§ 63.111. Residential development on steep slopes.  


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  • In reviewing residential development on slopes of greater than twelve (12) percent, the zoning administrator shall, in addition to general site plan standards, consider the following requirements and standards:

    (a)

    An engineering report on slope stability and hydrology, if the zoning administrator determines that such a report is warranted. The zoning administrator shall establish and maintain written criteria to use in making this determination, which criteria may include the size of the proposed development and any official records of soil instability, groundwater, and erosion in the vicinity. An engineering report must be prepared by a registered hydrological, geotechnical or soils engineer. Before a grading permit will be issues, the following elements of the engineering report must be submitted to the city and approved:

    (1)

    An evaluation of existing conditions including slope stability, ground water, and surface water. Testing should use techniques that minimize disturbance to existing slopes and vegetation (for example, drilling cores for soil samples rather than digging with a back hoe).

    (2)

    Site-specific recommendations for construction. Recommendations will depend on site conditions but may include the use of drain tiles, water-proofing walls, poured concrete foundations and sump pumps.

    (3)

    A schedule of inspections to be attended by city staff, the builder and the engineer who prepared the report. As a minimum, inspections shall be scheduled prior to grading, after grading and during installation of any special measures required to deal with slope stability or water conditions.

    Before any additional building permits will be issued, a post-grading report must be submitted and approved by the city. This report must document conditions after grading, note any problems or conditions that were not anticipated or adequately addressed in the pre-grading portion of the engineering report and make recommendations for solutions to any problems found.

    (b)

    Buildings should be designed to fit into the hillside without significant regrading to protect the stability of the slope and preserve existing trees while preventing excessively tall retaining walls and unattractive trough-shaped yards between buildings and retaining walls. Multi-story buildings are encouraged to reduce the size of the building footprint.

    (c)

    Existing trees shall be preserved where possible and shall be protected during construction. New trees should be planted to partially obscure new hillside buildings and parking. To accomplish this a tree preservation plan shall be included with the site plan.

    (1)

    Tree preservation plan: Required information. The tree preservation plan shall include the following:

    a.

    The location, diameter at breast height (DBH) and species of all existing trees six (6) inches DBH or larger within the limits of disturbance.

    b.

    The location and dimension of all buildings (existing and proposed); the location of easements, adjacent roadways and vehicular access driveways; existing and proposed grading; site drainage facilities; parking areas; sidewalks and utilities.

    c.

    The location of all trees that will be preserved and incorporated into the proposed site design. All tree drip lines shall be noted.

    d.

    A description of how trees will be protected before and during construction.

    e.

    The location of trees to be removed, replacement trees and areas proposed for additional landscaping, including, but not limited to, the tree name (botanical and common); the quantity of each species; tree caliper, measured six (6) inches aboveground; and a typical planting detail.

    (2)

    Tree replacement. In areas with slopes steeper than twelve (12) percent, trees to be removed for development or reasonably anticipated to be lost due to development shall be replaced according to the following requirements:

    a.

    Individual trees of at least twelve (12) inches DBH but less than eighteen (18) inches DBH shall be replaced on the basis of one (1) replacement tree for every one (1) tree removed.

    b.

    Individual trees of at least eighteen (18) inches DBH but less than twenty-four (24) inches DBH shall be replaced on the basis of two (2) replacement trees for every one (1) tree removed.

    c.

    Individual trees of twenty-four (24) inches DBH or larger shall be replaced on the basis of three (3) replacement trees for every one (1) tree removed.

    d.

    Replacement shall not be required for removal of trees in areas to be occupied by buildings, private streets, driveways, areas required for accessory parking or within a distance of fifteen (15) feet of a building foundation or for trees determined by the superintendent of parks to be hazardous, diseased, dying or dead.

    e.

    Trees designated for removal within the limits of disturbance may be transplanted within the site and counted as replacement trees.

    f.

    Deciduous replacement trees of nursery stock shall be at least two and one-half (2½) caliper inches and of a species similar to the tree(s) lost or removed. Coniferous replacement trees shall be at least six (6) feet in height and of species similar to the tree(s) lost or removed.

    (d)

    Retaining walls taller than four feet shall be constructed under city permit with frost footings as required by the state building code and shall be engineered to retain lateral earth pressures consistent with the principles of soils mechanics, and shall be detailed to minimize hydrostatic pressures. On a case by case basis, the zoning administrator may relax these standards for retaining walls that serve minor landscaping purposes.

    (e)

    On Irvine Avenue and on Pleasant Avenue between Ramsey Street and the Walnut Street public stairway, additional hillside design standards and guidelines apply as listed in the Irvine Avenue Development Plan of 2003.