With wood construction, there will probably always be a dead air space between floors, but with concrete, a trend in some construction projects makes a single slab of concrete both ceiling and floor. Regardless of the type of construction, though, property owners recognize that a quiet building generates more rent, and building dwellers know that life in a quiet building is worth the extra expense of sound attenuation.
For the construction industry, there are two types of sound and two different rating systems for sound control. One type of sound, referred to as STC (Sound Transmission Class), is airborne sound such as what is generated by voices or broadcast sounds. The other type of sound is known as IIC (Impact Insulation Class), and it includes impact noise such as footsteps, moving furniture, and dropped objects. STC ratings rely, to a large extent, on the solid mass of a structure. For example, one system claiming a high STC sound attenuation rating does so with a highly unusual construction detail: two layers of 5/8-gypsum drywall for the ceiling.
Eliminating any reliance on structural attributes, IIC ratings are based primarily on the properties of the membrane or system used to reduce sound transmission. Construction techniques for all types of sound reduction systems made for use with tile vary considerably. Some system allow the direct bonding of tiles to the membrane while other systems may need to be covered with additional materials prior to the application of ceramic or stone tile. Industry details involving sound control for walls have been around for some time, but sound control for floors is changing. For the most current information regarding sound control for both walls and floors, please consult the 2005 edition of the TCA Handbook (Tile Council of North America, www.tileusa.com).
In addition to the obvious problems associated with hard materials installed in multi-occupant buildings, sound rated tile floors require special consideration because of the problems of compressibility and loading. In addition to the caution stated in the previous paragraph, some sound reduction systems require larger tiles to help spread the load. Sound reduction systems for carpet, sheet goods, and strip flooring are readily available but not all are rated for use with ceramic tile. For best results when working with ceramic or stone tiles, only use sound reduction systems that have gone through ASTM C627 (commonly known as the Robinson Floor Test) and have achieved a rating equal to the requirements of the installation. Avoid using installation materials that are not tile-specific.
Concrete floors of all types are known for a common property: the ability to transmit unwanted sound. Suspended ceilings can provide significant reduction in sound transmission, but when a suspended ceiling is not possible, or when a suspended ceiling system, alone, cannot provide the required sound attenuation, a floating floor system composed of a sound reduction membrane, and other materials applied to the floor, can be employed with good results. Wood construction can be just as challenging as concrete since, in some applications, adding ceramic or stone tiles can actually increase sound transmission! With sound reduction over wood construction, structural performance is very important since some systems call for double-layer plywood sub-floors and ceilings in addition to the weight of the sound reduction system materials.
Sound reduction may not be the only requirement of a ceramic or stone tile installation which could also include waterproofing and crack isolation. Changes in the sound reducing performance of a system can arise when using untested combinations of different manufacturer's products. For this reason, many specifiers include a provision for testing an unrated sound rated system. This can add layers of expense as well as an increase in the build time. I solve this problem by specifying a single membrane that has sound attenuation, crack isolation, and waterproofing properties in a single membrane sheet (NOBLESEAL SIS, made by the Noble Company, www.noblecompany.com).
With direct-install systems, an upturn at the baseboard is generally not required for sound reduction unless the membrane can also be used as a waterproofing membrane. When a sound reduction membrane is used as part of a waterproofing system, follow the manufacturer's instructions regarding the height and other details related to the upturn, and make sure there is a 1/4-inch minimum gap between the edges of the tiles and any hard surfaces. The upturned membrane helps control IIC sounds while the 1/4-inch gap reduces STC sounds.
On non-waterproofed installations, the direct-bond membrane sheet can terminate at the baseboard without an upturn. This, along with a 1/4-inch gap between the edges of the tiles and the baseboard, will help control the IIC sounds. To reduce the airborne (STC) sounds, though, the edge of the membrane sheet, and the 1/4-inch gap, should be sealed and filled with a flexible acoustical sealant. Even more so in a sound reduction system-to break direct contact between the tiles and the surrounding walls-the movement joint is an essential part of the tile installation system.
It should be noted that significant differences have been reported in test results obtained from the field and the lab, owing to the increased number of variables inherent with field testing. A lab test based on identical jobsite conditions can provide a good starting point for a field test verification, but for testing unrated subfloor assemblies, two field tests are required: one before and one after the installation.
Sound reduction techniques and materials for tiles installed in multi-occupant buildings can be successful only through careful attention to details in the planning and design phase, and through a thoughtful application of all the materials in the tile installation sandwich. Consult the information found in the TCA Handbook on pages 64 to 67, compare manufacturer's performance specs, and develop a quality control installation program for best results.