Green buildings are designed, constructed and operated for the purpose of providing the occupants with a space that is both healthy and productive, while also being energy efficient and sustainable. Unfortunately, current approaches to green building design and construction don’t always meet occupants’ indoor environmental quality (IEQ) needs for “acoustic comfort.”
Acoustic comfort refers to an indoor environment that is conducive to providing speech intelligibility, speech privacy, low distractions and annoyance, and sound quality.
And, according to ongoing research at the Center for the Built Environment (CBE), it is the lowest performing IEQ factor in green buildings. Moreover, in all buildings surveyed, the level of acoustic satisfaction was rated as the lowest performance IEQ factor, and the only negative (dissatisfaction) factor overall.
There is no need, however, to sacrifice good acoustics when selecting products for green buildings. Architects and interior designers do not have to choose between sustainability, design and acoustic needs—they can have all three.
Outlined below are a number of acoustic considerations for green buildings in three market segments: healthcare facilities, commercial offices and educational facilities.
Acoustics are a key element in the IEQ of healthcare facilities because they play an important role in supporting the safety, health and well-being of patients and staff alike.
In general, ambient noise levels in hospitals are high, and have been shown to be a source of annoyance and stress to both patients and staff. They can also interfere with the staff’s ability to work effectively. Because of this, both the FGI 2010 Guidelines and LEED for Healthcare address the issue.
One reason healthcare facilities are so noisy is the predominance of hard, sound-reflecting surfaces that cause speech and activity sounds to persist much too long. When acoustic conditions are characterized by long reverberation, spoken words are perceived to overlap, resulting in reduced speech intelligibility.
To reduce reverberation and noise levels, acoustical ceiling panels should have a noise reduction coefficient (NRC) of 0.70 or greater. (The NRC indicates the average percentage of sound a material absorbs; an NRC of 0.70 means the material absorbs about 70 percent of the sound that strikes it.) They should also meet healthcare standards for washability, mold and microbial resistance, and fire safety. Ceiling panels with these characteristics are ideal for patient rooms, treatment rooms and other spaces that require a balance of cleanliness and quiet.
Ceiling panels with a NRC of 0.95 are recommended for areas that require even higher levels of sound absorption to ensure patient privacy and meet HIPAA regulations. These include open plan spaces such as waiting areas, pharmacies, nurses’ stations and closed plan spaces where walls extend up to the deck above.
Whether for a space with cubicles and teaming areas or private offices and conference rooms, there are acoustic options that also address sustainable needs. For example, a wide range of continuous and wall-to-wall acoustical ceilings are available that not only enhance the acoustic environment, but also contain high recycled content and can be recycled at the end of their service life.
There are also a variety of “free-floating” ceiling treatments including acoustical clouds, canopies and baffles that are ideal for open plenum or exposed structure spaces—a design trend in green buildings that continues to grow.
Unfortunately, this “warehouse look” can often cause acoustical problems due to sound reflecting off the deck, resulting in excessive reverberation. Any large space of this type will usually need some sound-absorbing elements to help control noise and reverberation within it. In addition, if the exposed deck is less than 15 feet high, reflections between open plan cubicles can cause distractions for nearby occupants.
Designed for use in either new construction or retrofit applications, acoustical clouds, canopies and baffles can add sound absorption in open spaces, provide visual interest and make a design statement, all without sacrificing that exposed look.
Available in a myriad of shapes, acoustical ceiling clouds suspended above work areas provide a type of interrupted ceiling plane. As such, they help control both distant reverberations and reflections, reducing occupant annoyance and distractions. Acoustical clouds actually provide greater sound absorption than a continuous ceiling of the same surface area because they absorb sound on both their front and back surfaces. In fact, reverberation time can be reduced nearly 50 percent with only 20 percent coverage.
Acoustical canopies also help reduce reverberation in the space below them, but are much different in size and look compared to acoustical clouds. For example, cloud systems are available in standard sizes up to 14 by 14 feet, while canopies are usually 3 by 3 or 4 by 6 feet in size. Visually, acoustical clouds are flat, while canopies are curved and can be installed as hills or valleys.
Currently, there is no standard credit in the IEQ section of LEED for acoustic performance. However, an innovation credit can be applied for by demonstrating that the acoustics of a building are superior to what would normally be considered typical, thereby improving the quality of the indoor environment. The LEED v4 proposal (in a fifth public comment at the time of this writing) does, however, include a requirement for acoustic performance as part of the IEQ section.
Considering that the primary mode of teaching involves speech and listening, the quality of the acoustic environment in a classroom is crucial. LEED for Schools recognized the unique nature of the design and use of K-12 schools, and was the first of the U.S. Green Building Council (USGBC) rating systems to include acoustics as an integral and important element of IEQ.
To provide classrooms that enhance learning, LEED for Schools includes a minimum acoustical performance prerequisite. To meet it, two requirements must be achieved:
- Classrooms and other core learning spaces must include sufficient sound-absorptive finishes to comply with a maximum reverberation time of 0.60 seconds (classrooms less than 20,000 cubic feet).
- Classrooms and other core learning spaces must meet a maximum background noise level from HVAC systems of 45 decibels A-weighted (dBA).
Compliance with the first requirement is accomplished in one of two ways:
- By confirming that 100 percent of all ceiling areas (excluding lights, diffusers and grilles) are finished with a material that has a NRC of 0.70 or higher.
- By confirming that the total area of acoustical wall panels, ceiling finishes and other sound-absorbent finishes equals or exceeds the total ceiling area of the room (excluding lights, diffusers and grilles). All materials in the calculation must have an NRC of 0.70 or higher.
The proper use of sound-absorbing materials will significantly reduce reverberation, however, the location of acoustic treatments is a vital consideration. In classrooms where there is no fixed position for the teacher and ceiling heights are about 10 feet, the best and most cost-effective option is to place most, if not all, of the sound-absorbing material on the ceiling, in the form of a suspended acoustical ceiling.
If ceiling heights are greater than 12 feet, an increasing amount of sound-absorbing material should be placed on the walls. If there is no possibility for wall treatment, consider placing three-dimensional furnishings such as bookshelves along the walls to ensure sound waves are scattered, thereby reducing the possibility of distant echoes.
Kenneth P. Roy, Ph.D., FASA, is a senior principal research scientist for acoustic technologies for Armstrong Building Products in Lancaster, Pa. He can be reached at firstname.lastname@example.org.