1.0 for normal-weight concrete
0.85 for sand-lightweight concrete
0.75 for all-lightweight concrete Precast-concrete members are assembled and fastened together on the jobsite. They may be unreinforced, reinforced, or prestressed. Precasting is especially advantageous when it permits mass production of concrete units. But precasting is also beneficial because it facilitates quality control and use of higher-strength concrete. Form costs may be greatly reduced, because reusable forms can be located on a casting-plant floor or on the ground at a construction site in protected locations and convenient positions, where workmen can move about freely. Many complex thinshell structures are economical when precast, but would be uneconomical if cast in place. Design of precast-concrete members under the ACI 318 Building Code follows the same rules as for cast-in-place concrete. In some cases, however, design may not be governed by service loads, because transportation and erection loads on precast members may exceed the service loads. Design of joints and connections must provide for transmission of any forces due to shrinkage, creep, temperature, elastic deformation, gravity loads, wind loads, and earthquake motion. (Design and Typical Details of Connections for Precast and Prestressed Concrete, 2d ed., Precast / Prestressed Concrete Institute.) Less concrete cover is required for reinforcement in precast-concrete members manufactured under plant control conditions than in cast-in-place members because the control for proportioning, placing, and curing is better. Minimum concrete cover for reinforcement required by ACI 318-99 is listed in Table 9.26. For all sizes of reinforcement in precast-concrete wall panels, minimum cover of 3/4 in is acceptable at nontreated surfaces exposed to weather and 3/8 in at interior

A window usually consists of transparent glass or plastics (glazing) held in place by light framing, called sash. The window is fitted into a frame secured to the walls (Fig. 1.5a). For sliding windows, the frame carries guides in which the sash slides. For swinging windows, stops against which the window closes are built into the frame. Hardware is provided to enable the window to function as required. For movable windows, the hardware includes grips for moving them, locks, hinges for swinging windows, and sash balances and pulleys for vertically sliding windows. The main purposes of windows are to illuminate the building interior with daylight, to ventilate the interior, and to give occupants a view of the outside. For retail stores, windows may have the major purpose of giving passersby a view of items displayed inside. (See also Sec. 11.) Doors are installed in exterior walls to give access to or from the interior or to prevent such access. For similar reasons, doors are also provided in interior walls and partitions. Thus, a door may be part of a system for enclosing a building or a component of a system for enclosing interior spaces. Systems for Enclosing Interior Spaces. The interior of a building usually is compartmented into spaces or rooms by horizontal dividers (floor-ceiling or roof-ceiling systems) and vertical dividers (interior walls and partitions). (The term partitions is generally applied to non-load-bearing walls.) Floor-Ceiling Systems. The basic element of a floor is a load-carrying deck. For protection against wear, esthetic reasons, foot comfort, or noise control, a floor covering often is placed over the deck, which then may be referred to as a subfloor. Figure 1.6a shows a concrete subfloor with a flexible-tile floor covering. A hollowcold- formed steel deck is incorporated in the subfloor to house electric wiring.

Guidelines for Roof Mounted Outdoor Air-Conditioner Installations, 1992, Air- Conditioning & Refrigeration Institute, Arlington, Va., National Roofing Contractors Association, Rosemont, Ill., Sheet Metal and Air Conditioning Contractors National Association Inc., Chantilly, Va. C. W. Griffin and Richard Fricklas, The Manual of Low-Slope Roof Systems, 1996, McGraw-Hill, New York, N.Y. Quality Control Guidelines in Application of Built-Up Roofing, 1993, Asphalt Roofing Manufacturers Association, Calverton, Md., National Roofing Contractors Association, Rosemont, Ill. The Manual for Inspection and Maintenance of Built-Up and Modified Bitumen Roof Systems: A Guide for Building Owners, 1996, Asphalt Roofing Manufacturers Association, Calverton, Md., National Roofing Contractors Association, Rosemont, Ill. Quality Control Guidelines for the Application of Polymer Modified Bitumen Roofing, 1996, Asphalt Roofing Manufacturers Association, Calverton, Md., National Roofing Contractors Association, Rosemont, Ill. Quality Control Guidelines for the Applications of Thermoset Single-Ply Roof Membranes, 1997, National Roofing Contractors Association, Rosemont, Ill., Single Ply Roofing Institute, Needham, Mass. SPRI/NRCA Manual of Roof Inspection, Maintenance, and Emergency Repair for Existing Single-Ply Roofing Systems, 1992, National Roofing Contractors Association, Rosemont, Ill., Single Ply Roofing Institute, Needham, Mass. Quality Control Guidelines for the Application of Sprayed Polyurethane Foam Roofing, 1997, National Roofing Contractors Association, Rosemont, Ill., Spray Polyurethane Foam Division, Washington, D.C. The Manual for Inspection and Maintenance of Spray Polyurethane Foam-Based Roof Systems: A Guide for Building Owners, 1998, National Roofing Contractors Association, Rosemont, Ill., Spray Polyurethane Foam Division,Washington, Repair Manual for Low-Slope Membrane Roof Systems, 1997, Asphalt Roofing Manufacturers Association, Calverton, Md., National Roofing Contractors Association, Rosemont, Ill., Single Ply Roofing Institute, Needham, Mass. Steep-Slope Roofing Materials Guide, 2000, National Roofing Contractors Association,