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Standing Seam metal Roofing: The Next Big Disaster in the Roofing Industry?

May 15, 2005

A P R I L 2005 I N T E R FA C E • 1 5
Iinterviewed with a school district
several years ago for an open-end
contract for roof consulting services.
At the conclusion of our typical presentation,
one of the board members
asked my opinion of metal roofing,
and specifically, “slope conversions.” At the
time, I was not aware that their intent was
to install slope-conversion metal roofs to all
of their existing schools. I made the statement
that “standing seam metal roofs”
would be the next major disaster in the
roofing industry, that the details are critical,
and the ability to “fix” these roofs after
construction can be difficult. I then tried to
explain the problem is not the product or
system, but the need for knowledge of these
systems from the manufacturer, design professional,
roofing contractor, and other subcontractors.
This could not be accomplished
within the remaining 45 seconds of
the interview, and we obviously were not
selected for the project. A valuable lesson
was learned. Do not make bold, firm statements
on an issue without adequate opportunity
to explain your position.
Why then the outrageous title of this
article? To give myself the opportunity to
explain that with proper knowledge and
guidelines, standing seam metal roofing is a
valuable option for many owners, and many
common problems can be easily eliminated.
We have completed numerous investigations
of metal roof
systems, the majority
of which were less
than five years old
and had numerous
leaks. Often the reported
leaks disappeared
for a period of
time after “repairs”
had been completed,
then reappeared at a
later date. The focus
of our investigations
was not for litigation,
which we refrain from
whenever possible, but to identify the problems
and provide potential long-term solutions.
In this evolution, we have developed a
design checklist intended to eliminate the
majority of problems before they happen.
METAL ROOFING DESIGN CHECKLIST
1. A roof design should obviously meet
the applicable code requirements
(these are minimum standards).
Please note the previous three model
codes and the International Building
Code 2000 and 2003 have made
some significant changes in regard
to roofing. Also realize the definitions
within the code may not parallel
industry standards. (See Figure 1.)
2. As a starting point, the following
industry standards contain good,
generic construction requirements
and detail recommendations:
a. The Roofing and Waterproofing
Manual 5th Edition, National
Roofing Contractors Association
(NRCA), Architectural Sheet Metal
Manual, Sheet Metal & Air
Conditioning Contractors’ National
Association, Inc. (SMACNA),
and Metal Roofing Systems
Design Manual, Metal Building
Manufacturers Association
(MBMA).
b. As a minimum, the NRCA
Roofing and Waterproofing
Manual, 5th Edition and the
Figure 1 – IBC definition.
Standing Seam Metal Roofing
(SSMR) Construction Details for
both architectural and structural
systems should be the
basis for all design development.
Specific, custom details will still
be required for unique or special
penetrations and project-specific
terminations.
c. As a minimum, recommend
adding the following to your general
notes and specifications:
“All clarifications or additional
information needed
shall be in accordance with
the criteria and details of
the NRCA Roofing and Waterproofing
Manual and the
Architectural Sheet Metal
Manual. Any deviation from
the specified or indicated
requirements shall be submitted
for approval by the
designer or owner’s representative
prior to installation.”
3. Exposed fasteners in the flat of the
roof panel, although commonly
accepted or allowed by the manufacturer,
should be avoided to the
greatest extent possible. Exceptions
do exist, especially in high wind
zones.
4. The SMACNA Architectural Sheet
Metal Manual, 6th Edition, is a good
source for details and criteria for
various sheet metal systems and
components but requires specific
needs to be identified for the job
since various configurations exist
for different components and are
typically recommended versus required.
5. Do not write specifications that rely
on or allow the manufacturer to
determine the acceptability of a condition
or the details to be used. The
specifier’s design (details) should
establish the minimum requirements.
Proprietary specifications for
contractors, suppliers, or manufacturers
are also not recommended;
neither are open specifications that
everyone meets (i.e., typical ASTM
specifications).
6. Clearly show sections of construction
requirements for the roof
assembly, including structural
framing, deck, insulation, underlayment
systems, and the transition
into the various terminations.
7. Metal does not leak; the penetrations
and terminations do. For this
reason, specific custom details will
still be required for penetrations and
terminations. Exposed sealants are
a good indicator that improper
details are being used.
8. Provide a new roof plan. Identify
slopes and indicate all penetrations
and terminations. Provide applicable
details and references for the pene-
Figure 2 –
Gutter interior
corner baffle/
conductor
head.
16 • I N T E R FA C E A P R I L 2005
Figure 3 – “Z”
purlin/bearing plate
(clip assemblies).
trations and terminations. Isometric
details are preferred.
9. For roof replacements and slope
conversions, provide an “Existing
Roof Plan,” identifying existing
assemblies and locations of penetrations
and terminations. Indicate
which penetrations are to be abandoned
and show on the “New Roof
Plan” which penetrations are to
extend through the SSMR.
10. For roof replacements and slope
conversions, coordinate the “Existing
Roof Plan” and “New Roof Plan”
with the structural specifications
and drawings.
11. The drainage design of metal roof
systems must address the typical
sizing of gutters and downspouts,
but must also address problems
unique to these types of systems
(see Figure 2).
a. The location and size of the gutter
must compensate for the
slope of the roof so that the gutter
is not overshot or overloaded
in individual locations.
A common problem is at valleys
where the standing seam
configuration directs water to
valleys and overshoots or overloads
gutters at these locations.
Valleys may need baffles on the
outer edge at the gutters. At
larger roof areas or longer valleys,
a conductor or collector
head may also be incorporated
Photo 1 – Drainage deficiency on a one-year-old project.
A P R I L 2005 I N T E R FA C E • 1 7
into the gutter system (see
Figure 3).
b. Downspout sizes and locations
must also consider drainage at
“the worst case locations” and
gutter expansion joint locations.
Due to the standing seams, a
large area of roof drainage can
be directed to a single location.
(See Photo 1.)
12. The low end of a valley should not
terminate into a wall or at a corner.
It must extend at least one foot
beyond the corner to permit proper
detailing and sufficient drainage.
This conflicts with typical structural
design/detailing. An inverted “V” or
diverter is recommended in the valley
(see Photo 2.)
13. Two types of metal roof systems are
most commonly used commercially
today: Architectural Standing Seam
Metal Roofs (ASSMR) and Structural
Standing Seam Metal Roofs
(SSSMR). Significant differences
exist in the supporting structures,
materials, profiles, insulation, installation,
and details of the systems.
Hybrids of these two types
also exist, causing further confusion.
Also, metal roof systems are often
proprietary in some respect, and
selecting and specifying systems
takes effort and research.
14. All SSSMR should ensure positive
drainage with a minimum finished
one-quarter-inch-per-foot slope, per
industry standards. (ADC Engineering,
Inc. recommends a minimum
1:12.) Architectural SSMR typically
requires a minimum 3:12 slope.
(ADC Engineering, Inc. recommends
a 4:12.)
15. Structural or non-structural metal
roof systems designed over rigid
board insulation (polyisocyanurate)
and metal decks are unique. This
configuration is becoming common
in the industry, but there are limited
data available for wind and fire
ratings and detailing.
Two common but different attachment
methods also exist: (1) a “Z”
purlin that rests in the bottom of the
rib opening of the metal deck and
matches the thickness of the insulation;
or (2) a metal-bearing plate
that sits on the insulation, the clip
assembly sits on the bearing plate,
and two long fasteners attach
through the insulation into the
metal deck (see Figure 4).
In either case, the availability of
adequate testing of these assemblies
is the issue, and the level of uplift
performance they have achieved
must be coordinated.
The specified type of metal (commonly
aluminum, Galvalume®, or
galvanized steel), the gauge, the
panel profile, and the width of the
panel will also affect the wind rating
of the metal roof system.
16. Panel gauges and profiles can also
significantly affect performance,
flashing compatability, wind resistance,
oil canning, and structural
compatibilities, not just aesthetics.
17. Design requirements for wind uplift
are addressed by: (1) completing calculations
based on the appropriate
design standard (i.e., ASCE 7 or the
applicable code); and (2) determining
the increased uplift forces at the
various corner and perimeter locations.
Actual uplift testing based on the
specific standard (UL, FM, ASTM E-
1592, etc.) must also be completed
for a similar assembly including the
type, gauge, profile, and seam configuration.
The design professional must then
Photo 2 – Improper valley detail and termination.
Figure 4 –
Ridge cap
flashing
(double
closure).
18 • I N T E R FA C E A P R I L 2005
make a determination that the specific
assembly can meet the specific
uplift forces based on a clearly
defined attachment method for the
panel in the field, corner, and perimeter
locations.
Although the design requirements
and uplift testing provide limited
information specific to flashing,
appropriate requirements must be
incorporated into the various termination
details (i.e., eave, rake, hips,
ridges, etc.) for these forces and
must be shown in the design and
submittal process.
18. All roof systems experience varying
uplift forces at corners and perimeter.
Ensure that the design and submittals
clearly identify boundaries of
the perimeter and corners and how
the increased attachment occurs at
these locations. Secondary framing
is often in these locations. Also be
aware of the restrictions on wind
speeds with warranties for metal
roof systems. Requirements for thermal
calculations are needed to
determine the anticipated movement
and to allow this movement
within the detailing of penetrations
and terminations.
a. The type of clip and its positioning
are critical to provide the
ability for movement.
b. The state of expansion of the
metal during application affects
the installation and detailing.
c. The point of fixation varies in the
industry. Some fix the panel at
the eave, others fix the panel at
the ridge, and on occasion it is
fixed at a midpoint. This will
affect the wind uplift resistance
and detailing.
19. Additional or secondary steel framing
are always a controversial issue.
Numerous benefits are gained by
providing these members around
the perimeter of buildings and at
various penetrations. In re-roofing
applications, the existing structure
often requires additional framing at
perimeters. Do not recommend eliminating
these members without
proper research and coordination.
20. All ridge and hip closures should
have redundancy within the detail.
Panels should have end dams and a
closure detail to provide long-term
performance. This is a common
problem area, especially on lower
slopes (see Figure 5).
21. Penetrations through roofs should
consider the location of the standing
seams and the width of the panel to
ensure that the penetration occurs
in the flat portion of the panel and
that adequate drainage can occur
around the penetration. As noted
above, the size at the opening
around the penetration must allow
for thermal movement (see Photo 3).
22. Oi1 canning is not a uniformly
defined term in the roofing industry,
and the level of acceptable oil canning
is always a difficult problem to
resolve in the field. Establishing a
level of acceptance prior to construction
based on a similar project or
mock-up within the contract is an
option to consider.
The type of metal, slope of the roof,
color, width of panel, and panel configuration
are design items that can
have an effect on the degree of oil
canning. Storage, placement, and
installation methods can also have a
significant effect, as can the coil
A P R I L 2005 I N T E R FA C E • 2 1
stock and roll forming methods
(especially smaller, on-site units).
23. Factory color finishes can pose several
problems: (Note that painted
Galvalume® is AZ50 vs. uncoated
AZ55. Many specs wrongly call for
AZ55 with Kynar finish.)
a. Submittals seldom provide the
required test data for the various
color finish tests, especially with
federal guide specifications.
b. Warranties do not provide protection
that the finish will perform
in line with the specified
tests. As always, warranties
have substantial exclusions and
are written for the benefit of the
manufacturer, not to protect the
owner.
c. Also be aware, there is a “shell
game” as to who is responsible
for what — the panel manufacturer,
the coating manufacturer,
the coil coater, or the coil metal
manufacturer.
d. Note that many warranties do
not cover projects in coastal
environments or certain types of
facilities (i.e., residential, condominiums,
etc.)
24. Manufacturers’ warranties should
be based on the owner’s requirements.
Warranties do not protect
owners; they limit liabilities of the
manufacturers. Do not make decisions
in regard to the roofing system,
its details, or variations based
on a warranty being provided. Also,
all jobs should require an independent
two-year contractor warranty
as a minimum.
25. Two types of insulation are commonly
installed directly under a
SSMR System.
a. Batt (fiberglass) insulation is
commonly used under SSMR
systems. A common issue is the
decreased insulation R-value at
structural members where the
insulation is compressed. This is
also a potential condensation
area.
b. Rigid board insulation is used
below both architectural and
SSMR. Available testing of these
assemblies, noted previously,
must be confirmed. Also, thermal
efficiency should consider
the thermal bridging created by
the clip assembly and fasteners
and gaps in the insulation, especially
at “z” purlins.
26. Rigid board insulation should be
installed in at least two layers with
joints staggered between layers for
most roofing systems. Insulation
should be thick enough to span rib
openings on metal deck and fall
within minimum and maximum
thickness limitations of FM or UL as
applicable.
a. Clip assemblies and attachments
can affect the ability to
provide two layers of insulation.
b. Maximum thickness of insulation
can affect the uplift resistance
of the clip attachment.
27. The heights of penetrations, parapet
walls, and insulation must be considered
and addressed, especially
perimeter conditions and penetrations
such as roof-mounted equipment.
28. Use crickets and diverters to direct
water away from penetrations. As a
minimum, provide two times the primary
slope to ensure resulting surfaces
drain properly. Also consider
the size of penetrations and the
metal panel widths.
Photo 3 – Classic improper penetration flashing.
22 • I N T E R FA C E A P R I L 2005
Figure 5 –
Deficiency
roof plan.
29. Do not use interior built-in gutters
or built-in downspout systems unless
unavoidable. When used, incorporate
waterproof liners and plan for
regular inspections and maintenance.
30. Vapor retarders or barriers may be
required within some roof assemblies
based on geographic location
and interior humidity levels (see
Photo 4).
31. Counterflashings should include
pre-fabricated inside and outside
corners, two-piece arrangements,
and hemmed edges. Coordinate or
merge metal roof specifications and
sheet metal specification requirements
and materials.
32. Coordinate lightning arrestor systems,
photoelectric sensors, fire
alarm transmitters, antennas, and
other unique penetrations by showing
them on the roof plan and providing
appropriate details for attachment
and penetration through the
specific roof system.
33. A minimum distance of twelve inches
between all penetrations and terminations
should be maintained for
proper flashing. Penetrations should
occur in the middle (in between the
standing seams) of a panel, or if
wider than an individual panel
cricket, incorporated into the detail.
34. Minimize penetrations to the greatest
extent possible.
a. Use round shapes to construct
equipment supports and avoid
use of pitch pans. For lower
sloped metal roofs, the equipment
supports should be a minimum
of 14 inches high, but not
less than shown in the table
below. Note that these are guidelines
and must be varied based
on the slope of the roof.
35. If milestone or full-time quality
assurance services are planned for a
project, early involvement (i.e., during
the design process) by the consulting
firm can provide numerous
benefits. Recommend the consulting
firm conduct pre-roofing conference
meetings as the highest priority and
then milestone inspections during
the early stages of the project.
A P R I L 2005 I N T E R FA C E • 2 3
Photo 4 – Significant condensation within ridge cap.
WIDTH OF HEIGHT OF LEGS
EQUIPMENT (ROUND PIPE
PREFERRED)
Up to 25″ 14″
25″ to 37″ 18″
37” to 49″ 24″
49″ to 61″ 30″
61″ and wider 48″
fiberology.
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I N T E L L I G E N T R O O F I N G S O L U T I O N S
YEARS OF PROVEN
PERFORMANCE
VISIT US AT RCI BOOTH #115
The exponential increase in demand for construction materials in China has affected prices worldwide, impacting U.S. materials costs,
according to Construction Executive magazine. In the middle of the tenth phase of its 50-Year Plan, China consumes 25% of the world’s
steel supply and 40% of its cement supply. China, a large producer of steel, has redirected
previously exported steel to fill its own domestic demand and reduced the material’s
availability on the open market. U.S. tariffs on imported steel were removed in
2004, but rising domestic demand keeps prices high.
According to a study done by Engineering News Record in September 2004, reinforcing
bar prices had risen 45.2% in the U.S. between September 2003 and September
2004. During the same period, lumber prices rose 28.8%; structural steel, 25.7%; plywood,
21.5%; ready-mix concrete, 2.8%; and cement, 2.5%.
China’s gross domestic product (GDP) increased by 9.1% in 2003. Its GDP is
expected to reach $1.5 trillion in 2004 and $1.61 trillion in 2005, with the gross value
of its construction industry reaching $522 billion in 2005.
— Construction Executive and Professional Roofing
Inspections made after problems
occur or at the end of the project
focus on defining what can be
accepted versus providing a quality
roof system.
CONCLUSION
The above checklist will bore some and
infuriate others, but hopefully it will provide
some insight and information for most
readers. It was not intended to answer all
questions or to discuss all of the problems
with standing seam metal roofs, but outline
many of the common plights and shortcomings.
The viewpoint is intended to be generic
and objective from a design professional
perspective.
ADDITIONAL SOURCES OF INFORMATION
1. Architectural Sheet Metal Manual,
6th Edition, Sheet Metal & Air
Conditioning National Association
(SMACNA), 1993.
2. Manual for Inspection and Maintenance
of Low-Sloped Structural
Metal Panel Roof Assemblies, National
Roofing Contractors Association,
2002.
3. Newman, Alexander, Metal Building
Systems Design and Specifications,
1997.
4. Metal Roofing Systems Design (First
Edition), Metal Building Manufacturers
Association for the Metal Roofing
Systems Industry, 2000.
5. The NRCA Roofing and Waterproofing
Manual, Fifth Edition, National
Roofing Contractors Association.
6. Haddock, Rob, Metal Roofing From A
to Z.
24 • I N T E R FA C E A P R I L 2005
Richard L. Cook Jr., RRC, RWC, RRO, is a principal of ADC
Engineering Inc., Hanahan, SC. Rick has authored numerous
papers on the subject of roofing systems and wind-related
damages. He has presented several papers at national symposia
and conferences, including the American Society of
Civil Engineers, the Construction Specifications Institute,
RCI, and the Federal Construction Committee in Washington,
D.C. Cook has also presented dozens of papers at local and
regional meetings and conferences related to roofing and
waterproofing in the construction industry.
Richard L. Cook Jr., RRC, RWC, RRO
A survey recently published in Roofing Contractor magazine of over 1,500 professionals
responsible for commercial properties revealed some interesting responses.
One question asked who performs scheduled maintenance on the roof. Answers were:
44% internal; 44% contractor; and 12% roof consultant.
Copies of the survey are available for purchase at www.roofingcontractor.com.
— Roofing Contractor
The U.S. Department of Labor
(DOL) issued its final ruling on the Fair
Labor Standards Act’s child labor standards
in the Dec. 16, 2004, Federal
Register.
A provision was added prohibiting
workers under 18 years old from “all
work on or about a roof, including work
performed upon or in close proximity
to a roof.” Previously, youths were
banned from all roofing occupations but
not from working on or near them.
Youths in a roofing apprenticeship or
student-learner program are exempt
from the ban.
— U.S. Dept. of Labor
TEENS
RESTRICTED
IN ROOFING
China Growth Affecting U.S. Construction Prices
Survey Shows Maintenance Breakdown