In order to maximize comfort and productivity, the workplace should provide employees with speech privacy and freedom from distracting noises. To meet these goals, acoustic professionals typically follow the “ABC Rule,” which stands for absorb, block and cover. Unfortunately, many current green design practices inadvertently contravene this formula, creating interiors that are noisy, stressful and lack speech privacy. But, using the ABC Rule correctly can contribute to the green commitment.
Acoustics in green buildings are often worse than in their traditional counterparts, as shown by the Center for the Built Environment’s post-occupancy surveys. Respondents frequently complain about being able to overhear others and also express dissatisfaction with their own level of speech privacy. Furthermore, 60% feel that noise inhibits their work.
Although green buildings may have acoustical challenges, there are solutions. By applying the ABC Rule in the context of sustainable design, new projects can steer clear of these problems. Here’s how.
Absorb Many green buildings feature an exposed deck. While it may help with temperature regulation and daylighting, this tactic also eliminates what is often the most significant source of absorption in a facility: a suspended ceiling. Ideally, open spaces should feature a ceiling tile with at least a 0.75 noise-reduction coefficient. Tiles used in closed spaces should have a high-ceiling attenuation class because they will be better at containing sounds.
If this route is not taken, absorption needs to be provided by other means. Even adding absorptive panels to 30% of the deck will have some impact. Another option is to use vertical baffles. If a concrete deck is not being used to implement passive heating/cooling, but an open ceiling is still desired, an alternative 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 also be absorptive – at least on the inside, above the work surface – in order to reduce the volume of the occupant’s voice before it is reflected into the space. If the space is narrow to promote natural-light penetration, absorptive wall panels should also be used to prevent sounds from ricocheting between the exterior wall and core.
Soft flooring should be used to reduce footfall or traffic noise.
Block Green buildings generally feature a large percentage of open plan. In these areas, the height of workstation panels is essential to blocking noise. Panels should extend beyond seated head height (60 to 65 in.), or they will do little more than hold up the desks. If daylighting is a concern, compromise by using absorptive panels to a 48-in.-height and top them with 12 in. of glass or another transparent material. Also ensure that the panels have a high sound transmission class and that they are well sealed along any joints, with no significant openings between or below them.
In order to reduce waste, many green designs use movable walls to create private offices and meeting rooms. However, these walls may not provide the level of sound isolation needed from one space to another. Gaps along the ceiling, exterior walls and floor should be addressed during installation. A good septum dividing each side of the wall is also advisable in order to prevent sound leakage along any cable raceways.
Cover Due to their use of natural ventilation, the background sound level is often lower in green buildings than in traditional facilities. The absence of mechanical or forced air sounds makes it easier to hear conversations and noises, even from a distance. If open windows are used to assist with air circulation, occupants can also be disrupted by exterior sounds. In some cases, different strategies are used along the exterior and core, creating variable acoustic conditions across the space.
A networked sound-masking system should be used to replenish the background sound level and maintain it at an appropriate volume, typically between 42 and 48 decibels in commercial interiors.
This type of system consists of a series of loudspeakers usually installed in a grid-like pattern in or above the ceiling. Unlike airflow, the sound they 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 the baseline and peak volumes, improving overall acoustical comfort.
Finally, by using a networked masking system, users have the flexibility to easily make adjustments to its setup as their needs change (e.g. volume changes in a specific area).
Attention to acoustics does not have to be at odds with sustainability. Indeed, one could argue that providing a fully functional environment is vital to creating a truly green space: one that, as the U.S. Green Building Council stipulates, not only wastes minimal resources but is also healthy and nurturing to occupants. Though applying the ABCs incurs some cost, even a small, positive impact on productivity can easily outweigh this initial investment.Niklas Moeller is vice president of K.R. Moeller Associates Ltd., a global developer and manufacturer of sound-masking systems. He can be reached by e-mail: email@example.com.