An acoustic environment that is conducive to learning requires low ambient sound levels and a high degree of speech intelligibility. Prior to 2021, unless a school was pursuing LEED or had adopted ANSI S12.60-2010 Acoustical Performance Criteria, Design Requirement, and Guidelines for Schools, classroom acoustics were guidelines, not requirements. That all changed with the 2021 International Building Code (IBC) which has incorporated Enhanced Acoustics for Classrooms criteria. Read on to brush up on the new requirements as more schools and states begin to adopt the most recent IBC.
For classrooms that are under 20,000 cubic feet and support six or more occupants, Section 1207 of the 2021 IBC requires maximum reverberation times (RT) and ambient sound levels. For good speech intelligibility, a classroom needs to have an RT of 0.70 seconds or less; it is important to reduce excessive reflections, which make speech less intelligible. The finishes and volume of a classroom determine the RT. Finishes like acoustic ceiling tile, carpet, and acoustic wall panels reduce the RT, while reflective surfaces like painted CMU, gypsum wallboard, glass, and vinyl tile contribute to longer RTs. Additionally, the greater the volume, the higher the RT will be. Finishes must be balanced against the room volume to achieve the IBC criteria.
To ensure that students can adequately understand what their teacher is saying, it is important to maintain low ambient sound levels in a classroom. Sources of ambient sound can come from inside the classroom, for example HVAC systems, and outside the classroom from roadways, air traffic, and railways. The sound level inside the classroom from both interior and exterior sources is limited to 35 dBA/55 dBC.
A-weighting (dBA) is fairly common for acoustical design criteria as it provides spectral corrections, mostly to low- and high-frequencies, to replicate human hearing at typical listening levels. C-weighting (dBC) replicates human hearing at elevated sound levels where human hearing becomes more uniform; this can be helpful in evaluating louder sources that have significant low-frequency content such as planes, trains, trucks, or large MEP equipment. Acoustical services to assist with achieving the ambient sound level criteria include exterior sound surveys to measure and document typical sources; façade upgrades to exterior wall, window, door, and roof assemblies; upgrades to interior partitions where adjacent to equipment rooms; and recommendations for mechanical system noise and vibration control.
It is important to note that widespread adoption of 2021 IBC has not yet happened, and that some localities may elect to remove the classroom acoustic requirements. However, when your local school district does adopt the 2021 IBC, you’ll be thankful to know that Metropolitan Acoustics can help you navigate the new code requirements!