Page 325 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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FLOOR AND ROOF SYSTEMS

FLOOR AND ROOF SYSTEMS 7.9

ROOF DECKS

The systems used for floor decks (Arts. 7.1 to 7.3) can also be used for roof decks. When used as
roof decks, these systems are overlaid by roofing materials, to provide a weathertight enclosure.
Other roof-deck systems are described in Arts. 7.4 to 7.7.

7.4 METAL ROOF DECK

Steel-framed buildings often utilize a roof deck composed simply of metal deck. When properly sloped
for drainage, the metal deck itself can serve as a watertight enclosure. Alternatively, roofing materials
can be placed on top of the deck. In either case, diaphragm action can be achieved by proper sizing and
attachment of the metal deck. A fire rating can be provided by applying spray-on fire protection to the
underside of the roof deck, or by installing a fire-rated ceiling system below the deck.
Metal roof deck usually is used for noncomposite construction. It is commonly available in depths of
1
1
1
1 / 2, 2, and 3 in. Long-span roof deck is available with depths of 4 / 2, 6, and 7 / 2 in from some manufac-
turers. Cellular roof deck is sometimes used to provide a smooth soffit. When a lightweight insulating
concrete fill is placed over the roof deck, the deck should be galvanized and also vented (perforated) to
accelerate the drying time of the insulating fill, and prevent entrapment of water vapor. Acoustical deck
is also available for use in applications where enhanced sound absorption is desired.
Standing-Seam System. When the metal roof deck is to serve as a weathertight enclosure, connection
of deck units with standing seams offers the advantage of placing the deck seam above the drainage
surface of the roof, thereby minimizing the potential for water leakage (Fig. 7.9). The seams can simply
be snapped together or, to enhance their weathertightness, can be continuously seamed by mechanical

FIGURE 7.9 Standing-seam roof deck. (a) With snapped seam; (b) with mechanical seam;
(c) steps in forming a seam.

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