Appearance
A major function of interior finish components is to make the interior of the building look neat and clean by covering the rougher and less organized portions of the framing, insulation, vapor retarder, electrical wiring, ductwork, and piping. Beyond this, the architect designs the finishes to carry out a particular concept of interior space, light, color, pattern, and texture. The form and height of the ceiling, changes in floor level, interpenetrations of space from one floor to another, and the configurations of the partitions are primary factors in determining the character of the interior space. Light originates from windows and electric lighting fixtures and is propagated by successive reflections off the interior surfaces of the building. Lighter-colored materials raise interior levels of illumination; darker colors and heavier textures result in a darker interior. Patterns and textures of interior finish materials are important in bringing the building down to a scale of interest that can be appreciated readily by the human eye and hand. No two buildings have the same requirements: Deep carpets and rich, polished marbles in muted tones may be chosen to give an air of affluence to a corporate lobby, brightly colored surfaces to create a happy atmosphere in a day care center, or slick plastic and highly reflective surfaces to provide a trendy ambience for the sale of designer clothing.
Durability and Maintenance
Expected levels of wear and tear must be considered carefully in selecting finishes for a building. Highly durable finishes generally cost more than shorter-lived ones and are not always required. In a courthouse, a transportation terminal, a recreation building, or a retail store, traffic is intense, and long-wearing materials are essential. In a private office or an apartment, more economical finishes are usually adequate. Water resistance is an important attribute of finish materials in kitchens, bathrooms, locker and shower rooms, entrance lobbies, and some industrial buildings. In hospitals, medical offices, kitchens, and laboratories, finish surfaces must not trap dirt and must be easily cleaned and disinfected. Maintenance procedures and costs should be considered in selecting finishes for any building: How often will each surface be cleaned, with what type of equipment, and how much will this procedure add to the cost of owning the building? How long will each surface last, and what will it cost to replace it?
Acoustic Criteria
Interior finish materials strongly affect noise levels, the quality of listening conditions, and levels of acoustic privacy inside a building. In noisy environments, interior surfaces that are highly absorptive of sound can decrease the noise intensity to a tolerable level. In lecture rooms, classrooms, meeting rooms, theaters, and concert halls, acoustically reflective and absorptive surfaces must be proportioned and placed so as to create optimum hearing conditions.
Between rooms, acoustic privacy is created by partitions that are both heavy and airtight. The acoustic isolation properties of lighter-weight partitions can be enhanced by partition details that damp the transmission of sound vibrations by means of resilient mountings on one of the partition surfaces and sound-absorbing batts of mineral wool in the interior cavity of the partition. Manufacturers test full-scale sample partitions of every type of material for their ability to reduce the passage of sound between rooms in a procedure outlined in ASTM E90. The results of this test are converted to Sound Transmission Class (STC) numbers that can be related to accepted standards of acoustic privacy. In an actual building, however, if the cracks around the edges of a partition are not completely sealed, or if a loosely fitted door or even an unsealed electric outlet is inserted into the partition, its airtightness is compromised and the published STC value is meaningless. Similarly, a partition with a high STC is worthless if the rooms on both sides are served by a common air duct that also acts incidentally as a conduit for sound, or if the partition reaches only to a lightweight, porous suspended ceiling that allows sound to pass over the top of the partition.
Transmission of impact noise from footsteps and machinery through floor–ceiling assemblies can be a major problem. Impact noise transmission is measured according to ASTM E492, in which a standard machine taps on a floor above while instruments in a chamber below record sound levels. The results are reported as Impact Isolation Class (IIC) ratings. Impact noise transmission can be reduced by floor details that rely on soft materials that do not transmit vibration readily, such as carpeting, soft underlayment boards, or resilient underlayment matting.
Fire Criteria
A building code devotes many pages to provisions that control the materials and details for interior finishes in buildings. These code requirements are aimed at several important characteristics of interior finishes with respect to fire.
Combustibility
The surface burning characteristics of interior wall and ceiling finish materials are tested in accordance with ASTM E84, also called the Steiner Tunnel Test. In this test, a sample of material 20 inches wide by 24 feet long (500 × 7300 mm) forms the ceiling of a rectangular furnace into which a controlled flame is introduced at one end. The time the flame takes to spread across the face of the material from one end of the furnace to the other is recorded, along with the density of smoke developed. The results of this test are given as a flame-spread rating, which indicates the rapidity with which fire can spread across a surface of a given material, and a smoke-developed rating, which classifies a material according to the amount of smoke it gives off when it burns.
Figure 22.5 defines allowable flame-spread and smoke-developed ratings for interior finish materials for various occupancy groups of buildings according to the International Building Code (IBC). It assigns each material to one of three classes: A, B, or C. Class A materials are those with flame-spread ratings between 0 and 25, Class B between 26 and 75, and Class C between 76 and 200. (The scale of flame-spread numbers is established arbitrarily by assigning a value of 0 to cement–asbestos board and 100 to a Red oak board.) For all three classes, the smoke-developed rating may not exceed 450. Materials with higher smoke-developed ratings are not permitted to be used inside buildings, because smoke, not heat or flame, is the primary killer in building fires. Interior trim materials, if their total surface area in a room does not exceed 10 percent of the total wall and ceiling area of the room, may be of Class A, B, or C in any type of building.
Some especially flammable wall and ceiling finish materials, such as textile or vinyl coverings, are also subject to testing according to NFPA 265, a test that measures their room fire-growth contribution, that is, their potential to add fuel to an incipient fire. The building code sets limits on flame spread, flashover, and smoke generated during this test. In some Occupancies, restrictions on combustible draperies, wall hangings, and other decorative materials also apply.
The combustibility of some flooring materials used in exits, corridors, and areas connected to these spaces must be tested according to NFPA 253 for minimum critical radiant flux exposure. The purpose of this test is to ensure that flooring materials in essential parts of the egress system cannot be easily ignited by the radiant heat of fire and hot gases in adjacent spaces. Materials must meet either Class I (most resistant to radiant heat) or Class II (moderately resistant) ratings, depending on the Occupancy Group of the spaces and whether or not the area is protected with an automatic sprinkler system. Some traditional flooring materials, including solid wood, resilient materials, and terrazzo, which have historically demonstrated satisfactory resistance to ignition during building fires, are not required to meet this test standard.
In other areas of the building, flooring materials are subject to the pill test (Consumer Product Safety Commission DOC FF-1), which evaluates the material’s propensity for flame spread when exposed to a burning tablet intended to simulate a dropped lit cigarette, match, or similar hazard.
Fire Resistance
Fire resistance of a wall, ceiling, or floor assembly refers not to the assembly’s own combustibility, but rather to its ability to resist the passage of fire from one side of the assembly to the other. The building code regulates the fire resistance of assemblies used to protect the structure of the building, to separate various parts of a building from one another, and to separate one building from another.
Figure 22.6 is a table from the International Building Code that specifies the required fire resistance rating, in hours of separation, between different Occupancies housed in the same building. (See the figure caption for comments regarding when these requirements apply.) Fire resistance rating requirements found elsewhere in the code for various types of separations, such as shaft walls, exit hallways, exit stairs, dwelling unit separations, and other nonbearing partitions, are summarized in Figure 22.7. Requirements for the protection of structure, for the fire resistance of exterior walls, and for fire walls that separate buildings are shown in Figures 1.3 and 1.7. Such requirements can be related to fire resistance information provided in manufacturers’ literature similar to the examples shown in Figures 1.4–1.6.
FIGURE 22.6 IBC requirements for fire resistance ratings, in hours, for fire separation assemblies between Occupancy Groups. This code allows several alternative approaches to the design of buildings that contain more than one Occupancy Group. For larger buildings, parts of the building containing different occupancies must be separated by fire-resistance-rated walls and floor-ceilings as indicated in this table. For smaller buildings, an alternative approach allows occupancy areas to be nonseparated, that is, no fire-resistance-rated separations are required. Consult Chapter 5 of the IBC for more information. Portions of this publication reproduce tables from the 2006 International Building Code, International Code Council, Inc., Washington, D.C. Reproduced with Permission. All rights reserved.
FIGURE 22.7 This table summarizes IBC fire resistance rating requirements for various types of assemblies not included in other code tables reproduced in this book. Fire areas, listed in the last row of the table, are portions of a building that are limited in area or occupant number for the purpose of determining sprinkler requirements.
Fire resistance ratings are determined by full-scale fire endurance tests conducted in accordance with ASTM E119, which applies not only to partitions and walls, but also to beams, girders, columns, and floor–ceiling assemblies. In this test, the assembly is constructed in a large laboratory furnace and subjected to the structural load (if any) for which it is designed. The furnace is then heated according to a standard time–temperature curve, reaching 1700 degrees Fahrenheit (925°C) at 1 hour and 2000 degrees Fahrenheit (1093°C) after 4 hours. To achieve a given fire resistance rating in hours, an assembly must safely carry its design structural load for the designated period, must not develop any openings that permit the passage of flame or hot gases, and must insulate sufficiently against the heat of the fire to maintain surface temperatures on the side away from the fire within specified maximum levels. Wall and partition assemblies must also pass a test, called the hose stream test, intended to assess their durability while exposed to fire conditions. A duplicate sample of the assembly is subjected to half of its rated fire exposure, then sprayed with water from a calibrated fire nozzle for a specified period at a specified pressure. To pass this test, the assembly must not allow passage of the water stream.
Openings in floors, ceilings, and partitions with required fire resistance ratings are restricted in size by most codes and must be protected against the passage of fire in various ways. Doors must be rated for fire resistance in accordance with a table such as that shown in Figure 18.27. Ducts that pass through rated assemblies must be equipped with sheet metal dampers (fire dampers) that close automatically if hot gases from a fire enter the duct. Penetrations for pipes and conduits must be closed tightly with fire-resistive material.
As an example of the use of these tables, consider a multistory vocational high school building of Type IIA construction that includes both a number of classrooms and a woodworking shop and that is fully sprinklered. For purposes of the table reproduced in Figure 22.6, the International Building Code places classrooms in Occupancy Group E (Educational) and the shop into Occupancy Group F-1 (Industrial, Moderate Hazard). Assuming that the building is large enough that the requirements of this table apply, the two uses must be separated from each other by walls (called “fire barriers”) and, if applicable, floor–ceiling assemblies, of 1-hour construction. Doors through such walls must be rated at ¾ of an hour (Figure 18.27). Figure 22.5 indicates that, in the Occupancy E portion of the building, finish materials in exit stairway enclosures must have at least a Class B rating, while Class C finish materials are permitted throughout the remainder of the building. According to Figure 22.7, walls and floor–ceiling assemblies separating corridors from adjacent spaces must have a fire resistance rating between 0 and 1 hours, and exit stairways must be enclosed in construction rated between 1 and 2 hours (the final determination of these requirements depending also on other provisions of the code). Referring to Figure 1.3, we can see that the building’s structural system must be protected with 1-hour rated assemblies or, as explained in the footnotes to this table and depending on other requirements of the code, it may be permissible to leave the structure unprotected due to the presence of a sprinkler system.
Relationship to Mechanical and Electrical Services
Interior finish materials join the mechanical and electrical services of a building at the points of delivery of the services—the electrical outlets, the lighting fixtures, the ventilating diffusers and grills, the convectors, the lavatories and water closets. Leading up to these points, the services may or may not be concealed by the finish materials. If the service lines are to be concealed, the finish systems must provide space for them, as well as for maintenance access points in the form of access doors, panels, hatches, cover plates, or ceiling or floor components that can be lifted out to expose the lines. If service lines are to be left exposed, the architect should organize them visually and specify a sufficiently high standard of workmanship in their installation so that their appearance will be satisfactory.
Changeability
How often are the use patterns of a building likely to change? In a concert hall, a chapel, or a hotel, major changes will be infrequent, so fixed, unchangeable interior partitions are appropriate. Appropriate finishes include many of the heavier, more expensive, more luxurious materials such as tile, marble, masonry, and plaster, which are considered highly desirable by many building owners. In a rental office building or a retail shopping mall, changes will be frequent; lighting and partitions should be easily and economically adjustable to new use patterns without serious delay or disruption. The likelihood of frequent change may lead the designer to select either relatively inexpensive, easily demolished construction such as gypsum wallboard partitions or relatively expensive but durable and reusable construction such as proprietary systems of modular, relocatable partitions. The functional and financial choices must be weighed for each building.
Cost
The cost of interior finish systems may be measured in two different ways. First cost is the installed cost. First cost is often of paramount importance when the construction budget is tight or the expected life of the building is short. Life-cycle cost is a cost figured by any of several formulas that take into account not only first cost, but also the expected lifetime of the finish system, maintenance costs and fuel costs (if any) over that lifetime, replacement cost, an assumed rate of economic inflation, and the time value of money. Life-cycle cost is important to building owners who expect to retain ownership for an extended period of time. Because of its higher maintenance and replacement costs, a material that is inexpensive to buy and install may be more costly over the lifetime of a building than a material that is initially more expensive.
Toxic Emissions from Interior Materials
A number of common construction materials give off substances that may be objectionable in interior environments. Many synthetics and wood panel products emit formaldehyde fumes for extended periods of time after the completion of construction. Solvents from paints, varnishes, and carpet adhesives often permeate the air of a new building. Airborne fibers of asbestos and glass can constitute health hazards. Some materials harbor molds and mildews whose airborne spores many people cannot tolerate. In isolated instances, stone and masonry products have proven to be sources of radon gas. Construction dust, even from chemically inert materials, can inflame respiratory passages. There is increasing pressure, both legal and societal, on building designers to select interior materials that do not create objectionable odors or endanger the health of building occupants. Compliance with these criteria is complicated by the fact that data on the toxicity of various indoor air pollutants are inconclusive. But data on emissions of pollutants from interior materials are becoming increasingly available to designers, and it is wise to select materials that give off the smallest possible quantities of irritating or unhealthful substances.
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