Download Unit 9 Cladding System

Unit 9
Cladding System
Part ⅠIllustrated Words and Concepts
Figure 9-1 Stick System
Figure 9-2 Unit System and Unit-and-Mullion System
Figure 9-3 Panel System and Column Cover and Spandrel System
Part Ⅱ Passages
Passage A The Design Requirements for Cladding
Passage B The Curtain Wall
Unit 9
Cladding System
Part Ⅰ Illustrated Words and Concepts
Figure 9-1 Stick System
1-Anchors
2-Mullion
3-Horizontal rail( gutter section at window head)
4-Spandrel panel (may be installed from inside building) 5-Horizontal rail (window sill
section) 6-Vision glass (installed from inside building)
7-Interior mullion trim
Other variations: Mullion and rail sections may be longer or shorter than shown
Vision glass may be set directly in recesses in framing members, may be set with
applied stops, may be set in sub-frame, or may include operable sash.
Unit 9
Cladding System
Part Ⅰ Illustrated Words and Concepts
Figure 9-2 Unit System and Unit-and-Mullion System
(A) Unit System—Schematic of typical version 1-Anchor
2-Pre assembled framed
unit. Other variations: Mullion sections may be interlocking “spilt” type or may be
channel shapes with applied inside and outside joint covers. Units may be unglazed
or may be Pre-plazed .Spandrel panel may be either at top or bottom of unit.
(B) Unit-and-Mullion System—Schematic of typical version
1-Anchors
2-Mullion(either one-or two-story lengths)
3-Pre assembled unitlowered into place behind mullion from floor above
4-Interior mullion trim. Other
variations :Framed units may be full-story height (as shown)，either unglazed or
pre-glazed, or may be separate spandrel cover units and vision glass units.
Horizontal rail sections are sometimes used between units.
Unit 9
Cladding System
Part Ⅰ Illustrated Words and Concepts
Figure 9-3 Panel System and Column Cover and Spandrel System
(A) Panel System—Schematic of typical version 1-Anchor
2-Panel Other variations
:Panels may be formed sheet or castings, may be full story height (as shown) or
smaller units, and may be either pre-glazed or glazed after installation.
(B) Column Cover and Spandrel System—Schematic of typical version
1-Column cover section
2-Spandrel panel
3-Glazing infill. Other variations:
Column covers may be one piece or an assembly, may be of any cross-sectional
profile, and either one or two stories in height. Spandrel panel may be plain,
textured or patterned. Glazing infill may be a pre-assembly, either glazed or
unglazed, or be assembled in place.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage A
The Design Requirements for Cladding
Primary Functions of Cladding
The major purpose of cladding is to separate
the indoor environment of a building from the outdoors
in such a way that indoor environmental conditions can
be maintained at levels suitable for the building’s
intended use. This translates into a number of separate
and diverse functional requirements.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage A
Keeping Water Out
Cladding must prevent the entry of rain, snow,
and ice into a building. This requirement is complicated
by the fact that water on the face of building is often
driven by wind at high velocities and high air pressures
not just in a downward direction, but in every direction,
even upward.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage A
Water problems are especially acute on tall
buildings, which present a large profile to the wind at
altitudes where wind velocities are much higher than at
ground level. Enormous amounts of water must be
drained from the windward face of a tall building during
a heavy rainstorm, and the water, pushed by wind
tends to accumulate in crevices and against projecting
mullions, where it will readily penetrate the smallest
crack or hole and enter the building. We will devote a
considerable portion of this chapter to methods for
keeping water out.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage A
Preventing Air Leakage
The cladding of a building must prevent the
unintended passage of air between indoors and
outdoors. At a gross scale, this is necessary to regulate
velocities within the building.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage A
Smaller air leaks are harmful because they
waste conditioned air, carry water through the wall,
allow moisture vapor to condense inside the wall, and
allow noise to penetrate the building from outside.
Building code requirements for airtightness of building
cladding are growing more stringent. Sealants, gaskets,
weatherstrips and air barrier membranes of various
types are all used to prevent air leakage through
cladding.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage A
Controlling Light
The cladding of a building must control the
passage of light, especially sunlight. Sunlight is heat
that may be welcome or unwelcome. Sunlight is visible
light, useful for illumination but bothersome if it causes
glare within a building.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage A
Sunlight includes destructive ultraviolet
wavelengths that must be kept off human skin and
away from interior materials that will fade or
disintegrate. Windows should be placed and
proportioned with these considerations in mind.
Cladding systems sometimes include external shading
devices to keep light and solar heat away from
windows. The glass in windows is often selected to
control light and heat. Interior shades, blinds, and
curtains may be added for further control.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage A
Controlling the Radiation of Heat
Beyond its role in regulating the flow of radiant
heat from the sun, the cladding of a building should
also present interior surfaces that are at temperatures
that will not cause radiant discomfort.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage A
A very cold interior surface will make people feel
chilly when they are near the wall, even if the air in the
building is warmed to a comfortable level. A hot interior
surface or direct sunlight in summer can cause
overheating of the body despite the coolness of the
interior air. External sun shading devices, adequate
thermal insulation and thermal breaks, and appropriate
selection of glass are potential strategies in controlling
heat radiation.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage A
Controlling the Conduction of Heat
The cladding of a building must resist the
conduction of heat into and out of the building. This
requires not merely a satisfactory overall resistance of
the wall to the passage of heat, but the avoidance of
thermal bridges,
Unit 9
Part Ⅱ
Cladding System
Passages
Passage A
wall components such as metal framing members
that are highly conductive of heat and therefore likely to
cause localized condensation on interior surfaces.
Thermal insulation, appropriate glazing, and thermal
breaks are used to control heat conduction through
cladding. Building codes specify minimum values of
thermal resistance of wall components as a way of
limiting the conduction of heat, and also as a way of
controlling the condensation of moisture on cold interior
surfaces.
Unit 9
Cladding System
Part Ⅱ Passages
Passage A
Controlling Sound
Cladding serves to isolate the inside of a building
from noises outside and vice versa . Noise isolation is
best achieved by walls that are airtight, massive, and
resilient. The required degree of noise isolation varies
from one building to another, depending on the noise
levels and noise tolerances of the inside and outside
environments. Cladding for a hospital near a major
airport requires a high level of noise isolation. Cladding
for a commercial office in a suburban office park need
not perform to as high a standard.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
The Curtain Wall
The Curtain Wall
The first steel-framed skyscrapers, built late in
the 19th century, introduced the concept of the curtain
wall, an exterior cladding supported at each story by
the frame. The name “curtain wall” derives from the
idea that the wall is thin and “hangs” like a curtain on
the structural frame.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
The earliest curtain walls were constructed of
masonry. The principal advantage of the curtain wall is
that, because it bears no vertical load, it can be thin
and light in weight regardless of the height of the
building, as compared to a masonry load-bearing wall,
which may become prohibitively t hick and weighty at
the base of a very tall building. Curtain walls may be
constructed of any noncombustible material that is
suitable for exposure to the weather. They may be
either constructed in place or prefabricated. Curtain
walls may be made of masonry and concrete or made
of metal and glass. Some types of walls are
constructed in place, and others are prefabricated, but
all are supported by the frame of the building.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
Modes of Assembly
Metal curtain wall systems can be classified
according to their degree or mode of assembly at the
time of installation on the building. Many metal-andglass curtain walls are furnished as stick systems
whose principal components are metal mullions and
rectangular panels of glass and spandrel material that
are assembled in place on the building.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
Stick systems have a high degree of ability to
adjust to unforeseen site conditions, but they must be
assembled on site, under highly variable conditions,
rather than in a factory with its ideal tooling, controlled
environmental conditions, and lower wage rates.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
The unit system of curtain wall installation takes
full advantage of factory assembly and minimizes on
site labor, but the units require more space during
shipping and more protection from damage than stick
system components. The unit-and-mullion system
which is seldom used today, offers a middle ground
between the stick and unit systems.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
The panel system is made up of homogenous
units that are formed from metal sheet. Its advantages
and disadvantages are similar to those of the unit
system, but its production involves the higher tooling
costs of a custom-made die or mold, which makes it
advantageous only for a building that requires a large
number of identical panels.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
The column-cover-and-spandrel system
emphasizes the structural module of the building rather
than creating its own grid on the facade, as the
previously described systems do. A custom design
must be created for each project because there is no
standard column or floor spacing for buildings. Special
care is required in detailing the spandrel panel support
to ensure that the panels do not deflect when loads are
applied to the spandrel beams of the building frame;
otherwise, the window strips could be subjected to
loadings that would deform the mullions and crack the
glass.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
Outside Glazing and Inside Glazing
A metal cladding system may be designed to
be outside glazed, which means that glass must be
installed or replaced by workers standing on scaffolding
or staging outside the building.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
Alternatively, it may be designed to be inside
glazed by workers who stand inside the building. Inside
glazing is more convenient and is more economical for
a tall building, but it requires a somewhat more
elaborate set of extrusions. Outside glazing systems
utilize a relatively simple set of extrusions and are less
expensive for a building that is only one to three stories
tall. Some curtain wall systems are designed so that
they may be glazed from either side.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
The Process of Curtain Wall Design
When an architect sets out to design a new
system of metal cladding, as is often done for large,
important buildings, other professionals are brought into
the process. An independent cladding consultant can
bring a large body of experience and expertise to this
effort and minimize the risk to the architect. The
structural engineer of the building is involved at least to
the extent of understanding the weight and attachment
requirements of the system.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
A curtain wall manufacturer is also brought into the
design team early in the process. The manufacturer
understands better than any other member of the team
the manufacturing, assembly, installation, and cost
implications of a new curtain wall design. The
manufacturer often does the installation as well as the
manufacturing of the components , or it subcontracts
the installation work to companies that it certifies to be
well qualified and familiar with the manufacturer’s
products and standards.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
This installation experience is also invaluable
during the design process. From conceptual drawings
prepared by the architect and cladding consultant, the
manufacturer prepares a more detailed set of design
drawings as a basis for reaching preliminary agreement
on the design. The manufacturer then prepares a very
detailed set of shop drawings and installation drawings.
Unit 9
Part Ⅱ
Cladding System
Passages
Passage B
These are checked carefully by the architect
engineer, and cladding consultant to assure compliance
with design intentions and the structural capabilities of
the building frame. Full-scale testing of the curtain wall
is usually carried before the manufacture of a custom
designed curtain wall system is authorized to begin.
The curtain manufacturer may wish to visit the
construction site during the erection of the building
frame to become familiar with the level of dimensional
accuracy of the structural surfaces to which the curtain
wall will be fastened.