18J.15.070 Noise Attenuating Barriers and Structural Walls

18J.15.070 Noise Attenuating Barriers and Structural Walls.

The purpose of this Section is to provide standards for the design, placement, and construction of noise attenuating barriers between incompatible land uses. A "noise attenuating barrier" means any buffer strip, wall, or berm constructed for the purpose of reducing noise from a noise-generating activity.

A. Applicability. These standards apply to any barrier being built to attenuate noise from a proposed or existing land use, as required by the Hearing Examiner, Director, Responsible Official, or voluntarily constructed on any parcel of land.

1. An Acoustical Expert must certify that the building plans comply with the noise regulations in Chapter 8.76 PCC and the standards and guidelines of this Section prior to the issuance of a Building Permit.

2. No barrier may be located within the right-of-way without express permission from the County Engineer pursuant to PCC 12.28.010.

3. Maintenance of the barrier shall be the responsibility of the property owner, applicant, or successor.

4. Barriers shall not limit access for maintenance equipment, traffic service vehicles, emergency vehicles, pedestrians, and bicycles.

5. A noise barrier shall not have anything affixed to it, such as a light fixture or sign, and shall not protrude in such a way as to interfere with pedestrian or vehicle traffic.

6. When a Noise Attenuating Barrier, Structural Wall, or retaining wall greater than 6 feet in height is visible from a public arterial roadway, it shall be screened from public view utilizing a vegetative screen. This landscaping ensures that a noise barrier and related buffer is visually attractive and consistent with the character of the community.

(1) The Vegetation Screen shall consist of a mix of evergreen and deciduous shrubs and trees across the buffer strips and any berm associated with a noise-attenuating barrier;

(2) Landscaping shall be installed on each side of any wall or berm, as follows:

(a) Evergreen and deciduous shrubs, in a mix of at least 60 percent evergreen, at a rate of 1 per 5 lineal feet of landscape strip;

(b) Closely spaced evergreen trees, at a rate of 1 per 10 lineal feet of landscape strip; and

(c) Closely spaced deciduous trees, at a rate of 1 per 20 lineal feet of landscape strip. The screen may consist of either overlapping clusters or a solid row of material. If overlapping clusters are used, the overlap shall be at least one-half plant width;

(3) Vegetative screening materials shall have a mix of mature heights ranging from 4 to 6 feet for shrubs and 10 to 12 feet for trees;

(4) In the event only a buffer strip is used for noise attenuation, landscaping shall be installed at the same rate as for two sides of a berm or wall; and

(5) Installation of vegetative groundcover that is native and drought-tolerant is encouraged but not required within the planting area.

(6) Native and drought-tolerant vegetation shall be considered.

C. Design Options. The proponent may choose one of the following options for a noise-attenuating barrier, provided the required mitigation of noise is achieved to meet the noise standards in Chapter 8.76 PCC, as certified by the Acoustical Expert and the conditions of the permit.

1. Buffer Strip. A vegetated buffer strip may be used to attenuate noise, if determined to be effective, given the noise impacts, topography, and other characteristics of the site.

(1) If a buffer is used, the width of the buffer must be 40 feet, or a width specified by the Acoustical Expert as necessary to mitigate the noise.

2. Berm. A vegetated berm may be used to attenuate noise, if determined to be effective, given the noise impacts, topography, and other characteristics of the site. A berm is defined as an earthen strip barrier with permanent vegetative cover that is free from broken concrete, asphalt, large rocks, or other debris and placed as a continuous ridge of earth.

(1) The height of the berm shall be at least 6 feet, or the height specified by the Acoustical Expert as necessary to mitigate the noise. The berm shall be measured from street curb or the crown of the adjacent paved way for road frontages or existing grade for interior lot lines;

(2) The berm shall be placed on a strip of land (buffer strip) at least 30 feet in width; and

(3) Berm slopes shall be no steeper than 2:1. The end of the berm shall be designed with a lead-in slope of 10:1 and curved toward the right-of-way line.

3. Wall. A solid, opaque wall with noise-attenuating qualities may be constructed as a noise-attenuating barrier if determined to be effective, given the noise impacts, topography, and other characteristics of the site.

(1) The height of the wall shall be at least 6 feet, or the height specified by the Acoustical Expert as necessary to mitigate the noise. The wall shall be no higher than 9 feet;

(2) The wall shall be placed on a strip of land (buffer strip) at least 20 feet in width;

(3) The wall shall be constructed of stone, masonry, or concrete with a stone, corrugated, or exposed aggregate finish with horizontal and vertical modulation to reduce the appearance of a barrier and look more like a design element that fits the character of the adjacent developments; and

(4) The wall shall be set back from the adjoining property line or right-of-way by at least 10 feet.

4. Combination of Berm and Wall. A wall may be combined with a berm to achieve the required noise reduction. The separate standard for the berm and wall shall be met, except that the buffer strip shall be at least 20 feet in width and the wall no taller than 6 feet.