6.8 HUD CRITERIA

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The U.S. Department of Housing and Urban Development (HUD) was

charged with developing guides for zoning modifications or for siting of

dwellings where the noise and zoning regulations were already in existence.

There was evidence that annoyance for a specific noise exposure depended

on both the average level of the noise and on the variability of the source of

noise (Griffiths and Langdon, 1968). The noise pollution level, LNP, was

developed to recognize this phenomenon (Schultz, 1972).

The noise pollution level is defined by the following expression:

LNP ј Leq ю 2:56 (6-10)

The quantity Leq is the energy-weighted equivalent A-weighted sound level,

and  is the standard deviation of the A-weighted levels. The coefficient 2.56

was selected as the best fit to data from studies of subjective response to

variable noise levels. The standard deviation of the noise levels may be

determined from the following equation:

2 ј _tjL2j

_ р_tjLj Ю2 (6-11)

The quantities tj are the fractions of time that the noise level Lj occurs,

usually over a 24-hour period. If the probability distribution of the noise

over time is approximately gaussian, the noise pollution level may be estimated

by the following expression:

LNP ј L50 ю _ ю _2=60 (6-12)

The quantity _ ј рL10 _ L90Ю, and L10, L50, and L90 are the A-weighted

sound levels that are exceeded 10%, 50%, and 90% of the time, respectively.

Acoustic Criteria 253

Copyright © 2003 Marcel Dekker, Inc.

The first term рLeqЮ in Eq. (6-10) represents the equivalent continuous

noise level, and the second term (2.56) represents the effect of fluctuations

in the noise level, or the difference between the steady background noise and

the intruding noise.

The HUD criteria for allowable noise pollution levels for new residential

construction are given in Table 6-19 (Schultz, 1970). A builder may not

be able to obtain federal funding or federally guaranteed loans unless the

noise level at the proposed site is acceptable. The clearly acceptable category

means that no special acoustic treatment is required for the construction

because of environmental noise. The normally acceptable category means

that the housing site may be acceptable (discretionary) if special acoustic

treatment, such as an acoustic barrier, is used to reduce the noise level at the

site. Also, the builder would need to assure the authorities that the indoor

noise level would not exceed 55dBAfor more than 60 minutes or not exceed

45 dBA for more than 8 hours per day.

Example 6-8. The noise levels on the A-scale in a normal suburban area

are given in Table 6-18. Determine the noise pollution level for the environmental

noise and the HUD category for the noise.

Ordinarily, date would be gathered over shorter time periods than 1

hour for a noise impact study, and the data set would be much more extensive

than that given in Table 6-18. This problem, however, is designed to

illustrate the principles involved, without getting mired in mountains of

data.

254 Chapter 6

TABLE 6-19 Environmental Noise Level Criteria (HUD) for New Residential

Construction

Category Description LNP, dBA(NP)

Clearly acceptable Noise does not exceed 45 dBA for 30

minutes in 24 hours

<62

Normally acceptable Noise does not exceed 65 dBA for 8

hours in 24 hours

62–74

Normally unacceptable Noise exceeds 65dBA for 8 hours in

24 hours, or loud repetitive sounds

are present

74–88

Clearly unacceptable Noise exceeds 80dBA for 6 minutes

in 24 hours or exceeds 75dBA for

8 hours in 24 hours

>88

Source: Schultz (1970).

Copyright © 2003 Marcel Dekker, Inc.

The fractions of the entire day at which each sound level occurs may

be calculated as follows:

At 60dBA: t ј 4=24 ј 0:1667

At 55dBA: t ј 6=24 ј 0:2500

At 50dBA: t ј 5=24 ј 0:2083

At 45dBA: t ј 2=24 ј 0:0833

At 40dBA: t ј 7=24 ј 0:2917

The equivalent sound level is found from Eq. (6-7):

Leq ј 10 log10Ѕр0:1667Ю 106:0 юр0:2500Ю 105:5 юр0:2083Ю 105:0 ю_ _ __

Leq ј 10 log10р272,109Ю ј 54:3dBA

The quantities needed in calculating the standard deviation are determined

as follows:

_tjрLjЮ2 ј р0:1667Юр60Ю2 юр0:2500Юр55Ю2 юр0:2083Юр50Ю2ю_ _ _ ј 2512:5

_tjLj ј р0:1667Юр60Ю ю р0:2500Юр55Ю ю р0:2083Юр50Юю_ _ _ ј 49:583

The standard deviation for the data may be determined from Eq. (6-11):

2 ј 2512:5_р49:583Ю2 ј 53:993

 ј р53:993Ю1=2 ј 7:348 dBA

The noise pollution level is found from Eq. (6-10):

LNP ј 54:3юр2:56Юр7:348Ю ј 54:3ю18:8 ј 73:1dBAрNPЮ

It is noted from Table 6-19 that this value of noise pollution level falls into

the normally acceptable category. It is also noted fromthe data in Table 6-18

that the noise does not exceed 65 dBA at all during the 24-hour period.

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