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Effective Low-Slope Roofing Begins With Secure Roof Edges

May 15, 2010

The edge of every low-slope roof can
become the cause of serious waterproofing
and roof system failures. Poor detailing of
perimeter securement systems can lead to
water ingress and, ultimately, failure of the
complete roof system. FM Global Loss
Prevention Data Sheet 1-49 cites a study of
insured losses involving built-up roofing
(BUR), showing that 59% of the cases
occurred because the perimeter membrane
securement failed. Further, the Roofing
Industry Committee on Weather Issues
(RICOWI), a nonprofit industry and re –
search organization assisted by Oak Ridge
National Laboratory, has consistently ob –
served similar consequences in each of its
Wind Investigation Reports,
which date back to Hur –
ricanes Charley and Ivan in
2004. One such RICOWI
report states, “The studies
reinforced the need for se –
cure roof edges, and codes
that require secure roof
edging to be enforced.”
Another report references
in surance industry estimates
that show wind-related
events result in more
than half of all insured disaster
losses, which totaled
over $300 billion between
1988 and 2007.
In spite of building code
requirements for performance
testing of edge metal
systems, these instances of
roof damage and failure due to insufficient
edge securement serve as evidence of the
lack of adequate design, construction, and
code enforcement prevalent in the industry
today. The International Building Code
(IBC) includes specific requirements for performance
testing of edge metal systems,
which, if properly applied and enforced,
could dramatically reduce losses during
wind events. Since the 2003 code cycle, the
IBC has required the following performance
and testing requirements for edge securement
of flat roofs:
1504.5 Edge securement for lowslope
roofs. Low-slope membrane
roof system metal-edge securement,
except gutters, shall be designed
and installed for wind loads in
accordance with Chapter 16 and
tested for resistance in accordance
with ANSI/SPRI ES-1, except the
basic wind speed shall be determined
from Figure 1609.
Notwithstanding the clear code requirement
that has been adopted in some similar
form by each state building code, it unfortunately
remains an exception, not the rule,
when an American National Standards
Institute/Single Ply Roofing Institute
(ANSI/SPRI) ES-1 tested edge metal system
is specified and installed.
The ES-1 standard
includes an analytical procedure
to determine the
required resistance of an
edge-securement system for
a specific project application,
as well as three test
methods to quantify the
ultimate capacity of a particular
edge-securement de –
vice or system.
The first test method,
RE-1, is known as the
“membrane pull” test and is
one of two required test
methods for fascia and
gravel-stop systems. This
Figure 1 – Hurricane Charley, 2004: Edge flashing damage initiates roof
blow-off. Photo courtesy of RICOWI.
S E P T E M B E R 2010 I N T E R FA C E • 2 1
test originates from the observed failure
mechanism of nonfully adhered membranes,
which can separate from the edge
securement and allow water ingress and
membrane failure due to rapid air infiltration
between the membrane and roof deck.
Note that edge-securement systems for use
with fully adhered roof membranes are
exempt from this test method.
For the RE-1 test method, sample specimens
of the edge-securement system and
membrane are constructed per manufacturer
or project details. The membrane is
then pulled upward and away from the roof
edge at a 45-degree angle. The edgesecurement
system is deemed to comply
with the standard if it provides a minimum
resistance of 100 pounds per linear foot for
ballasted roof systems or a calculated load
resistance based on fastener spacing and
applied wind pressure for mechanically
attached roof systems.
The RE-2 test method, “Pull-Off Test for
Edge Flashings,” is also applicable to fasciaand
gravel-stop-type systems defined as
having an exposed horizontal component of
4 in or less. For this test method, a full-size
specimen not less than 8 ft long is constructed
and statically loaded in a manner
that pulls the vertical leg of fascia or gravel
stop in a horizontal, outward direction. The
fascia is sequentially loaded with everincreasing
loads in accordance with the
procedure of the test method. Prior to each
increase in loading, the specimen is
unloaded to simulate the cyclic and transient
nature of wind pressures. It is often as
the specimen is being unloaded and allowed
to relax that many systems experience disengagement
of the fascia from the anchor-
Figure 2 – RE-2 pull-off test for edge flashing. Photo courtesy of Hurricane Test Laboratory
Patent #5,367,848
􀀃 􀀃􀀃
􀀃 􀀃
􀁎􀁡􀁫􀁡􀁬􀀃􀁧􀁭􀁪􀀃􀁯􀁝􀁚􀁫􀁡􀁬􀁝􀀃􀁙􀁬􀀲 􀁯􀁯􀁯􀀦􀁪􀁧􀁧􀁞􀁠􀁭􀁟􀁇􀁪 􀁞􀁙􀁰 􀁭􀁫 􀁙􀁬􀀲 􀀰􀀯􀀯􀀥􀀪􀀨􀀪􀀥􀀪􀀪
22 • I N T E R FA C E S E P T E M B E R 2010
ing cleat. For this method, the highest load
achieved prior to system failure or disengagement
is recorded as the ultimate blowoff
capacity of the edge-securement system.
The last test method, RE-3, is the “Pull-
Off Test for Coping.” By definition, any
edge-securement system for flat roof membranes
with an exposed horizontal exposure
greater than 4 in shall be tested in accordance
with RE-3. Similar to the RE-2
method, full-size sample specimens are
tested to failure. However, unlike the RE-2
method for fascia systems, the RE-3
method requires the wall coping system to
be loaded simultaneously in both an
upward direction (on the horizontally
exposed face) and in an outward direction
(on one of the vertically exposed faces). As
there are frequently variations in both the
exposed height and attachment method of
each of the vertical coping legs, the RE-3
method requires each coping system to be
tested twice —once while loading the outer
vertical leg and coping top face, and once
while loading the inner vertical leg and coping
top face. The testing procedure is similar
to the RE-2 method in that the copings
are successively loaded with higher and
higher applied static forces and are
unloaded and allowed to relax between each
successive loading. The lesser of the two
resultant ultimate loads prior to failure or
disengagement (either the outer or inner
vertical leg loaded simultaneously with the
top face) is recorded as the ultimate blowoff
capacity of the coping system.
Building codes require that edgesecurement
systems be performance tested
to meet or exceed the wind loads prescribed
by the code, but neither the International
Code Council (the body responsible for the
IBC) nor ANSI or SPRI provides a listing of
“certified” testing agencies or maintains a
registry of “approved” systems. Regarding
the qualifications of those performing the
test procedures and reporting the resulting
system capacities, a credible recommendation
would be to specify that “ES-1 testing
shall be witnessed by, and test reports prepared
and sealed by, a professional engineer
acting on behalf of a third-party international
accreditation service (IAS) ISO
17025-compliant testing laboratory.” Al –
though the code is nebulous as to what
might constitute acceptance of an ES-1 test
report, this measure of professional competence
will certainly ensure a large measure
of credibility for the submitted performance
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S E P T E M B E R 2010 I N T E R FA C E • 2 3
data. Considering the numerous manufacturers
and fabricators who have already
conducted ES-1 testing in accordance with
the above suggested specification, the availability
of systems capable of meeting the
building code requirements is certainly substantial.
To use the ES-1 test results for project
design and code compliance, it is first necessary
to determine the applicable design
wind loads to which the edgesecurement
system will be subjected. These
loads are given in the ES-1 standard and
are based upon the analytical design procedure
outlined in American Society for Civil
Engineers (ASCE) 7-02, “Minimum Design
Loads for Buildings and Other Structures.”
When calculating wind loads acting on the
edge-securement system at service-level
loads, there are a number of key factors to
note. First, the IBC wind speed map supersedes
that of ASCE 7-02 and the ES-1 standard.
However, through the IBC 2009 code
cycle, the wind speed maps have remained
identical to ASCE 7-02.
There are two other particular differences
between ANSI/SPRI ES-1 and the
provisions of ASCE 7-02. First, the directionality
factor, Kd, for building components
and cladding is given as 0.85 in ASCE 7-02
Table 6-4, while the ES-1 standard conservatively
takes this factor to be 1.0.
Secondly, ASCE 7 allows for a 10% reduction
in the external pressure coefficient,
GCp, for walls less than 60 ft high when the
roof slope is less than 10 degrees (ref. ASCE
7-02, Figure 6-11A, Note 5). Again, the
ES-1 standard conservatively ignores this
potential reduction of the design outward
wind pressure.
Perhaps the most important design consideration
when applying the ultimate ES-1
test capacity to building code design
service-level wind pressure is the (at best)
vague reference to allowable stress safety
Figure 3 – RE-3 pull-off test for copings. Photo courtesy of Hurricane Test Laboratory and IMETCO.
24 • I N T E R FA C E S E P T E M B E R 2010
factors or strength design load and resistance
factors within the ES-1 standard and
commentary. By studying the design example
and commentary within the standard
and from other sources, a designer may
mistakenly assume that any tested edgesecurement
that achieves an ultimate
failure load in
excess of the calculated
design wind
pressure is of sufficient
strength for a
given project application.
However, this
design methodology
leaves no “reserve
capacity” to account
for variation in test
values, equipment cal –
ibration, or—most
im portant—construction
tolerances, in –
staller craftsmanship,
and potential
wind events that may
exceed the design
wind speed. Like
every other material and system design
analysis, it is imperative that the designer
apply a factor to account for the potential
“real-world” deviations from laboratory predictions.
The SPRI ES-1 Task Force Com –
mittee has taken the official position that a
RCI 2011
􀏭􀆐􀆚􀀃􀁗􀅯􀄂􀄐􀄞􀀃􀇁􀅝􀅶􀅶􀄞􀆌􀆐􀀃􀍘􀍘􀍘􀍘􀍘􀍘􀍘􀍘􀍘􀀃 􀏯􀏬􀏬􀀃􀁚􀀒􀀯􀀃􀀘􀅽􀅯􀅯􀄂􀆌􀆐
􀏮nd􀀃􀁗􀅯􀄂􀄐􀄞􀀃􀇁􀅝􀅶􀅶􀄞􀆌􀆐􀀃􀍘􀍘􀍘􀍘􀍘􀍘􀍘􀍘􀍘􀀃 􀏭􀏱􀏬􀀃􀁚􀀒􀀯􀀃􀀘􀅽􀅯􀅯􀄂􀆌􀆐
3rd􀀃􀁗􀅯􀄂􀄐􀄞􀀃􀇁􀅝􀅶􀅶􀄞􀆌􀆐􀀃􀍘􀍘􀍘􀍘􀍘􀍘􀍘􀍘􀍘􀀃 􀏱􀏬􀀃􀁚􀀒􀀯􀀃􀀘􀅽􀅯􀅯􀄂􀆌􀆐
See What it Takes to Get Involved
􀀃 􀀃 􀀃
Test your knowledge of building en –
velope consulting with the follow ing
ques tions devel oped by Donald E.
Bush, Sr., RRC, FRCI, PE, past chair –
man of RCI’s RRC Examination
Develop ment Subcommittee.
1. What is the difference
between a hydrokinetic
metal roof system and a
hydrostatic metal roof
2. How much does a metal
roof move? The formula
used to determine the
estimated expansion of a
metal roof panel is
AL = L · ΔT · CX.
What does each component
of the formula represent?
3. How is side-to-side thermal
movement handled?
4. Aluminum panels are also
used in the metal roof
industry but are not as
popular as coated steel
panels. What two factors
are most responsible for
the difference in
5. Define the term “chalking”
in regard to a metal roof.
6. Define the term “fading” in
regard to a metal roof.
Answers on page 26
S E P T E M B E R 2010 I N T E R FA C E • 2 5
Figure 4 – Hurricane Charley, 2004: Coping blow-off. Photo
courtesy of RICOWI.
safety factor of 2.0 must be applied to the
ultimate test value prior to comparing the
system capacity to the applied design wind
pressure. In effect, we are comparing one
half of the tested system capacity to the full
magnitude of the anticipated wind force.
The newly published SPRI/FM4435/ES-1
(2010) standard now clarifies this design
methodology by explicitly multiplying the
design wind pressure by 2.0.
An excerpt from the RICOWI Executive
Summary of the Hurricane Ike investigation
should serve as an indisputable real-world
lesson on the importance of performance
testing, project design application, product
submittal review, and building code
The major problems were most often
caused by edge failure, leading to
membrane dislodgement and/or
punctures and tears due to flying
debris. Since 2003, the Inter na –
tional Building Code (IBC) has re –
quired that edge metal be designed
and installed in accordance with
ANSI/SPRI ES-1. Compliance with
the standard could significantly
reduce the damage from hurricanes.
Frank Resso, PE, is the director of engineering for IMETCO,
Inc. ( in Tucker, GA. For more than 13
years, he has been involved in project design and system
selection, product development, testing, and approvals of
metal roofing, wall panel, and edge-securement systems.
Resso is a member of several professional organizations,
including RCI, ASCE/SEI/AEI, and ASTM.
Frank Resso, PE
Answers to questions from page 25:
1. Hydrokinetic roof systems
are steep-sloped but not
watertight. Hydrostatic
roof systems are low-sloped
but watertight.
2. AL = Change in length of
metal panel.
L = The original length
of panel.
ΔT = The change in
CX = The coefficient of
expansion for the
metal being used.
3. By flexure at the side
seam, since the roof panel
width is only a few feet.
4. Cost and coefficient of
5. A release of pigment and
filler as the resin breaks
down from weathering.
6. Fade of coatings is a
permanent color shift,
generally with a loss of
color intensity.
Roof Technology and Science II
(RCI educational program)
26 • I N T E R FA C E S E P T E M B E R 2010
An investigation into the process used by California public school districts in
bidding reroofing projects has been conducted by the Assembly Accountability and
Administrative Review Committee. It determined that statewide, the practice of
what amounts to noncompetitive bidding is costing school districts $30 to $125
million each year.
The increased costs are “the product of aggressive marketing techniques by
roofing manufacturers, a tendency of districts to stick with manufacturers hired by
previous administrations, and a convenient reliance by district officials on the
manufacturers to write project specifications,” the legislative inquiry found.
State law requires competitive bidding in public projects, including schools,
but there’s little enforcement, industry experts said. Public agencies are allowed to
specify particular brand name products but must also include an “or equal” clause
that allows alternative manufacturers to be considered. The noncompetitive bids,
often written as a “convenience” for the school district by a manufacturer, get
around that clause by listing product requirements that are so specific that no
other manufacturer could qualify.
Assemblyman Hector De La Torre, D-South Gate (Los Angeles County), chairman
of the investigating committee that began the investigation after being tipped
off by a whistle-blower, called it a “systemic breach of trust,” saying he wants a fix
that will survive the constant churn of district facility administrators and legislators.
State officials don’t believe kickbacks or other misconduct are part of the
problem. The noncompetitive bidding is more a result of taking the path of least
resistance and little or no oversight of the process.
— San Francisco Chronicle
Proprietary Roof Bidding
Examined by CA Assembly