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Building a Sound Future for Students
  Figure 3. Typical (top) and unique (bottom) features characteris- tic of the 220 classrooms measured in the central midwestern United States. Top: Many classrooms in the United States use acoustical ceil- ing tile to add absorption to classrooms to limit reverberation time as well as to create easy access points to building systems above the tiles. Bottom: Some classrooms have unique features like those shown. Although this room’s ceiling is more sound reflective than acoustical ceiling tile, the brick walls are more diffusive and less reflective than gypsum wall board. Those considerations combined with a relatively small volume meant that this classroom’s reverberation time met the ANSI S12.60 guidelines.
that a building meets certain qualifications for sustainability. A building must meet prerequisite design criteria to obtain LEED certification but can add levels of distinction through earning credits associated with meeting more stringent
10 | Acoustics Today | Spring 2020, Special Issue
18 | Acoustics Today | Fall 2018 Reprinted from volume 14, issue 3
design criteria. Unoccupied background noise level is one of the LEED design criteria. In previous versions of LEED for building design and construction, the prerequisite background noise level was 45 dB(A), and a distinction credit was awarded to schools that met a background noise level of 40 dB(A) or lower. These levels are noticeably louder than the 35 dB(A) recommended by ANSI S12.60. Although 45 dB(A) is quieter than some of the unoccupied noise floors in classrooms observed in our study, it does not necessarily meet the needs of its occupants. In the most recent revision of LEED (v4), the prerequisite background noise level was adjusted to 40 dB(A), and the unoccupied background noise level requirement for the credit was adjusted to 35 dB(A) (USGBC, 2013), the level recommended in ANSI S12.60. LEED is one of the only programs in the United States that provides a means of incentivizing the achievement of acceptable background noise levels in classrooms, but buildings are not required to adopt LEED standards.
In contrast, the United Kingdom has implemented enforceable building regulations for classrooms to guide the design and construction of classrooms, published in Building Bulletin 93 (BB93) that was first issued in 2003 and last revised in 2015 (United Kingdom Department for Education and Skills, 2015). The requirements of BB93 for unoccupied noise levels are similar to those recommended by ANSI S12.60. Maximum limits for the indoor ambient noise levels (IANLs) are set to 35 dB(A) for new primary and secondary school classrooms designed as core learning spaces that are not open plan and to 40 dB(A) for refurbished classrooms redesigned for the same purposes. IANLs are A-weighted equivalent levels measured over 30 minutes during normal teaching hours, excluding noise contributions from instructional equipment and instructional activities. Noise contributions from adjacent classrooms are considered and mitigated with appropriately substantial wall construction between classrooms, deemed appropriate by the type of activities and noise sensitivities in the adjacent rooms.
The requirements of BB93 for reverberation time are also similar to those recommended by ANSI S12.60. There are, however, different requirements for primary school classrooms and secondary school classrooms. Reverberation times in general classrooms must not exceed 0.6 second in new primary schools and 0.8 second in refurbished primary schools. For secondary schools, the upper limits are slightly higher: 0.8 second for new construction and 1.0 second for refurbished. The stricter requirement for primary school

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