PV system. This leads to costly disassembly of the
PV array, reroofing, and reassembly. A standing
seam metal roof provides an ideal platform and is
the only commercial roof type featuring a service
life that exceeds the solar PV system.
It is also easier and less expensive to mount
solar to a metal roof than any other roof type. In
most cases, these cost savings are even sufficient
to offset the premium initial cost of a standing
seam roof. Solar PV can be mounted to the
standing seams of the roof penetration-free,
ballast-free, and with tested and engineered
mechanical attachment methods.
With the cost of solar decreasing over the last
decade, federal and local incentives, as well as
public policy mandates driving the popularity
of solar, the numbers improve every year. When
solar PV is incorporated into building design, the
standing seam roof makes sense from both a
financial and ecological perspective.
LIFETIME ROI
Once the decision is made to utilize solar, metal
roofing is a driver for roof type selection because
not only is a solar-and-metal roof system less
expensive up front than other roof system
combinations, but it also improves the real
lifetime return on investment (ROI) of the system.
When computing ROI within the solar pro
forma, inverter replacement is usually factored
in at about year 15—but what about the cost
of roof replacement? The solar array must be
totally dismantled and then reinstalled on the
replacement roof. Often, even the initial cost of
the solar-and-metal roof is less than that of solar
and other roof type alternatives. Factor in roof
replacement, and the cost advantages become
grossly magnified. Hence, the PV array and the
roof should be regarded as a single asset.
A number of exorbitant expenses associated
with completing a PV system/reroof include
removing the solar modules, removing the
mounting and racking system, decommissioning
the system during the reroof, reroofing,
reinstalling the PV system, recommissioning the
system, the potential for damaged components
during this process, and some new wiring and
loss of power production during the project.
With metal, roof replacement is avoided. The
roof will perform long after the service life of
the solar array has expired. When considering
new construction, the standing seam metal
roof actually lasts the lifetime of the first solar
array as well as the second. In the case of solar
retrofit, 30-year-old standing seam roofs that are
properly designed, installed and maintained are
still viable candidates for consideration.
January 2025 IIBEC Interface • 29
For these and other reasons, metal has
become a preferred roof type for the solar roof.
The solar-and-metal roof can achieve significant
improvements in the lifetime ROI and provides
lower upfront costs than alternative roof system
combinations. It is not only rational but vital to
consider the roof and PV as a solitary asset, as the
two are mutually dependent.
INVESTMENT TAX CREDITS AND
OTHER INCENTIVES ON ROI
Since the introduction of the Inflation Reduction
Act (IRA), the US solar market is now poised
to reach the goal of 30% of US electricity
generation by 2030. The legislation includes
a 10-year extension of the solar Investment
Tax Credits (ITC), additional incentives also
known as adders, significant incentives to boost
domestic manufacturing throughout the solar
production supply chain, tax credits for energy
storage, workforce development provisions,
and additional policies that promote a clean
energy economy. These policies are expected
to accelerate growth, triggering an avalanche of
solar development throughout the US.
WHY IS THIS IMPORTANT TO
NEW SOLAR INSTALLATIONS?
Solar projects built through 2033 are eligible for
the 30% ITC and can increase their tax credits
significantly by qualifying for “adders.” These
include domestic content, energy communities,
and low-income communities.
For the domestic content adder, if at least 40%
of the products are made in the US, a project
qualifies for 10% additional tax credits. For
energy communities, installing solar in eligible
areas, such as brownfields or closed coal mines,
qualifies for another 10% tax credit. Installations
in low-income areas receive an additional
10–20% tax credit.
In addition to ITCs, there is other federal
money available, including the USDA’s Rural
Energy for America Program for designated
rural areas. Some states, municipalities, and
utilities are also offering loans, grants, and other
incentives.
An important piece of the IRA is to grow US
businesses, especially manufacturers, and the
combination of the supply-side incentives and
the ITC adder provides that opportunity to the
solar industry in the US. Besides economic
reasons, this is important because in the wake of
the pandemic, US companies quickly realized the
need to limit their reliance on foreign goods and
services and increase domestic manufacturing to
meet the demand. Ongoing supply chain issues
also underscore the importance of domestic
production.
An increase in domestic production of solar
components should offset potential price
increases, reduce shipping and import costs, and
likely increase the level of support for solar PV
and other renewables in the US.
HOW DO NATIONAL AND/OR
LOCAL ENERGY POLICIES AND
BUILDING/ ELECTRICAL CODES
PLAY INTO THE USE OF SOLAR?
The role of codes and regulations is a
double-edged sword. Some are very positive
for solar, such as the residential solar mandates
required for all new construction enacted in
California a few years ago, while others may
increase hurdles, making it more complex
and difficult to install solar. As the use of solar
increases, so do the number and revisions of
codes, standards, and policies. This is inevitable
and the right thing to do but may inadvertently
increase the hurdles to deploying solar. Some
energy conservation policies are focused on
energy efficiency first, which may reduce the
demand for solar.
That said, various municipalities and even
entire states have enacted regulations, building
codes, and public policy mandating the
installation of solar PV or solar-ready design on
new building construction. This is a major shift
from the past, when there was no consideration
for accommodating solar with new construction
design, and solar was retroactively fitted to the
roof in the best way possible. New mandates will
result in the accelerated growth of rooftop solar,
with the intent also to reduce costs and maximize
the energy output of solar installations—leading
to higher ROIs with fewer hurdles in deploying
solar PV.
The key to complying with these mandates
is in the upfront planning and design of new
buildings with respect to factors not traditionally
considered—factors focused on the anticipation
of a solar installation on a new building.
For example, according to the solar-ready
regulation St. Louis, Missouri, passed in
December 2019, the area of a new commercial
building’s roof that is functional for solar must be
at least 40% of the total roof area, often referred
to as the “solar-ready zone.” For new residential
homes, the solar-ready zone must be at least
600 square feet and oriented between 110 and
270 degrees from true north to the southernmost
point as possible—to produce more energy.
As more buildings are constructed with
solar installed or solar-ready, the demand for
better solutions will foster greater innovation
of products and technology to allow a building,
its roof, and its solar PV to work as a single
system. This could be new products performing
multiple functions, such as building-integrated
PV, which has been around the industry for years
but has also been relatively unsuccessful due to
economic and technical difficulties.
DESIGNING A SOLAR-READY
ROOF AND THE EFFECTS
OF ORIENTATION ON THE
SYSTEM’S OUTPUT
Whether mandated or not, it is a good idea to plan
for a solar-ready roof during the design stages, as
up-front planning can minimize cost and increase
feasibility. Planning for a solar installation in the
future ensures informed decision-making with
regard to the timing of the installation and ensures
optimal power production.
Mounting rooftop PV should always be
consistent with the design principles of the host
roof and vary according to the specific roof type.
Further, a PV array on a rooftop is exposed to
the environmental forces of wind, snow, rain,
hail, and even earthquakes. These forces can
be complex, making secure attachments of
PV crucial. PV arrays improperly designed and
installed can become airborne during a wind
event and pose a serious threat of personal
injury or property damage. Therefore, skilled
design, engineering, and production of these
components are required. All these criteria point
directly to metal. So, a working knowledge of
metallurgy, sealant chemistries, metal roof types,
and other variables is also critical to a long-lasting
solar-and-metal-roof combined asset.
When planning the location of the rooftop solar
array, the orientation of the building should be
considered to maximize the solar gain (increase
in solar absorption of the area due to the natural
direct exposure to the sun) and power production
of the system. When a steep-slope roof (a slope
approaching latitude) is involved, a south-facing
roof surface is the optimal location for the array.
Southwest and southeast orientation can also
be good options affecting power production
minimally. As the module orientation moves away
from a south-facing orientation, the solar gain
and total energy produced on any given day are
reduced. Orientation is not as critical for low-slope
roofs (roofs 5% or lower).
Today, solar modules are normally installed
planar to the roof surface on steep roofs and
planar or very slightly tilted on low-slope
applications. Aggressive tilting of modules
is seldom done primarily due to economic
considerations (adversely affecting the ROI
payback period) but also due to adverse wind
effects on roof systems and structures.
Tilted systems are still sometimes used in
very northern geographies or on roofs that are
not oriented to the south. It is a delicate balance
30 • IIBEC Interface January 2025
between increased cost and increased power
production.
When designing a project, structural
analysis should always include the potential
added collateral load, as solar modules add
approximately 2½ pounds per square foot. A
rail-mounted system adds 3 pounds or more per
square foot. A rail-less system is lighter weight
because it eliminates the need for 85% of the
collateral load of rails.
Another design consideration is an
unobstructed roof area(s), free of shading issues.
Building components, such as plumbing stacks,
skylights, chimneys, and adjacent walls and
roofs, can create shadows on the solar system;
therefore, the system should be designed
to avoid obstacles and eliminate shadows.
Consideration should also be given to any future
buildings or trees planted near the building that
could cast a shadow on the system.
After the building design is finalized,
there should be a specific area called out as
the solar zone for the PV system. This is the
predetermined maximum roof area usable
and best suited for solar mounting considering
roof orientation, free space availability, and the
building’s consumption. Other issues that affect
the size of the solar zone include building and
fire codes, roof access paths for maintenance,
the balance of system components, and the size
of the array.
TYPES OF SOLAR MOUNTING
SYSTEMS ON METAL ROOFS
AND BEST PRACTICES
Solar modules are secured to metal roofs by
several methods, generally falling into two
categories: either flush mounted to achieve
maximum module density or tilted to achieve
optimal sun angle. Both methods result
in different energy outputs from a given
module or number of modules. These options
may have differing roof inter-row spacing,
structural engineering factors, and serious cost
implications, so initial cost and ROI should be
analyzed individually when considering and
comparing the two options.
In years past, when PV modules were at their
highest cost per watt and lower efficiencies, tilted
systems were the norm to achieve optimal sun
angle and were also demonstrably financially
prudent. Solar array design was driven primarily by
the high cost of the PV module, hence achieving
optimal sun angle using tilted mounting systems
was worth the added costs. Within the last decade,
PV costs per watt have fallen from dollars-to-dimes/
watt, so the gain in power production from optimal
sun angle seldom offsets the added costs of
tilting. Trends now favor lower-cost, flush-mounted
systems that facilitate higher power density (watts
per square foot) with less-severe wind effects and
other structural considerations.
The next consideration concerns further
details of the actual flush-mounting method.
RAIL MOUNTED
As demonstrated in Fig. 1, a typical rail-mounted
system utilizes aluminum or light-gauge coated
steel rails mounted above the seams or ribs of a
metal roof.
This method normally orients the rails traversing
the seams or ribs of the south-facing metal roof.
Most module producers specify the “grabs”
(hold-down clamps) for the module to engage
the module along the long dimension, resulting
in modules with “portrait” orientation to the roof
slope. In high-wind areas, additional rails are
sometimes necessary to provide another module
attachment point (Fig. 2). Continuous rail allows
neighboring modules to be within an inch or less
of each other, which may maximize power density.
The offset above the base roof surface
(usually 7 to 9 inches) allows easy access during
installation and extra space for microinverters,
optimizers, and rapid-shutdown equipment.
In climates prone to snow accumulation, the
forces acting on the surface of the module create
an eccentric loading (or moment arm) at the rails’
attachment points, increasing the forces applied
to the attachment components. This effect is
increased by higher offset dimensions (height
above the roof), snow load, and roof slope. These
variables must be considered in the design of the
system. The disadvantages of this configuration
Figure 1. Flush Rail Mounting; Use of rails on the metal roof is redundant and adds unnecessary
collateral load.
January 2025 IIBEC Interface • 31
include structural design complications, the
resulting additional material and labor costs
(over rail-less mounting), higher collateral loads,
and the (perceived or real) negative aesthetics of
a system raised above the roof.
Another version of a flush-rail PV mounting
system is a flush “short-rail” (aka mini-rail or
micro-rail), where short sections of rail are
mounted on metal roof ribs as needed, to mount
solar modules. These short-rails are installed
parallel or perpendicular to ribs, depending
on module orientation, and are sheet-only
attachments when used on face-fastened roofs.
While a short rail may save material costs and
lessen collateral loads compared with continuous
rails, the method of attachment should be
carefully scrutinized.
Many products simply use one or two sheet
metal screws on the top of the roof panels’
ribs. This method puts the fastening in direct
withdrawal and yields very low pull-out values in
light-gauge sheet metal. In contrast, fastening to
the side of the rib wall puts the fastening in shear
rather than direct withdrawal and is generally
preferred (Fig. 3).
RAIL-LESS MOUNTED
(DIRECT-ATTACHED)
Solar modules may also mount directly to the
seams of a standing seam metal roof or to the
ribs of a face-fastened metal roof, eliminating the
rail and related components entirely. Instead, the
seams or ribs inherent to the metal roof serve as
the mounting rails. The modules are installed in
landscape orientation (Fig. 4 and 5), still enabling
recommended anchorage at the long side.
This method is like the flush-rail mounted
system; however, it is lower in profile (usually 4
to 5¾ inches above the plane of the roof). This
mounting method provides a more uniform load
distribution to the roof and/or roof structure with
as little as 15% of the weight (collateral load) of
rails. Cost savings can be dramatic, especially in
regions experiencing high-wind exposure, as in
such cases the third rail is also obviated.
Another advantage of this method is that the
roof is replete with ribs or seams, so there is
increased module placement flexibility. Any loss
(if it occurs) of power and energy density should
be balanced against the rail material and labor
cost savings in the financial analysis.
CONCLUSION
With increasing popularity, the metal roof is
the ideal host for mounting solar PV due to its
extended service life. Alternative roofing types
will likely expire years before the life of the PV
system, leading to erosion of the aforementioned
ROI model.
Figure 2. Flush Rail Mounted Portrait with 3 attachment points per side.
Figure 4. Flush Rail-less Mounted Landscape with 3 attachment points per side.
Figure 3. Wind Uplift Load Reactions with fastener in pull-out and shear.
January 2025 IIBEC Interface • 33
Designers and owners should know about
roofing alternatives and their service lives
to bring added value to their customers.
When it comes to attaching solar modules to
metal rooftops, using conventional rails has
been the traditional method. Yet, familiar
concepts don’t necessarily deliver the best
outcomes. By installing solar on metal roofs
with lower material, labor, and shipping costs,
the rail-less attachment solution is proving
to be a green innovation in both the solar
and roofing industries. Solar engineering
procurement construction companies are often
underinformed on all these subjects.
Recyclable metal roofs have a demonstrated
service life several times that of any other
roof type and are never destined for a landfill.
Therefore, solar metal roof attachments enable
installation on most aged roofs without a roof
replacement. Production of rail-less systems
saves an estimated 90% of the energy used
to produce rail mountings and 85% of carbon
emissions in transportation, hence a much
lower carbon footprint.
Because of significant cost savings, time
savings, ease of installation and flexibility
of module layouts, simplified and low-cost
logistics, and a greater return on investment,
rail-less mounting on metal roofs is
gaining traction—fast. As more industry
professionals experience these benefits
firsthand, these innovations will continue to
be a go-to solution for metal rooftop solar
mounting.
ABOUT THE AUTHORS
Rob Haddock is a
metal roofing expert
who has worked in
the industry for 5
decades—first as a
laborer, then as a
contractor, forensic
analyst, technical
author, innovator, and
founder of S-5! He is
a member of NRCA,
ASHRAE, the American
Society of Civil Engineers, the Construction
Specifiers Institute, IIBEC, and ASTM. He is
also a lifetime honorary member of the Metal
Building Contractors and Erectors Association
and the Metal Construction Association.
Haddock innovated the concept of seam
clamps for standing-seam roof profiles. He
has served as faculty for the Roofing Industry
Educational Institute, RCI, and the University
of Wisconsin. He is a recipient of numerous
awards, including the RCI Richard M. Horowitz
Award and was a charter inductee to the Metal
Construction Hall of Fame.
Mark Gies is
director of product
management at S-5!
He has nearly 15 years
of solar experience
and over 30 years
of engineering
and management
experience. Prior
to S-5!, he held
management
positions at a mounting system company
and with a solar project developer.
His solar expertise includes product
development, operations, installation,
codes and standards, and sales and
business development. Gies is vice-chair
of the Mounting Systems Manufacturers
Committee at the Solar Energy Industry
Association, a member of the Structural
Engineers Association of California PV
Committee, and a founding member of
UL2703’s Standards Technical Panel.
REFERENCES
Metal Construction Association, Service Life
Assessment of Low-Slope Metal Roof Systems, Metal
University (white paper), https://metalconstruction.
org/index.php/ online-education/service-life-assessment-
of-low-slope-unpainted-55-al-zn-alloy-coated-
steel-standing-seam-metal-roof-systems—
published-102018.
Modern Steel Construction magazine, Sustainability By the
Numbers, May 2023, https://lsc-pagepro.mydigitalpublication.
com/publication/?m=7946&i=787638&p=20
&ver=html5.
Wiser, Ryan, Mark Bolinger, and Joachim Seel,
“Benchmarking Utility-Scale PV Operational Expenses
and Project Lifetimes,” Lawrence Berkeley National
Laboratory Electricity Markets & Policy Technical Brief,
June 2020, https://eta-publications.lbl.gov/sites/
default/files/ solar_life_and_opex_report.pdf.
Metal Construction Association, Metal Roofing and
Solar PV Systems: Part 1—Service Life Comparisons
(white paper), https://metalconstruction.org/index.
php/online-education/ metal-roofing-and-solar-pv-systems—
part-1—service-life-comparisons.
The White House, Inflation Reduction Act Guidebook,
https://www.whitehouse.gov/cleanenergy/ inflation-
reduction-act-guidebook.
Metal Construction Association, Metal Roofing
and Solar PV Systems: Part 2—Mounting System
Methods (white paper), https://metalconstruction.
org/index.php/ online-education/metal-roofing-
and-solar-pv-systems—part-2.
Figure 5. Flush Rail-less Mount.
MARK GIES
ROB HADDOCK
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January 2025 IIBEC Interface • 35