ACOUSTICAL CHALLENGES IN GREEN BUILDINGS

ACOUSTICAL CHALLENGES IN GREEN BUILDINGS An introduction to the effects of sustainable design strategies on acoustics and how to address them.

Sustainability is one of the driving forces in the field of architecture and design today, a road that has largely been paved by the United States Green Building Council s (USGBC s) Leadership in Energy and Environmental Design (LEED ) rating system. USGBC s leadership in this area is often attributed not only to the appeal of its point system, but to the fact that its proponents drew attention to the business case for sustainability. Aside from being the right thing to do in terms of both human and environmental health, going green certainly provides compelling financial incentives, including reduced operating costs, enhanced corporate reputation, increased sales, improved workplace flexibility and higher building value. However, the lack of attention historically paid to acoustics has been detrimental to the overall performance of sustainable spaces. In fact, postoccupancy evaluations conducted by the Center for the Built Environment (CBE) at the University of California, Berkeley reveal green building acoustics are typically worse than their traditional counterparts. Occupants are dissatisfied with being able to hear people talking in open areas, in workstations, and on the telephone, as well as with their own level of speech privacy. Ringing telephones, mechanical equipment, traffic noise, and people talking in corridors are further sources of distraction. Over half of respondents feel noise inhibits their work. Open plans are by far the worst performing, particularly those employing open benching or desking rather than the now traditional workstations. Yet, these are also the environments in which most green building occupants work. Although the trend is to emphasize the workplace s positive impact on communication and collaboration, most employees still spend at least 60 to 70 percent of their time on individual work requiring concentration, and a further 20 percent on the telephone or in conversation within their workspace. Their environment should support these activities by providing speech privacy and freedom from distracting noises. Indeed, USGBC has attempted to deal with the acoustical deficiencies of green buildings, first by providing specific credits in LEED programs for schools and healthcare and, in November 2010, by introducing LEED Pilot Credit 24: Acoustics, which is available for testing in New Construction (NC) and Commercial Interiors (CI).* Having acoustic credits helps draw attention to this vital aspect of Indoor Environmental Quality (IEQ). However, it is also important to have a solid understanding of the elements involved in creating an effective acoustic environment and why many of the typical strategies used to improve airflow, temperature regulation, energy conservation, and daylighting in green buildings tend to lower acoustical performance. The ABC Rule provides a clear framework for this discussion. It describes three principal methods used by acoustic professionals to achieve speech privacy and noise control: absorb, block and cover. Though these strategies involve the shell, interior fit-out, and furnishings, this article primarily focuses on interior construction. Absorb noise Absorptive materials reduce the volume of noise reflected back into a space, the length of time they last, and the distance over which they travel. The amount of absorption in a room is generally indicated by the Reverberation Time (RT) measured within the space. Attaining a low RT is essential to reducing the room s echo or liveliness. Unfortunately, the majority of green buildings use hard-surfaced materials such as glass, metal and concrete at the expense of absorptive ones. These surfaces are highly reflective, causing sounds and conversations to echo, overlap, linger and travel greater distances. The resulting environment is noisy, distracting and tiring for occupants. Addressing acoustical issues A strong business case can easily be made for the need to address acoustics. The well-recognized benefits not only include increased productivity, but also reduced error rates, stronger morale, and decreased absenteeism. Diagram 1: Absorb Noise

Because the ceiling is usually the largest uninterrupted surface in a facility, a good absorptive tile is important. Open plans should feature a ceiling tile with at least a 0.75 Noise Reduction Coefficient (NRC). Tiles used in closed spaces should not only provide absorption, but also have a high Ceiling Attenuation Class (CAC) because they will be better at containing noises. Most manufacturers suggest a rating of 35+ indicating a high-performing tile suitable for closed offices. Ideally, ceiling coverage should be uninterrupted (i.e. no openings or cloud-style designs). Many green buildings have open ceilings because they promote natural light penetration from the windows. It is also thought that the exposed deck can be used as a heat-sink to help control the temperature within the building, and that eliminating the suspended ceiling will reduce material costs. If an exposed deck is being considered because of a desire to implement passive heating/cooling, it is important to ensure there will be at least 8 inches (200 mm) of concrete to provide any meaningful thermal storage beyond what is lost through the building envelope. If this requirement is not met, there is insufficient mass for thermal regulation and the ceiling tile will be eliminated without cause. If cost is the reason for eliminating the tile, it is important to look beyond initial savings. For example, the Ceilings and Interior Systems Construction Association (CISCA) found that while suspended ceilings cost more upfront, they showed significant energy savings over their life due to the HVAC efficiency (i.e. of the plenum) and better light reflectance. CISCA showed overall energy savings to be between 9 and 10.3 percent. They also determined that payback on ceilings never exceeds 1.6 years. If an exposed structure is still desired, an appropriate percentage of the deck must be treated with an absorptive material sufficient to provide the RT deemed acceptable for the type of space (i.e. open or closed). Generally speaking, this strategy will have an impact, as will vertical baffles. Depending on the building construction, another effective option is to use a perforated and corrugated metal deck with an absorptive material placed behind the perforations before the concrete is poured. Workstation panels should be absorptive, particularly if there is no acoustic ceiling tile. Ideally, workstation partitions integrate absorptive panels over their entire surface. However, if cost is a concern, a good fallback is to include absorptive panels on the inside of the partition above the work surface, reducing the reflection of the occupant s voice into the neighboring workspace. Many green designs feature narrow spaces in order to promote natural light penetration. Because narrow spaces reflect more sound over distance, similar to the bowling-alley effect experienced in long corridors (i.e. sounds ricochet between the exterior wall and the core), absorptive panels should be used at points along the long space in order to reduce reflection. Footfall noise on hard flooring is particularly intrusive and difficult to address once generated. Therefore, soft flooring finishes should be used to reduce it at least in high-traffic areas. Since they account for such a large percentage of the space, the materials selected for the ceiling, workstations, walls, and flooring can greatly contribute to a project s overall sustainability goals. Renewable, reusable, recycled or recyclable absorptive materials are available. Block noise Another method of controlling noise is to block sound transmission. Barriers such as walls, windows, doors, workstations and other physical structures are typically used for this purpose. However, blocking involves more than merely installing barriers because noise does not only travel through air; it can also pass through partitions, under, over, and around obstructions, and by means of ventilation ducts and other penetrations. If these structural elements are not controlled, speech privacy is compromised and spaces potentially become unsuitable for their intended purpose. This is true for closed offices in which confidential conversations are to take place and for neighboring spaces requiring noise control. Diagram 2: Block Noise

If walls are used, many factors need to be considered. If there is no ceiling, walls should be built to the deck. If there is a suspended ceiling, walls can stop at the ceiling. The wall s Sound Transmission Class (STC) rating indicates how well it attenuates airborne noise. In general, the higher the STC rating, the better the wall is at preventing airborne transmission. This rating should be real-world rather than lab-tested. Field STC (FSTC) and lab tests should follow ASTM E 413, Classification for Rating Sound Insulation, standards. Transmission loss measurement should follow ASTM E 336, Standard Test Method for Measurement of Airborne Sound Attenuation between Rooms in Buildings. Keep in mind that sound isolation is not only achieved through the type of wall, but the combined performance of all aspects of the room s design. Penetrations such as outlets and switches should not be located back-to-back on opposite sides of the wall. One should ensure walls are well-sealed with an acoustic sealant or gasket. Cable raceways along the base of the wall should include a demising partition that provides some level of acoustical isolation. The STC rating of doors and interior windows should at least meet the wall standard or they become the weak links in the barrier. Gasketing material or sweeps can be added to the doors depending on the level of speech privacy needed when they are closed. HVAC systems must also meet several criteria to avoid compromising acoustical isolation. Supply ducts should not connect adjoining closed rooms before connection to the main supply duct. Air return grills should not be placed straddling walls between closed spaces. Many requirements for traditional walls also apply to demountable wall systems, which are often used to enclose spaces in green buildings. These systems may have lower STC ratings than standard walls, and the joints between the panels may provide conduits for sound, preventing the desired sound isolation level from being achieved (i.e. between closed offices and meeting rooms). Any gaps along the ceiling, exterior perimeter walls, and floor also easily transmit sound and should be addressed during installation. Many such systems provide cable management raceways. In this case, a good septum dividing each side of the wall is advisable to prevent this opening from undermining the wall s acoustical performance. Unfortunately, the drive to maximize daylighting and promote air circulation in green buildings often involves the sacrifice of many of the key elements involved in blocking. For example, most green designs feature a higher percentage of open plan than traditional buildings, as well as low workstation partitions or, in some cases, none at all. These open spaces allow sounds to travel unimpeded over greater distances, contributing to overall noise levels. Open spaces also allow conversations to easily travel to unintended listeners. Furthermore, lowering or eliminating partitions decreases the amount of absorption they could have otherwise provided. In open-plan spaces, workstation partitions above seated head height of 60 to 65 inches (1.52 to 1.65 meters) are essential to attenuate the noises passing to an occupant s nearest neighbors. There is general agreement among the acoustical community that partitions much lower than 60 inches provide little value when it comes to sound control. Where daylighting is a concern, one should use workstation partitions that rise to 48 inches (1.22 meters), but are topped with 12 inches (305 mm) of glass. This format will provide the physical barrier needed between close neighbors, while not impeding daylighting. Additionally, they will not obstruct sight lines, lending a more open feel to the space another frequently stated reason for lowering panels. Of course, if the top 12 inches are glass, this introduces an acoustically reflective surface, but the reduction in absorption relative to the increase in physical blocking is an acceptable compromise. One should also ensure the panels have a high STC rating and that they are well sealed along any joints, with no significant openings between or below them. In situations where raised floors are used, there should be prescriptive requirements for the acoustical performance of these floors to prevent cross-talk between rooms. Cover noise Everyone has heard the old adage silence is golden and, indeed, many people believe they will achieve effective acoustics by implementing just the first two strategies involved in the ABC Rule, which simply reduce and contain noise. However, just as with lighting and temperature, there is a comfort zone for the volume of sound and it is actually not zero. For this reason, the final step of the ABC Rule involves ensuring the background sound level in the space is sufficient to cover speech and incidental noises.

The sound masking system should also provide control such that volume variation is ideally no more than 1 dba total to ensure consistent performance and minimize noticeability as occupants cross the open plan or move between similar closed rooms. Diagram 3: Cover Noise The background sound level in most conventional offices is already too low. The use of high-efficiency heating and cooling systems means it is generally even lower in green buildings. Conversations and noises can easily be heard, even from afar, and are more disruptive. These problems are exacerbated when open windows are used to assist with air circulation, allowing exterior sounds to drift inside. In some cases, different strategies are used along the exterior and core, creating variable acoustic conditions across the space. A sound masking system is used to replenish the background sound level and maintain it at an appropriate volume. This technology consists of a series of loudspeakers, which are typically installed in a grid-like pattern above the ceiling, and a method of controlling both their zoning and output. Most people compare the masking sound to that of softly blowing air. However, unlike airflow, the sound the loudspeakers distribute is continuous and has been specifically engineered to increase speech privacy. Masking also covers up intermittent noises or reduces their impact by decreasing the amount of change between baseline and peak volumes, improving overall acoustical comfort. In open-plan spaces, the generally accepted masking volume is between 43 and 48 dba. In closed spaces, masking volumes are typically several decibels lower because higher ambient volumes are less expected and, therefore, less accepted in smaller spaces. Here, the masking volume should be between 40 and 45 dba, unless the required speech privacy levels cannot be met due to the manner in which the closed rooms were constructed. Spot treatment of local areas is discouraged because it draws attention to the masking sound and risks lowering occupant satisfaction. A few decibels of variation in masking volume can dramatically impact the system s effectiveness, even without taking into consideration the consistency of frequency levels. In many situations, users can expect a 10 percent reduction in performance for each decibel variation below the target masking volume. A poorly designed system, or one that features large adjustment zones (i.e. from eight to dozens or even hundreds of loudspeakers), can allow as much as 4 to 6 dba variation, meaning the system s effectiveness will be halved in some areas of the user s space. Zone size also affects the ease with which the user can make changes to the system in the future. In this case, less truly is more one to three loudspeakers in each zone provides a high degree of flexibility. To achieve optimal comfort and effectiveness, the system must also provide the correct sound masking spectrum. A good reference curve is available from the National Research Council of Canada (NRC), which strongly conforms to curves specified by many acoustical consultants for decades. One should also identify an acceptable range of variation in the volume of each thirdoctave frequency band, which is ±2 dba in each band (4 dba total). Using a sound masking system can help support other sustainable endeavors, especially when included in the project s design stage. For instance, masking increases noise isolation in open areas. Natural ventilation can be employed without affecting speech privacy and the amount of disruptions occupants experience due to noise. It can also pave the way for using demountable wall systems, contributing to the space s overall flexibility and reducing waste following future renovations. Green factors to consider when selecting a sound masking system include: Energy consumption: Ask how much power the system will consume. Most use less than that of a typical light bulb to cover an area of 10,000 ft 2. Environmental programs: Find out if the manufacturer adheres to programs such as the Restriction of Hazardous Substances (RoHS) initiative, which ensures that products meet the requirements for low levels of heavy metals, such as lead and cadmium.

Lifecycle and maintenance: Most masking systems have a long lifespan and can easily be expanded or relocated. Ask how changes can be made to the system s settings and zoning in the future. Recycling program: Check if the manufacturer offers a recycling program for end-of-life products, ensuring zero landfill. If the facility or a percentage of it will feature an open ceiling, the appearance of the sound masking system s loudspeakers should also be considered. Reduce noise There is an additional tactic the ABC Rule overlooks: reducing noise at the source. This strategy involves identifying and subsequently reducing or eliminating unnecessary causes of sound and vibration. One should definitely implement workplace rules to lessen noise-producing behaviours, but people will always generate noise as they go about accomplishing their tasks. The goal of good acoustic design is to allow them to perform these tasks without feeling as though they are irritating or disrupting others within the space. Additional strategies include lowering the ring volume on telephones, using quieter office/ mechanical equipment, ensuring noisy activities are located away from those requiring more quiet, and situating mechanical rooms as far from occupied areas as possible. Using damping and isolating materials on mechanical/electrical and plumbing equipment not only reduces noise, but also prevents vibration from transferring to the structure. Conclusion Noise control and speech privacy are not irreconcilable with green buildings. To the contrary, green buildings must perform better acoustically to succeed. As Jan Barowitz said in a 2007 interview with Fast Company, You could make a building that s very energy-efficient by not having any windows in it and having only one elevator, but this is not a building that people are going to want to work in (The Green Standard, Issue 119, October 2007). A green building cannot simply mean one that wastes minimal resources. As USGBC stipulates, these facilities must also be environments in which employees can thrive and productivity can soar. While the prescriptive design standards described in this article are effective and their diligent use will improve comfort, reduce noise distractions, and provide some level of speech privacy, the project team may also choose to establish measurable performance targets, including those for auditory privacy, reverberation time, and background sound levels. These goals are best set with the assistance of an acoustic professional, who will then measure them upon project completion. A professional can also provide the big picture that allows the various elements described above to be selected so the combination provides the necessary level of acoustical performance. However, for those project teams that potentially lack the budget for a consultant, this article provides a clear list of the required steps and technologies, which is preferable to ignoring acoustics altogether. Focusing on occupant satisfaction from the outset helps to avoid the costs, not to mention the headaches, which arise when IEQ issues must be later remedied. * Note: By the time of publication, the LEED Pilot Credit 24: Acoustics may have been officially added to USGBC s commercial rating system. This credit reinforces the need to set acoustic goals for a space, including those regarding speech privacy, sound isolation and background sound levels. It also asks for the sound absorbing qualities of surface materials as well as any sound reinforcement or sound masking systems used in the project to be described in the submittal.