Acoustic Performance

Noisy, chaotic environments have always been unpleasant, but decades of research confirm that they are also unhealthy and unproductive. The acoustics of a space can directly affect human performance—not just in theaters and concert halls but in all the other spaces where people spend much more time: health-care settings, where quiet has a direct impact on sleep and healing; educational settings for concentration and clear communications; and workspaces to create the ability to focus when needed, or to achieve speech privacy, productivity, and to minimize stress and discomfort that damages performance and leads to low employee satisfaction. Office spaces with open plenums and exposed structures have proven to be especially problematic, as sound reflects off the deck above and bounces between open-plan cubicles, resulting in excessive reverberation and high overall noise levels.

Avoiding negative acoustic conditions is one issue. Creating positive responses and improved performance is another. Multisensory integration is a concept originating in cutting-edge neurological research and videogame design, now being applied to the design of interior spaces to enhance positive human response. In simple terms, the idea is that the five senses, particularly the dominant ones of vision and hearing, work closely together, and when both are stimulated, the result is “superadditive:” intensified far beyond the sum of what each sense might contribute separately.

Until very recently, however, in the case of ceilings, there was a severe tradeoff between sight and sound, aesthetics, and acoustics. Today, there is a broad range of options that effect acoustical performance; panel size, edge details, trims, and accessories, all enhancing the acoustics in traditional and specialty ceilings.

For ceilings and walls in particular, how well materials and systems will accomplish the desired acoustic performance in the space is basically a combination of sound absorption (noise reduction coefficient, or NRC), and sound blocking (ceiling attenuation class, or CAC). NRC measurements are on a scale from 0, representing perfect reflection, and 1, perfect absorption. A ceiling system with an NRC of 0.65 would absorb 65 percent of the noise energy striking it.

The CAC metric indicates how well the material blocks sound transmission, including noise traveling from one room to another through the ceiling plenum or to spaces above or below a room. For example, a ceiling system with a CAC of less than 35 would be unable to achieve sound blocking that would deliver confidential speech privacy. A CAC of 35 or greater represents high performance.

For effective acoustic performance within a space, both NRC AND CAC numbers are important. To simplify a complex interaction, higher NRC absorbs noise within a space from bouncing back into the room off the ceiling, reducing noise levels and reverberation time and enhancing speech intelligibility for clear communication. Higher CAC reduces noise from adjacent spaces, ensuring speech privacy and providing the quiet needed for concentration and focus.

In the past, only NRC values were available for wood, but now both NRC and CAC are possible, allowing wood specialty ceilings to provide a range of creative options, including integrated systems that can provide several levels of measured acoustic performance on a “good, better, best” model to fit the needs of the specific space.

The two most important strategies for improving the acoustic performance of wood ceilings generally work together: perforations that allow sound to penetrate the panel and the addition of acoustical material to absorb the sound energy. A variety of design styles allows varying degrees of openness, blending aesthetics with acoustics.

The percentage of open area has significant impact on the acoustical absorption of the panels. The NRC can range from 0.15 with no acoustical backing to as high as 0.85 for a 20 percent open panel with acoustical backing. Perforation pattern examples include round, oval, slotted, straight, and diagonal or unique patterns. The openings can also be virtually invisible and still absorb significant sound striking the panel surface.

Acoustical materials used with wood ceilings include either “fleece,” composed of materials such as mineral and plant fiber, factory-applied backing on panels, or separate panels or infill, in varying configurations, including options for channeled ceilings.

Installing panels to create acoustical clouds can also have an impact on acoustic performance. In some designs acoustical canopies and clouds can provide greater sound absorption than a continuous ceiling of the same surface area because sound is absorbed from both the front and back surfaces.

In the Lyric Opera Administration Building (Figure 7), five acoustical clouds consisting of dark cherry wood veneer panels were suspended in a sloped, ribbon-like pattern above the concrete and glass lobby area. While adding warmth to an industrial space, the wood veneer panels also improved acoustics in the noisy lobby and reception areas. The panels are perforated in an oval, straight-slotted pattern and backed with a fiberglass infill for noise absorption.

The College Football Hall of Fame (Figure 8) also needed to control noise from large numbers of visitors in a space with a high ceiling and hard surfaces. In the Hall of Fame room where the game’s greatest legends are revered, the channeled wall panels contribute to the formal atmosphere of the space. Perforated with an acoustical backing, the panels have an NRC of 0.70. In the theater, the perforated linear panels are installed in folded planes that go up the walls and across the ceiling, with an NRC of 0.60. Layers of specialized acoustic panels with an NRC of 0.90 are installed between the folds in the ceiling to bounce sound within the space and keep it from traveling into other spaces.

Fire Performance

Increasing the fire performance of wood in all construction materials has been a focus of intense research, product development, and testing in recent years. Wood walls and ceilings meet the levels of fire ratings appropriate for applications in virtually all commercial interiors. Although fire protection is a complex issue, there are a number of basic considerations important for comparing wood ceiling materials for the critical life safety criterion of fire performance.

The majority of regional, state, and local codes are based on the International Building Code (IBC), which defines classifications for the flame spread and smoke development of a building material. The classifications are based on the material’s test results according to ASTM E84: Standard Test Method for Surface Burning Characteristics of Building Materials. Different maximum values are permitted depending on building occupancy, where the material will be located in the building, and the presence of active fire protection systems, such as sprinklers.

Class A, the highest performance rating, typically requires flame spread ratings (FSI) of 25 or less. Many codes also require the smoke developed index rating (SDI) to be 50 or less.

Achieving both ratings—25/50—is a higher standard for building materials. ASTM E1264: Standard Classification for Acoustical Ceiling Products states that Class A products must have a flame spread of 25 or less and a composite smoke developed rating of 50 or less. The National Fire Protection Association (NFPA) requires 25/50 performance in order for panels to be used in a return-air plenum assembly.

Solid wood panels cannot meet this standard, as mentioned earlier, and there are strict limitations on how solid wood can be used in commercial interiors, although they can be highly attractive design elements for decorative features like accents, moldings, and railings. However, ceiling and wall systems composed of high-quality veneered wood can meet a range of fire performance requirements, including the highest ratings.

The following are additional important considerations when evaluating a specific manufacturer’s product information.

• Make sure all references to codes are up to date. For example, some manufacturers of wood ceiling and wall material still incorrectly reference UBC, the now obsolete Uniform Building Code.
• In all cases, tests should be conducted on a complete, assembled, composite panel, exactly as it is intended to be used in the space: veneer fully adhered to substrate, using the same adhesives as the final product. Testing individual components does not represent the data necessary to determine actual performance.

The importance of factory finishing of wood panels is critical to fire performance. The stringent requirements for low flame spread and low smoke development are generally not possible with millwork because it is often finished with “conversion varnishes,” lower-cost two-part lacquers applied by hand. It is not possible to predict fire performance consistently with this type of finishing.

Seismic Performance

Just as with fire performance, designing and specifying buildings and interiors for seismic performance involves many complex technical issues, but there are a number of key considerations related to wood ceiling and wall systems.

Seismic performance in wood ceilings is primarily determined by the installation of the suspension system. The purpose of installation requirements for suspended ceilings in areas where seismic performance is a factor is to provide a suspension system strong enough to resist lateral forces imposed upon it without failing and to prevent border panels from falling from the ceiling plane.

Currently, all 50 states, Washington, D.C., and the Virgin Islands use the IBC at a local or state-wide level. The IBC states that a Seismic Design Category, designated A–F, must be established for each construction project based on anticipated ground motion, soil type in a specified geographic area, and occupancy category. These are determined for the entire building and specified by a professional engineer or registered architect on the project drawings.

The installation of ceilings can be divided into three tiers of increasingly stringent requirements, based on the designated Seismic Design Category:

1. Categories A & B ceilings are installed to meet requirements in ASTM C636.
2. Category C projects must meet ASTM C636, plus additional provisions listed in ASTM E580 for light to moderate seismic.
3. Categories D–F must follow ASTM C636 and ASTM E580 for severe seismic.

The titles of these standards refer to metal ceilings, but the requirements are the same for wood ceilings. Some additional points applying specifically to wood ceilings include:

• No matter the building Design Category, any panel weighing 2.5 pounds per square foot or more (which is most wood) must be installed per the additional installation requirements of Seismic Design Category D, E, and F.
• Some jurisdictions, including the California Building Code, require wood or other hard or heavy panels to be positively attached to the suspension system.
• In some applications or areas with high seismic risk, there may be a need for additional measures, such as specialized clips or safety cables, to prevent heavy panels from falling during a seismic event.

Working with manufacturers who perform substantive, documented seismic performance testing on a large scale is a major advantage in code compliance and streamlined installation. Ceiling panel performance is not well defined in the IBC requirements. A large manufacturer with specialized research partnerships and capabilities can provide tested and approved safety and performance data based on full-scale seismic tests for standard and non-standard ceilings. Integrated preengineered ceiling solutions have been developed that include tested seismic suspension systems, with all components and installation support from a single source, as well as a range of options for veneer, surface configuration, acoustic performance, fire rating, accessibility, and environmental features.