Specifying acoustical ceilings in green buildings

by Katie Daniel | July 31, 2015 9:00 am

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by Kenneth P. Roy, PhD, FASA, and Nathan Baxter
Until now, acoustics in commercial office buildings had not been a formal part of the Leadership in Energy and Environmental Design (LEED) rating systems except on a case-by-case basis[2]. The new LEED v4 criteria, however, now takes into account the value of good acoustics in enhancing occupant satisfaction and productivity.

Under LEED v4, it is now possible to qualify for two points toward the new Acoustic Performance credit in the Indoor Environmental Quality (EQ) section of the Interior Design and Construction (Commercial Interiors) rating system, and one point in the Building Design and Construction (New Construction) system.

The intent [3]of the credit in both systems is to provide workspaces that promote occupants’ well-being, productivity, and communications through acoustic design that takes into account HVAC background noise, sound isolation, reverberation time, and sound reinforcement and masking systems.

Measures that can be taken in new construction projects to enhance the acoustic environment of commercial office spaces and, at the same time, meet LEED acoustic criteria will be described in this article. However, it is important to note the same measures can also be taken in retrofit and renovation projects as well—regardless of whether green certification is being sought.

Occupant dissatisfaction
The addition of acoustic performance to the LEED rating systems recognizes the results of occupant surveys the Center for the Built Environment (CBE) has conducted over the years. For example, CBE surveyed[4] nearly 22,000 occupants in U.S. commercial office buildings and found acoustic quality to be the only negative factor in terms of the indoor environment. On a scale of +3.0 (satisfied) to −3.0 (dissatisfied), acoustics scored −0.30.

Additionally, nearly 5000 occupants were surveyed in LEED-certified office buildings, and acoustics was once again the only negative factor (−0.35). In terms of acoustics, there is little differentiation between LEED buildings and non-LEED buildings.

CBE survey results in office buildings also show the higher the LEED certification level, the lower the occupant satisfaction with acoustics. Acoustic satisfaction measured −0.53 in Platinum buildings, −0.47 in Gold, and −0.16 in Silver. As architects strive for higher certification levels, acoustics seem to be overlooked in preference to accumulating points.

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Speech privacy
The studies[6] also indicate most of the acoustic complaints relate to speech privacy—overhearing an unwanted conversation or even the feeling one is being overheard. Keeping private conversations private is thus a key concern in conference rooms, executive offices, and other similar spaces in an office environment.

The degree of speech privacy attained in a particular space is indicated by its Privacy Index (PI). Expressed as a percentage, it takes into account the acoustical performance of everything in the space, including ceiling, walls, floorcovering, furniture, and background noise level. The higher the percentage, the better the speech privacy.

The recognized levels of speech privacy as defined by ASTM E1130, Standard Test Method for Objective Measurement of Speech Privacy in Open-plan Spaces Using Articulation Index, are covered in the following paragraphs.

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Confidential
‘Confidential’ represents a PI rating of 95 to 100 percent. Conversations within a space may be partially heard, but definitely not understood beyond the confines of the space. Any nearby occupants may hear muffled sounds but spoken words are not intelligible.

Non-intrusive
Representing a PI rating between 80 and 95 percent, in ‘non-intrusive’ (or ‘normal’), conversations can be partially overheard, and some words or phrases may be intelligible. Nearby occupants may hear some of the conversation, but the loudness of speech is not distracting, and they can generally continue what they are doing.

Non-intrusive speech privacy is a common goal for open-plan environments, especially where ‘knowledge worker’ productivity is a key issue. However, it is generally not adequate in functional environments with closed plans such as medical facilities, law firms, financial service organizations, or human resource departments, where confidential privacy levels are generally required.

Marginal
‘Marginal’ (or ‘poor’) means a PI rating of 60 to 80 percent. Most conversations can be overheard and are likely intelligible. Nearby occupants can understand most words and sentences, and the loudness of speech can be distracting to them.

No privacy
At a PI rating of 60 percent or less, virtually all conversations can be clearly overheard and are fully intelligible. Nearby occupants can typically understand all words and sentences, and the loudness of speech can be a constant distraction.

Open- or closed-plan spaces
Improving the acoustic environment in commercial office spaces to meet LEED criteria regarding reverberation time and, in turn, both speech intelligibility and speech privacy, is not difficult as long as attention is paid to matching the performance features of the ceiling to the needs of the space. One of the best solutions for keeping noise levels down and conversations private in open- or closed-plan spaces is the use of a high-performance acoustical ceiling that combines the right mix of sound absorption as denoted by its noise reduction coefficient (NRC) and sound blocking as denoted by its ceiling attenuation class (CAC).

The NRC indicates the ability of a ceiling to absorb sound from all angles. It is expressed as a number between 0.00 and 1.00, and indicates the average percentage of sound that it absorbs. An NRC of 0.60 means a ceiling absorbs 60 percent of the sound striking it. The higher the number, the better the ceiling acts as a sound-absorber. A ceiling with an NRC less than 0.50 is considered low performance, one with an NRC greater than 0.70 as high performance. It is measured according to ASTM C423, Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method.

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The CAC indicates the ability of a ceiling to block sound in one space from passing up into the plenum and transmitting back down into an adjacent space that shares the same plenum. The higher the number, the better the ceiling will act as a barrier to sound intrusion between the spaces. A ceiling with a CAC of 25 or less is considered low-performance, one with a CAC of 35 or greater as high-performance. It is measured according to ASTM E1414, Standard Test Method for Airborne Sound Attenuation Between Rooms Sharing a Common Ceiling Plenum.

CAC is the acoustical ceiling rating most often associated with speech privacy. As a result, it is an important consideration between adjacent closed spaces as well as between adjacent closed and open spaces, and in open spaces where collaboration or teaming areas are located.

Ceiling selection
The right combination of NRC and CAC represents the best approach to ceiling selection tailored to the needs of a space. In closed-plan spaces, speech privacy between adjacent spaces and speech intelligibility within the space itself is essential. As a result, one should select ceilings combining
a high CAC of 35 to 40 to block sound from traveling into adjoining spaces, and a moderate to high NRC to decrease unwanted sound within the space. An NRC of 0.60 to 0.70 is generally adequate for smaller spaces, while an NRC of 0.75 to 0.85 is preferred for larger ones.

In open-plan spaces where both focus areas and collaboration areas are located, one should specify ceilings that combine a moderate to high NRC (0.65 to 0.90) to decrease reverberant sound, and a moderate to high CAC (30 to 40) to block sound from traveling into adjoining spaces. Selection will depend on the degree of ceiling coverage above the space.

When comparing NRC and CAC ratings, it is best to make ceiling selection based on Underwriters Laboratories (UL)-classified acoustical performance parameters. A UL label on a carton certifies the ceiling panels have been tested by an independent third party on a continuing basis to ensure the panels’ performance meets or exceeds published values.

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Open-plenum spaces
Design trends often call for open-plenum or exposed structures, meaning those where there are no acoustical ceilings, and where building service elements such as ductwork and piping are directly overhead. Unless the sound control normally provided by the acoustical ceiling is replaced with an equivalent alternative system, there will be acoustical problems due to sound reflecting off the deck, resulting in excessive noise and reverberation.

Large spaces of this design will always need some type of sound-absorbing elements to control noise and reverberation. Additionally, when the exposed deck is less than 4.6 m (15 ft) high, reflections between cubicles can cause distractions for nearby occupants.

Noise issues related to open-plenum designs can be addressed in several ways, including acoustic elements attached close to the exposed deck or suspended down into the space. One such option is a discontinuous, high-NRC ceiling system designed specifically to provide excellent sound absorption while maintaining the look and feel of the exposed structure design.

These systems can be installed ‘tight’ to an exposed deck to maximize ceiling height, directly onto drywall, or suspended with wires. When suspended over only 20 percent of an area, systems that utilize panels with an NRC of 0.90 can reduce reverberation up to 50 percent.

Free-floating options
Noise issues in open-plenum spaces can also be addressed through the use of acoustical clouds, canopies, baffles, and blades—four types of ‘free-floating’ setups that add sound absorption while still allowing for the exposed look. All four options can absorb sound on two surfaces—both front and back in the case of clouds and canopies, and left and right sides in the case of baffles and blades. As a result, they can provide greater sound absorption than a continuous ceiling.

Acoustical ceiling clouds are available in a wide variety of standard sizes, ranging from 1.2 x 1.2 m to 3.3 x 4.3 m (4 x 4 ft to 14 x 14 ft). Depending on the panel, standard shapes range from squares, circles, and rectangles to hexagons, trapezoids, and convex or concave panels. Custom sizes and shapes are also available.

Acoustical clouds provide a type of interrupted ceiling plane when suspended above work areas. As such, they help control both reflections between cubicles and distant reverberation, reducing occupant annoyance and distractions. If the clouds are sufficiently large, ceiling panels with an NRC of 0.60 and above and a CAC of 30 and above can be very advantageous in collaboration areas to provide sound absorption and reduce noise intrusion.

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Sound absorption
Acoustical canopies also reduce noise and reverberation in the space below them, but are much different in size and look compared to acoustical clouds. Acoustical canopies are smaller in size, ranging from 1 x 1 m to 1.2 x 2.4 m (3 x 3 ft to 4 x 8 ft). Visually, acoustical clouds are usually flat, while canopies are curved and can be installed as hills or valleys.

Baffles and blades are suspended vertically to impart an upscale visual while providing substantial sound absorption. Installation is easy because all the components needed to suspend a baffle or blade are contained in a hanging kit.

Whereas the sound absorption of a continuous ceiling is indicated by its NRC rating, the equivalent rating for ‘free-floating’ ceilings is the Sabin of absorption per element, such as a baffle or blade. The number of Sabin per element is approximately equal to the total surface area (in square meters) that is exposed to sound (either front and back or two sides), multiplied by the absorption coefficient of the material. Total Sabin absorption is measured according to ASTM C423, Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method.

Acoustics plus aesthetics
Regardless of the space, it is important to note aesthetics do not have to be compromised when using a high performance acoustical ceiling. For example, one of the more recent developments in aesthetic appeal is the introduction of high-performing acoustical ceiling panels with a smooth, drywall-like surface visual.

Another is the availability of acoustical ceiling systems that organize lighting fixtures, air diffusers, and sprinkler heads in a very narrow, technical ‘zone’ or strip to create a cleaner, more monolithic ceiling visual, eliminating the need for penetrations in the ceiling panels, and making them more aesthetically pleasing and easier to replace. Additional aesthetic options include panels with an edge detail that produces a 6.4-mm (¼-in.) reveal, minimizing visible grid and creating a ceiling plane that is more monolithic in appearance than ordinary suspended ceilings.

Panels are also available with a tegular or reveal edge to create a shadow line that helps camouflage the suspension system. In addition to their aesthetic appeal, tegular ceiling panels provide better sound blocking than square lay-in panels because there is less leakage at the interface between the panel and the grid.

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Metal and wood
Specifiers should also consider metal and wood ceilings. Metal ceilings continue to increase in popularity because of their durability and aesthetics. They are offered in a variety of finishes that can impart a very high tech or sophisticated look to a space.

Even though it is metal, this type of ceiling can provide both sound absorption and sound blocking. To achieve the acoustic benefits, the panels must be perforated and backed with an acoustic fleece. Perforations vary in size depending on aesthetic appeal, although it is possible today to have extra micro-perforated panels in which the holes are so small, they are virtually invisible.

Wood ceilings are increasing in popularity because of their beauty and the warm ambiance they impart to a space. Available in various rich, natural finishes, wood ceilings also provide access to the plenum. As with metal, perforated wood panels provide better acoustic performance than non-perforated panels.

In addition to their application in continuous ceilings, both metal and wood panels can also be used in acoustical ceiling clouds, canopies, baffles, and blades.

Other LEED credits
Acoustical ceilings can not only contribute to the new LEED credit for acoustic performance, but also to a number of other credits, including

Waste Management
Specifiers need to be aware that when acoustical ceilings come to the end of their useful life, they can be recycled rather than dumped in a landfill. Ceiling recycling programs began in 1999. They enable building owners to ship ceilings from renovation projects to the nearest ceiling plant as an alternative to landfill disposal. The discarded ceilings are then used to manufacture new ceilings.

Ceiling panels removed from a space are either stacked on a pallet and wrapped for delivery to a ceilings plant, or dumped into a roll-off container and collected by a construction and demolition processor that will bale the tiles for delivery.

Every pound of returned ceiling panels displaces the virgin material and energy required to produce new panels, as well as the waste associated with the extraction and processing of the virgin raw materials.

The recycling of discarded ceiling panels thus has a positive impact on the sustainability of buildings while providing architectural materials that satisfy acoustical requirements within the built environment. In terms of LEED criteria, this closed-loop process can contribute to the Materials and Resources (MR) prerequisite, Construction and Demolition Waste Management, which requires development and implementation of a construction and demolition waste management plan and a final report [12]detailing all major waste streams generated, including disposal and diversion rates.

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Recycled content
Acoustical ceiling panels can also contribute to the new MR credit[14], Building Product Disclosure and Optimization: Sourcing of Raw Materials, Option 2: Leadership Extraction Practices. This is because mineral fiber panels can contain recycled content up to 80 percent, and fiberglass panels up to 71 percent. Wood and metal ceilings can also contribute. Wood panels contain up to 92 percent recycled content, and metal panels up to 98 percent when made from aluminum, and 25 percent when made from steel.

New ceilings panels manufactured from the discarded ceilings reclaimed as part of a ceiling recycling program contain a high level of post-consumer recycled content. These levels are particularly important in projects seeking LEED certification in which a high level of post-consumer content is desired. For the purpose of credit achievement, recycled content is determined by the sum of the post-consumer recycled content plus half of the pre-consumer recycled content. Manufacturers should be contacted for exact percentages and the pre-consumer/post-consumer breakdowns.

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Energy performance
Acoustical ceiling panels with a high light reflectance surface[16]—meaning those with a Light Reflectance (LR) value of 0.83 or higher—can make lighting systems more effective while reducing the amount of energy required to illuminate a room. As a result, they can contribute to the Energy and Atmosphere (EA) credit, Optimize Energy Performance.

The benefits of these panels are most significant with indirect lighting systems because the ceiling reflects and distributes light back into the space. For example, fewer fixtures may be needed to obtain a given illumination level, resulting in less energy required to power them. Fewer fixtures can also result in a reduced cooling load.

Daylighting
Acoustical ceiling panels with high light reflectance can also be a factor in the EQ Daylight cr[17]edit[18]. This is because they help ‘extend’ natural daylighting into a space, resulting in increased occupant satisfaction as well decreased use of artificial lighting.

Conclusion
As this article makes clear, by choosing appropriate acoustical ceilings, green buildings—even those with exposed structures—can be designed to meet the performance and sustainability demands of today’s LEED criteria, while still being sensitive to the needs of those occupying the building tomorrow.

Further, it is important to remember this article focuses on new construction and attainment of LEED certification, the measures to improve the acoustic environment of a space apply equally well to renovations and individual space retrofits, including those in non-LEED buildings. The benefits of improved sound control affect all occupants, regardless of whether a building is certified under the USGBC rating program or not.

Kenneth P. Roy, PhD, FASA, is senior principal research scientist for Armstrong Commercial Ceiling & Wall Systems. In his position, he is responsible for all global research and development in the area of acoustics technology. Roy holds degrees in electrical engineering from the University of Maine and architectural engineering and PhD in acoustics from Pennsylvania State University. He was elected a Fellow in the Acoustical Society of America in 1999. Roy can be reached via e-mail at kproy@armstrong.com[19].

Nathan Baxter is associate marketing manager for Armstrong Commercial Ceiling & Wall Systems. Prior to his present position, he was a principal designer for the company’s Architectural Specialties Group. In that position, Baxter designed and developed new products from concept through commercialization, and provided design services for custom ceiling projects. He has a degree in industrial design from Philadelphia University. Baxter can be e-mailed at nbaxter@armstrong.com[20].

Source URL: https://www.constructionspecifier.com/specifying-acoustical-ceilings-in-green-buildings/

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