The specific purposes of the HD hillside development overlay district are to:
A. 
Maintain an environmental equilibrium consistent with existing vegetation, soils, geology, slopes, and drainage patterns, and to preserve the natural topography, including swales, canyons, knolls, ridgelines, and rock outcrops, wherever feasible;
B. 
Avoid development that would result in unacceptable fire, flood, slide, or other safety hazards;
C. 
Avoid unwarranted, high maintenance costs for public facilities;
D. 
Provide a mechanism for flexible design of residential development projects in hillside areas so that development may be concentrated in those areas with the greatest environmental carrying capacity and areas with low environment carrying capacity developed at very low density or reserved as permanent open space;
E. 
Avoid residential densities that would generate traffic requiring extensive grading to provide an adequate street system.
(Ord. 87-4 N.S., 1987)
The HD hillside development overlay district may be combined with any R district and applied to property, portions of which have a natural gradient in excess of 20 percent (20 feet of vertical distance for each 100 feet of horizontal distance). It may be initiated by an applicant or by the city under the procedures established in Chapter 17.120 BMC, Amendments. Each HD hillside development overlay district shall be shown on the zoning map by adding the designator "-HD" to the base district designation, and a hillside development plan shall be required for all development, consistent with the provisions of BMC § 17.50.060 et seq.
(Ord. 87-4 N.S., 1987)
Development regulations shall be those of the base district with which an HD district is combined, unless modified by another overlay district; provided, that the requirements in the following schedule shall be in addition and shall govern where conflicts arise. The first column of the schedule prescribes basic requirements for permitted and conditional uses. Letters in parentheses in the "Additional Regulations" column refer to the "Additional Development Regulations" following the schedule.
HD District: Development Regulations
Basic Regulations
Additional Regulations
Minimum Lot Area
(A)
Minimum Site Area Per Unit (sq. ft.)
(B)
Minimum Yards:
Front (feet)
15
(C)(D)
Side (feet)
10 percent of width;
5 feet min.;
10 feet max.
(D)
Corner Side (feet)
10 percent of width;
10 feet min.;
15 feet max.
(D)
Rear (feet)
25
(D)
Maximum Height (feet)
30
(E) (F) (G)
Screening of Mechanical Equipment
(H)
Exterior Structural Supports
(I)
Driveways and Off-Street Parking
(J)
HD District: Additional Regulations
(A) See BMC § 17.50.090, Hillside development plan – Minimum lot size – Maximum number of dwelling units.
(B) As determined by slope/density formula in BMC § 17.50.050.
(C) If the existing lot elevation at the rear of the normally required front yard (20 feet) at its centerline is 10 feet above or below the elevation of the adjoining street, the minimum front yard shall be 10 feet, but the garage proscenium shall be set back at least 20 feet from the front property line.
(D) See BMC § 17.70.150, Building projections into yards and courts.
(E) See BMC § 17.70.170, Measurement of height.
(F) Structures within 20 feet of the front property line shall not intercept a 1:1 daylight plane inclined inward from a height 20 feet above existing grade at the front setback line.
(G) See BMC § 17.70.180, Exceptions to height limits.
(H) See BMC § 17.70.210, Screening of mechanical equipment.
(I) Exterior structural supports and undersides of floors and decks not enclosed by walls and more than 15 feet high may be approved only if the development services director finds that no alternative type of construction is feasible, and fire-safety and design considerations have been adequately addressed.
(J) Driveways that are not entirely visible from both ends shall have passing turnouts. All driveways shall comply with minimum widths and maximum grades prescribed by the standard engineering specifications adopted pursuant to BMC Title 15, Buildings and Construction. A dwelling unit adjoining a street having parking prohibited on both sides shall provide a minimum of two independently accessible off-street parking places for guests. Required parking for guests may be in a required front yard if the existing lot elevation is 10 feet above or below street elevation at the rear of the normally required front yard, or within 100 feet of every dwelling unit. The provisions of this subsection shall apply only to lots created or developed after the effective date of the ordinance codified in this title.
(F) MINIMUM FRONT YARD: HILLSIDE OVERLAY DISTRICT
(The diagram is illustrative)
HD DISTRICT: SLOPE DENSITY RELATIONSHIP
Average Slope (percent)
Yield (Units per Gross Acre)
0 – 10
7
11
6.70
12
6.40
13
6.10
14
5.80
15
5.50
16
5.20
17
4.90
18
4.60
19
4.30
20
4.00
21
3.70
22
3.40
23
3.10
24
2.80
25
2.50
26
2.20
27
1.90
28
1.60
29
1.30
30
1.00
31
.90
32
.80
33
.70
34
.60
35
.50
36
.40
37
.30
38
.20
39
.10
40 or more
.05
(Ord. 87-4 N.S., 1987; Ord. 25-09 § 4)
A. 
The maximum number of dwelling units permitted by an HD plan shall be determined by the formula: N = A x Y, where:
"N" is the maximum number of units;
"A" is gross developable area in acres inclusive of any public right-of-way and easements established by a parcel map or subdivision map consistent with an HD plan but exclusive of any existing rights-of-way; and
"Y" (yield in units per net acre) is 7.00 for an average slope between 0 and 10 percent. For average slopes between 10 and 30 percent, the yield shall decline 0.30 per acre for each one percent increase in slope. For slopes between 30 and 39 percent, the yield shall decline 0.10 per acre for each one percent increase in slope; for average slopes of 40 percent or more, the yield shall be 0.05 per acre.
B. 
Slope shall be calculated by the formula:
S =
I x L x (.00229)
A
, where
S
=
Average ground slope in percent, calculated for the entire site, to be divided and rounded to the nearest whole number.
I
=
Contour interval in feet. The contour interval shall be 10 feet or less.
L
=
The combined length in feet of all contour lines within the site.
A
=
Gross area for the site in acres prior to further subdivision.
.00229
=
The factor for conversion of square feet to acres times 100 percent.
(Ord. 87-4 N.S., 1987)
A. 
A project in an HD district for which a grading permit is required shall have an approved HD hillside development plan prior to issuance of a grading permit or approval of a subdivision map.
B. 
An HD plan that will permit a subdivision of five or more parcels shall be approved, approved with conditions, or disapproved by the city council.
C. 
An HD plan that will only permit a subdivision of four or fewer parcels shall be approved, approved with conditions, or disapproved by the planning commission, with the commission's decision appealable to the city council.
(Ord. 87-4 N.S., 1987)
An application to approve an HD hillside development plan shall be initiated by a property owner or authorized agent. If the property is not under a single ownership, all owners shall join the application, and a map showing the extent of ownership shall be submitted with the application.
(Ord. 87-4 N.S., 1987)
An HD plan shall include any or all of the following items deemed necessary by the development services director to determine compliance with the purposes of this chapter:
A. 
A map of the HD plan area showing sufficient topographic data to indicate clearly the nature of the terrain and the type, location, and condition of mature trees and other natural vegetation.
B. 
A fully dimensioned site and circulation plan delineating proposed uses, building locations and density, public and private streets, and parking areas, and a conceptual grading plan indicating the nature and general extent of grading proposed. A tentative map prepared pursuant to BMC Title 16, Subdivisions, may be substituted for this requirement.
C. 
A soil engineering report including, but not limited to, data regarding the nature, distribution, and strengths of existing soils; conclusions and recommendations for grading procedures; design criteria for any identified corrective measures; and opinions and recommendations covering the adequacy of sites to be developed. The investigation shall be compiled by a California-registered soil engineer.
D. 
A geology report including, but not limited to, the surface and subsurface geology of the site; degree of seismic hazard; conclusions and recommendations regarding the effect of geologic conditions on the proposed development; opinions and recommendations covering the adequacy of sites to be developed; and design criteria to mitigate any identified geologic hazards. The investigation and report shall be compiled by a California-registered geologist or engineering geologist.
E. 
A hydrology report including, but not limited to, the hydrologic conditions on the site; possible flood inundation with existing development and with future development under the general plan and the HD plan; downstream flood hazards, including cumulative impacts of development in the drainage basin; natural drainage courses; conclusions and recommendations regarding the effect of hydrologic conditions on the proposed development; opinions and recommendations covering the adequacy of the site to be developed; and design criteria to mitigate any identified hydrologic hazards, including cumulative impacts consistent with these regulations. This report shall account for all runoff and debris from tributary areas and shall provide consideration for each lot or dwelling unit site in a proposed hillside development project. The investigation and report shall be compiled by a California-registered civil engineer experienced in hydrology and hydrologic investigation.
F. 
A three-dimensional scale model of the project site of a scale sufficient to evaluate the project as prescribed by the development services director. The development services director may waive this requirement if circumstances warrant.
G. 
A landscape plan consistent with the provisions of BMC § 17.70.190.
(Ord. 87-4 N.S., 1987; Ord. 25-09 § 4)
The city council or the planning commission, as the case may be, may approve an HD plan including lots smaller than those required by the base district, but shall not approve a total number of dwelling units on a parcel or in a subdivision greater than permitted by the slope/density formula established in BMC § 17.50.050. Restrictions on the number of dwelling units permitted shall be recorded with a subdivision map or prior to issuance of a zoning permit.
(Ord. 87-4 N.S., 1987)
A. 
General Procedures. An application for approval of an HD hillside development plan shall be processed as a use permit application in accord with the provisions of Chapter 17.104 BMC with the responsibilities for approval as prescribed in BMC § 17.50.060.
B. 
Required Findings. The planning commission or the city council, as the case may be, shall approve or conditionally approve a proposed hillside development plan upon finding that it:
1. 
Conforms to the general plan;
2. 
Complies with the land use and development regulations of the base zoning district, the HD overlay district, and any other overlay districts applied to the property; and
3. 
Can be adequately, reasonably and conveniently served by public services, utilities and public facilities.
(Ord. 87-4 N.S., 1987)
An HD plan shall become void two years following the date of approval unless actions specified in the conditions of approval have been taken or unless the initial approval was for a stated period longer than two years. An HD plan may be renewed by the planning commission or the city council, whichever approved the plan, upon application 30 but not more than 60 days prior to expiration if the planning commission or the city council finds that circumstances have not changed to make the plan inconsistent with the purposes of this chapter.
(Ord. 87-4 N.S., 1987)
Plans for a project requiring an HD plan shall be accepted for development plan review only if they are consistent with a valid HD plan and with all other applicable requirements of this code.
(Ord. 87-4 N.S., 1987)