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1207 Add the following sections:
1207.6 Definitions. The following definitions apply to Sections 1207.4 through 1207.9 of this Code.
COMMUNITY NOISE EQUIVALENT LEVEL (CNEL) is a metric similar to the Ldn, except that a 5 dB adjustment is added to the equivalent continuous sound exposure level for evening hours (7 p.m. to 10 p.m.) in addition to the 10 dB nighttime adjustment used in the Ldn.
DAY-NIGHT AVERAGE SOUND LEVEL (Ldn) is the A-weighted equivalent continuous sound exposure level for a 24-hour period with a 10 dB adjustment added to sound levels occurring during nighttime hours (10 p.m. to 7 a.m.).
NORMALIZED A-WEIGHTED SOUND LEVEL DIFFERENCE (Dn) means for a specified source room sound spectrum, the difference, in decibels, between the average sound levels produced in two rooms after adjustment to the expected acoustical conditions when the receiving room under test is normally furnished.
1207.7 Exterior Sound Transmission Control.
1207.7.1 Application. Residential structures located in noise critical areas, such as in proximity to highways, county roads, city streets, railroads, rapid transit lines, airports, nighttime entertainment venues, or industrial areas, shall be designed to prevent the intrusion of exterior noises beyond levels prescribed by the Municipal Code. Proper design to accomplish this goal shall include, but not be limited to, orientation of the residential structure, setbacks, shielding, and sound insulation of the building.
1207.7.2 Allowable interior noise levels. Interior noise levels attributable to exterior sources shall not exceed 45 dB in any habitable room. The noise metric shall be either the day-night average sound level (Ldn) or the community noise equivalent level (CNEL), whichever results in a higher measurement of noise level.
1207.7.3 Other noise sources. Residential structures to be located where the Ldn or CNEL exceeds 60 dB shall require an acoustical analysis showing that the proposed design will limit exterior noise to the prescribed allowable interior level. The Planning Department’s map titled Areas Potentially Requiring Noise Insulations, and similar maps and guidance produced by the Planning Department, shall be used where possible to identify sites with noise levels potentially greater than 60 dB.
1207.8 Compliance.
(a) Evidence of compliance with Section 1207.7 shall consist of submittal of an acoustical analysis report, prepared under the supervision of a person experienced in the field of acoustical engineering, with the application for a building permit. The report shall show topographical relationships of noise sources and dwelling sites, identification of noise sources and their characteristics, predicted noise spectra and levels at the exterior of the proposed dwelling structure considering present and future land usage, the basis or bases for the prediction (measured or obtained from published data), noise attenuation measures to be applied and an analysis of the noise insulation effectiveness of the proposed construction showing that the prescribed interior noise level requirements are met.
(b) If interior allowable noise levels are met by requiring that windows be unopenable or closed the design for the structure must also specify a ventilation or air-conditioning system to provide a habitable interior environment. The ventilation system must not compromise the dwelling unit or guest room noise reduction.
1207.9 Field Testing.
(a) When inspection indicates that the construction is not in accordance with the approved design, or that the noise reduction is compromised due to sound leaks or flanking paths, field testing may be required. A test report showing compliance or noncompliance with prescribed interior allowable levels shall be submitted to the building official.
(b) Field measurements of outdoor sound levels shall generally follow the guidelines prepared by the American Society for Testing and Materials (ASTM) in ASTM E 1014.
(c) Field measurements of the A-weighted airborne sound insulation of buildings from exterior sources shall generally follow the guidelines prepared by the American Society for Testing and Materials (ASTM) in ASTM E 966.
(d) For the purpose of this Section 1207.9, sound level differences measured in unoccupied units shall be normalized to a receiving room reverberation time of one-half second. Sound level differences measured in occupied units shall not be normalized to a standard reverberation time.
1207.10 The Department of Building Inspection shall consult with the Planning Department to ensure that notice to sponsors of residential development projects affected by Sections 1207.6 through 1207.9 are provided with notice of the requirements of this Section as soon as practicable in the project approval process.