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 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.
An Alternative to Encasement in or Shielding by a Fire-resistant Material
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 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.
Partitions May be Built and Installed to be Easily Shifted
Non-load-bearing partitions do not support floors or roof. Hence, partitions may be made of such thin materials as sheet metal (Fig. 1.7a), brittle materials as glass (Fig. 1.7a), or weak materials as gypsum (Fig. 1.7c). Light framing may be used to hold these materials in place. Because they are non-load-bearing, partitions may be built and installed to be easily shifted or to be foldable, like a horizontally sliding door.
Acoustic Properties Appropriate to the Occupancy
Wall Finishes. Walls are usually given a facing that meets specific architectural requirements for the spaces enclosed. Such requirements include durability under indoor conditions, ease of maintenance, attractive appearance, fire resistance, water resistance, and acoustic properties appropriate to the occupancy of the space enclosed. The finish may be the treated surface of the exposed wall material, such as the smooth, painted face of a sheet-metal panel, or a separate material, such as plaster, gypsumboard, plywood, or wallpaper.
Openings are provided in interior walls and partitions to permit passage of people and equipment from one space to another. Doors are installed in the openings to provide privacy, temperature, odor and sound control, and control passage.