Chapter 16.22 — CONSTRUCTION LOCATED NEAR ARTERIALS, RAILROADS AND AIRPORTS

The purpose of this chapter is to establish standards of insulation against noise for areas in the vicinity of arterials, railroads, and airports where the exterior community noise equivalent level (CNEL) exceeds 60 dB. Residential developments such as noise impacted areas shall be designed and constructed so as to isolate them appropriately from the interior noise exposures produced by arterial traffic, train pass-bys, and aircraft operations.

(Code 1972, § 16.22.010; Ord. No. 684, § 1(part), 1987)

The following words, terms and phrases, when used in this chapter, shall have the meanings ascribed to them in this section, except where the context clearly indicates a different meaning:

Ambient noise means the composite noise from all sources near and far. In this context, the ambient noise level constitutes the normal or existing level of environmental noise at a given location.

A-weighted sound pressure level, db(A) means the sound pressure level, in decibels, as measured on a sound level meter using the A-weighting filter network. The A-weighting filter deemphasizes the very low and very high frequency components of the sound in a manner similar to the response to the human ear and gives good correlation with subjective reactions to noise.

Community noise equivalent level (CNEL) means a measure of noise exposure which recognizes that a given level of noise may be more or less tolerable depending on the duration of exposure and the time of day during which the noise is experienced. This measure weights the average noise level for the evening

hours (7:00 p.m. to 10:00 p.m.) by five dB, and the late evening and early morning hours (10:00 p.m. to 7:00 a.m.) by ten dB. The unweighted daytime noise levels are combined with these weighted levels and averaged to obtain a CNEL value.

Decibel (dB) means a unit for describing the amplitude of sound, equal to 20 times the logarithm to the base ten of the ratio of the pressure of the sound measured to the reference pressure, which is 20 micropascals.

Maximum noise level means the maximum instantaneous noise level that occurs during a specific time interval. In acoustics, the maximum sound pressure level is understood to be for single events unless some other kind of level is specified.

Noise means annoying, harmful, or unwanted sound.

Noise contour means a line drawn about a noise source indicating constant levels of noise exposure. CNEL is the metric utilized herein to describe community exposure to noise.

Noise impact area means a specific area exposed to significant levels of noise.

Noise level reduction (NLR) means the difference in noise level from outside to inside of the building. NLR is a difference, in decibels, between A-weighted sound level. It depends primarily on the nature of the wall, ceiling, windows, doors, and vents, and to a lesser extent on the amount of sound absorbing material in the room in which the sound is received. It shall be measured, if so required, in a completed and furnished building.

Noise-sensitive land uses include, but are not limited to, residences, schools, libraries, hospitals, churches, offices, hotels, motels, and outdoor recreational areas. Noise-sensitivity factors include interference with speech communication, subjective judgment of noise acceptability and relative noisiness, priced for freedom from noise intrusion, and sleep interference criteria.

Qualified consultant means a person who by reason of his training and experience in the science and technology of acoustical engineering is considered qualified to pass judgment on acoustical design, materials, and methods of construction for the attenuation of noise. The qualifications of the consultant relative to acoustical design must be submitted to and found to be acceptable by the city and the state office of noise control.

Sound absorption means the capacity of the materials and furnishings in a habitable room to absorb sound.

Sound level means, in decibels, the quantity measured by an instrument that satisfies American National Standards Specification for Sound Level Meters 51.4-1971 or the most recent revision thereof. Sound level is understood to be measured with the A-weighted filter and slow response of the instrument.

Sound level meter means a measurement instrument containing a microphone, an amplifier, an output meter, and one or more frequency weighting networks. It is used for the determination of sound levels.

Sound transmission class (STC) of a partition means a single-figure rating of the sound insulating properties of a partition which takes into account the relative importance of the sound transmission loss of the

partition at different frequencies. The determination of the sound transmission class of a partition is described in "Determination of Sound Transmission Class," American Society for Testing and Materials Designation E413-73.

Sound transmission loss of a partition means a measure of the sound insulating properties of a wall, floor, ceiling, window, or door that is a characteristic of the partition itself and not the room of which it is a part. The determination of sound transmission loss of a partition of the field is described in "Measurement of Airborne Sound Insulation in Buildings," American Society for Testing and Materials Designation E336-77 or the latest revision thereof.

(Code 1972, § 16.22.020; Ord. No. 684, § 1(part), 1987)

Residential projects, or portions thereof, which are exposed to a community noise equivalent level (CNEL) of 60 dB or greater are considered to be impacted by excessive noise. Such projects shall be required to include noise isolation design and construction such that the exterior and interior noise standards of the city's noise element of its general plan are not exceeded. Year 2000 CNEL contour maps maintained by the city's planning department shall be used to identify those areas in proximity to arterials, railroads, and/or airfields that are impacted by a CNEL which is 60 dB or greater.

(Code 1972, § 16.22.030; Ord. No. 684, § 1(part), 1987)

Residential development will be considered acceptable by the city's building official for mitigating interior noise exposures if it incorporates the features described in section 16.22.060. Alternative materials and methods of construction may be permitted provided such alternatives are demonstrated to the satisfaction of the city's building official to be equivalent to those described in this chapter.

(Code 1972, § 16.22.040; Ord. No. 684, § 1(part), 1987)

An analysis and design report signed by and prepared under the supervision of a qualified architect or engineer shall be submitted with the application for building permits. The report shall comply with the requirements of section 16.22.070 and shall identify the noise sources and characteristics, provide the predicted noise spectra, indicate the basis for the prediction (measured or obtained from published data), and quantify the effectiveness of the proposed building construction to ensure that the CNEL standard of 45 dB is met within the interior living spaces. In the event that the analysis and design report includes a challenge of the AICUZ noise contours for March Air Force Base, it shall also comply with the requirements and procedures for a challenge study, as established by resolution of the city council.

(Code 1972, § 16.22.050; Ord. No. 684, § 1(part), 1987)

(a)

All residential buildings located within a CNEL contour of 60 dB or greater shall be designed to cause isolation against exterior noise with at least a noise level reduction (NLR) that will reduce the exterior noise to an acceptable level. Residential buildings shall be constructed with sufficient sound insulation so that in any habitable room, furnished for normal use with doors and windows closed, the noise exposure due to exterior sources does not exceed a community noise equivalent level (CNEL) of 45 dB. The exterior CNEL at the project site shall be obtained from city approved noise contour maps.

(b)

The minimum NLR required at any residential unit shall be determined as follows:

Range of Exterior Minimum NLR CNEL

60—65 dB 20 dB

66—70 dB 25 dB

71—75 dB 30 dB

76 + dB Not permitted

(c)

The following tables specify the construction standards necessary to meet the minimum NLRs indicated above and the interior noise standards specified in the noise element of the city's general plan.

TABLE 1. CONSTRUCTION STANDARDS TO ACHIEVE A NOISE LEVEL REDUCTION (NLR) OF 20 dB

Assembly Construction Standards

Ventilation Arrangements for any habitable room shall be such that any exterior door or window can be kept closed when the room is in use. A forced air circulation system shall be provided which will give a minimum of two complete air changes per hour, of which at least 20 percent is fresh air in accordance with the requirements of the Uniform Mechanical Code.

Glazing and All windows and sliding glass doors shall be doors tightly fitted assemblies, and all Doors entry doors from exterior spaces shall be well weather-stripped. Air gaps and rattling shall not be permitted.

TABLE 2. CONSTRUCTION STANDARDS TO ACHIEVE A NOISE LEVEL REDUCTION (NLR) OF 25 dB

Assembly Construction

Exterior Walls If wood construction is used, exterior walls shall be furnished on the outside with siding-on-sheathing, stucco, or brick veneer. The interior surface shall be at least one- half-inch gypsum board. Insulation having a minimum of R-11 shall be placed between the studs.

Masonry walls, if used, shall have at least one surface of the wall plastered, painted, or covered with gypsum wallboard or approved materials.

For mobile home construction, the interior surface shall have a minimum density of two psf and the exterior surface should have a minimum density of three psf. At least R-11 insulation shall be placed between the studs.

There shall be no direct openings such as mail slots or ventilation units.

Glazing All windows and sliding glass doors shall be well fitted, well weather-stripped assemblies and shall have a minimum STC of 32. Air gaps and rattling shall not be permitted.

The total area of glass shall not exceed 20 percent of the floor area in any room.

Doors All exterior doors shall be well weather-stripped solid core assemblies at least 1¾-inch thick.

Roof Roof sheathing of wood construction shall be well fitted or caulked plywood of at least one-half inch thick. Ceilings shall be well fitted, well sealed gypsum board of at least one-half-inch thick.

Insulation with at least a rating of R-19 shall be used in the attic space.

For mobile home construction, the interior surface shall have a minimum density of two psf and the exterior surface shall have a minimum density of three psf. At least R-11 insulation shall be placed between the studs. Skylights shall have a minimum STC of 32.

Floor For mobile home construction, the skirt shall extend to the ground and shall be of the same construction as the exterior walls. Any access doors or windows shall be tightly fitted and weather-stripped.

Ventilation Arrangements for any habitable room shall be such that any exterior door or window can be kept closed when the room is in use. A forced air circulation system shall be provided which will give a minimum of two complete air changes per hour, of which at least 20 percent is fresh air per requirements of the Uniform Mechanical Code. Any air duct or connection to an outdoor elevation must contain an interior sound absorbent lining which is at least acoustically equivalent to one-inch thick fiberglassed duct liner. The liner shall be five times greater in length than the diameter of the duct. All such ducts shall contain a bend which eliminates the line-of-sight to the outside. All fireplaces shall be provided with a well-fitted damper.

Furnishings All rooms, when in use, are expected to contain furniture or other materials that absorb sound equivalent to the absorption provided by wall-to-wall carpeting over a conventional pad.

TABLE 3. CONSTRUCTION STANDARDS TO ACHIEVE A NOISE LEVEL REDUCTION (NLR) OF 30 dB

Assembly Construction Standards

Exterior Walls If wood construction is used, exterior walls shall be finished on the outside with siding- on-sheathing, stucco, or brick veneer. The interior surfaces shall be at least one-half inch gypsum board. Insulation having a minimum value of R-11 shall be placed between the studs.

Masonry walls, if used, shall have at least one surface of the wall plastered, painted, or covered with gypsum wallboard or approved material.

The surface weight of the wall should be at least 40 psf. For mobile home construction, the interior surface shall have a minimum density of two psf and the exterior surface shall have a minimum density of five psf. At least R-11 insulation shall be placed between the studs.

There shall be no direct openings such as mail slots or ventilation units.

Glazing All windows and sliding glass doors shall be well fitted, well weather-stripped assemblies and shall have a minimum STC of 38. Air gaps and rattling shall not be permitted. The total area of glass shall not exceed 20 percent of the floor area within any room.

Doors All exterior doors shall be well weather-stripped solid core assemblies at least 1¾-inch thick.

Roof Roof sheathing of wood construction shall be well fitted or caulked plywood at least one-half-inch thick. Ceiling shall be well fitted, well-sealed gypsum board of at least one-half-inch thick. For mobile home construction, the interior surface shall have a minimum density of five psf. At least R-11 insulation shall be placed between the studs. Insulation with at least a rating of R-19 shall be used in the attic space. Skylights shall have a minimum SW of 38.

Floor The floor of the lowest occupied room shall be concrete slab or shall be well sealed against the noise intrusion. For mobile home construction, the skirt shall extend to the ground and shall be the same construction as the exterior walls. Any access doors or windows shall be tightly fitted and weather-stripped.

Ventilation Arrangements for any habitable room shall be such that any exterior door or window can be kept closed when the room is in use. A forced air circulation system shall be provided which will give a minimum of two complete air changes per hour, of which at least 20 percent is fresh air in accordance with the requirements of the Uniform Mechanical Code. Any air duct or connection to an outdoor elevation must contain an interior sound absorbent lining which is at least acoustically equivalent to one-inch thick fiberglass duct liner. The liner shall be five times greater in length than the

diameter of the duct. All such ducts shall contain a bend which eliminates the line-of- sight to the outside. Fireplaces shall not be permitted.

Furnishings All rooms, when in use, are expected to contain furniture or other materials that absorb sound equivalent to the absorption provided by wall-to-wall carpeting over a conventional pad.

(Code 1972, § 16.22.060; Ord. No. 684, § 1(part), 1987)

(a)

Acoustical analysis reports shall be prepared for all residential projects for approval by the city's planning department. Such reports shall describe the exterior noise environment in detail and, as necessary, propose measures to satisfy both interior and exterior noise level criteria. The acoustical consultant shall uniquely identify each acoustical report by a report number and certify that the report is true and accurate. Each report shall include the following:

(1)

A city-issued project identification number (e.g., use permit, site plan, tentative tract, parcel map, etc.);

(2)

A street address if one has been assigned;

(3)

A vicinity map clearly showing the site for the development;

(4)

The conditions of approval applied to the project by the city, in their entirety. (This will notify the consultant if any special modifications were made in the standard conditions of the approval);

(5)

A legible plot plan and floor plan at a scale not less than one inch equals 40 feet, folded in an 8½-inch by 11-inch format. The scale is to ensure that distance can be accurately determined and that the exhibit is legible.

(b)

The acoustical report shall also state the methodology used for measurement or prediction of motor vehicular noise levels. The procedures in FHWA-RD-77-108, as modified for CNEL, shall be used for traffic noise prediction, with all variables identified and justified where appropriate (e.g., absorptive (soft) or reflective (hard); gradient; stop-and-go conditions; number and width of travel lanes and medians, etc.).

(1)

Vehicle speeds, ADTs and traffic mix, per level of service "C," shall be stated and source of information identified.

(2)

Equivalent distance, per the FHWA model for calculations of noise impact shall be used.

(3)

The centerline of the roadway shall be used for reference distance to observer, structure, etc., not the centerline of the near travel lane for reference.

(4)

No credit shall be given for future quieting of motor vehicle noise sources.

(5)

CNEL shall be used.

(6)

On-site measurement data, if used to validate the predicted noise levels for an acoustical analysis, shall be adjusted to reflect the annualized ADT for the site prior to determination of existing noise impact levels. The dates, times and exact locations of the measurements shall be stated.

(c)

Where applicable a detailed barrier analysis shall be submitted with the report, including:

(1)

Locations of barriers, usable outdoor living area, etc.;

(2)

Worst-case section view of site, including elevations, either scaled or dimensioned;

(3)

Barrier geometry (NOTE: Five-foot observer height above datum and source heights per the FHWA model shall be used.);

(4)

Discussion of the structural details required to maintain acoustical integrity of the barrier, including treatment of penetrations, gates, etc.

(d)

If railroad or aircraft noise affects the site, measurement of noise impact or the method of prediction shall be stated. Where city developed or approved CNEL contour maps are available, their use may be required by the city. If railroad or aircraft noise does not affect the site, so state.

(e)

Each report shall further:

(1)

Indicate in tabular form the required sound transmission loss of windows, along with typical thickness and configuration, required to satisfy thickness and configuration, required to satisfy city standards for interior noise levels. When specifying windows of greater than 3/16 -inch thickness, list one or more products by manufacturer's name and model number that will satisfy the acoustical requirements.

(2)

Include a summary section on colored paper in which specifications and location of all sound attenuating design features or products shall be listed, preferably in a tabular form.

(3)

Include worksheets for composite wall analyses including transmission loss assumptions, unless the prescriptive A-weighted insertion losses of 20 dB (windows closed) or 12 dB (windows open) are used.

(4)

Specify in text of report which residential structures and units, if any, require closed windows to meet interior noise standards and in such cases, include the following paragraph:

Where windows are required to be openable or kept closed in order to meet the interior noise standards, mechanical ventilation and cooling, if necessary, shall be provided to maintain a habitable environment. The system shall supply two air changes per hour to each habitable room including 20 percent fresh make-up air obtained directly from the outdoors. The fresh air inlet duct shall be of sound attenuating construction and shall consist of a minimum of ten feet plus one sharp 90-degree bend.

(5)

State the requirements for maintaining building shell acoustical integrity and enumerate items of a critical nature: e.g., tight-fit chimney damper, exhaust fan backdraft damper, no mail slot, full skirting for mobile home coaches, air-conditioning intake and exhaust ducting, etc. A through-the-wall air-conditioner shall be treated as a separate component when calculating composite wall attenuation values.

(f)

The following CNEL data shall be provided as appropriate:

(1)

Existing and future CNEL, before mitigation;

(2)

Worst case outdoor living area CNEL, before mitigation;

(3)

Worst-case CNEL incident upon structure prior to mitigation; and

(4)

Worst-case interior CNEL after mitigation by building components and/or exterior barriers.

(Code 1972, § 16.22.070; Ord. No. 684, § 1(part), 1987)