Conventional and Nonconventional Repair of Curtain Wall Systems

Conventional and Nonconventional
Repair of Curtain Wall Syst ems
Kamran Farahmandp ur,
FRCI, RRC, RWC, REWC, RBEC, PE, CCS, CCCA, FNAFE
Building Technology Consultants, PC
1845 E. Rand Road, Arlington Heights, Illinois 60004
Phone: 847-454-8814 • Fax: 847-454-8801 • E-mail: kamif@btcpc.com
S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 5 F a r a h m a n d p o u r • 5 5
ABSTRACT
This paper will cover the typical failure mechanisms in curtain wall systems, the conventional
repair approaches, and a discussion of advantages and disadvantages of each repair
approach.
A case history involving nonconventional repairs to a large commercial building curtain
wall system will be presented. These repairs included retrofitting an existing curtain
wall system with new custom-extruded external pressure bars and caps to address several
issues, correcting displaced mullions, and replacing mechanical louvers integrated into
the curtain wall system. The repairs also included overcladding the barrier panels between
curtain wall sections with a new system that incorporated an air and water-resistive barrier
and a drainage plane.
SPEAKER
Kamran Farahmandpour, FRCI, RR C, RWC, RE WC, RBE C, PE , CCS, CCCA, FNAFE
— Building Technology Consultants, PC
Kam RAN Farahma ndpour is the principal of Building Technology Consultants, PC.
He specializes in the forensic investigation and repair of building envelope systems. Kami is
a Fellow of RCI and a Fellow of the National Academy of forensic Engineers. He has served on
many technical committees and boards of directors of various organizations. His involvement
with the building envelope industry has earned him many awards—both for his contributions
to the industry, and for his work on various projects.
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ABSTRACT
Many buildings built in the late 20th
and early 21st centuries included glass and
metal curtain walls. Some of these buildings
are approaching the age when deterioration
of glazing gaskets and internal curtain wall
seals can result in leaks. In other buildings,
fading of exterior components, failure of
insulated glass units, and/or the need to
improve energy efficiency is necessitating
major rehabilitation of these curtain walls.
This paper will summarize the typical
failure mechanisms in curtain wall systems,
the conventional repair approaches, and
a discussion of advantages and disadvantages
of each repair approach. For a more
detailed discussion of deterioration mechanisms
in curtain wall systems, refer to SWR
Institute’s A Practical Guide to Waterproofing
Exterior Walls, Chapter 4.
A case history involving nonconventional
repairs to a large commercial building
curtain wall system will be presented. These
nonconventional repairs included retrofitting
the curtain wall system with new customextruded
external pressure bars and caps to
address several issues, correcting displaced
mullions, and replacing mechanical louvers
integrated into the curtain wall system.
The repairs also included over-cladding the
decorative metal cladding panels between
curtain wall sections with a new system that
incorporated an air and water-resistive barrier,
and a drainage plane.
INTRODUCTION
Glass and metal curtain wall systems
have been used to construct all or portions
of building exterior walls since the mid-
1900s. New innovations in glass, glazing,
and thermal technologies have improved
the performance of these systems over the
years. Modern curtain wall systems provide
many advantages such as improved aesthetics,
lighter weight, rapid construction,
flexibility in design, abundant daylighting,
and even improved thermal performance.
Although older glass technologies such as
insulated glass units (IGUs) helped improve
the thermal performance of curtain wall
and window systems, recent advancements
including low-e coatings and low-conductivity
gas fills have helped glazed systems
achieve more acceptable thermal performance
for the exterior walls.
Early curtain wall systems did not include
insulated glass and were constructed of steel
framing members. Newer systems include
variations of IGUs and thermally broken
aluminum frame systems. Typically, thermal
performance, water and air infiltration
resistance, fabrication and erection methods,
and structural performance requirements
dictate the type of curtain wall system that is
selected for each application. Obviously, cost
is also a consideration, but should not override
the importance of system performance.
The thermal performance of a curtain
wall system is a function of its framing
assembly and glazing. Although possible,
upgrading the framing systems is costly and
not practical in many cases. Upgrading the
glazing is typically more feasible, depending
on the original design of the glazing pocket
and the system’s framing.
Curtain wall systems are different from
storefronts and many windows in that
they incorporate elaborate internal drainage
mechanisms and often include pressure
equalization and complex water management
technologies to reduce potential for
water infiltration.
Water infiltration and air infiltration
resistance of curtain wall systems typically
depend on the integrity of their glazing seals
and internal drainage system. The outer
glazing seal system typically provides the
first line of defense against water infiltration,
while the interior glazing seals provide
resistance against air infiltration, a critical
aspect of pressure equalization. The internal
drainage system typically consists of
end dams or zone dams at ends of each
horizontal mullion, and weeps that allow for
water to drain to the exterior. Deterioration
of exposed sealant joints can also impact
water and air infiltration resistance of a
curtain wall or window system.
Typically, the aesthetics of the system
are dictated by the overall design of the
framing system, feature strips (metal cladding
panels integrated into the design of the
curtain wall system), and glass appearance.
Changing the configuration of a curtain
wall’s framing system is usually not practical.
However, changing glazing will typically
provide an opportunity to upgrade the system’s
appearance. Retrofitting the framing
or replacement of exterior mullion caps can
also provide an opportunity to change or
upgrade the appearance of the system.
DETERIORATION MECHANISMS IN
GLAZED SYSTEMS
Typical deterioration mechanisms of
curtain wall and window systems can be
divided into the following three categories:
Aesthetics Degradation
The aesthetics of a curtain wall system
can be adversely affected by long-term
exposure to elements. Such degradation can
consist of fading or peeling of metal frame
finishes, as well as staining of glass and
metal components due to sealant plasticizer
migration or etching of the glass and metal
because of alkalinity of adjacent cementitious
materials.
Fading of metal frame systems is directly
related to the quality of finishes and
exposure to ultraviolet (UV). Peeling of metal
finishes can be due to improper surface
preparation during the original coating process,
or exposure to salts in service (such
as areas of curtain walls in coastal environments,
or those adjacent to walks where
deicing salts are used).
Glass staining is sometimes referred to
as “picture framing.” This phenomenon has
been well-documented and is typically due
to migration of plasticizers from older silicone
sealants that may have been used as
glazing, used in repairs, or used in adjacent
joints. This phenomenon can also impact
the metal framing components.
Water and Air Infiltration Issues
Water and air infiltration issues are
some of the most common problems with
curtain wall systems. When manifested
Conventional and Nonconventional
Repair of Curtain Wall Syst ems
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in recently installed
curtain wall systems,
they are typically
indicative of installation
or design issues.
However, as properly
designed and installed
curtain wall systems
approach 20 or more
years in service, many
of their internal seals
and exterior weather
seals deteriorate,
resulting in air and/
or water infiltration issues. Other factors
such as deterioration of expansion joints
can also lead to air and/or water infiltration
problems.
Glazing Gaskets
One of the most common deterioration
mechanisms in curtain wall systems is the
degradation of glazing gaskets. Most curtain
wall systems rely on preformed gaskets for
a watertight seal between the glass or spandrel
panels and metal components. These
gaskets serve as the primary seal against
air and water infiltration. Glazing gaskets
are made of various materials, including
neoprene, EPDM, silicone, and other elastomeric
materials. Gaskets are either molded
or extruded. Extruded gaskets have to be
cut to length and jointed with adhesive at
the mitered corners. In some cases, the corners
are simply miter-cut at the appropriate
angle and not adhered. In other cases, the
gaskets may be cut at 90-degree angles and
simply butted against the gasket on the
adjacent side of the glazing. Molded gaskets
have integrated mitered corners with no
seams and typically provide a better seal at
the corners.
Inside set-glass curtain wall systems
typically incorporate a combination of a
preset “bedding” gasket on the exterior, and
a “drive-in” wedge gasket on the interior.
Outside set-glass systems have a “bedding”
gasket on the interior and a “drive-in” wedge
gasket on the exterior. Preset gaskets can
typically not be removed and replaced easily,
while drive-in wedge gaskets can.
Depending on gasket type, prolonged
exposure to UV can result in hardening,
shrinkage, and crazing (cracking) of the gasket
material (Photos 1 and 2). In some cases,
gasket shrinkage is significant enough that
the gaskets shrink
away from glass corners,
resulting in
loss of watertightness.
Molded gaskets
can pull out of their
retaining grooves due
to shrinkage, and
extruded gaskets can
simply shrink away
from the corners,
leaving the corners
with no waterproofing
protection (Photo
3). Although most
curtain wall systems
incorporate internal weep systems, a weep
system typically cannot accommodate significant
water infiltration due to gasket
deterioration and shrinkage.
Exterior Sealants and Expansion Joints
Curtain walls systems also depend on
exterior sealants and expansion joints to
prevent air and water infiltration. In fact,
many building façades are comprised of
curtain wall sections adjoining other types
of cladding systems. In such systems, the
exterior sealant joints between the curtain
wall system and the adjacent cladding
materials are critical in maintaining the
watertight integrity of the façade. Sealants
are also used to form expansion joints
within the curtain wall systems.
A discussion of failure mechanisms in
sealant joints is beyond the scope of this
article. However, it should be noted that
due to their low thermal mass, curtain
wall systems are subject to frequent thermal
movements. If sealant joints within
the system or around the perimeter of the
system are not designed properly, failures
can occur. Proper design of the joint, proper
selection of the sealant materials, and
proper installation are key in ensuring longterm
performance of the joints. Industry
standards such as ASTM C1472,1 ASTM
C1193,2 and SWR Institute’s “Sealants: The
Professional’s Guide” provide good information
on these topics.
Building expansion joint accessories are
often incorporated into the building façade
to accommodate building movements. If not
properly integrated with the curtain wall
system, or if not able to accommodate inservice
movements, expansion joints can
also be a source of water or air infiltration.
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Photo 1 – Crazing
of glazing gaskets
in a curtain wall
system.
Photo 3 ––Extruded glazing gasket shrinkage.
Photo 2 –
Shrinkage
of glazing
gaskets.
Internal Seals
Most curtain wall systems rely on their
internal drainage system to accommodate
incidental water that can bypass the primary
seals. The internal drainage system typically
consists of horizontal troughs formed
by various framing members (often referred
to as “glazing pockets”), end dams, or zone
dams to control flow of water in those
troughs, and sealants to ensure watertight
integrity at various joints. In most cases,
original deficiencies in the application of
the internal seals may not manifest until
the primary seals deteriorate sufficiently
to allow a significant amount of water to
enter the system. In other cases, material
deterioration or movement at the connection
can cause failure of the internal seals.
Once internal seals fail, the drainage system
will not be able to control incidental water,
resulting in water infiltration.
Another issue with internal seals is
the shrinkage of thermal breaks. Thermal
breaks are incorporated in the same members
that form the drainage troughs in the
system. Once thermal breaks shrink, they
result in either separation from the end
dams or separation from the shoulders of
the thermal break. In either case, water
leakage can result.
Thermal Performance Issues
Curtain wall systems can also suffer
from thermal performance issues. These
issues can result in excessive energy usage,
condensation, and thermal discomfort for
building occupants.
In most cases, thermal performance
deficiencies are due to original design and
construction of the system, and are not
related to ongoing deterioration or aging.
However, some in-service deterioration or
damage can cause thermal performance
issues. As examples, IGU seal failures can
be considered a thermal performance issue
that is a result of ongoing deterioration.
Additionally, in-service damage to interior
vapor retarders of spandrel panel insulation
can also cause localized condensation.
Structural and Safety Issues
Many other distress or deterioration
mechanisms in curtain wall systems can
pose structural or safety concerns. These
include, but are not limited to, loose mullion
caps, glass breakage, and corroded or
distressed connections.
Many curtain wall systems incorporate
snapped-on, prefinished aluminum extrusions
that cover the mullions. Typically,
these components only serve an aesthetic
function and do not impact the performance
of the system.3 However, in some
thermally improved systems, mullion caps
can contribute to additional thermal performance
for the system. The proper fit of
these components is dependent on tight
manufacturing tolerances. Temperature
changes, frequent removal and reinstallation,
or improper manufacturing tolerances
can result in dislodgement of these covers.
If dislodged, mullion covers can pose a serious
fall hazard.
As previously discussed, curtain wall
systems are subjected to extreme thermal
fluctuations. Unlike other building envelope
systems such as masonry, stone, or concrete,
curtain wall systems have a relatively
small thermal mass. This characteristic
results in rapid thermal changes in the system
components. During a hot summer day,
a portion of a dark curtain frame exposed
to sunlight can reach 170ºF or more. While
a masonry wall may take several hours to
reach such peak temperatures, a curtain
wall can reach these temperatures after a
short period of exposure to sunlight on a
warm summer day. Conversely, a curtain
wall system can also cool rapidly due to its
small thermal mass.
The small thermal mass of curtain wall
systems, combined with extensive use of
aluminum in curtain wall frames (aluminum
has a relatively high coefficient of
thermal expansion), make curtain wall systems
particularly prone to thermal-induced
deterioration. The thermal expansion of a
20-ft.-tall aluminum mullion subjected to
a temperature range of -20 to 170ºF is over
5/8 inch. While the curtain wall system can
undergo such significant movements, the
structural frame of the building, which is
protected from temperature fluctuations,
undergoes very little thermal movement.
This results in differential thermal movements
between the curtain wall system
and the building frame. Building frame
deformations such as creep and deflections
also exacerbate such differential movement
between the curtain wall system and the
building frame. The connections of the curtain
wall system to the building frame must
be designed to accommodate such movements,
while properly transferring curtain
wall gravity and wind loads to the building
frame.
Thermal cycles can result in loosening
of bolted connections to the building frame
or failure of the connections. If not designed
or installed properly, curtain wall framing
members are overstressed, resulting in bowing
or deformation to accommodate thermal
movements.
In addition to thermal movements,
attachment brackets can fail due to other
causes, including the following:
1. Attachment brackets can fail due to
improper design of the gravity support
brackets. Typically, the gravity
load of the curtain wall system is
transferred to a limited number of
attachment brackets within a section
of the curtain wall, usually
referred to as “dead-load connections.”
The remaining brackets within
that section of the curtain wall are
designed to only resist wind loads
and accommodate the in-plane thermal
movements of the curtain wall
system. These “wind-load connections”
cannot support gravity loads.
This typical configuration results in
large gravity loads to be transferred
to the dead-load connections. If not
properly designed, the dead-load
connections can fail. The failure may
be in the form of complete fracture
of the connection brackets, failure of
the bolts, or yielding of the components.
2. One often overlooked failure mechanism
is the failure of the connection
brackets due to lateral thermal
movements. As mentioned above,
in most cases, the wind-load connection
brackets are designed to
accommodate vertical movements.
However, they are not designed
to accommodate horizontal movements.
In such cases, the horizontal
thermal movements are accommodated
by flexing of the brackets.
The author is familiar with projects
at which building occupants have
reported loud noises during periods
of rapid temperature change. These
noises have been traced to unaccommodated
horizontal movement of
the curtain wall system.
3. The attachment brackets can also
fail due to corrosion. While most
curtain wall components are constructed
of corrosion-resistant components,
the attachment brackets
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or anchors can be made of carbon
steel without any corrosion protection.
In combination with condensation
or continued water leakage,
such components can sufficiently
corrode to cause failure of the connection.
Another contributing factor
is galvanic corrosion due to contact
between dissimilar metals.
REPAIR APPROACHES FOR CURTAIN
WALL SYSTEMS
Repair methodologies to address curtain
wall issues can range from simple cleaning
or sealing to complete replacement. This
section provides a brief summary of typical
repair approaches used to address various
curtain wall issues.
Before any repair program can be undertaken,
the scope of the project needs to be
thoroughly defined through the investigative
process. All too often, repairs have been
undertaken to address one known symptom,
only to find later that the root cause has not
been addressed, and the original symptoms
reappear. For this reason, it is important to
understand the cause(s) of each encountered
issue, so that an appropriate solution can
be developed. It is also important to evaluate
the effectiveness of each repair through
mock-ups and verification testing.
Any repair design should consider costs,
anticipated service life of the repairs, maintenance
requirements for the repairs, reliability
of the repairs in addressing the
issues, and inconvenience to the building
occupants. When developing repair alternatives,
it is imperative to discuss the advantages
and disadvantages of each repair
approach with the building owner so that
he or she can make an informed decision
regarding the repairs.
This section focuses
on addressing water
infiltration issues. For
more information on
repair approaches for
other issues, refer
to SWR Institute’s
A Practical Guide to
Waterproofing Exterior
Walls, Chapter 4.
Conventional Water
Infiltration Repairs
Weep Cleaning and
Baffle Replacement
Where the system’s
weeps and baffles are accessible, they
can be cleaned to ensure optimum performance
of the drainage system. In some
cases, such cleaning may be sufficient to
relieve the system of excessive water that
results in interior leaks. If accessible, cleaning
of the weeps and replacement of baffles
can be far less costly than other repairs.
Wet Glazing
One of the most common and least
expensive repair approaches to address curtain
wall water infiltration issues is to seal
all exposed glazing and frame joinery with
sealant. This approach is typically referred to
as “wet-sealing.” Wet-sealing involves application
of sealant over glazing gaskets and at
all other locations where water infiltration
into the system can occur. Although sealing
of exposed frame joinery need not necessarily
be included in a wet-sealing project, it often
is. Wet-sealing of glazing typically consists of
cutting and removing the exterior portion of
the glazing gaskets and applying a cap bead
of sealant around the
glazing. In addition,
frame joinery can be
sealed. However, in
most cases, decorative
mullion caps are not
removed to seal frame
joinery. Instead, sealant
is applied at all
mullion cap interfaces.
Some wet-sealing
projects involve the
use of silicone strips
or premolded silicone
shapes to seal mullion
and frame joinery
(Photo 4).
The wet-sealing approach attempts to
minimize the impact of internal seal issues
by minimizing water penetrating into the
system. Ideally, a wet-sealing repair renders
the curtain wall system a barrier system.
However, the success of wet-sealing is highly
dependent upon workmanship and the
geometry of sealant joints used for the wetsealing
project. Rarely, adequate geometry
can be accomplished at exposed frame or
mullion cap joinery that can accommodate
differential movements between those components.
In such cases, the use of silicone
strips or premolded custom silicone boots
can help provide for a watertight condition.
While wet-sealing can yield adequate
results, it is often considered a shorter-term
repair because it is highly dependent on
performance of the sealant joints. Although
the sealant materials used for the repairs
can last more than 20 years, joint failures
can occur due to improper geometry and/or
workmanship issues. As such, wet-sealing
is not considered a long-term solution to
water infiltration issues. Nonetheless, this
approach can provide some building owners
with an economically viable repair with a
reasonable level of service.
Glazing Gasket Replacement
Where severely deteriorated glazing gaskets
cause excessive water infiltration into
the system, they can be replaced. Glazing
gasket replacement poses some challenges.
These include the difficulty in removal and
replacement of preset gaskets. In such cases,
deglazing (removal of IGU) may be necessary
to accommodate gasket replacement.
Removal and replacement of glazing gaskets
only on the exterior side of the system
may not necessarily be sufficient. The inte-
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Photo 4 – Premolded silicone boots used to seal framing
joints.
Photo 5 – Repair of internal seals by deglazing.
rior gaskets provide for an air seal and are
a part of the pressure equalization system.
If interior gaskets have shrunk, causing
large openings, they have to be removed
and replaced, as well. In many cases, due
to interior finishes concealing spandrel panels,
some interior gaskets cannot be easily
accessed for removal and replacement.
Internal Seal and Thermal Break Repairs
Repair of internal seals is not performed
on a routine basis. Such replacement will
necessarily require deglazing to expose the
internal seals (Photo 5). In some cases,
repair of internal seals may be possible by
removing exterior pressure bars to expose
glazing pockets. However, such repairs are
difficult and not as reliable as those made
where glazing is removed from the system.
Deglazing and internal seal repairs are
very costly when performed on the entire
curtain wall system. However, performing
such repairs on a localized basis to address
certain water leakage issues is commonly
performed.
Addressing thermal break issues will
also require deglazing to expose the thermal
breaks. Once the thermal breaks are
exposed, they can be cleaned and sealed.
An important consideration for internal
seal and thermal break repairs is ensuring
proper surface preparation and removal of
old deteriorated sealant. Due to complex
geometry of glazing pockets and such joints,
complete removal of existing sealant may
not be practical.
Complete
Replacement
Complete replacement
of the entire
system is always an option. This approach
can help resolve all performance issues,
including aesthetic degradation, air and
water penetration, thermal performance,
and failed or inadequate connections.
Although typically the most costly option
and most disruptive to building operations,
complete replacement of the system may be
a good option for some building owners who
demand energy efficiency, watertightness,
and updated aesthetics.
Unconventional Water Infiltration
Repairs
The original design and construction of
each curtain wall system can be unique. As
such, it may be possible to develop specific
repair schemes to address each curtain wall
system.
One such unconventional repair scheme
is the use of custom extruded pressure bars
and mullion caps to retrofit existing systems.
This approach can be used to modify
the size of the glazing pocket to accommodate
IGUs, provide a thermal break in the
mullions, and/or provide improved geometry
for wet-glazing. In most cases, such
repairs can cost a fraction of replacement
and can be performed from the building
exterior to minimize disruption to building
operations.
Development of unconventional repairs
poses a risk to the designer and building
owner since these repairs are not “tried and
true.” For that reason, careful consideration
should be given to the repair objectives.
In many cases, 3-D modeling of custom
extrusions and their intersections may be
needed to properly design a profile that can
accommodate complex joinery. Design of
snapped-on components also requires careful
consideration to avoid parts that would
be too difficult to fit onto each other or too
loose to maintain mechanical interlock.
The author has designed unconventional
repairs to many curtain wall and window
systems. In all those cases, custom-extruded
components have been used to improve the
performance of the system. The case history
presented in this paper discusses an example
project where unconventional repairs
were designed and implemented.
CASE HISTORY
The subject building is an eight-story
office structure with mechanical penthouse
level on the top floor. The building was built
approximately 25 years ago.
The building frame consists of structural
steel. The building façades along the
south, east, and west elevations are primarily
clad with an aluminum-framed and glass
curtain wall system (Photo 6). At the north
elevation, the building façade consists of
aluminum-framed and glass curtain wall
along the ground level and the stair enclosure,
and precast panels with punched
storefront window systems on the remainder
of the façade. Where the building is
clad with a curtain wall system, the system
consists of interior-set vision and spandrel
glass panels. Glazing pockets at horizontal
mullions have integrated internal drainage
with end dams at the ends of each mullion.
The curtain wall system is panelized
between column lines with a barrier-type
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Photo 7 – Barrier-type metal cladding
strips between curtain wall sections.
Photo 6 – Overall view of the south
and west elevations of the building.
decorative metal cladding system separating
the curtain wall panels (Photo 7). The joints
in the barrier metal cladding are sealed with
field-applied liquid sealant. On the east and
west elevations of the penthouse level, large
aluminum louvers serving the HVAC equipment
have been integrated into the curtain
wall system (Photo 8).
On the south elevation, the building
columns extended above a setback terrace
area forming decorative buttresses (also
Photo 8). These buttresses had been clad
with a barrier-type prefinished aluminum
cladding system.
The building had suffered from façaderelated
water leaks since its original construction.
Most of the leaks were reported
along the south and east elevations. The
curtain wall-related water leakage had been
so pervasive that plastic buckets had been
placed along vision glass sills throughout
the building. After each rainstorm, the
building engineering staff reported hundreds
of leaks throughout the areas clad
with the curtain wall system.
The author’s firm was retained by the
building owner’s architectural consulting
firm to evaluate the water infiltration issues
into the building and to develop repair recommendations.
The scope of the investigation consisted
of review of the curtain wall shop drawings,
a visual review of the building exterior,
water testing, removal of mullion caps to
examine frame joinery, and preparation of
a report.
The investigation revealed several issues
associated with the curtain wall system.
These included faded aluminum finishes,
deteriorated glazing gaskets,
deteriorated or open sealant
joints at barrier metal cladding
(Photo 9), inadequate
internal seals, open-frame
joinery, displaced or rotated
mullions, and extensive water
leakage issues below the louver
assemblies. In addition,
dislodged and loose mullion
caps were observed at several
locations. Extensive water
leakage below the louvers
was also confirmed through
water testing.
Repair Options Developed
for the Building Owner
Based on the findings of
the investigation, four repair options were
developed for the owner’s consideration.
These repair options were as follows:
1. Option 1 – Surface Repairs: This
option consisted of removal of the
exposed portions of the glazing
gaskets and application of sealant,
replacement of sealant joints at barrier
cladding system, and installation
of custom-molded silicone boots
at mullion cap intersections. The
estimated cost of these repairs was
$800,000 to $1,200,000.
2. Option 2 – Sealing Frame Joinery
and Wet-Sealing: This option consisted
of removal of the exposed
portions of the glazing gaskets and
application of a cap seal, at the
replacement of sealant joints at barrier
cladding system, removal of
existing mullion caps to allow sealing
of frame joinery, and attachment
of new mullion caps. The estimated
cost was $1,500,000
to $2,000,000. This
option would provide
for better aesthetics,
improved
durability, and
improved reliability
as compared to
Option 1.
3. Option 3 – Retrofit
With Custom-
Extruded Components:
This option
consisted of removing
the existing mullion
caps, installing
a new custom-extruded pressure bar
system over the existing frame, wetsealing
the perimeter of the glazing,
providing a self-adhered air barrier
over the existing barrier metal cladding,
and over-cladding the metal
cladding components with a drainable
cladding system. Estimated cost
was $2,500,000 to $3,000,000. This
option would provide for better aesthetics
and improved durability and
performance as compared to Option 2.
4. Option 4 – Complete Removal and
Replacement: This option consisted
of complete removal and replacement
of the curtain wall system. The
estimated cost for this work would
exceed $10,000,000.
The advantages and disadvantages of
the above options were discussed with the
building owners on several occasions. The
implementation of Option 4 would make
it difficult to occupy the building during
construction. As such, this option was
eliminated in the early stages of discussions
with the building owner. Of the remaining
options, the advantages of Option 3 were
most appealing to the building owner without
a significant financial penalty. As such,
the building owner opted to authorize the
design and implementation of Option 3.
Design of Repairs
Figure 1 depicts the basic concept of
Option 3 repairs at a typical horizontal mullion.
The repairs would consist of trimming
the exposed portions of the glazing gaskets,
removing the existing snapped-on mullion
caps, cleaning the frame surfaces, installing
a custom-extruded aluminum pressure bar
set in sealant, applying perimeter glazing
6 2 • F a r a h m a n d p o u r S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 5
Photo 8 – Large HVAC louvers installed within the
curtain wall framing.
Photo 9 – Failed sealant joint at decorative metal
cladding joint.
sealant, and installing a
new custom-extruded,
prefinished aluminum
snapped-on cap. The
new pressure bar would
be 1/2 inch wider than
the existing frame members,
allowing a glazing
sealant depth of 1/4
inch. In addition, the
new pressure bar sealant
shoulder would be
placed approximately 3/8
inch away from the exterior
face of the IGU to
allow for suitable sealant
geometry. Such sealant
geometry is far more reliable
than a sealant cap
bead typically used for wet-seal repairs.
Once the new pressure bar was installed,
weep holes would be drilled at the same
locations as the existing weeps so that the
internal water management of the system
would function as originally intended.
Although the repair concept of Option 3
was relatively simple, adopting it to various
details throughout the façade was challenging.
These challenging details included the
interface of the curtain wall at the barrier
metal cladding areas, the configuration of
the system at the HVAC louvers, and intersection
of numerous extruded sections.
While these repairs would not address
any of the internal seal issues within the
system, they would provide for a reliable
method of sealing the exterior face of the
curtain wall system.
Figure 2 depicts the typical design detail
at one of the horizontal decorative strips,
which originally consisted of a barrier-type
metal cladding system. At those locations, a
self-adhesive air barrier would be installed
over the existing metal cladding and terminated
below the outer lips of the new
curtain wall pressure bars. Then, the new
metal cladding panel would be installed
over a series of vertical aluminum spacer
bars. These bars were designed to provide
a drainage cavity between the new air barrier
and the back of the new metal cladding
panels. That cavity was designed to weep to
the exterior through the horizontal mullion
cover below each strip. In order to avoid fastening
the new metal spacers and cladding
through the air barrier, the design team
opted to use structural tape to adhere the
spacer bars to the back of the new metal
cladding in the shop, and structural glazing
to adhere the assembly to the air barrier in
the field.
One of the challenges was selection
of an appropriate air barrier that could
resist the anticipated
maximum temperature
of 160ºF (the surface of the curtain
wall could reach 160ºF under warm, sunny
conditions), and be compatible with the
structural glazing sealant used to attach
the spacer bars to the air barrier. After
researching available products, an aluminum-
faced rubberized asphalt membrane
with a maximum in-service temperature
of 230ºF was selected for the project. The
aluminum facing of the product would make
the product compatible with the specified
S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 5 F a r a h m a n d p o u r • 6 3
Figure 1 – Typical horizontal mullion.
Figure 3B – Sealing end of existing mullion.
Figure 2 – Typical horizontal metal
cladding detail and drainage pattern.
Figure 3A
– Removal
of existing
louver.
structural silicone-glazing sealant. In order
to provide redundancy for attachment of the
new metal cladding panels, the design team
also ensured that the new metal cladding
strips were captured by the mechanically
attached pressure bars, making it impossible
for them to dislodge in the event the
adhesive tapes or structural glazing failed.
Another challenge for the design team
was the configuration of the HVAC louvers.
Field-testing has indicated extensive water
leakage below the louvers. The interiors of
the louvers were either blanked off or directly
connected to large ductwork. In order to
ensure water management below the louvers,
the louvers would have to be removed
so that a pan flashing could be installed
below them. The louvers had originally been
installed from the interior. However, removal
of the louvers would require removal
of the interior ductwork that was deemed
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Figure 3C – Installation of pan flashing.
Figure 3E – Installation of sealant for new pressure bars.
Figure 3G – Installation of glazing sealant.
Figure 3F – Installation of new pressure bars.
Figure 3H – Installation of new mullion caps.
Figure 3D –
Reinstallation
of louver and
installation of
air barrier.
impractical. As such, the design team opted
to trim the exterior flanges of the vertical
mullions to allow removal of the louvers
from the exterior of the building. Once the
flanges were trimmed, the louvers could
be disconnected from the interior ductwork
and removed. The design documents
included an alternate to replace the louvers
with new high-performance louvers.
Figures 3A through 3H depict the
sequence of work related to the louvers.
Once the louvers were removed, a stainless
steel pan flashing was designed to
be installed below the louvers. Due to the
complex geometry of the new pressure
bars, the louvers, and their new pan flashing
end dams, the louver assemblies and
their surrounding curtain wall framing were
modeled using 3-D solid modeling software.
This modeling allowed the design team to
evaluate the sequence of work during construction
and
to develop an
appropriate
end-dam configuration
for
the louver pan
flashing.
Figure 4
depicts the
configuration
of new metal
cladding at
the seventhfloor
terrace
butt resses.
The buttresses
were treated
similarly to
other metalclad
areas by installing an air barrier
over the existing cladding, installing
spacer bars, and installing new
metal cladding over the spacer bars.
Care was taken to ensure the gap
between the new and existing metal
cladding was drained to the exterior.
All in all, the design required
19 custom-extruded profiles. Figure
5 depicts the design details for a
pressure bar and its companion
cap. Those profiles were carefully
designed to provide for sealant geometry
and grooves in the components
to allow field technicians to properly
locate fasteners. In addition to the
custom-extruded profiles, many of
the metal cladding components were
to be custom-fabricated and prefinished.
The specifications required prefinishing of
all exposed aluminum components using
a fluoropolymer coating meeting requirements
of AAMA 2605. The owners opted to
maintain the original
color scheme
of the building. As
such, custom colors
matching the existing
colors were specified
for the aluminum
finishes, as well
as custom colors for
the exposed sealant
components.
Construction Phase
The implementation
of the repairs
included resealing of
precast panel joints on the north elevation
of the building. Repairs spanned more than
two years and were performed in phases to
minimize disruption to the building occupants.
During the entire repair project, the
building remained fully operational.
The implementation of the repairs posed
many challenges for the project team. The
first challenge was access to the building
exterior. To facilitate access to most of the
façade areas, the existing building scaffolding
davits were tested and recertified.
This allowed the use of the building
davit system to erect swing-stage scaffolding
over most of the façade. However, at the
terrace areas, pipe scaffolding was installed
to gain access to the building exterior (Photo
10). As is typically done with façade-repair
projects, building entrances and entrance
canopies were protected with temporary
canopies.
The second challenge was to identify
manufacturers and fabricators who could
produce the custom-extruded profiles, fabricators
who could fabricate the metal cladding
components, and finishers who could
prefinish all exposed metal components.
After selection of an extrusion manufacturer,
a fabricator, and a finisher, the
contractor had to verify all field dimensions
prior to submission of shop drawings and
fabrication. Original erection of the curtain
wall system had resulted in variations in
standard daylight openings, making field
measurement of each component necessary.
In order to ensure proper fit of all
components and the ability of the repairs
to resist water penetration, two in-place
mock-ups were specified—one at a typical
curtain wall section (including a decorative
metal cladding strip), and one at a louver.
S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 5 F a r a h m a n d p o u r • 6 5
Figure 4 – Buttress base detail.
Figure 5 – Typical extrusion profile.
Photo 10 – Pipe scaffolding on setback terraces.
The mock-ups were constructed using millfinish
components to reduce lead time for
mock-up components. Once the mock-ups
were constructed, they were water tested
by the design team to ensure they performed
properly. The testing revealed no
leaks through a section of the curtain wall
that had exhibited chronic leaks before the
repairs.
After the mock-ups were constructed
and evaluated, materials were ordered by
the contractor. The lead time for some of
the components included fabrication and
finishing by two separate subcontractors,
requiring shipment of components among
multiple subcontractors. In some cases,
the entire process took several months to
complete. The materials were delivered to
the site and stored in an indoor warehouse
provided by the owners.
A preliminary review of the prefinished
components revealed inconsistent finish
texture and gloss. This triggered a series of
inspections and tests by the design team.
The design team utilized a color spectrophotometer
to quantitatively measure gloss
of the finished components (Photo 11). The
measured values were then compared to
limits set by the specified standard (AAMA
2605) and the manufacturer’s stated gloss
value. The evaluation of the finishing gloss
revealed that several curved panels were
significantly out of the acceptable range of
gloss. As such, those components were sent
back to the finisher for refinishing. This
issue caused some delays in installing those
components and forced the contractor to
revise its project sequence.
During the repairs, the existing sign
on the building, which was
attached to the terrace buttresses,
had to be changed
to reflect the name and logo
of the new parent company
of the building owner.
This change required modifications
to the structural
members that supported
the sign, and integration of
those components with the
new column and buttress
cladding system.
The construction cost
for the project was slightly
less than $2,600,000. This
cost included the complete
resealing of all precast
panel joints on the north
elevation of the building and installation of
all new louvers on the east and west elevations
of the building.
Post-Construction
The project team closely monitored
the performance of the repairs over several
months after completion of the repairs.
During the first few months after completion
of the curtain wall repairs, a few localized
leaks were reported by the building
engineering staff. The locations and patterns
of those leaks were carefully documented.
Field inspection of the curtain
wall at the affected areas and water testing
revealed a few localized workmanship deficiencies,
which were promptly repaired by
the contractor.
The building has not experienced any
water leakage issues since the completion
of those repairs. However, the project team
continues to monitor the building.
Conclusions
Many curtain wall systems are reaching
an age when they will require comprehensive
repairs. Prior to implementing
any repairs, a thorough understanding of
how the system functions, the deterioration
mechanism, and the cause(s) of water leakage
are needed.
Although several conventional repair
approaches are available to the designers,
unconventional repairs should be considered
for each application. Such repairs can
provide the building owners with alternative
options that can meet their specific needs.
Design and implementation of unique
and unconventional repairs require careful
consideration by the design team. Since
many such repairs are not tried and true,
they may pose undue risks to the designers.
However, by educating the client regarding
the advantages and disadvantages of
each repair approach and documenting
the design rationale, designers can reduce
their risk. Moreover, using sound engineering
approaches, careful material selection,
careful study of design details through the
use of 3-D modeling, and construction of
mock-ups, the designers can further minimize
their risks.
Implementation of unconventional
repairs also requires a contractor who is
committed to working with the design team
to work through issues and achieve the
ultimate project objectives. Although many
contractors will not be able to demonstrate
prior experience with unconventional
repairs (since those repairs are uncommon
or unique), the project team can base its
selection on prior experience with that contractor
and how that contractor should be
able to address issues that arise.
References
1. ASTM C1472, Standard Guide for
Calculating Movement and Other
Effects When Establishing Sealant
Joint Width.
2. ASTM C1193, Standard Guide for
Use of Joint Sealants.
3. There are systems that integrate
the exterior glazing gaskets or thermal
isolation within the snapped-on
mullion covers.
6 6 • F a r a h m a n d p o u r S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 5
Photo 11 – Measurements of finish gloss using a color
spectrophotometer.