Acoustics in Multifamily Dwellings

For multifamily dwellings, the International Building Code (IBC) references both the IIC and STC laboratory and field tests. The code specifies that IIC and STC ratings be at a minimum of 50 if tested in the lab, and 45 if tested in the field.

These requirements are often satisfied when carpet is used as the floor covering. However, hard-surfaced flooring creates real sound transmission problems. The trend towards stone and tile flooring, in particular, means that designers of multifamily dwellings can no longer depend on carpeting to solve the problem. Designers need to pay more attention to the design of floor-ceiling assemblies to meet specific standards.

The code is simply a minimum. Owner's expectations, particularly in high-end and luxury housing, need to reach beyond this standard. In its Guide to Airborne, Impact, and Structure: Borne Noise Control in Multifamily Dwellings, the U.S. Dept. of Housing and Urban Development has largely set the standards for controlling noise in multifamily dwellings (see Table 5). These guidelines establish three grades for acoustic environments. The minimum grade reflects the IIC requirements of the IBC for floor-ceiling assemblies.

The U.S. Dept. of Housing and Urban Development (HUD) provides descriptive definitions of three grades of acoustic environments, which largely set the standards for controlling noise in multifamily dwellings. *The Minimum grade reflects the IIC requirements of the International Building Code (IBC) for floor/ceiling assemblies.

Acoustics in Healthcare Facilities

Healthcare facilities feature a broad range of buildings. This includes hospitals, nursing homes, hospice facilities, assisted living facilities, independent living settings, adult day care facilities, wellness centers, and outpatient rehabilitation centers. These environments must be designed to meet published standards described in the Sound and Vibration Design Guidelines for Hospital and Healthcare Settings. These standards are laid out to support the Health Insurance Portability and Accountability Act (HIPAA) and set guidelines for how to ensure sound isolation and speech privacy in healthcare facilities. HIPAA is meant to prevent intentional or unintentional privacy breaches, and the privacy standards it establishes apply to both new construction and healthcare renovations of all types. The HIPAA guidelines serve as the reference standard for the acoustics section of the 2010 FGI/ASHE Guidelines for Design and Construction for Healthcare Facilities; the Green Guide for Healthcare version 2.2; and LEED for Healthcare, version 4, which is currently under development.

Recommended daytime noise levels for patient areas in healthcare facilities is 35 dB(A)—a target that is difficult to achieve. According to a 2005 study of noise levels in hospitals, noise levels at Johns Hopkins Hospital, a top-ranked U.S. hospital, exceeded 45 to 50 dB(A). This is higher than the typical conversational speech level.

As in other institutional buildings, sound is transmitted through common partitions, common suspended ceilings, and flanking paths, such as open doors. HVAC systems and ductwork add to the sound levels. In healthcare facilities, mechanical sounds include a wide assortment of patient-care equipment, emergency alarms, and other equipment, such as service carts. Other sound sources that must be managed by designers of healthcare facilities include amplified paging and intercom systems and conversational speech during patient/doctor communications and family visits. All these sounds will require the use of acoustically absorptive materials, both as finishes on interior surfaces to control room acoustics and as underlayments, isolation membranes, and gaskets to reduce sound transmission. Because of the clean-room requirements, carpet is rarely acceptable as a floor finish.

Nursing stations and staff rooms have proven to be a major source of noise. While this noise may be unavoidable, efforts should be made to isolate nursing stations from patient rooms, counseling rooms, and other areas of the facility where privacy and sustained periods of quiet are needed. The use of acoustic underlayments and soft floor finishes in nursing stations not only helps this isolation but provides some joint relief for nurses.

Designers should also be aware that expansion breaks and transitions between floor surfaces increase the vibrations from rolling equipment when they pass over these transitions. Smooth, continuous, cleanable floor surfaces should be the goal.

Classroom Acoustics

Consider a young student that has a tenuous grasp on vocabulary and linguistic sounds. Moderate levels of noise and poor room acoustics can impair this student's ability to understand words, even when they are clearly spoken. The problems become more acute for hearing-impaired and second-language listeners.

Much of the acoustic management comes from school teachers and staff (e.g. keeping classroom noise to a minimum, cooperation with scheduling activities in adjacent spaces, etc.). However, building designers have an enormous impact on how successful those efforts will be. The goal should be to create learning spaces capable of isolating outdoor noise and achieving indoor levels below 40 dB (A). This is a quiet space.

General strategies for accomplishing this include:

• Locate buildings away from noisy roads and other noise sources.

• Provide better sound isolation in exterior walls and windows to limit the intrusion of outdoor noises.

• Include high-quality acoustical floor underlayments in floor-ceiling assemblies

• In addition to the use of acoustical underlayments, floor-ceiling assemblies also need 2-hour rated ceilings on resilient channel and sound-isolated wall plates.

• Provide quieter ducted central ventilation systems and locate HVAC units away from classrooms and learning centers. Rooftop HVAC systems are recommended.

Controlling sound transmission alone is not enough for controlling noises in educational settings. Efforts to control room acoustics, such as providing sound absorbing surface finishes have proven successful. It is also recommended that classroom sizes be limited. In rooms greater than 1,500-square-feet, speech can reverberate a second or longer, degrading speech intelligibility.

Bottom Line

Regardless of what building type a designer may be detailing, there are only two ways to evaluate the sound transmission characteristics of building assemblies:

• STC – Sound Transmission Class; measures airborne sound

• IIC – Impact Insulation Class; measures structure-borne sound between floors.

The IBC specifies that IIC and STC levels be at a minimum of 50 in the lab and 45 in the field. To reach these levels in multifamily, healthcare, and educational facilities, sound transmission can be reduced in the floor-ceiling assembly using an impact sound attenuation material. But, be careful when specifying these materials. Building designers must pay close attention to the product evaluation reports to make sure that laboratory and field tests are not misused or the wrong tests cited.

 

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