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Part 2: LEED v4 Tackles Acoustics With New Noise Control Pilot Credit, Expanded Acoustic Performance Credits
By Daniel Overbey
April 2014 -
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Over the past several years, the U.S. Green Building Council (USGBC) has endeavored to migrate the LEED rating system toward a single global standard that tackles various environmental design issues holistically. For instance, with LEED version 4 (LEED v4) the notorious "bike rack credit" is now integrated into a broader credit focused on access to a viable bicycle network. Regarding indoor environmental quality, USGBC first recognized the virtues of acoustical comfort within environments for learning (i.e., schools) and healing (i.e., healthcare). With LEED v4, USGBC is attempting to broaden the notion of acoustic performance as an important IEQ issue by introducing a pilot credit for exterior noise control and expanding the niche acoustic performance credits into other building types.
With the intent of establishing a comprehensive acoustic performance credit, USGBC has decided to focus LEED on the following acoustic design considerations:
HVAC background noise: Mechanical equipment can make lots of noises, including low-frequency hums. Therefore, it needs to be located strategically to reduce its impact. Space pressurization methods, ventilation rates, and ductwork configurations all contribute to ambient background noise.
Sound transmission/isolation: Equipment and activities will generate sounds. Through a facility's design, appropriate construction assemblies and design strategies will mitigate sound movement between spaces.
Reverberation time: A metric to gauge how long a sound lingers, reverberation time criteria is based on room type and application and can be affected by space geometry, sound locations, as well as the presence and location of sound-absorptive finishes.
Sound reinforcement and masking systems: These systems can help improve the audible clarity and acoustic privacy in an interior, respectively. Successful implementation hinges on appropriate, calibrated system choices.
The LEED for Schools 2009 and LEED for Healthcare 2009 rating systems feature Indoor Environmental Quality (EQ) category credits (including a prerequisite requirement with Schools) for acoustical performance:
Schools-2009 EQp3: Minimal Acoustical Performance. This prerequisite acknowledges that good acoustical performance is not standard practice in many jurisdictions. Background noise from HVAC must be limited to 45 dBA (A-weighted decibels). Core learning spaces will need to reduce the reverberation time to 1.5 seconds or less — unless the spaces are smaller than 20,000 SF, in which case they will simply need to ensure that ceiling, wall and/or floor materials have a Noise Reduction Class (NRC) rating of 0.70 or higher.
Schools-2009 EQc9: Enhanced Acoustical Performance (1 point). Meeting this credit is a step up from the prerequisite. Project teams are required to limit the background noise to a more challenging 40 dBA. The credit also requires projects to meet ANSI Standard S12.60-2002, except windows — which must have a Sound Transmission Class (STC) rating of at least 35.
Healthcare-2009 EQc2: Acoustic Environment (2 points). The healthcare-related acoustical credit focuses on providing an indoor "healing environment" devoid of disruptive sounds. This is accomplished by designing the facility to meet or exceed the sound and vibration criteria outlined in the 2010 Facility Guidelines Institute's Guidelines for Design and Construction of Health Care Facilities (2010 FGI Guidelines) and the Sound & Vibration: Design Guidelines for Health Care Facilities (2010 SV Guidelines). Design, then calculate or measure, sound isolation and speech privacy descriptors and HVAC room noise achieved at representative conditions to confirm performance compliance.
For an additional point, teams must address acoustical finishes and site exterior noise. Teams must specify materials, installation details, and other design features to meet the 2010 FGI Guidelines. Then, teams must calculate or measure representative room average sound absorption coefficients.
Finally, teams must minimize the impact of site exterior noise on occupants as well as the impacts of the facility's MEP equipment on the surrounding community. This is accomplished through four criteria:
Part 1: LEED v4 Offers More Stringent Acoustical Standards
Part 3: LEED v4 Expands Acoustic Performance In Multiple Areas