Working Together: Acoustics and Green Design
By: Jeffrey Fullerton, LEED AP, Acentech Inc.
Though the rewards of building green have been well documented, the acoustics of these projects are not often as thoroughly considered. Green and acoustical design goals can complement each other through the use of energy efficient and quieter HVAC and elevator systems, improved thermal and acoustical isolation, and environmentally responsible acoustical materials. These synergies, and several conflicting objectives, are discussed below.
Sustainable Design Choices that Make for Good Acoustics
Sustainable renovation projects often focus on reducing energy consumption of building systems, improving thermal losses of the existing building, and introducing recycled or rapidly renewable products in the process. Each of these three areas can benefit the acoustical conditions of the final occupied spaces.
Energy efficient mechanical systems may also be quieter choices for a project. For example, projects that call for replacing a small- to moderate-size air-cooled chiller or condenser may gain significant energy and acoustical benefits by using a geothermal system, which operates with lower sound levels and eliminates the noisy exterior equipment that might bother the top-floor building tenants or the neighbors. Another potential source of noise in a commercial office space is the elevator system. Today, new energy efficient elevators using direct drive motors are quieter replacements to the noisy hydraulic compressors and geared elevator systems of the past.
A key facet of reducing energy use is considering the thermal performance of elements of the building envelope. This typically involves thicker insulation, comprehensive air sealing, and upgraded window and door assemblies. Because sound transmits through air, the side benefit of these thermal upgrades is better sound isolation. Some energy efficient buildings are even utilizing double-wall exterior façades to improve their thermal efficiency, with the additional benefit of extraordinary isolation from noisy exterior environments.
Designers can now choose from a range of green acoustical products. These include: batt insulation made from recycled cotton fibers that can be used for improving the sound isolation of demising walls between rooms; rapidly renewable substrates and veneers used for ceiling panel products where sound absorption is desired; and fiber-free products that provide sound absorption without fiberglass materials.
Other sustainable products can provide acoustical benefits, increase design flexibility, and minimize demolition waste. Demountable partitions are an excellent choice for laying out closed offices and rooms that require more acoustical separation than a typical open office area. These systems enable facility managers to significantly change the layout of spaces without the cost and waste associated with traditional stud construction. Still, it may be important to compensate for the demountable partitions’ lower privacy performance with electronically produced background noise.
When Sustainability and Acoustics Don’t Jive
Not all sustainable design ideas provide acoustical benefits; in fact several can conflict with acoustical design goals. Often, compromises or innovative, alternative solutions for sustainable renovation projects can be found.
For example, passive ventilation can be an ideal way to save significantly on energy while tempering the interior environment. However, this approach should be considered with some caution, as an open window allows noise in as well. It would be appropriate to consider passive ventilation designs in areas with quiet exterior sound levels or rooms that are less sensitive acoustically.
Another example is thermal insulation. It is a misconception that all thermal insulation provides excellent acoustical performance. In reality, thermal insulation provides the benefit of sound absorption – and in turn noise reduction – only when it is porous. The fibrous structure of typical batt insulations, made of fiberglass, mineral wool (or rock wool), recycled denim, or open cell foam, converts sound energy into heat. As a result, these porous insulations are very effective for sound absorption. On the other hand, closed cell foam insulations, which consist of small pockets of air, provide exceptional thermal insulation but prevent sound energy from being absorbed. For these reasons, exterior façades made with closed cell foams can be a concern for projects in high-noise areas.
Another misconception is that “triple pane” windows – windows with glazing that is spaced within a total thickness of about one inch (25 mm) or less – have great sound isolation performance. Within that one-inch, there may be three layers of glass (and two air cavities), which have very good thermal performance. However, the thin air spaces do not effectively isolate the panes from each other, and thereby transmit sound and provide little sound isolation. Acoustical test data of triple pane windows have demonstrated that there is little acoustical benefit over a double pane insulated system.
Lastly, many commercial office occupants benefit from natural light and views, a green design approach that involves lowering obstructions between people and the exterior windows. However, lowering or removing workstation barriers will limit the acoustical separation between occupants. A compromise could be to integrate office furniture that consists of workstation barriers made of transparent materials, such as glass or plexiglass. These have the desired optical qualities, but are also able to block sound transmission by increasing the height of the barrier.
As with every other design decision on a project, balance the goals and allow compromises for sustainability to create a project that works for its intended purpose. With a little extra thought and attention, sustainable changes can improve occupant productivity and comfort through better acoustic conditions.
