FIGURE 1.6 Examples of floor-ceiling and roof-ceiling systems. (a) Concrete structural slab carries hollow-steel deck, concrete fill, and flexible tile flooring. (b) Acoustical-tile ceiling incorporating a lighting fixture with provisions for air distribution is suspended below a floor. (c) Insulated roof and steel beams are sprayed with mineral fiber for fire protection. (d) Insulated roof and open-web joists are protected by a fire-rated suspended ceiling. In some cases, a subfloor may be strong and stiff enough to span, unaided, long distances between supports provided for it. In other cases, the subfloor is closely supported on beams. The subfloor in Fig. 1.6a, for example, is shown constructed integrally with concrete beams, which carry the loads from the subfloor to bearing walls or columns. The underside of a floor or roof and of beams supporting it, including decorative treatment when applied to that side, is called a ceiling. Often, however, a separate FIGURE 1.6 (Continued) ceiling is suspended below a floor or roof for esthetic or other reasons. Figure 1.6b shows such a ceiling. It is formed with acoustical panels and incorporates a lighting fixture and air-conditioning inlets and outlets. Metal and wood subfloors and beams require fire protection. Figure 1.6c shows a roof and its steel beams protected on the underside by a sprayed-on mineral fiber. Figure 1.6d shows a roof and open-web steel joists protected on the underside by a continuous, suspended, fire-resistant ceiling. As an alternative to encasement in or shielding by a fire-resistant material, wood may be made fire-resistant by treatment with a fire-retardant chemical. Fire Ratings. Tests have been made, usually in conformance with E119, Standard Methods of Tests of Building Construction and Materials, developed by ASTM, to determine the length of time specific assemblies of materials can withstand a standard fire, specified in E119. On the basis of test results, each construction is assigned a fire rating, which gives the time in hours that the assembly can withstand the fire. Fire ratings for various types of construction may be obtained from local, state, or model building codes or the Fire Resistance Design Manual, published by the Gypsum Association. Interior Walls and Partitions. Interior space dividers do not have to withstand such severe conditions as do exterior walls. For instance, they are not exposed to rain, snow, and solar radiation. Bearing walls, however, must be strong enough to FIGURE 1.7 Types of partitions: (a) non-load-bearing; (b) gypsumboard on metal studs; (c) gypsumboard face panels laminated to a gypsum core panel; (d) concrete bearing wall, floors, and beams. (Reprinted with permission from F. S. Merritt and J. Ambrose, Building Engineering and Systems Design, 2d ed., Van Nostrand Reinhold, New York.) transmit to supports below them the loads to which they are subjected. Usually, such interior walls extend vertically from the roof to the foundations of a building and carry floors and roof. The basic element of a bearing wall may be a solid core, as shown in Fig. 1.7d, or closely spaced vertical framing (studs), as shown in Fig.

Wood I joists are available with a wide range of depths and load/span capabilities. Although joist sizes vary with manufacturer preference, most manufacturers produce joists with depths of 91/2 in or 117/8 in for direct substitution for 2  10 and 2  12 dimension lumber. Other depths14 and 16 in and deeperalso are available. The deeper products are typically used in longer-span applications, such as for light commercial construction. Prefabricated wood I joists have many advantages that make them an economical construction material. Some of these advantages are: Manufactured product. They are shipped to the job site precut to length, thereby eliminating waste. Consistent product quality is assured by the manufacturing process so that all material arriving at the job site is usable. Wood I joists are manufactured from dry components, thus eliminating shrinkage, warping, and twisting. Long lengths available. I joists can be manufactured and shipped to the job site in long lengths. This minimizes labor costs due to handling and allows the joists to be used in multispan applications. Lightweight. Their low weight makes it very easy for construction workers to easily handle long lengths on the job site, whether for long clear spans or multiple spans. A typical residential I-joist only weighs 2 pounds per foot. Ease of fabrication. The structural panel webs are easily cut to permit passage of wiring, conduit, plumbing, and mechanical ductwork. Manufacturing provide charts that indicate the maximum permissible size of round or rectangular openings that can be cut in the web without adversely affecting structural performance of the joists. APA also publishes hole charts consistent with PRI 400. 10.30.4 Structural Composite Lumber Structural composite lumber (SCL) comprises a family of secondary manufactured engineered glued wood products. The most widely available type of SCL, laminated veneer lumber (LVL), is similar to plywood in that thin sheets of veneer are structurally bonded together to create large panels, usually in widths of 2 or 4 ft. These panels are typically produced in thicknesses of 11/2 or 13/4 in, and in long lengths. (Lengths vary, depending on the manufacturer). However, unlike plywood, which has the veneers cross-banded, all veneers in LVL products are oriented with grain approximately parallel, much like the positioning of sawn lumber in glulam timber. Another type of SCL, parallel-strand lumber (PSL), is manufactured from long strands of veneer rather than veneer sheets as used in LVL manufacturing. PSL is manufactured in a variety of widths ranging from 13/4 in up to 7 in. Various depths and lengths are also produced. Designers should consult the manufacturers for information

An individual vent, or back vent, is a pipe installed to vent a fixture trap and is connected to the venting system above the fixture served or terminated outdoors. FIGURE 14.11 Venting of waste branches: (a ) wet venting of bathtub drainage pipe; (b ) circuit venting, and (c ) loop venting of a battery of plumbing fixtures. To ensure that the vent will adequately protect the trap, plumbing codes generally limit the distance downstream that the vent opening may be placed from the trap. This distance generally ranges from 21/2 ft for a 11/4-in fixture drain to 10 ft for a 4-in fixture drain, but not less than two pipe diameters. The vent opening should be located above the bottom of the discharge end of the trap (Fig. 14.11). In general, all trapped fixtures are required to have an individual vent, although vents may be eliminated under some exceptional conditions. The plumbing code should be reviewed to determine where and how individual vents are to be installed. To reduce the amount of piping required, two fixtures may be set back to back, on opposite sides of a wall, and vented by a single vent (common vent). In that case, however, the fixtures should discharge wastewater separately into a double fitting with inlets at the same level. A branch vent is a pipe used to connect one or more individual vents to a vent stack or to a stack vent. A wet vent is a pipe that serves both as a vent and as a drainage pipe for wastes other than those from water closets. This type of vent reduces the amount of piping from that required with individual vents. For example, a bathroom group of fixtures may be vented through the drain from a lavatory, kitchen sink, or combination fixture if such a fixture has an individual vent (Fig. 14.lla). A battery of fixtures is any group of similar fixtures that discharges into a common horizontal waste or soil branch. A battery of fixtures should be vented by a circuit or loop vent. (Building codes usually set a limit on the number of fixtures that may be included in a battery.) A circuit vent is a branch vent that serves two or more traps and extends from the vent stack to a connection to the horizontal soil or waste branch just downstream from the farthest upstream connection to the branch (Fig. 14.11b). A loop vent is like a circuit vent but connects with a stack vent instead of a vent stack (Fig. 14.11c). Thus, air can circulate around a loop. In some instances, conventional venting methods cannot be applied, such as with island sink fixtures. Some codes allow the use of air admittance devices, commonly known as quick vents. These devices allow air to enter the vent system while preventing sewer gasses from escaping. Soil and waste stacks with more than 10 branch intervals should be provided with a relief vent at each tenth interval installed, starting with the top floor. A branch interval is a section of stack at least 8 ft high between connections of horizontal branches. A relief vent provides circulation of air between drainage and venting systems. The lower end of a relief vent should connect to the soil or waste stack, through a wye, below the horizontal branch serving a floor where the vent is required. The upper end of the relief vent should connect to the vent stack, through a wye, at least 3 ft above that floor. Such vents help to balance the pressures that are continuously changing within a plumbing system. 14.20.2 Slopes and Connections for Vent Pipes While the venting system is intended generally to convey only air to and from the drainage system, moisture may condense from the air onto the vent pipe walls. To remove the condensation from the venting system, all individual and branch vent pipes should be sloped and connected as to conduct the moisture back to soil or waste pipes by gravity. 14.20.3 Sizing of Vent Pipes Fixture units (Art. 14.19) are also used for sizing vents and vent stacks (Table 14.12). In general, the diameter of a branch vent or vent stack should be one-half or more of that of the branch or stack it serves, but not less than 11/4 in. Smaller diameters are prohibited, because they might restrict the venting action. 14.20.4 Combined Draining and Vent Systems These offer the possibility of considerable cost savings over the separate drainage and venting systems described in Art. 14.20.1. One such system, introduced by the Western Plumbing Officials Association, employs horizontal wet venting of one or more lavatories, sinks, or floor drains by means of a common waste and vent pipe adequately sized to provide free movement of air above the flow line of the pipe. Relief vents are connected at the beginning and end of the horizontal pipe. The traps of the fixtures are not individually vented. Some building codes permit such a system only where structural conditions preclude installation of a conventional system. Where this combined drainage and vent system may be used, it may require larger than normal waste pipes and traps. Each of the model codes has different requirements for this type of system and, therefore, the code in effect must be carefully reviewed during the design process. The Sovent system is another type of combination system. It requires drainage branches and soil stacks, with special fittings, but no individual and branch vents and no vent stacks. The system has four basic parts: a soil or waste stack with a stack vent extending through the roof, a Sovent aerator fitting on the stack at each floor, horizontal branches, and a Sovent deaerator fitting on the stack at its base and at horizontal offsets (Fig. 14.12). The aerator and deaerator provide means for self-venting the stack. In a conventional drainage system, a vent stack is installed to supply air to vent pipes connected to the drainage branches and to the soil or waste stack to prevent destruction of the trap seals. In the Solvent system, however, the vent stack is not needed because the aerator, deaerator, and stack vent avoid creation of a