A. Purpose and intent. The purpose and intent of establishing standards for retaining walls in the Hillside Residential zone is to ensure that the application of retaining walls is aesthetically pleasing, limited in quantity throughout a development, and not used to artificially create additional building area.
B. Prohibited retaining walls.
1. Use of utilitarian retaining wall designs such as crib walls and geogrids shall be prohibited.
2. No retaining walls shall be permitted between residential lots as a means of creating additional useable pad area.
C. Use of Loffelstein and similar living walls. The use of Loffelstein walls, and other similar living wall systems, that allow for landscaping opportunities with planting pockets and stepped designs is acceptable. Such walls shall be subject to the following development standards.
1. The minimum height shall be no less than fifteen (15) feet, with a maximum height of thirty (30) feet.
2. Such walls shall utilize a curvilinear slope pattern to mimic the appearance of natural hillside terrain.
3. Such walls shall be planted with landscape material suitable for the climate, wall exposure relative to the sun, and taking into consideration the landscape aesthetic effect to be achieved by the overall development. The color palette and materials selected for the retaining wall shall blend in with adjacent hillsides and landscape plant palette.
Figure 20.206.120.C.1
Loffelstein walls and similar living wall systems retain large amounts of earth while providing planting pockets for landscaping. Once landscaping matures, the wall will be masked and have a softer appearance than a hardscape wall surface.
D. Contour construction and wall materials. Retaining walls shall follow the natural contours of the slope, and all materials used to construct retaining walls shall consist of native stone, poured-in-place concrete, precast concrete block, and shall be of a color and texture that mimic the color and texture of surrounding native plant materials.
E. Required planting areas. Slopes requiring retaining at a height greater than three (3) feet shall be terraced for planting areas. Such planting areas shall have a minimum width of six (6) feet. No more than two (2) terraces of retaining walls shall be permitted on one (1) manufactured slope.
Figure 20.206.120.E and 20.206.120.G
F. Irrigation systems required. All planting areas for retaining walls shall be provided with an automatic irrigation system. Such irrigation system shall be approved and inspected prior to the construction of any wall.
G. Height standards.
1. Retaining walls shall be constructed at varying heights throughout a development.
2. The cumulative height of any retaining wall, other than a Loffelstein wall or similar living wall, built to retain a cut slope or fill slope shall not exceed six (6) feet in height. Cumulative height shall mean the combined height of any wall or series of walls required to retain a single slope.
(Ord. 1079, passed 11-2-04)