In Between: Designing Joints Within Facades

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IN BETWEEN: DESIGNING JOINTS WITHIN FAÇADES
MINJUNG MAING, PE, LEED AP, ASSOC. AIA
SIMPSON GUMPERTZ & HEGER INC.
1055 W. 7th Street, Suite 2500, Los Angeles, CA 90017
Phone: 213-271-1919 • Fax: 213-617-0411 • E-mail: mxmaing@sgh.com
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ABSTRACT
How the façade elements join with the adjoining materials, assemblies, and systems
should be considered early in the design phase. Left to the end, the joinery of the building
systems creates abrupt conditions at terminations, transitions, and corners. This can, in
turn, lead to building covers that do not address issues of thermal performance of materials,
weather protection (including air infiltration and water penetration), fire resistance, and
plumbing systems of the building. Although there are general guidelines for designing smaller
joints such as sealant-joint performance parameters, wider joints such as expansion and
seismic joints are underrepresented, creating delays and confusion during construction.
This paper will discuss how to detail the different types of joints, using case studies and
examples of joints that were nonconforming and that were redesigned to comply with performance
criteria. The principles presented are relevant to design and construction teams
and researchers. It is critical that these joints be considered for the climactic conditions that
façade assemblies are meant to address in order to design a holistic façade system with the
desired performance requirements.
SPEAKER
MINJUNG MAING, PE, LEED AP, ASSOC. AIA — SIMPSON GUMPERTZ & HEGER INC.
Minjung Maing, PE, LEED AP, Assoc. AIA, is a senior staff editor with Simpson
Gumpertz & Heger, Inc., and an assistant professor with the Georgia Institute of Technology
School of Architecture. She has ten years of industry experience ranging from architecture
and structural engineering to building technology. Her focus is on building envelope performance
and integration of design, testing, and construction processes toward a holistic
design approach. She has been involved in various remedial design and new-construction
projects, including custom design of curtain walls, windows, roofing, wall cladding systems
as precast panels, EIFS, cement plaster, brick and stone veneer, metal panels, and plaza
and below-grade waterproofing. She received dual bachelor’s degrees in architecture and
engineering from the University of Pennsylvania and an MS in civil/structural engineering
from Stanford University as well as a professional master’s degree in architecture from the
Massachusetts Institute of Technology (MIT). She is a registered professional engineer in
California and currently teaches at Georgia Institute of Technology in the School of
Architecture.
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Designing a façade—also referred to as a
building envelope system—while maintaining
desired aesthetics and avoiding performance
problems, requires attention to
materials and process of assembly.
Materials—their installation, physical properties,
and compatibility issues—should be
carefully considered and clearly detailed to
include the design of joints that subsequently
affect building performance.
Joinery of façade components is often
assumed by the designer and not closely
examined until the later stages of construction
documents and sometimes not thoroughly
discussed until installation on the
project. Joints within the façade are relatively
small elements and account for a
small percentage of the wall system and
entire building envelope. However, if the
subject joints are not designed properly,
they become points of moisture intrusion
that create problems with air, moisture, and
thermal energy leakage. Since these elements
travel along paths of least resistance,
these breaches in the façade will significantly
affect the building envelope performance
and, inevitably, the building as a
whole. To describe joints, their functions,
design options, and problems associated
with poor details, this paper is presented in
the following sections:
1. Role of joints
2. Types of vertical joints
3. How joints are typically designed and
common problems that arise from
the choice of joint infill material
4. Design principles for a better performing
joint system
5. Conclusion
ROLE OF JOINTS
Joints are prevalent in many applications
and play a critical role in the function
of the façade cladding components. The
human body is an example in which joints
between our bones allow us to move and
give each limb a function within a coordinated
structure. Joints between our body
organs that are different from bone joints
have specific functions, such as opening
and closing, allowing us to breathe and live.
In buildings, there are several types of
joints of differing scales and functions;
however, façade joints can be categorized
into three main types, excluding façade
structural attachment joints.
• Control joints
• Expansion joints
• Lateral drift (seismic) joints
Although there are three types, a joint
within a façade can consist of a hybrid,
such as a seismic expansion joint that is
designed to address lateral drift of the
building and material expansion and contraction.
All joints should be designed to
handle the expansive and contractive properties
of the wall-cladding materials within
and adjacent to the joints due to the effects
of the environment on structural and nonstructural
components. For the purpose of
this discussion, focus will be given to the
latter two types of joints—expansion and
lateral joints—which are prominent inclusions
within prefabricated façade components/
unit assemblies.
Better understanding and representation
through three-dimensional isometric
details are essential for the design team to
ensure a consistent level of performance
across the joint, as with the building façade.
To accentuate the importance of joint
design, there are some instances where a
joint subcontractor who is responsible for
installing all the joint material within the
façade is hired—particularly where there
are several different types of façade materials,
and manufacturer/installers are reluctant
to install joint material to connect their
systems to other manufacturer systems.
The design team then decides that having
one subcontracting entity to install sealant
joints throughout the project will result in
better quality and liability control. The conditions
that arise from this arrangement are
thorough details of joints in the various project
conditions, coordination among trades
to ensure proper sequencing, testing of
assemblies to assure proper installation of
joint and façade materials, and integration
with adjacent wall systems.
TYPES OF VERTICAL JOINTS
Expansion Joints
Expansion joints are introduced to
accommodate building movements caused
by temperature changes: expansion; contraction;
and, in some instances, moisture;
and (particularly when designing with concrete)
creep. Although control joints will not
be discussed in depth in this paper, the following
description is important to differentiate
them from expansion joints. Control
joints occur within façade systems, and
their main function is to break up the
façade surface to control the shrinkage tensile
stresses within the cladding material
which cause excessive cracking if not alleviated.
They are commonly found in cementitious-
based wall cladding systems, such as
cement plaster, concrete masonry, and concrete,
and run as deep as the cladding system
or, in the example of concrete, 25% of
the depth of the concrete wall. Section 3 of
ASTM C1063 states that a control joint
“accommodates movement of plaster
shrinkage and curing along predetermined,
usually straight lines.” The key word being
“predetermined,” therefore controlling
where the designer will be able to tolerate
cracks or lines where control-joint accessories
will exist within their façades.
Expansion joints are often one-way
joints, primarily intended to accommodate
movements in the direction perpendicular
to the joint, and are commonly placed at
regular intervals of length, based on the
expected rate of expansion and contraction
over the building length. They are similar to
control joints in that they are required at
regular intervals due to the linear coefficient
of thermal expansion of materials [as
calculated by Δ(ft) = 0.0000065*L(ft)*ΔT(°F)] and yet differ from control joints, in that
whereas the expansion of the framing and
structure are being accounted for they penetrate
through the entire wall section and
not just the cladding system. All materials
expand and contract when exposed to temperature
differentials; therefore, expansion
joints should take into account expansion
of the structure as well as the façadecladding
materials.
IN BETWEEN: DESIGNING JOINTS WITHIN FAÇADES
In structural design, there are no definitive
guidelines, and expansion joints are
regarded as a serviceability issue. ASCE 7-
02 states, “Dimensional changes in a structure
and its elements due to variations in
temperature, relative humidity, or other
effects shall not impair the serviceability of
the structure.” Given this scenario, there is
an inherent ambiguity as to which design
professional is responsible for the inclusion,
placement, and design of expansion joints,
perhaps the reason that these joints do not
get adequate attention early in the design
phase.
The typical approach is that the architect
will locate and show control joints on
the drawings as well as expansion joints of
façade materials, while expansion joints
that include movement of structure are
determined by the structural engineer. Even
so, this ambiguity of design responsibility
for expansion joints affects the process of
how the joints are designed; consequently,
they are frequently left to the end, resulting
in inadequate detailing, which causes problems
during construction and too often is
remedied with “bandage”-type installations
such as excessive use of sealant (Photo 1) to
seal these joints and tie them into the adjacent
façade systems.
Seismic Joints
Seismic joints are designed to accommodate
lateral movement in seismically
active areas, in both orthogonal directions
simultaneously; and, unlike expansion
joints, their spacing is not typically affected
by building length or size. Structural engineers
place seismic joints in irregularshaped
buildings: for example, at reentrant
corners, to break up the building into
smaller parts to simplify building analysis.
However, with the adoption of the 1988
Uniform Building Code (UBC) and advanced
computer modeling in structural analysis,
the number of seismic joints was decreased
as desired by the architect. The code
changes led to an increase in the size of the
joints due to the increased stiffness of the
building. One general rule for where seismic
joints are absolutely necessary is within the
preexisting interstitial between new and
existing buildings.
The width of seismic joints varies from
about two to several inches. They run continuously
along the façade both horizontally
and vertically and through the entire
building wall and building at the line of the
joint. Seismic joints account for total drift;
however, interstory drift is accounted for in
drift joints at every level, terminating at vertical
seismic joints. The structural system is
separated at seismic joints, and joint size is
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Photo 1A — A seismic expansion joint is located in the reentrant corner of an H-shaped building complex. The joint continues
vertically and horizontally along this gridline. Fire resistance and thermal insulation are required, since the joint runs
through a living unit. 1B — A polymeric bellows material was used, and corners and transitions were detailed using
excessive sealant. 1C — The sealant used does not bond to the bellows material, creating gaps at the bellows joints and
transitions.
A B
C
In structural design, there are no definitive
guidelines, and expansion joints are
regarded as a serviceability issue. ASCE 7-
02 states, “Dimensional changes in a structure
and its elements due to variations in
temperature, relative humidity, or other
effects shall not impair the serviceability of
the structure.” Given this scenario, there is
an inherent ambiguity as to which design
professional is responsible for the inclusion,
placement, and design of expansion joints,
perhaps the reason that these joints do not
get adequate attention early in the design
phase.
The typical approach is that the architect
will locate and show control joints on
the drawings as well as expansion joints of
façade materials, while expansion joints
that include movement of structure are
determined by the structural engineer. Even
so, this ambiguity of design responsibility
for expansion joints affects the process of
how the joints are designed; consequently,
they are frequently left to the end, resulting
in inadequate detailing, which causes problems
during construction and too often is
remedied with “bandage”-type installations
such as excessive use of sealant (Photo 1) to
seal these joints and tie them into the adjacent
façade systems.
Seismic Joints
Seismic joints are designed to accommodate
lateral movement in seismically
active areas, in both orthogonal directions
simultaneously; and, unlike expansion
joints, their spacing is not typically affected
by building length or size. Structural engineers
place seismic joints in irregularshaped
buildings: for example, at reentrant
corners, to break up the building into
smaller parts to simplify building analysis.
However, with the adoption of the 1988
Uniform Building Code (UBC) and advanced
computer modeling in structural analysis,
the number of seismic joints was decreased
as desired by the architect. The code
changes led to an increase in the size of the
joints due to the increased stiffness of the
building. One general rule for where seismic
joints are absolutely necessary is within the
preexisting interstitial between new and
existing buildings.
The width of seismic joints varies from
about two to several inches. They run continuously
along the façade both horizontally
and vertically and through the entire
building wall and building at the line of the
joint. Seismic joints account for total drift;
however, interstory drift is accounted for in
drift joints at every level, terminating at vertical
seismic joints. The structural system is
separated at seismic joints, and joint size is
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Photo 1A — A seismic expansion joint is located in the reentrant corner of an H-shaped building complex. The joint continues
vertically and horizontally along this gridline. Fire resistance and thermal insulation are required, since the joint runs
through a living unit. 1B — A polymeric bellows material was used, and corners and transitions were detailed using
excessive sealant. 1C — The sealant used does not bond to the bellows material, creating gaps at the bellows joints and
transitions.
A B
C
generally the sum of story drift of the two
isolated building sections adjacent to the
joint. Special structural and architectural
detailing are required to maintain the separation
while, in some cases, creating a continuous
building façade to cover these
joints. Designers tend to turn to prefabricated
joint cover assemblies that do not
take into account building aesthetics and
custom conditions, in some cases leaving
designers unhappy at the strikingly obvious
mark left on the building exterior.
HOW JOINTS ARE TYPICALLY
DESIGNED AND COMMON
PROBLEMS THAT ARISE FROM THE
CHOICE OF JOINT INFILL MATERIAL
In current construction, most expansion
and seismic joints are designed and sealed
using either sealant materials (liquid or
impregnated foam sealant), or preformed
joint-cover assemblies. The choice of joint
material is based on the size of the joint;
generally, designers tend to turn to liquid
sealant where applicable
and revert to preformed
joint covers for larger
joints when liquid
sealant is no longer an
option.
Liquid Sealant and
Foam Joints
Sealant joint materials
come either in liquid
form or solid-state impregnated
foam. Liquid
sealants, due to their
limitation in application,
are commonly used to
span across small joints
(generally ¼ to 1 in), seal
laps, and butt the joints
of materials. However,
for larger joints, which
can be considered 2 in or
wider, sealant can be
considered inappropriate
due to installation issues,
as discussed below.
Sealant compounds
vary and should be carefully
reviewed to understand
their limitations.
Dow Corning, in its technical
manual, recommends
that its silicone
sealants be used for
joints that range from ¼
in to a maximum of 4 in
wide; however, for larger joint sizes (greater
than 2 in), application of the sealant material
into the joint may require a double application,
and extra precaution should be
taken to ensure that the maximum allowable
depth of the sealant joint not exceed ½
in. The ideal performance of a sealant joint
is signified by its failure; cohesive failure in
tensile loads that exceed the joint material
capacity (i.e., the sealant itself fails) means
that the adhesion of the sealant to the substrate
was acceptable, the sealant was properly
installed, and sealant strength capacity
was exceeded. However, with larger joint
sizes, it becomes more difficult to control the
depth of the sealant joint, and failures in
adhesion to the substrate are more common.
An example of a 2-in sealant showing
adhesive failure when put under lateral
loading is shown in Photo 2.
An alternate to liquid sealants within
the sealant family is impregnated foam
sealant, which is also available in a hybrid
form with silicone-impregnated foam covered
by a factory-applied liquid sealant
exterior layer, cured, compressed, and
packaged in the factory. Impregnated foam
provides the advantages of offering fire- and
thermal-resistance and is able to span
joints of up to 6 in and have similar limitations
to liquid sealant in that both are not
complete solutions for all types of walls.
Both liquid and impregnated foam
sealants are applicable for sealing joints in
one plane and need to be carefully considered
when designing for different wall types.
The three main types of walls are facesealed
(barrier) walls, drainage (water-managed)
walls, and pressure-equalized rainscreen
walls. For face-sealed walls, sealants
may be adequate, assuming the joints are
within the size limitations; however, for
drainage and rainscreen walls, joint sealers
are needed on two planes. Sealants can be
installed on two planes, creating a double
sealant joint; but on the water-resistive barrier
(WRB) layer, the sealant joint needs to
form effective transitions to the WRB. The
latter is sometimes not
feasible if the joint is too
small (as explained in
the Design Example
given later in this paper).
Preformed Joint Seals
and Covers
Alternatives to
sealant materials for
small joints are extruded-
rubber (EPDM) gasket
seals, which can be
extruded into any shape
and installed by compression
into the joint.
Common uses are within
windows and curtainwall
systems at mullion
intersections, and
against glass panes
installed within mullion
extrusions (often denoted
as a “dry seal” versus
a sealant joint, denoted
as a “wet seal”). They are
also used in stack joints
of curtain walls, expansion
and seismic joints
within the curtain wall
system.
For larger joints (2 in
or greater), using preformed
joint covers to fill
these joints is more commonplace,
especially
Photo 2 — Two-inch vertical seismic joint intersecting with 1-in drift
joint. Adhesion failure of the sealant joint occurred after seismic load
testing was performed on the assembly. Removal of this section of the
sealant joint revealed the joint was 1¼ in thick in lieu of the required
thickness of ½ in. Sealant was not properly installed and had varying
depths.
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when liquid sealant and impregnated foam
sealant materials are inappropriate (joint
sizes are 4 to 6 in and greater). Joint covers
are specialty items, are therefore costly, and
sacrifice greater lead time as joint width
grows. These joint covers are prefabricated,
typically metal or extruded polymer covers,
and may also include flexible bellows made
of extruded polymer (neoprene, EPDM)
clamped into place by aluminum frames
(also referred to as mounting rails), which
are fastened into the adjacent wall surfaces
or clamped to metal flanges fastened into the
adjacent framing. As an example, Photos 3A
through 3D show a preformed joint cover
consisting of aluminum frames, webbed
extruded-polymer cover, and intermediate
neoprene bellows. The big challenge with
this installation was the need for a continuous
transition of the convex bellows of the
roof expansion joint with the vertical expansion
joint to maintain air, heat, and moisture
resistance. In addition, the issue of
ensuring proper drainage of the incidental
water that would accumulate in the convex
roof bellows needed to be addressed since
the roof metal cover over the bellows had
open joints to accommodate movement. The
solution used was installing a drain at this
corner and directing the drain to the plumbing
system.
Although the shop-fabricated jointcover
assemblies are tested by the manufacturer,
the joinery and termination of the
components are seldom included in the
testing, and some manufacturers do not
offer details to show how they recommend
these elements should be joined at transitions
and terminations. This leads to
installers reverting to liquid sealants as the
solution, and inevitably problems are more
prominent at these sealed locations. The
base of an expansion joint should also be
able to accommodate movement, as well as
divert any water collected along the expansion-
joint cover back out to the exterior.
This is typically achieved using two-piece
sheet-metal flashings. Photo 4 shows excessive
use of sealant at the two-piece sheet
metal base, which still leaked during testing.
(See Figure 1.)
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A C
B D
Photo 3A — Mock-up of 14-in seismic expansion joint using preformed joint covers and assembly. Main purpose for the mockup
was to review transition of horizontal bellows with the vertical joint assembly. Notice how the transition is made by
carving the roof bellows around the aluminum intermediate frame and sealing them to these frames using sealant material.
3B — Inboard side of the joint cover showing the adjustable frame used to center the joint system in the event of movement.
3C — Joint cover assembly installed on building, showing transition of vertical and horizontal seismic joint. 3D — Joint
cover detail provided by manufacturer shows a secondary backup polymeric membrane (as seen in 3A) to function as bellows,
which, however, does not provide a tie-in to lap over the WRB for non-face-sealed walls.
One common feature of preformed joints
is that they are not designed for various
types of walls. Preformed joint covers are
derivations from roof expansion joint or
horizontal concrete-slab joint covers, which
are typically face-sealed assemblies that do
not take into account the function of different
layers within drainage and rainscreen
wall types. Designers are faced with joint
covers that require modifications to integrate
with their façade designs and limited
assistance from the cover manufacturers.
Custom-Designed Joints
As a response to the lack of design flexibility
offered by a single-source joint system
(sealants, preformed joint seals, or covers),
when dealing with drainage and rainscreen
wall systems, different design
approaches are undertaken to better integrate
with the WRB layer to form an airtight,
weathertight, and thermally insulated
wall joint. To further explain this approach,
an example was needed in which small
joints (1 in) and larger joints (2¼ in) were
needed to accommodate the design lateral.
Design Example
A 1-in horizontal interstory drift joint
and a 2¼-in vertical seismic joint were
required in a project that had a façade system
consisting of rainscreen composite wall
panels attached with furring aluminum
channels and strip windows (Photo 5).
Liquid sealant or impregnated foam sealant
was not appropriate for the 1-in joint since
there was inadequate space for the sealant
joint to be installed properly and effectively
tied in to the WRB on both sides of the joint.
A self-adhesive, rubberized-asphalt sheet
membrane compatible with the proprietary
polypropylene WRB sheet material was
selected to span across both joints and lap
onto the WRB.
The 1-in drift joint extended back to the
exterior sheathing; the wall framing at this
Photo 4A — 2-inch vertical seismic joint between precast concrete panel and curtain wall system. Joint cover system consists
of extruded polymeric cover system with integrated bellows attached to aluminum frames (mounting rails). The frames are
bedded in sealant on each side and bolted to the adjacent façade systems.; 4B — The interior side of the seismic joint showing
the bellows and the frames set in thick beds of sealant. During performance testing, voids in the sealant were discovered, and
additional sealant was applied resulting in thick vertical beads of sealant on both sides. The base of the seismic joint
consists of a two-piece sheet metal base flashing that is sealed together and onto the wall surface with sealant. Once again,
the use of sealant at the base flashing is excessive; and yet, during the first round of testing, the flashing failed.
A B
Figure 1 — Detail of seismic joint shown in Photos 4A and 4B. The seismic jointcover
system is reliant on sealant to maintain standards in air- and waterpenetration
resistance.
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location used a drift track system that separated
each side of the sheathing (Photo 5C).
The sheet membrane was installed as a convex
bellow to accommodate movement and
to avoid being torn. The sheet membrane,
being self-adhesive, needed to be unadhered
within the joint gap to avoid damage
and rupture of the membrane during building
movement. There were two options: one,
to leave the release paper intact at that
location up to a couple of inches beyond
each side, leaving about 4 in on both sides
to lap onto and adhere to the WRB; and
another was to adhere a piece of the sheet
membrane to itself at this location and similarly
extend a couple of inches beyond,
with 4 in on each to adhere to WRB. The latter
option, which was used for the project,
is the preferred and more reliable option
since, if installed properly, there is little
chance of delamination (i.e., release paper
peeling off at certain locations, either during
installation or after some building movement).
During installation, the sheet membrane
did not pass the pull test since it did
not fully adhere to the polypropylene WRB
and easily peeled away. To remedy this
problem, an adhesive that was able to effectively
bond to the membrane and WRB and
to meet compatibility requirements was
applied between the two components.
The same principles applied to the vertical
seismic joint (Photo 5B) in that the selfadhered
sheet membrane was unadhered
within the joint and bonded to the WRB
with a compatible adhesive. The difference
was that the vertical joint was wider, requiring
more material; continued vertically up
the building; and separated the stud framing,
meaning that special provisions needed
to be taken to ensure thermal-resistance
values (R-value) and fire resistance of the
walls within the joint gap. Use of fire blanket
bellows or expansive foam fire-resistive
insulation had to be considered. The challenge
then became having a custom, fourway-
intersection, convex-shaped membrane
connection where the horizontal and vertical
joints intersected. Isometric drawings
showing the assembly and installation
sequence were particularly vital for these
instances in showing the installers how the
membrane should be prepared and installed.
Termination and continuation of
these joints needed to be addressed (Photo
5D).
Continuity with the WRB is crucial in
drainage and rainscreen walls to avoid gaps
within the building envelope and maintain
wall performance standards of air and
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A C
B D
Photo 5A — A 2¼-in vertical seismic joint and 1-in interstory horizontal drift joint intersection. 5B — Vertical sheet
membrane bellow, continuous with no mechanical panel attachments within the joint. 5C — Membrane bellows unadhered
within drift joint to allow for movement. 5D — Bellows termination is inadequate and will not be able to take any movement,
resulting in damage to the membrane bellows.
moisture penetration and thermal insulation.
Figures 2 and 3 are custom joint
details for drainage and rainscreen façades
with similar design strategies used in the
design example. The two details show how
sealants—both liquid and foam types—can
be used in conjunction with other materials
such as self-adhesive sheet membrane bellows.
The advantages to using customdesigned
joints are that it gives the design
team more control, requires better understanding
of the function of the materials
within and surrounding the joint, and
makes manufacturers aware of the necessary
tie-in of the joint system to the adjacent
materials. It does not eliminate the
need for the preformed joint covers or
sealants but, instead, allows the designer to
use a combination of different materials
and prefabricated covers that are compatible
and form a well-sealed performing joint.
For drainage-wall systems, installations of
membrane bellows similar to the design
example can be used; however, an outer
seal (Figure 2) or flashing should be introduced
to cover the joint to maintain the primary,
outer weather-protection surface. For
rainscreen façade systems, the attachments
should be clear of the expansion and seismic
joints, and the panel joints can be left
open as in Photo 5B or sealed as in Figure 3.
DESIGN PRINCIPLES FOR A BETTERPERFORMING
JOINT SYSTEM
To avoid costly problems resulting from
inadequate joint design, insufficient detailing,
and poor coordination when installing
expansion- and seismic-joint infill and covers,
the following design principles should
be considered:
1. Determine where joints occur
throughout the building and façade
(e.g., where an addition meets the
original building, irregular building
corners, material changes, etc.).
Once façade materials are selected,
designers should consult with the
manufacturer for information on
minimum expansion joint sizes and
intervals, both vertically and horizontally,
based on performance testing
results, a successful track
record, and material properties. It is
important to note that seismic and
some expansion joints are continuous
in that vertical joints will join
with horizontal and roof expansion
joints.
2. Review the joint sizes required and
Figure 2 — Detail showing how two lines of sealant are required for drainage
wall systems. The inner expansive foam provides fire resistance, and thermal
insulation values can be achieved by varying the thickness of the specialized
foam. A membrane bellows is used to make an airtight and weathertight
transition with the WRB layer. An exterior sealant joint is used as a primary line
of defense. Note that the sheet membrane should be unadhered within the joint.
Figure 3 — Detail showing how two lines of impregnated foam sealant material
are needed for certain types of rainscreen systems. The outer sealant joint may be
optional, depending on the rainscreen system used for the project. Similar to
Figure 1, a membrane bellows is used to make an airtight and weathertight
transition with the WRB layer. The inner foam joint is mainly used to provide
required fire resistance and thermal insulation. Note that the sheet membrane
should be unadhered within the joint.
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whether they are expansion or seismic
joints. Note that seismic joints
will also undergo expansion and
contraction, generally smaller than
the anticipated lateral drift.
3. Identify the different types of joints,
based on size, whether the joint gap
extends past the façade into the
structural framing, and even the
adjacent materials. This will give an
idea of how many different condition
details will be needed to document
the different joint designs.
4. Select joint infill material. For small
joints, sealant materials may be
acceptable; however, depending on
the wall type (face-sealed, drainage,
or rainscreen), customized design
joints may be more effective. For
larger joints, preformed joint covers
should be carefully reviewed; and
most likely for drainage or rainscreen
walls, customization will be
needed to include compatible bellows
behind joint covers that form a
continuous transition with the WRB.
5. Research the materials selected
within and adjacent to the joints for
compatibility and performance properties
to assure that the joint can
handle the anticipated movement.
6. Review thermal-insulation and fire
resistance requirements for adjacent
walls, and select materials within the
joints that will maintain the same
values. Batt insulation is not appropriate
to be put into movement joints
since it may not remain in place for
long periods and inevitably loses its
insulating properties.
7. Create joint details at typical sections,
transitions, intersections, and
terminations. Use 3-D isometric
details to show sequencing, especially
at planar changes and terminations.
8. As early in the design phase as possible,
review details and discuss
with manufacturers and installers
warranties relating to the assemblies
within and adjacent to the
joint. This will give designers time to
make alterations that will achieve
the desired aesthetics, performance
requirements, and warranty coverage.
9. Coordinate installation of the joints
with all trades involved to ensure
proper sequencing and tie-ins.
10. Perform mock-ups of the joint
assemblies both to clarify how the
joints should be installed and
assure compatibility of materials
within the joint and at tie-ins to
adjacent materials (WRB). This will
also give the designer a chance to
review aesthetics of the joint.
CONCLUSION
As buildings become more complex and
designers deploy a wide spectrum of materials
while pursuing high-performance buildings,
it is ever more important to understand
and carefully design for expansion
and seismic joints within façades to avoid
the weak-link scenario. Failures within the
façade can occur on any scale; however,
failure of joints is typically most common
and largely due to neglect from the design
team and lack of coordination by the construction
team. Proper sizing and detailing
of horizontal and vertical expansion joints
and detailing of seismic joints within
façades are critical for achieving desired
building envelope performance. As demonstrated
throughout this article, joint design
must consider building movement (including
thermal, moisture, creep, shrinkage,
and frame shortening, and, in some locations,
lateral design loads) and façade
assemblies in selecting the appropriate
materials for this interstitial zone. Customdesigned
joint systems will increasingly
become more appropriate as designers turn
to custom façade systems and because preformed
assemblies lack design flexibility.
Performance mock-ups are recommended
to test the custom façade systems and custom-
designed joints to assure façade performance,
as well as a learning ground for all
parties involved to become aware of joint
functions, assemblies, and integration with
façade components.
REFERENCES
American Society of Civil Engineers,
Minimum Design Loads for Buildings
and Other Structures, ASCE/SEI 7-
05.
ASTM International, ASTM C1063,
Standard Specification for
Installation of Lathing and Furring to
Receive Interior and Exterior Portland
Cement-Based Plaster, 2008.
Dow Corning Americas, Technical
Manual, June 2007.
Federal Construction Council, Technical
Report No. 65, Expansion Joints in
Buildings, National Research
Council, Washington, DC, 1974.
James M. Fisher, “Expansion Joints:
Where, When, and How,” NASCC
Proceedings, April 2005.
Mark C. Saunders, “Seismic Joints in
Steel Frame Buildings,” Modern
Steel Construction, April 2005.
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