[Code of Federal Regulations]
[Title 24, Volume 1]
[Revised as of April 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 24CFR51.103]

[Page 378-379]
 
                 TITLE 24--HOUSING AND URBAN DEVELOPMENT
 
PART 51_ENVIRONMENTAL CRITERIA AND STANDARDS--Table of Contents
 
                  Subpart B_Noise Abatement and Control
 
Sec. 51.103  Criteria and standards.

    These standards apply to all programs as indicated in Sec. 51.101.
    (a) Measure of external noise environments. The magnitude of the 
external noise environment at a site is determined by the value of the 
day-night average sound level produced as the result of the accumulation 
of noise from all sources contributing to the external noise environment 
at the site. Day-night average sound level, abbreviated as DNL and 
symbolized as Ldn, is the 24-hour average sound level, in 
decibels, obtained after addition of 10 decibels to sound levels in the 
night from 10 p.m. to 7 a.m. Mathematical expressions for average sound 
level and day-night average sound level are stated in the Appendix I to 
this subpart.
    (b) Loud impulsive sounds. On an interim basis, when loud impulsive 
sounds, such as explosions or sonic booms, are experienced at a site, 
the

[[Page 379]]

day-night average sound level produced by the loud impulsive sounds 
alone shall have 8 decibels added to it in assessing the acceptability 
of the site (see Appendix I to this subpart). Alternatively, the C-
weighted day-night average sound level (LCdn) may be used 
without the 8 decibel addition, as indicated in Sec. 51.106(a)(3). 
Methods for assessing the contribution of loud impulsive sounds to day-
night average sound level at a site and mathematical expressions for 
determining whether a sound is classed as ``loud impulsive'' are 
provided in the Appendix I to this subpart.
    (c) Exterior standards. (1) The degree of acceptability of the noise 
environment at a site is determined by the sound levels external to 
buildings or other facilities containing noise sensitive uses. The 
standards shall usually apply at a location 2 meters (6.5 feet) from the 
building housing noise sensitive activities in the direction of the 
predominant noise source. Where the building location is undetermined, 
the standards shall apply 2 meters (6.5 feet) from the building setback 
line nearest to the predominant noise source. The standards shall also 
apply at other locations where it is determined that quiet outdoor space 
is required in an area ancillary to the principal use on the site.
    (2) The noise environment inside a building is considered acceptable 
if: (i) The noise environment external to the building complies with 
these standards, and (ii) the building is constructed in a manner common 
to the area or, if of uncommon construction, has at least the equivalent 
noise attenuation characteristics.

                      Site Acceptability Standards
------------------------------------------------------------------------
                                   Day-night average         Special
                                    sound level (in       approvals and
                                       decibels)          requirements
------------------------------------------------------------------------
Acceptable....................  Not exceeding 65 dB(1)  None.
Normally Unacceptable.........  Above 65 dB but not     Special
                                 exceeding 75 dB.        Approvals (2)
                                                        Environmental
                                                         Review (3).
                                                        Attenuation (4).
Unacceptable..................  Above 75 dB...........  Special
                                                         Approvals (2).
                                                        Environmental
                                                         Review (3).
                                                        Attenuation (5).
------------------------------------------------------------------------
Notes: (1) Acceptable threshold may be shifted to 70 dB in special
  circumstances pursuant to Sec. 51.105(a).
(2) See Sec. 51.104(b) for requirements.
(3) See Sec. 51.104(b) for requirements.
(4) 5 dB additional attenuation required for sites above 65 dB but not
  exceeding 70 dB and 10 dB additional attenuation required for sites
  above 70 dB but not exceeding 75 dB. (See Sec. 51.104(a).)
(5) Attenuation measures to be submitted to the Assistant Secretary for
  CPD for approval on a case-by-case basis.


[44 FR 40861, July 12, 1979, as amended at 49 FR 12214, Mar. 29, 1984]