Wind
Resistance Begins at the Edge
By Amy Stokes
As
we
head into the heart of the 2007 storm season, I am reminded
of the annual barrage of photos flashed across television screens and
news papers depicting the countless damage inflicted by storms all
across the nation.
|
Hurricane season is a harsh reminder that
vulnerabilities in the design, manufacture and installation of roofing
systems carry a high cost. But hurricanes are not the only high wind
events that threaten roofs, and no area of the country is
exempt from
wind-related roofing damage.
FEMA
has divided the United States into four zones that reflect the number
and strength of extreme windstorms encountered in these regions. These
maps illustrate that, even if your building is not in the direct
path
of a potential hurricane, 40 years of tornadic and windstorm history
across our dynamic nation teaches us that any roof in any place at
any
time may be called upon to protect the building below and the
contents
within from devastating winds.
In recent years, codes and standards have evolved in response to
evaluations of roof performance during some noteworthy storms.
Organizations such as ANSI/SPRI, RICOWI, and
FM Global have led the
charge toward improving how roofing systems are designed, manufactured
and installed in hopes of preventing the kind of storm devastation our
country has seen in the past 15 years.
|
 |
 |
Last year, the
Roofing
Industry Committee on Weather Issues (RICOWI)
released its
investigative
report of the damage caused by Hurricanes
Charley (August 13, 2004) and Ivan (September 16, 2004). The goal of
this initiative is “to perform unbiased, detailed investigations by
credible personnel from the roofing industry, the insurance industry,
and academia. Data from these investigations will, it is hoped, lead
to
overall improvement in roofing system durability and a reduction in
insured losses, which may lead to lower overall costs to the public.”
  The
RICOWI report states “the mode of initial damage was
typically
related to perimeter edge flashing,” and that “most damage was
related
to perimeter problems.”
The frequency of roof perimeter damage found during RICOWI’s
investigation clearly supports conservative estimates from
organizations
such as Factory Mutual (FM) Global, that 75 percent of all
wind-related
roofing failures are attributed to insufficient or poorly installed
perimeter metals. RICOWI Investigators recommended that roof
perimeters
should be designed and installed following roof material
manufacturers’
recommendations in accordance with high-wind design guidelines such as
ASCE-7
and
ANSI/SPRI
ES-1.
ANSI/SPRI
ES-1 is acknowledged as the most important standard for roof
edge performance, and is incorporated into the 2003 (and subsequent)
International Building Code (IBC).
The ANSI/SPRI ES-1 standard is comprised of three tests:
|
RE-1
-
Test to failure – failure occurs when
the membrane detaches from the
edge termination, or the termination detaches from its mounting
-
Static test with 100-pound load every
foot used for ballasted systems;
a calculation based on fastener placement is used for mechanically
attached systems
-
Membrane is pulled at a 45-degree angle
to the roof deck to simulate
billowing
RE-2
-
Test to failure - securement loss of
any component of the roof edge
system, or deformation that would hinder weather protection at the
edge
-
Incremental load applied to fascia and
held for at least 60 seconds,
then removed and increased in increments of 25 psf until 150 psf, then
increments of 10 psf are applied
RE-3
-
Test to failure - securement loss of
any component of the roof edge
system, or deformation that would hinder weather protection at the
edge
-
Incrementally loads are applies as with the RE-2 test
-
Simultaneous loads applied to face and
top (back leg and top for one
sample, front leg and top for another). The lowest test results are
used.
Codes and standards aside, it is incumbent upon designers,
manufacturers
and installers to provide
performance-inspired
roofing and edge systems
to our customers who depend on our expertise. Designers bear the
burden
of specifying products that will perform as needed when needed, and
comply with ANSI/SPRI ES-1.
Contractors are responsible for correctly procuring and installing
those
systems. And, in addition to fabricating
fully
tested metal edge
systems, manufacturers must be prepared to
support
designers and
installers with guidance and instruction, and to provide a
Certificate of ANSI/SPRI ES-1 Compliance for each project.
|
 |
Click
here to request
more information about IMETCO's high-performance
metal edge, roofing and
wall systems.
|
