Bringing the Outside In? A bit about site selection.

Outdoor noise and selection of sites for learning facilities; Site background noise levels should be measured by a qualified professional. The noise level evaluation should consider all current and future sources.   It is critically important that learning facilities not be located at sites where, depending on the anticipated construction method, greatest outdoor one-hour average A-weighted sound level, herein called “background noise level” *  exceeds the following limits:

Note: OITC is the abbreviation for “Outdoor-to-Indoor Transmission Class” and is a single number descriptor (similar to STC or “Sound Transmission Class”) that rates the airborne sound attenuation qualities of a building element (roof, wall, door, window). A higher OITC indicates a greater ability to reduce airborne sound, from outdoors, through the assembly. As with the STC rating, it is measured in accordance with procedures specified by ASTM Standards. See Clause ______ in ANSI S12.60, Part 1, for further details. STC will be covered in detail in section 11 and 13.

<55 dBA

1. Where the outdoor background noise level is less than 55 dBA, conventional construction methods may be used, provided the external walls are designed to have an OITC rating not less than 30 dB

55 – 60 dBA

2. Where background noise level is between 55 dBA and 60 dBA, conventional construction methods may be used, provided the external walls are designed to have an OITC rating not less than 25 dB below the greatest outdoor one-hour average A-weighted sound level [e.g. if the greatest outdoor one-hour average A-weighted sound level is 60 dB, the OITC rating must not be less than 60 – 25 or 35dB]

60 – 65 dBA

3.  Where background noise level is between 61 dBA and 65 dBA, the external shell must be designed to provide adequate noise isolation and to conform to the limits for background noise levels (as listed in table X in the previous section.) The external walls shall be designed to have an OITC rating not less than 26 dB below the greatest outdoor one-hour average A-weighted sound level. Construction techniques are not typical and construction workmanship must be carefully monitored.

66 – 70 dBA

4.Where background noise level is between 66 dBA and 70 dBA, the external shell must be designed to provide adequate noise isolation and to conform to the limits for background noise levels (as listed in table X in the previous section) and the external walls designed to have an OITC rating not less than 27 dB below the greatest outdoor one-hour average A-weighted sound level. Construction techniques are not typical and construction workmanship must be carefully monitored.

71 – 75 dBA

5. Where background noise level is between 71 dBA and 75 dBA, the external shell must be designed to provide adequate noise isolation and to conform to the limits for background noise levels (as listed in table X in the previous section) and the external walls designed to have an OITC rating not less than 28 dB below the greatest outdoor one-hour average A-weighted sound level. Construction techniques are not typical and construction workmanship must be carefully monitored.

76 – 80 dBA

6. Where background noise level is between 76 dBA and 80 dBA, the external shell must be designed to provide adequate noise isolation and to conform to the limits for background noise levels (as listed in table X in the previous section). Construction techniques are not typical and construction workmanship must be carefully monitored and the external walls designed to have an OITC rating not less than 29 dB below the greatest outdoor one-hour average A-weighted sound level but not greater than 50 dB.

> 75 dBA

7. Where the background level is greater than 80 dBA, do not build. Another, quieter site should be selected as allowable noise levels will be extremely difficult to achieve regardless of construction method or workmanship.

(*note: In determining the greatest outdoor one-hour average A-weighted sound level , current and future levels must be considered, including a margin for safety for an increase in level in the future and other uncertainties. Widely accepted models of industrial and transportation noise are available from environmental planners and acoustical consultants.)

(**note:  Sound pressure level in the ANSI 12.60 Standard is measured in A-weighted decibels and is often expressed as dB.)

A detailed table of the above design requirements are in the ANSI 12.60 Standard under Table 3 in section 5.4.1.4.

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