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Unit 9 Cladding System. Part ⅠIllustrated Words and Concepts Figure 9-1 Stick System Figure 9-2 Unit System and Unit-and-Mullion System

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Unit 9 Cladding System


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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

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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.

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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 unit-lowered 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.

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Unit 9 Cladding System

Part Ⅰ Illustrated Words and Concepts

Figure 9-3 Panel System and Column Cover and SpandrelSystem

(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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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,

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part Ⅱ PassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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-and-glass 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassages 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.

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Unit 9 Cladding System

Part ⅡPassagesPassage 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.