Chapter 9 - Special Hillsides Preservation District (HS)
The "Special Hillsides Preservation District" (hereinafter also referred to as the "Special District") established in this Resolution is designed to promote and protect public health, safety and general welfare. These general goals include, among others, the following special purposes:
(a) to reduce hillside erosion, landslides and excessive storm water runoff associated with development by conserving vegetation and protecting natural terrain;
(b) to preserve hillsides having unique aesthetic value to the public;
(c) to guide development in areas of outstanding natural beauty in order to protect, maintain and enhance the natural features of such areas; and
(d) to promote the most desirable use of land and to guide future development in accordance with a comprehensive development plan, and to protect the neighborhood character of the district.
Definitions specially applicable to this Chapter are set forth in this Section. The definitions of other defined terms are set forth in Section 12-10 (DEFINITIONS).
Area of no disturbance
An "area of no disturbance" is an area designated on the site plan that is protected from all types of intrusion, including: site alteration, operation of construction equipment, storage of construction materials, excavation or regrading, tunneling for utilities, removal of trees, topsoil or any living vegetation, or construction of driveways, private roads, parking areas, patios, decks, swimming pools, walkways or other impervious surfaces. Areas of no disturbance shall include steep slopes, steep slope buffers and the critical root zone of each tree proposed for preservation.
Average percent of slope
The "average percent of slope" of a zoning lot is the average slope of all portions of a zoning lot excluding steep slopes and shall be determined according to the following equation:
S - average percent of slope
I - contour interval in feet
L - combined length of contour lines in feet, excluding those portions bordering or lying within areas having a slope of 25 percent or greater and meeting the definition of steep slope
A - gross area in square feet of the zoning lot, excluding those portions of the zoning lot having a slope of 25 percent or greater and meeting the definition of steep slope. For a proposed site alteration on a tract of land not within a zoning lot, the portion of such tract of land owned by the applicant shall be considered to be part of the zoning lot.
100 - factor which yields slope as a percentage
CALCULATING AREAS HAVING A SLOPE EQUAL TO OR GREATER THAN 25 PERCENT (illustrative example)
contour interval in feet
X - distance between contour lines which indicates a slope of 25 percent
In order to calculate the area having a slope equal to or greater than 25 percent, one can use a map with two-foot contour intervals and a scale of one inch equals 20 feet, such as the map pictured above. A 25 percent slope, on a map with two-foot contour intervals, is indicated by contour lines which are 8.0 feet apart, rounded to the nearest tenth (0.1) of a foot. On a map whose scale is one inch to 20 feet, 8.0 feet is represented by 0.4 of an inch, rounded to the nearest tenth (0.1) of an inch.
Identify where the contour lines are 0.4 of an inch or less apart. Connect these contour lines (as indicated by the heavy lines on the map) and calculate the area.
A "buildable area" is a portion of a zoning lot excluding steep slopes.
Caliper (of a tree)
"Caliper" of a tree is the diameter of a tree trunk measured 4 feet, 6 inches from the ground. If a tree splits into multiple trunks below 4 feet, 6 inches from the ground, the trunk is measured at its most narrow point beneath the split.
Critical root zone
The "critical root zone" of a tree is the area containing the roots of a tree that must be maintained and protected to ensure the tree's survival. The area of the critical root zone is measured as one radial foot for every caliper inch of the tree, with a required minimum of four radial feet and maximum of 22 radial feet, measured from the surface of the tree trunk at grade.
A "hillside" is defined as ground where the ratio of change in elevation to horizontal distance results in a 10 percent or greater slope or average percent of slope.
For the purposes of this Chapter, a "site alteration" is an alteration on any vacant tract of land, land with minor improvements or any tract of land containing buildings or other structures. Site alterations shall include the following:
(a) removal of topsoil;
(b) excavating, filling, land contour work and other topographic modifications where the ground elevation of the land existing on June 30, 1987, is modified by two feet or more;
(c) dumping, changes in existing drainage systems and changes in grade, alignment or width of public rights-of-way; or
(d) removal of vegetation beyond 15 feet of the foundation of an existing building, except when the plant materials' continued presence would create hazards or dangers (such as an area affected by storm or plant disease) to persons, property or other plant material which it would not be possible or practical to eliminate by pruning or routine maintenance.
A "staging area" is any area on a zoning lot or other tract of land used during the construction of a development, enlargement or site alteration for the purposes of stockpiling soil or construction materials; storing, cleaning or servicing construction equipment, vehicles or tools; or storing leachable construction products, gases or other materials used to clean or service vehicles, equipment or tools.
A "steep slope" is a portion of a zoning lot or other tract of land with an incline of 25 percent or greater. However, a portion of a zoning lot or other tract of land with an incline of 25 percent or greater shall not be considered a steep slope if it occupies an area of less than 200 square feet or has a dimension of less than 10 feet, measured along the horizontal plane, unless such portions in the aggregate equal 10 percent or more of the area of the zoning lot.
Steep slope buffer
A "steep slope buffer" is a 15-foot wide area having a slope of less than 25 percent that adjoins the entire length of the crest of a steep slope.
Tier I site
A "Tier I site" is a zoning lot or other tract of land having an average percent of slope of less than 10 percent.
Tier II site
A "Tier II site" is a zoning lot or other tract of land having an average percent of slope equal to or greater than 10 percent.
"Topsoil" is soil containing undisturbed humus and organic matter capable of sustaining vigorous plant growth and is generally the top six inches of soil.
A "tree credit" is a credit for preserving an existing tree of six-inch caliper or more which is counted toward a tree preservation requirement, or a credit for a newly planted tree of three-inch caliper or more which is counted toward a tree planting requirement.
Tree protection plan
A "tree protection plan" is a plan that modifies the area of no disturbance around a tree proposed for preservation while protecting and preserving the tree during construction. A tree protection plan is prepared by an arborist certified by the International Society of Arborculturists (ISA) or equivalent professional organization that includes:
(a) a survey of the current condition and health of such trees of six-inch caliper or more;
(b) methods for tree protection and preservation based on best management practices, including the prevention of damage due to compaction, grade and drainage pattern changes and tunneling for utilities;
(c) a schedule for site monitoring during construction;
(d) a procedure to communicate protection measures to contractor and workers; and
(e) post-construction treatment.
In harmony with the general purpose and intent of this Resolution and the general purposes of the Special Hillsides Preservation District, the regulations of the districts upon which this Special District is superimposed are supplemented or modified in accordance with the provisions of this Chapter. Except as modified by the express provisions of this Chapter, the regulations of the underlying districts remain in effect.
Any development, enlargement or site alteration on the buildable area of a zoning lot where the average percent of slope is less than 10 percent shall be regulated by the provisions set forth in Section 119-10 (PROVISIONS REGULATING TIER I SITES). Any development, enlargement or site alteration on the buildable area of a zoning lot having an average percent of slope equal to or greater than 10 percent shall be governed by the provisions set forth in Section 119-20 (PROVISIONS REGULATING TIER II SITES).
No development, enlargement or site alteration is permitted within any area of no disturbance on a zoning lot or other tract of land. Areas of no disturbance shall remain in their natural state, except:
(a) for steep slopes or steep slope buffers, an authorization may be granted by the City Planning Commission, pursuant to Section 119-30 (SPECIAL REVIEW PROVISIONS);
(b) vegetation and topsoil may be removed from a steep slope buffer during construction on a Tier I site, provided that the development, enlargement or site alteration complies with the requirements of Sections 119-215 (Landscaping controls to preserve trees, shrubs and ground cover), 119-217 (Tier II controls during construction) and 119-22 (Tier II Submission Requirements); or
(c) in accordance with a tree protection plan.
Those portions of a zoning lot having areas of no disturbance, however, may count as lot area for the purposes of the applicable regulations on yards, floor area ratio, open space ratio or maximum number of dwelling units or rooming units.
The following uses, including enlargements to such uses, shall not be permitted within the Special Hillsides Preservation District unless an authorization is granted by the Commission pursuant to Section 119-30: community facility uses, group parking facilities of 30 cars or more, whether or not they are necessary to satisfy parking requirements.
When the Special Hillsides Preservation District is designated on a public park, or portion thereof, site alterations, the construction of new park-related facilities such as, but not limited to, roadways, parking lots, comfort stations, storage facilities, swimming pools, eating establishments, tennis courts, amphitheaters and stadiums, and improvements to existing park-related facilities, shall not be subject to the provisions of Sections 119-10 or 119-20 but shall require an authorization from the Commission, pursuant to Section 119-31 (Authorizations).
Any development on a zoning lot having an average percent of slope of 10 percent or greater, which is used predominantly for residential use, may be treated as a large-scale residential development and special authorizations or special permits for such developments may be granted in accordance with the provisions of Article VII, Chapter 8, as modified herein, regardless of whether such development will have the area, number of buildings or number of dwelling units specified in the definition of large-scale residential developments as set forth in Section 12-10 (DEFINITIONS). However, bonuses that may be granted for large-scale residential developments under the provisions of Sections 78-32 (Bonus for Good Site Plan), 78-33 (Bonus for Common Open Space) or 78-35 (Special Bonus Provisions) may not be granted for developments that have less than the minimum area, number of buildings or number of dwelling units required by the definition of a large-scale residential development.
Notwithstanding the provisions of Section 78-06 (Ownership), a zoning lot having an average percent of slope of 10 percent or greater that is the subject of an application under this Section may include adjacent properties in more than one ownership, provided that the application is filed jointly by the owners of all the properties included. Any subdivision of the tract before, during or after development shall be subject to the provisions of Section 78-51 (General Provisions).
Within the Special Hillsides Preservation District, no zoning lot existing on June 30, 1987, may be subdivided without certification by the City Planning Commission that the proposed subdivision complies with the regulations of the Special Hillsides Preservation District and that all hillsides are preserved to the greatest extent possible under future development options.
A plan for such subdivision shall be filed with the Commission and shall include a survey map indicating existing topography at two-foot contour intervals and all individual trees of six-inch caliper or more.
When a zoning lot existing on June 30, 1987, is intended to be subdivided and is more than five acres, a site plan of the entire subdivision shall be filed with the Commission. The site plan shall include the proposed vehicular circulation system within the area, block and zoning lot layouts and any other information required by the Commission.
In the event that any zoning lot proposed for subdivision contains a development, enlargement or site alteration that has been undertaken contrary to the provisions of this Chapter, the Commission shall not approve the subdivision until violations are removed from the zoning lot, in accordance with the Commission's requirements under Section 119-40 (COMPLIANCE).
The parking regulations applicable to lower density growth management areas are modified to allow required accessory parking spaces to be located in a front yard.
Tier I sites shall be regulated by the provisions set forth in this Section, inclusive.