You won’t meet the requirements for this credit with conventional building design. You’re likely to need additional insulation, increased wall mass, adjust wall assemblies and layout, and make changes to the mechanical system design.
Making it cost-effective
The credit does not have to be difficult, though, and it can be cost-effective in any project as long as you consider acoustics in the early stages of design. Waiting to consider acoustics until the design is set can lead to additional costs and needless frustration as mechanical systems and the building envelope will likely need some redesign.
Having the entire design team focused on acoustics—including stakeholders such school board members, the principal, and teachers—helps to ensure a consistent focus throughout the project and to overcome obstacles that may arise.
The payoff for earning this credit is likely to be more effective and less-fatigued teachers, and better student performance, as both teachers and students can focus better, not talk over distractions, and communicate effectively.
Understanding the credit requirements
To earn this credit, you have to meet two requirements, one of which is a step up from IEQp3, and one of which is not considered in the prerequisite. (Reverberation time, a measure of how long it takes for sound to be absorbed by a room’s interior materials, is not covered by this credit.)
Background Noise Level of HVAC
Background noise may come from a variety of sources: traffic on nearby streets, mechanical equipment, sounds from adjacent classrooms or multi-purpose spaces, and more. LEED only addresses background noise from HVAC equipment. The noise level is determined through calculations that the mechanical engineer or acoustics consultant can run.
This credit requires a background noise level of 40 dBA or less—a step up from IEQp3, which requires 45dBA or less. Meet this requirement by focusing on mechanical system design, with measures such as avoiding the placement of fans and mechanical systems directly above classrooms, insulating ducts, and using low-velocity air delivery or displacement ventilation.
Sound Transmission Class
Sound Transmission Class (STC) is a measure of the capacity of a partition (a wall, window, door, ceiling, or floor) to isolate noise from adjacent spaces. The required STC rating for a given partition varies and is determined by the adjacent spaces and the requirements of ANSI standard S12.60-2002. For example, a classroom wall located next to the gym will have to meet a different STC rating (STC rating of 60) than a different wall in the same classroom that is near the library (STC rating of 50).
Higher STC ratings for partitions can be met with thicker, more massive walls, and higher-STC rated products like specially insulated windows and doors. All of these typically translate to higher costs. To meet the STC requirements cost-effectively, start by locating classrooms away from noisy exterior and interior spaces, so that the STC ratings for the partitions don’t need to be as high.
Compliance Options
Both of the credit requirements (HVAC background noise level reduction and STC ratings) have two compliance paths, one requiring calculations during design and the other requiring onsite measurements after construction.
The calculation option is recommended because it is far safer. If you wait till after construction to take these measurements, and you find areas that are non-compliant, making changes will be expensive and inconvenient.
You will likely need an acoustics consultant
Meeting IEQp3 can be relatively easy without the help of an acoustics consultant. However, many projects find the requirements of even the prerequisite beyond their capability and opt for professional acoustical help. Analyzing the STC of the wall assemblies for the credit will likely require the expertise of a consultant. STC ratings for assemblies come from laboratory tests and it may be difficult to find the required STC testing information on your own and verify that it is accurate and appropriate for your project.