Acoustics in Green Buildings

Several green strategies compromise acoustics – discover which have the most impact and how to address them

Green buildings do many things well – but noise control and speech privacy can’t always be counted as items on that list. Post-occupancy evaluations collected and studied by the Center for the Built Environment at University of California Berkeley offer proof. “If you looked at their surveys three or four years ago, you’d find that, relative to acoustics, satisfaction was slightly lower in green buildings than it was in regular buildings,” says Ken Roy, senior research scientist and acoustician at Armstrong World Industries.

Unfortunately, some of the approaches that make green buildings green also result in poor acoustics. “Many of the strategies employed to produce energy savings, reduce waste, and increase indoor environmental quality (IEQ) can contribute to a workplace that has less ambient (background) noise and fewer barriers between the sources of distracting noises, speech, etc., and don’t include the proper amount of absorption,” explains Brian Riley, president of Margenau Associates Inc.

Not only are acoustics often ignored by architecture professionals when it comes to green buildings, but they’ve also been ignored by the organizations responsible for defining green buildings. According to Niklas Moeller, vice president of KR Moeller Associates, “Some green building rating systems, such as LEED, have traditionally excluded credits for anything acoustical. At best, they’ve offered it up as an optional credit.” That problem may be changing, though: Acoustical professionals view the USGBC’s efforts to include acoustical credits in LEED for Schools and LEED for Healthcare as a good step in the right direction.

Spaces designed to allow natural sunlight into the interior reduce energy use by cutting down on lighting, but many of the strategies used to achieve good daylighting result in an inferior acoustical environment. As Professor Ralph T. Muehleisen of the Illinois Institute of Technology in Chicago explained in the January 2010 InformeDesign newsletter, glass often has low sound isolation; an excessive number of windows let street noise into a building, and interior glass doesn’t absorb sound.

Even the ideal shape for a daylit building can be detrimental. “The overall geometry of the spaces tends to be long and narrow to ensure that no spot is too far away from a window. But long, narrow spaces provide a bowling alley effect for sound because it bounces between the two exterior walls,” explains Moeller. “A more traditional, square floorplate allows sound to decay before it hits an outside wall and bounces back into the space.”

Changing the space plan to accommodate daylighting can cut down on speech privacy, too. “Private offices are moving away from the perimeter to allow for daylight harvesting. This creates an increase in the amount of conversations surrounding the private office and the potential for confidential conversations to be overheard,” says Riley. Low furniture panels can exacerbate the situation. Tall panels create a barrier between occupants, absorbing and blocking sound.

Natural Ventilation
Natural ventilation improves energy efficiency, but wreaks havoc on acoustics. Operable windows let in more exterior background noise, especially in urban settings. “When you open the windows for air, there’s always noise,” says Roy. To prevent airflow from being restricted in green buildings with natural ventilation, the interior is designed with as few barriers as possible; this open design, however, can limit speech privacy.

Underfloor Air Distribution
Unlike natural ventilation and daylighting, which can lead to increased noise, underfloor air distribution systems actually decrease background sound. The white noise of conventional HVAC systems inadvertently helps mask conversations. “HVAC is being delivered utilizing lower fan speed and horsepower through raised floor plenums. These systems are much quieter than traditional ducted systems, allowing conversations to carry through the workspace,” explains Riley.

Active/Passive Heating and Cooling Systems
Nontraditional heating and cooling, such as radiant floor heating or the use of thermal mass, requires exposed concrete surfaces. Using thermal slabs eliminates the sound-deadening capabilities of carpet underfoot and the absorption overhead that acoustical ceiling tile typically provides.

Use of Hard Surfaces/Materials
The right surface materials will function acoustically by absorbing noise and blocking the transmission of sound from one space to the next. In green spaces, architects and designers tend to specify harder materials, often avoiding mineral fiber ceilings, carpet, or fabric wallcoverings. They do this, explains Moeller, because harder materials give off the impression of being easier to maintain and offer a longer lifespan; however, they also eliminate absorption. Unless designed with acoustics in mind, spaces without sound-absorbing finishes, such as acoustic ceilings, can have poor acoustics due to reverberation, echo, and elevated noise levels.

More Open Plan
To accommodate daylighting and natural ventilation, green buildings often feature a very high percentage of open-plan space, which eliminates key acoustical control methods (physical barriers). “Within those open areas, workstations and partitions tend to be lower,” says Moeller. Maximizing the usage of the space increases the occupant density. “Conversational distractions are greater with less separation between occupants,” adds Riley.

Because acoustical distractions rank as the greatest area of dissatisfaction in LEED buildings, it’s best to consider the acoustical influences of the design as early as possible, suggests Riley. Understand the acoustical ramifications of green design decisions, be aware of trade-offs, and, seek compromises that offer sustainable and acoustical features.

  • Strike a balance between the glass required for daylighting and the solid-wall construction that provides acoustics.
  • Use acoustic baffles and full-height walls with acoustic louvers in naturally ventilated buildings, advises Muehleisen.
  •  Investigate acoustically attenuated passive stack systems when designing a building with natural ventilation. According to BKL Consultants, acoustically attenuated openings and acoustically attenuated passive stack systems have been successfully used in naturally ventilated buildings. However, the buildings have to be designed around the requirements of the ventilation system and the acoustic design.
  • When underfloor air distribution lowers background sound levels, employ soundmasking.

If you’re designing a school or healthcare facility, follow published guidelines. Spend a little time with the FGI Guidelines for the Design and Construction of Health Care Facilities. This document’s acoustic recommendations are the basis for the acoustic requirements in LEED for Healthcare. If your next building project is a school, study ANSI Standard S12.50.

Software can also help. According to Anita Snader, sustainability manager at Armstrong World Industries, there are software programs designed to improve the acoustical design of indoor spaces. These programs can help you predict the acoustics of spaces before construction even begins.

Seek green acoustical products. “There are solutions that provide all the attributes you’re looking for in terms of materials: recycled content, recyclability, low-VOC emissions,” says Snader. “In addition, you’re getting the functional performance benefit of having an acoustical treatment.”

Don’t let value engineering kill acoustics. “Attempts to reduce the costs can have a minimal impact on the initial price and a large impact on lifetime performance,” warns Riley.

Jana J. Madsen is a Cedar Rapids, IA-based freelance writer with 10 years of experience in writing about the commercial buildings industry.