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Curtainwall Failures – Design or Products

November 23, 2017

Curtainwall Failures –
Design or Products
Karim P. Allana, RRC, RWC, PE
Allana Buick & Bers, Inc.
990 Commercial Street, Palo Alto CA 94303
Phone: 650-543-5600 • E-mail: bd@abbae.com
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Abstract
This presentation will examine recent window and curtainwall assembly failures and
performance issues for insulated glazing units (IGUs). With the advent of the globalization of
the construction industry, façade glazing systems are beginning to experience new types of
failure in their assembled components, resulting in performance issues with high-rise projects.
The speaker will present forensic study results from a dozen high-rise buildings with
curtain and window wall assembly failures.
Speaker
Karim Allana, RRC, RWC, PE — Allana Buick & Bers, Inc., Palo Alto, CA
Karim P. Allana is the CEO and senior principal of his firm. He
is a licensed professional engineer in California, Hawaii, Nevada, North
Carolina, and Washington. Allana has been in the construction industry
for over 30 years. He specializes in forensic analysis and sustainable
construction of roofing, waterproofing, and the building envelope.
He has acted as a consultant and expert witness in more than 250
construction defect projects and is a frequent speaker and presenter at
professional forums.
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This paper will focus on the causes
of the increasing number of window and
curtainwall assembly failures we are seeing
in high-rise buildings. Over the last 20
years, many developments have been made
in the construction of building skins that
impact the performance and life expectancy
of curtainwall and window assemblies.
These developments include advancements
in energy efficiency, recyclable content
in materials, global manufacturing, and
more prominent air barrier, LEED, and
International Code Council (ICC) requirements.
While developments are necessary
to improve energy efficiency, cost efficiency,
and sustainability, they can result in unexpected
consequences. We will examine how
these developments impact curtainwall and
glazing assemblies and contribute to unexpected
air and water intrusion stemming
from coating, seals, sealant, and insulating
glass unit (IGU) failures.
CURTAINWALL DEFINITION
According to the Whole Building Design
Guide, curtainwalls are walls that do not
carry floor or roof loads. Wind loads and
the curtainwall’s dead loads are transferred
back to the structure at the slab
edge. Curtainwalls are typically thin and
aluminum framed, with glass panels or
thin stone panels that “hang” like a curtain
from the building’s structure. The glazed
curtainwall system is often a metal frame
(usually aluminum) that frames glass, brick
veneer, metal panels, thin stone or precast
concrete. The inclusion of infill panels
within the curtainwall provides different
challenges. Challenges include maintaining
internal building temperatures, inhibiting
wind and water intrusion, and sustaining
the long-term performance of the building.
Remember, the main function of a curtainwall
is to keep the outside out.
The advent of glazed curtainwalls was
a marvel when first introduced, and many
American architects embraced them. Glazed
curtainwalls provide more interior space
than traditional bearing walls, they are less
expensive, quicker to construct, and provide
clean lines and greater sightlines. Over 100
years ago (circa 1909), one of the first examples
of a curtainwall was built in Kansas
City, Missouri. Architect Louis Curtiss combined
the new technology with established
period design elements to design a structure
that is still used today. The six-story Boley
Clothing Company Building features glazed
curtainwalls framed by traditional cast iron
and terra cotta ornamentation.
Over the course of time, cast iron has
given way to aluminum. Aluminum is lighter,
can be extruded, and can be coated
with a variety of high-performance coatings.
Glazing systems have improved over the
decades. Modern curtainwalls use double
or triple panes of glass, coated with silver
to provide low emissivity and improve thermal
efficiency. Gas filling with compounds
such as argon and krypton is often used to
improve an IGU’s “U” value. Air- or gas-filled
double/triple pane units have desiccants to
absorb moisture from within the glass and
prevent “fogging” or interior condensation.
TYPICAL CURTAINWALL SYSTEMS
Curtainwalls are comprised of two primary
components: the frame and the infill
panels. The components are commonly connected
to the building slab edge by means
of embeds and typically bypass one or more
floor slab edges. Curtainwall assemblies are
typically “unitized” or “panelized,” allowing
complete factory assembly of the curtainwall
components. They are engineered to
carry their own weight and to resist lateral
wind pressures and both thermal and seismic
movement.
THE FRAME
A typical curtainwall frame is composed
of steel, aluminum, multi-laminate glass, or
other resilient materials. The frame is the
support grid that holds the glass in place.
Common framing systems include in following:
• Stick systems are the most basic
type of curtainwall, with individual
mullions or framing elements
assembled in the field.
• Unitized systems apply the same
design principles as stick systems,
but sections of the curtainwall are
assembled (unitized) in the shop and
installed as a unit.
• Unit mullion systems combine
the preassembled panels of unitized
systems with the multi-story
vertical mullions of stick systems.
Upright mullions are installed first,
with horizontal mullions and glazing
installed as a unit.
• Column cover and spandrel systems
articulate the building frame
by aligning mullions to structural
columns. Preassembled or fieldassembled
infill units of glass or
opaque panels are fitted between the
column covers.
• Point-loaded structural glazing
systems eliminate the visible metal
framework by incorporating tension
cables, trusses, glass mullions, or
other custom support structures
behind the glass panels. Glazing is
anchored by brackets or by proprietary
hardware embedded in the
glass.
THE GLASS
Alastair Pilkington developed float
glass in the 1950s, which enabled production
of the large glass sheets that characterize
curtainwall construction. Plate glass
production begins when molten glass is
fed onto a bath of tin where it flows along
the tin surface and forms smooth glass
with even thickness. The glass is then
further fabricated, including cutting to
size, heat-treating, and application of lowemissivity
(low-E) coatings. Curtainwall
glazing ranges in price, durability, impact
resistance, and safety, depending upon
the manufacturing process of the glass.
Common glass types include these:
• Annealed glass undergoes a controlled
heating and cooling process
that improves its fracture resistance.
Despite its improved durability,
annealed glass can break
into sharp pieces, and many building
codes limit its use in construction.
Curtainwall Failures –
Design or Products
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• Tempered glass is either chemically
or thermally treated to provide
improved strength and shatter resistance.
On impact, tempered glass
shatters into tiny pieces that are
less likely to cause injury than larger
shards.
• Heat-strengthened glass and
chemically strengthened glass fall
between annealed and tempered
glass in terms of strength. Unlike
tempered glass, strengthened glass
can be sharp when shattered, so it
is best suited to areas with limited
access. Scratches in strengthened
glass have also been shown to compromise
its strength.
• Laminated glass bonds two or more
sheets of glass to an interlayer of
plastic, generally polyvinyl butyral
(PVB), which holds the glass in
place if broken. Laminated glass is
often specified for curtainwalls in
hurricane-prone regions or in areas
requiring blast protection.
• IGUs improve thermal performance
with double or triple panes of glass
separated by a space filled with air
or an inert gas.
• Spandrel glass, which is darkened
or opaque, may be used between
the head of one window and the sill
of the next. To create the illusion of
depth at spandrel areas, transparent
glass may be used in a “shadow
box,” with a metal sheet at some
distance behind the glass.
SYSTEM MANAGEMENT:
WATER PENETRATION
AND AIR INFILTRATION
All types of assemblies have to manage
water and air infiltration under wind-driven
pressure. Wind-driven pressure increases
with building height and allows for floor
deflection, seismic forces, and wind pressure.
High-rise buildings are subject to
higher winds, which create a positive pressure
on the windward side of the skin and
negative pressure on the leeward side. The
pressure differential can have the effect of
forcing air and water through or around the
skin assembly and into the building.
Generally, a curtainwall manages
water as a rainscreen design principal.
Rainscreens carefully manage the water and
air infiltration by allowing water to partially
enter the “wet” areas of the skin where it
can be managed and effectively expelled.
A rainscreen system (Figure 1) attempts
to maintain the same pressure in the wet
zone as the exterior face by unitizing an air
barrier between the interior and exterior
face of the building skin. The air barrier
prevents or reduces the differential pressure
gradient. Since the pressure differential is
responsible for driving the water inside, the
rainscreen system reduces the likelihood of
water intrusion. In addition to the air barrier,
seals and sealants are used to further
prevent air and water infiltration through
curtainwall skins.
Other more traditional systems of water
management include dry-gasket glaze and
wet-sealed barrier-type approaches. Drygasket
type systems assume that water will
bypass the exterior gasket. Once inside the
glazing rabbit or pocket, a series of internal
weeps or drainage holes is used to channel
or manage the infiltrated water back to
the building exterior. By contrast, the wetsealed
or barrier-type systems aim to completely
eliminate water infiltration and are
often used as repairs for previously failed
glazing systems.
SYSTEM MANAGEMENT:
THERMAL PERFORMANCE
A curtainwall’s thermal performance can
be divided between the framing and the
glass. While aluminum curtainwall frames
have many advantages, one disadvantage is
that they are inefficient at disrupting thermal
transfer. Aluminum frames quickly heat up
in warm temperatures and quickly cool down
in cold temperatures. This creates a thermal
bridge between the less conductive materials,
which allows for easy heat and cool flow.
The primary method for discouraging thermal
transfer is by creating thermal breaks.
The goal of a thermal break is to separate
the internal aluminum from the exterior
aluminum, preventing heat and cold transfers.
Polyamide is a typical material used in
thermal breaks and is an efficient isolator
between exterior and interior environments.
Glass is often the largest single component
of a curtainwall system and plays a
large role in determining “U” and solar heat
gain coefficient (SHGC) values. To reduce
heat transfer through the glass, a low-E
coating is added to the glass. Emissivity is
a measure of the ability of a surface to radiate
energy. In warm temperatures, low-E
coatings reflect a larger percentage of solar
radiation which, if left untreated, passes
through the glass as heat. During cool temperatures,
low-E coatings reduce convection
at the interior window surface and aid in
maintaining ambient interior temperatures.
Modern high-performance, low-E coatings
are comprised of multiple metallic layers
coupled with either one, two, or three
layers of silver. Many of the additional
metallic layers are utilized to reduce the
inherent reflectivity of the silver layer. Silver
is highly reflective and creates a mirror
effect if not otherwise dampened.
Building skins, especially those constructed
like curtainwalls, need to handle
many forces such as wind, rain, seismic
movement, and temperature differentials.
In order to properly ensure an effective
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Figure 1 – Detail of a unitized rainscreen curtainwall.
curtainwall design, laboratory and field
mock-ups are necessary based on ASTM
standards and American Architectural
Manufacturers Association (AAMA) tests:
AAMA 501.1 (water resistance), AAMA
501.2 (field testing), ASTM E330 (structural),
ASTM E331 (water resistance),
ASTM E283 (air resistance), and ASTM
E1105 (field testing). See Figure 2.
In theory, if the building skins are
designed, fabricated, and installed correctly,
in accordance with good industry
practices, they can stand for many
decades and perform as designed without
major issues. The Empire State
Building, which is over 80 years old,
was retrofitted with dual, energy-efficient
glazing in the existing curtainwall skin,
which is still performing. However, our
forensic studies have shown that even
the best designs are subject to failure.
Failure can occur for a number of reasons,
including substandard materials
and components, improper application
of coatings, cutting corners in fabrication
or erection, and poor design of assemblies.
These failures can result in air or
water intrusion, interior condensation,
aluminum coating failures, insulating
glass failure, glass breakage, and other
deficiencies.
COMMON MODES OF FAILURE
Repairs to fix building skins are often
very expensive, sometimes exceeding four
times the cost of the original construction.
Knowing what to look for, how to extend the
serviceable life, and when it is time to retain
a glazing expert are all critical in avoiding
costly and disruptive failures.
Like all building elements,
curtainwalls have weak points.
Although issues vary with
frame material, construction
methods, and glazing type,
there are some common concerns
that design professionals
look for when evaluating
the condition of a curtainwall
system.
GASKET AND SEAL
DEGRADATION
A common cause of curtainwall
complications is
failure of the gaskets and
seals that secure the glazing.
Gaskets are strips of synthetic
rubber (e.g., EPDM or silicone)
or similar types of tapes
compressed between the glazing
and the frame, forming a
water-resistant seal. Gaskets
also serve to cushion the glass
and accommodate movement
from wind, thermal, or seismic loads.
As gaskets age, they begin to dry out,
shrink, and crack. The elastic material
degrades when subjected to ultraviolet radiation
and freeze-thaw cycles, much like an
old rubber band. At first, air spaces are created
by the shrinking, dried gaskets, which
admit air and moisture into the system
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Figure 2 – ASTM E1105 water testing of a curtainwall.
Figure 3 – Example of gasketing failure.
(Figure 3). This can lead to condensation,
drafts, and leaks. As the gaskets further
disintegrate, they may loosen and pull away
from the frame. Without the support of flexible
gaskets, the glass loses stability and
may shatter or blow out. For this reason,
it is important to maintain and routinely
replace gaskets to keep the curtainwall system
operational and safe.
Shrinking of exterior gaskets is a common
concern and is not always easy to
fix. Although some systems, such as those
incorporating pressure bars, allow for gasket
replacement without removal of the glazing,
it is difficult or impossible to replace gaskets
in most curtainwall systems without
removing the glass. Wet sealing may be an
option. It involves cutting out worn gaskets
and adding perimeter sealant. However, wet
sealing does not generally result in a reliable
water barrier. It also creates a demand
for ongoing maintenance. In many cases,
the required ¼-in. minimum dimension
for the wet sealing is not present. Where
possible, it is best to maintain the original
glazing system and start with sustainable
gaskets capable of long-term performance
like silicone.
In addition to what one would normally
expect as failure-causing situations,
the advent of new sealants, gaskets, and
the associated chemicals has proven that
designers need to be conscientious of the
quality and durability of the gaskets incorporated
into these highly energy-efficient
curtainwall assemblies.
We have found that using a high-grade
rubber is not the only criteria for window
gaskets. While incorporating recycled materials
into new products is ecologically conscious
and commendable for many projects,
it can lead to additional gasket shrinkage
and inadvertent failure. Lastly, competition
and profit goals may drive manufacturers
to reduce polymers, ultraviolet (UV) protection,
anti-oxidation protection, and to add
more fillers.
In lieu of compression gaskets, some
curtainwall systems use structural sealant—
usually a high-strength silicone product—
to secure the glass to the frame. Like
gaskets, sealants have a finite service life
and require proper engineering to have the
necessary bond strength and waterproofing
characteristics. Signs that perimeter sealants
need replacement include shrinking
or pulling away from the surface, gaps or
holes, discoloration, and brittleness.
Sealants are known to break away
because of poor adhesion or improper application.
With thermal expansion, the difference
of aluminum expansion is 2.5 times
greater than that of glass, enabling large
relative displacements to cause many sealants
and seals to separate.
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Figure 4 – Path of water
intrusion over IGU glass edge.
Figure 5 – Example of glass
fogging in conjunction with
low-E corrosion.
A perfectly watertight designed curtainwall
cannot be maintained by sealants
alone. Redundancy in water protection that
incorporates an in-wall drainage system
and carefully considered sealant, is the best
way to avoid water infiltration and to mitigate
water damage.
IGU COATING AND
SEALANT FAILURE
All IGU manufacturers require their
units to be glazed within a framing system
that weeps water away from the insulating
glass perimeter seals. According to
the Glass Association of North America,
“Failure to properly glaze insulating glass
units may result in premature seal failure
and will void insulating glass warranties.
IGU sealants are also degraded by
prolonged exposure to water or excessive
moisture vapor.”
In the case in Figure 4, seals were ineffectively
executed or they degraded, allowing
water to enter the glazing system and
literally sit on top of the glass. As a result,
water or water vapor permeated the silicone
secondary seal and attacked the low-E
coating (located on the inside surface of the
exterior lite), causing glass corrosion.
High-performance, low-E coatings are
the most commonly used and have two or
three layers of silver in addition to other
metallic compounds. The black spots on a
mirror are analogous to the corrosion seen
in Figure 5.
Glazing seals typically incorporate a
combination of polyisobutylene (PIB) and
silicone sealants to hermetically seal the
inert air or gas between the dual or triple
glazing. Interior glazing seal failures can
occur due to a number of causes, including:
improper application of sealants, excessive
or prolonged exposure to moisture,
and changes in elevation and/or pressure
between the inboard and outboard glass.
See Figure 6.
In order to achieve the required bonding
between the PIB and the glass substrate,
insulating glass manufacturers remove the
low-E coating approximately ½ to ¾ of an
inch on the entire perimeter of a lite of
glass. This edge deletion allows the PIB and
secondary seals, such as silicone, to bond
properly to the glass. Failure of seals to
properly bond can result in PIB migration.
PIB migration (Figure 7) leads to both
a visually unappealing condition and a
potentially serious reduction in the insulating
glass unit longevity. There is no known
remediation method, and the condition is,
as far as we know, progressive. Over time,
the migration will worsen, leading to a
reduction in the service life of the IGU seal,
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Figure 6 – Example of a
total IGU seal failure.
Figure 7 – Example of PIB migration.
which in turn leads to premature fogging
and condensation within the IGU.
The migration of the PIB typically
takes place within the airspace of the
IGU, and the author believes it is triggered
or worsened by exposure to solar
radiation (heat) and
UV. Operable windows
also seem to display
more migration than
adjacent fixed panels,
which further reinforces
the notion of the
PIB as “thinning” as a
result of direct solar
exposure.
In the author’s
experience, this issue
is limited to PIB by a
particular manufacturer
that is gray in color.
In laboratory testing, it
has been determined
that the percentage of
solids (polymer) within
the gray-colored PIB is
64.8%, with plasticizers
as low as 2.6%.
This compares to control
samples of PIB that
have 97.5% polymer
and about 30% plasticizer
by weight.
GLASS FAILURES
Glass failures in curtainwalls can be
split up into several different categories.
Nickel sulfide (NiS) inclusions, thermal
cracking, and damage from impact are
the most common types of glass damage.
Nickel Sulfide Inclusions
NiS inclusions, also known as “glass cancer,”
are imperfections incorporated in glass
when it is manufactured. All glass has microscopic
inclusions resulting from the manufacturing
process which, generally speaking,
are of little concern. One exception is NiS
inclusions in tempered glass, which has led
to a number of dramatic glass failures.
As glass is heated during the tempering
process, NiS converts to a compressed
(alpha) phase. When the glass is cooled
rapidly to temper it, the trapped NiS lacks
sufficient time to return to a stable, lowtemperature
(beta) phase. The resulting
pressure leads to micro-cracks in the glass,
which can propagate until the glass structure
is thoroughly compromised and the
glass shatters in what seems to be a spontaneous
breakage.
In an existing structure, ultrasound,
laser imaging, or heat soak testing may be
used to identify NiS inclusions; however,
such test methods can be labor-intensive
and expensive. Specifiers should consider
not using tempered glass in these applications
or specifying “heat soaking” of the
glass, which virtually eliminates NiS inclusions.
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Figure 8 – Example of condensation failure.
Figure 9 – How condensation can occur.
Thermal Cracking
Thermal cracking is a notable concern
that engineers should consider when designing
curtainwall assemblies. When the sun
strikes the glass, it heats the exposed portion
of the pane, causing it to expand. The
unexposed edges remain cool, creating tensile
stress that can lead to cracking, particularly
in glass that has not been heat-strengthened
or tempered. Thermal cracks are easy to
detect, as they are usually perpendicular to
the frame and typically expand through the
entire window section.
Hairline cracks in glass may indicate
excessive thermal loading, particularly if the
glass has a coating, such as a low-E film or
tint. Low-emissivity coatings are placed on
the glass to reduce the building cooling load.
They redirect solar radiation away from the
glass while absorbing a fraction of that radiation
within the glass. This absorbed solar
radiation increases the temperature of the
glass and can cause it to expand unevenly,
resulting in thermal cracking. The more solar
radiation absorbed, the more likely the glass
will crack.
The likelihood of thermal cracking is
reduced by heat-treating the glass within
the IGU. Heat-strengthened glass can take
higher thermal stresses and is the typical
solution for heat absorption issues. In order
to properly design for low-E coatings, a specifier
should consider the stresses that will be
induced in the substrate glass and see if the
stresses will likely cause the glass to crack.
WATER INFILTRATION AND
CONDENSATION
Moisture damage is the most common
type of failure in curtainwall sections. Water
infiltration can cause glass corrosion, damage
interior finishes, lead to mold and mildew,
and degrade indoor air quality. Moisture damage
can be classified into two distinct parts:
water infiltration and condensation. In the
U.S. alone, water intrusion is responsible for
85% of all construction-related lawsuits.
Condensation on glass curtainwalls may
be an indication that the relative humidity
(RH) of the interior is too high, and an adjustment
to heating and cooling equipment is
necessary. However, condensation may also
point to failure of the curtainwall system.
Condensation on cold interior window
and curtainwall surfaces is caused when
warm, moist air comes into contact with a
window surface that is at or below the dew
point temperature. Modern aluminum window
and curtainwall design uses “thermal
breaks” to limit the transfer of outside cold
temperatures to the interior window or curtainwall
where warmer humid air can cause
condensation. As mentioned above, thermal
breaks attempt to disrupt a thermal bridge
between the exterior and the interior.
Condensation occurs when the temperature
of the glass or aluminum frame in a curtainwall
reaches the dew point temperature of
the interior space conditions. Water forms on
the surface of the glass or aluminum and can
cause damage to the interior finishes. Basic
design against condensation ensures that the
condensation resistance factor (CRF) of a given
curtainwall section meets the requirement of
the space, which is based on the expected temperature
and humidity of the space. Designers
should be aware that the CRF is an average
and cannot account for cold spaces in the
facility that can cause localized condensation
(Figure 8).
A proven method to prevent condensation
in curtainwall frames is to use thermally
broken aluminum. Thermal breaking is where
one or more pieces of polyamide or other
material are incorporated within the aluminum
frame, which significantly decreases
the temperature transfer from the aluminum
exterior of the curtainwall to the interior
surfaces.
For example, a reduction in the transfer
of cool exterior temperatures decreases the
possibility of condensation on the interior
aluminum surfaces. Another proven method
of limiting condensation is by incorporating
thermal breaks within the design, providing a
limited amount of non-thermally broken aluminum
to be exposed to exterior conditions.
Condensation can be just as damaging to
interior surfaces, such as drywall and wood
trim, as water infiltration. In some cases, it
appears that a window is leaking when, in
fact, it is condensation. Design guidelines
are particularly important for avoiding the
creation of thermal bridges that will actually
bypass the thermal breaks within a window
system. As our detail in Figure 9 shows, even
with a thermally broken aluminum window
frame, factors like the method of attachment
to the rough opening and under-functioning
window components such as gasketing can
cause exterior temperatures to be transferred
to interior surfaces.
The Whole Building Design Guide (WBDG)
states that when designing a curtainwall glass
unit in areas where high humidity is required
within the space (such as hospitals) or where
configurations are abnormal, software modeling
is a must to ensure that condensation (Figure
10) does not occur. The WBDG also states laboratory
tests simulating indoor and outdoor air
temperatures and humidity of the space are good
practice to see how a glass panel will perform.
Specified tests are AAMA 1503.1 and National
Fenestration Rating Council (NFRC) 500.
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Figure 10 – Condensation on an interior window surface.
DESIGN AND CONSTRUCTION
DEFECTS
As with any type of construction, curtainwalls
are subject to the shortcomings of
manufacturing, installation, and human capability.
Material failure and age-related deterioration
may be common causes of curtainwall
distress, but many premature and costly failures
are attributable to avoidable errors.
Missing, incorrectly applied, or otherwise
deficient sealants at frame corners and other
intersections can lead to serious water infiltration
issues. Failure on the part of the contractor
to follow manufacturer’s guidelines,
and improperly manufactured sealants and
gaskets can result in premature failure that
is both difficult to access and expensive to
repair.
Flashing detailing requires fastidious
attention to prevent leaks at intersections
between the curtainwall and other building
elements. Without detailed contract documents
that fully describe and illustrate perimeter
flashing conditions, along with coordination
between the curtainwall installer and construction
manager during installation, flashings
may not be adequately tied or terminated,
permitting water to enter the wall system.
Poorly installed trim covers and accessories
can also pose a danger to people
and property below. Trim covers (Figure 11)
and accessories can be snapped in place or
adhered using structural glazing tape alone
without mechanical attachments.
However, poor quality
control of the products during
the manufacturing process
can provide potential
problems in the long term.
Dies used for extruding covers
can wear out, resulting in
poor fit and holding strength.
Checking for tolerances and
proper preparation and adhesion
can be critical to longterm
performance.
We have found that corrosion
of metal surfaces is
accelerated if the proper preparation
and coating requirements
are not followed. When
measured with an Elcometer,
we have seen a 0.3-mil paint
coating that was found to be
0.1 mil or less.
There are several architectural-
grade paint finishes
available on the market, but
we typically recommend fluoropolymer paint
finishes (like Kynar) that meet AAMA 2605
certification. But like all paint, even Kynarbased
paint finishes need proper preparation
and application to perform as intended (see
Figures 12 and 13).
Paint finishes are either “wet,” like the
typical Kynar application, or “dry,” like powder-
based paint finishes. Both are applied
electrostatically, so application is limited to
factory environments.
Paint failures are relatively infrequent
when compared to some of the other failure
modes in window-wall and curtainwall systems,
but remediation of failures is particularly
difficult. Often, the failure is related to
lack of or inadequate pretreatment or where
primers are part of the application but were
improperly applied to the base metal being
painted.
There are firms that specialize in field
recoating of failed paint finishes. Most of
these firms use a water-based paint due
to concerns about volatile organic compounds
(VOCs) and toxic-smelling aftereffects
of painting. While warranty periods of
10-15 years are available from the recoating
applicators, the original warranty on AAMA
2605-compliant paint finishes ranges from
10-30 years with accelerated aging studies,
indicating that a properly applied paint finish
has a life expectancy exceeding 40 years.
CONCLUSIONS AND
LESSONS LEARNED
Curtainwall systems, particularly in
high-rise buildings, can fail for a variety
of reasons. They require specification,
inspection, testing, and verification to avoid
premature failure. Typical failure modes
include water infiltration, glazing failure,
and gasket and seal degradation.
While the IGU industry has made great
strides in the last 30 years to reduce failure,
we have seen new IGU failures over the last
five to ten years. The new failures include
flowing PIB sealants, as well as a lack of
edge deletion of the low-E coating from the
glass perimeter, leading to poor sealant
adhesion and corrosion of the low-E coatings
themselves.
IMPORTANCE OF
CONSCIENTIOUS DESIGN
From the descriptions of failures faced
in curtainwalls and the examples discussed
in this report and the presentation, several
different conclusions can be deduced. First
and foremost, an engineer or curtainwall
design professional should be involved in all
aspects of curtainwall design.
These professionals should be aware of
the proper techniques to prevent failures,
such as new performance issues plaguing
the industry. A thorough understanding of
waterproofing issues, glass failure issues,
installation issues, poor visual performance,
and poor thermal performance is necessary
during the design phase.
Design professionals should also be
aware of and consider the strengths and
weaknesses of various materials during
material selection. From our earlier discussion
about gaskets and seals, we have
learned that seals with excessive fillers or
recycled materials break down much quicker
than virgin material, possibly because
the recycled portion has lived its useful life
already and there is no longer the resiliency
or sealing capacity that there once was.
Unforeseen structural interactions
among building elements may lead to failure
if the curtainwall has not been properly
engineered. Inadequate provision for
differential movement, as well as incorrect
deflection calculations, may be responsible
for cracked or broken glass, seal failure, or
water intrusion. Glass and framing must be
evaluated not only independently, but also
as a system, with consideration given to the
impact of proximal building elements.
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Figure 11 – Sample of trim cover failure.
EVALUATION AND TESTING
If leaks, deflection, etched glass, or
other issues have become a concern, an
architect or engineer should conduct a systematic
evaluation of the curtainwall system,
beginning with close visual inspection.
ASTM and AAMA provide test standards for
the evaluation of air and water penetration,
as well as structural performance of glass
in curtainwall applications. Field tests for
water penetration, such as ASTM E1105,
use a calibrated spray rack system with a
positive air pressure differential to simulate
wind-driven rain. ASTM E783 specifies test
procedures for determining field air leakage
at specific pressures.
Laboratory and field tests on projectspecific
mock-ups should also be specified
to ensure proper performance according to
the manufacturer’s standards and guidelines.
These tests ensure that mistakes
caught early on in the project can be corrected
or rectified while changes to design
are at a less costly stage of construction.
Curtainwall failures can be prevented by
proper consideration of potential failures
and ensuring proper installation and maintenance
of curtainwall sections.
Glazing that displays systemic issues
or other defects after installation may need
to be evaluated for structural integrity. In
such cases, a representative sample of glass
units may be removed and tested under
laboratory conditions. ASTM E997 is one
test method for determining the probability
of breakage for a given design load.
MAINTENANCE CONSIDERATIONS
Anodized and painted aluminum frames
should be cleaned as part of a routine maintenance
program to restore an even finish.
For powder coats, fading and wear can be
addressed with field-applied fluoropolymer
products, although these tend to be less
durable than the original factory-applied
thermosetting coatings. Other coatings
on the market aim to improve durability,
but their track records and maintenance
requirements should be considered prior to
application.
With changes in building codes requiring
more energy efficiency, curtainwalls have
become more complex with new modes of
failures such as low-E coating failure, condensation,
air infiltration, etc. Global manufacturing
has resulted in its own set of issues
such as substandard gaskets, coating, and
seals, as well as fit and finish problems.
Design professionals and contractors need
to be vigilant and learn from these new types
of failures.
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Figure 12 – Example of paint failure.
Figure 13 – Example of paint failure.