Within a few years of LEED setting the standard for green building, occupancy surveys were starting to reveal a gap: many occupants were unhappy with the acoustics – noise, noise, noise! Open offices provided great daylight, views, and air movement, but the work environment suffered from inadequate sound isolation. At the same time, carpet and soft goods that can degrade indoor air quality were transitioning to hard surfaces, inadvertently creating echo chambers.
Noise + Echo = Unhappy clients!
Thankfully, LEED v4 has a new Acoustic Performance credit that provides common sense thresholds for typical building spaces, whether or not a project is pursuing LEED certification. Here’s a quick rundown of the credit’s four criteria and how it might apply to your project, whether new or existing:
1) Sound Isolation: Isolation for walls, floors and ceilings is measured by Sound Transmission Class (STC), with higher STC rating required between sensitive uses. Isolation between offices should be STC 45, Classrooms require STC 50, and if you have an equipment room, you’ll need STC 60 to keep the noise down. Make sure isolation includes the ceiling, interior glazing and doors. Here are typical STC Ratings:
Keep in mind that these STC ratings assume no sound flanking, i.e. sound that travels through unsealed walls, ungasketed electrical outlet boxes and recessed lighting, and dropped ceilings.
2) Reverberation Time: This can be complicated science but the LEED credit provides reasonable criteria for common uses so you have the right balance of sound absorption and reflection. For concert venues and some restaurants, you want spaces to be ‘live’ in strategic locations – leave this to your professional acoustic consultants! – but mostly the goal is to have speech be clear and understandable. A classroom building for the Air Force Reserve was designed with acoustic ceilings, but calculations showed that the reverberation times were still too long, so a few acoustic panels were added to the walls.
3) HVAC Background Noise: This element follows ASHRAE standards, depending on use, but it does need early evaluation. For a recent hotel project, the owner was considering PTAC units, commonly seen at the exterior wall in guest rooms. No reasonable isolation can bring down the noise for these units, so a more acoustics-friendly choice would be heat pumps or other traditional system where the HVAC equipment is more remote, with appropriate isolation springs or other treatment.
4) Sound Reinforcement and Masking: Finally, there are requirements to evaluate the need for and performance of sound reinforcement/amplification for any space accommodating 50 people or more.
Ideally, your project includes an acoustic consultant on the team. If not, or even just as a head start, using LEED Acoustic Performance criteria to evaluate sound isolation, reverberation time, background noise and sound reinforcement could trigger adjustments that will help create a more healthy, productive indoor environment and happy occupants.