The Hillside Development (HD) Overlay District is established
to ensure that development in hillside areas: Minimizes the potential
for earth movement and resultant hazards to life and property; protects
water quality by minimizing soil erosion and siltation; retains and
protects natural vegetation, natural water features and drainageways,
scenic quality and open space by minimizing vegetation removal in
sloped areas; assures the compatibility of new development with surrounding
areas; encourages site and building design that is consistent with
the natural topography in order to minimize the cost of providing
public infrastructure; provides for adequate access for emergency
services; and otherwise protects the public health and safety.
The HD Overlay District is applied in residential zoning districts
above 670 feet elevation or to development areas below 670 feet in
elevation where any portion of the development area exceeds 15 percent
slope as determined using the slope calculation described in SDC 3.3.520(A).
Development within the HD Overlay District is reviewed under
Type 2 procedure, submitted concurrently with the applicable application
for a: Site Plan Review, Property Line Adjustment, or a Partition
or Subdivision Tentative Plan.
(A)
All residential development within the HD Overlay District is subject
to the maximum development density requirements of this section, including,
but not limited to, the development of a detached single unit dwelling,
duplex, middle housing, or multiple unit housing.
(B)
Where the average slope of the portion of the development area below
670 feet in elevation is less than 15 percent, the number of dwelling
units allowed must be within the net density range provided below,
calculated in conformance with SDC 3.2.235.
For the purposes of this section, the “average slope”
is defined as follows:
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S
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=
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0.00229 I L
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A
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Where:
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S = Average % of slope for the area.
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I = Contour Interval (not greater than 10 feet).
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L = Summation of length of the contour lines within the area.
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A = Area.
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(C)
Where the average slope of the development area exceeds 15 percent
and/or is above 670 feet in elevation, an applicant may develop under
Option “A,” Option “B,” or a combination of
both, in conformance with this section. Option “A,” is
designed to correlate minimum lot/parcel sizes to the average slope
of the development area. Option “B,” is designed to allow
for a density transfer bonus to stimulate development on those portions
of the development area where the slope of the land is less than 15
percent.
(1)
OPTION “A”—AVERAGE SLOPE—MINIMUM LOT/PARCEL
SIZE. The site development requirements of the R-1 land use district
apply, with the exception of the minimum lot/parcel size and duplex
standards. Determination of minimum lot/parcel size where the slope
is 15 percent or greater is a 3-step process.
(a)
Step A-l. Determine the area of the lot/parcel where the slope of
the land is:
(i)
Less than 15 percent.
(ii)
From 15 percent to 35 percent.
(iii)
Greater than 35 percent.
Use the following formula to determine the % of slope:
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Vertical distance between contours =
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V x 100 = % slope
H
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Horizontal distance between contours
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Indicate the portions of the development area that are less
than 15 percent; from 15 percent to 35 percent; and greater than 35
percent then use a planimeter or other technology acceptable to the
City Engineer to determine the land area of each category.
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(b)
Step A-2. Determine the average slope of the portion of the development
area where the slope of land is from 15 percent to 35 percent by using
the following formula:
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S
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=
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0.00229 I L
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A
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Where:
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S = Average percent of slope for the area where the slope ranges
from 15 percent to 35 percent.
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I = Contour interval. (Not greater than 10 feet).
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L = Summation of the length of the contour lines within the
area where the slope is from 15 percent to 35 percent.
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A = Area in acres of the portion of the parcel where the slope
is from 15 percent to 35 percent.
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(c)
Step A-3. Determine the minimum lot/parcel size for the portion of
the development area where the slope of the land is greater than 15
percent by using the following table:
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Table 3.3-1
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Average Slope
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Minimum Lot/Parcel Size Per Dwelling Unit
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Minimum Per Lot/Parcel Frontage(1)*
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Less than 15% and below 670 feet
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See the applicable residential district density standards and
minimum lot size in SDC 3.2.215.
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Less than 15% on wooded lots(2)**
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10,000 sq. ft. per unit
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60 ft.
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15%—25%
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10,000 sq. ft. per unit
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90 ft.
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25%—35%
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20,000 sq. ft. per unit
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150 ft.
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Over 35%
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40,000 sq. ft. per unit
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200 ft.
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(1)
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Panhandles are permitted only when requirements of this section
pertaining to fire protection and lot/parcel size are met and the
lot/parcel cannot be served with a public street. Minimum frontage
standards for all other lots/parcels may be amended by the Director
when it is found that the topography or location of natural features
prevent achieving the standard. Cul-de-sac frontages are as specified
in SDC 3.2.215.
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(2)
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A lot/parcel that is 10,000 square feet or larger, above 670
feet in elevation, which contains more than 5 trees 8 inches or greater
dbh.
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(2)
OPTION “B” DENSITY TRANSFER BONUS. In order to promote
the preservation of natural slopes greater than 25 percent, and encourage
solar access, development density transfer is encouraged when dividing
land with slopes greater than 25 percent. The density transfer is
only feasible where there are sizable portions of the development
area which have slopes less than 25 percent. Determination of the
density transfer bonus is a 4-step process:
(b)
Step B-2. Determine the average slope of the area of the parcel where
the average slope of the land is greater than 15 percent by using
the formula identified in Option A, Step A-2.
(c)
Step B-3. Determine the number of potential lots/parcels for the
total development area which could have been permitted, for the portion
of the parcel where the average slope is greater than 15 percent,
if the average slope option had been considered by using Table 3.3-1
in Option “A,” Step A-3.
(d)
Step B-4. Multiply the number of potential lots/parcels by 1.2 to
determine the density that may be transferred to those sections of
the development area where the slopes are less than 25 percent. In
no case shall the density of the developed portion of the site exceed
8 dwelling units per developable acre, (i.e., excluding streets and
open space). Land of greater than 15 percent average slope used to
calculate a density transfer bonus shall be maintained as permanent
open space or dedicated for park use. Modification of standards as
specified in SDC 3.3-535 may be applied to the entire development
area.
(6443)
(A)
Streets shall be contoured in hillside areas to minimize environmental
and scenic disruption.
(B)
Street grades may exceed the 12 percent local street standard specified
in SDC 4.2.105, Street Standards—Public, only where topographical
conditions make it impractical to meet the 12 percent standard, subject
to the following conditions:
(1)
No new driveways or intersections shall be permitted where street
grades exceed 12 percent.
EXCEPTION: Lots/parcels created prior to the adoption
of the Comprehensive Zoning Code, 1982.
(2)
No street with a grade of 15 percent or greater shall be permitted
for a distance of more than 200 feet.
(3)
In no case shall a street grade exceed 18 percent for any distance.
Where the buildable portion of the land to be developed exceeds
15 percent average slope, the following reports are required and their
conclusions applied in order to prevent or mitigate possible hazards
to life and property and adverse impacts on the natural environment,
consistent with the purpose of this section. The applicant shall fund
peer review of the reports as deemed necessary by the City Engineer.
(A)
Geotechnical Report. This report shall include data regarding the
geology of the site, the nature, distribution, and strength of existing
soils, conclusions and recommendations for grading procedures, design
criteria for corrective measures, and options and recommendations
to maintain soil and slope stability and minimize erosion of the site
to be developed in a manner imposing the minimum variance from the
natural conditions. Where geologic conditions of the site indicate
that a hazard may exist, the report shall show that the proposed subdivision
or partition shall result in lots/parcels that are suitable for development.
The investigation and report shall be prepared by a civil engineer/geologist
or a geotechnical engineer.
(B)
Grading Plan Report. This plan shall include the following information:
(1)
Existing and proposed details and contours (5-foot intervals) of
property;
(2)
Details of terrain and area drainage;
(3)
Location of any existing buildings or structures on the property
where the work is to be performed, the location of any existing buildings
or structures on land of adjacent owners which are within 100 feet
of the property or which may be affected by the proposed grading operations,
and proposed or approximate locations of structures relative to adjacent
topography;
(4)
The direction of drainage flow and the approximate grade of all streets with the final determination to be made as specified in subsection (D), below;
(5)
Limiting dimensions, elevations, or finished contours to be achieved
by the grading, including all cut and fill slopes, proposed drainage
channels, and related construction;
(6)
Detailed plans and locations of all surface and subsurface drainage
devices, walls, dams, sediment basins, storage reservoirs, and other
protective devices to be constructed with, or as a part of, the proposed
work, together with a map showing drainage areas, the complete drainage
network, including outfall lines and natural drainageways which may
be affected by the proposed development, and the estimated run-off
of the area served by the drains;
(7)
A schedule showing when each phase of the project will be completed,
including the total area of soil surface which is to be disturbed
during each stage, and estimated starting and completion dates; the
schedule shall be drawn up to limit to the shortest possible period
the time that soil is exposed and unprotected. In no event shall the
existing “natural” vegetative ground cover be destroyed,
removed, or disturbed more than 15 days prior to grading or construction
of required improvements. Within 15 days of grading or other pre-development
activity that removes or significantly disturbs ground cover vegetation,
exposed soil shall either be built upon (i.e., covered with gravel,
a slab foundation or other construction), landscaped (i.e., seeded
or planted with ground cover) or otherwise protected; and
(8)
The Grading Plan shall be prepared by a civil engineer.
(C)
Vegetation and Re-vegetation Report. This report shall be as specified
in SDC 5.19.120, if tree felling is proposed.
(D)
Verification of Slope and Grade Percentages. Prior to acceptance
of the Final Plat, all streets shall be cross-sectioned and their
center-lines staked in the field, to determine the accuracy of preliminary
slope and grade percentages. If there are significant differences
between preliminary and final grade and slope determinations, i.e.,
density or street gradients exceed the limits specified in this section,
the Tentative Plan shall be modified to reflect the revised information
and resubmitted.
(E)
Development Plan Report. A proposed development plan shall be submitted,
depicting building envelopes for each lot/parcel, including driveway
approaches and all other associated impervious surface areas. The
applicant shall specify whether trees will be felled under one Tree
Felling Permit, as specified in SDC 5.19.100, as part of the subdivision
construction process or by separate Tree Felling Permit for each individual
lot/parcel prior to the issuance of a Building Permit. The plan shall
be based upon the findings of the required reports in this section
and the lot/parcel coverage standards of SDC 3.2.215. Building envelopes
shall be specified in Covenants, Conditions, and Restrictions recorded
with the Subdivision Plat.
The Director may modify the standards of this code, as they
apply to the entire development area, within the following prescribed
limits:
(A)
Front, side and rear yard setbacks may be reduced to zero (when
permitted by the Building Safety Codes); provided, however, where
attached dwellings are proposed, there shall not be more than 5 dwelling
units in any group.
(B)
The reduction of public right-of-way, pavement width, and/or
requirements for the installation of sidewalks as specified in Table
4.2.1, may be allowed if provisions are made to provide more off-street
parking spaces than the number of suggested parking spaces listed
for the particular use in SDC 4.6.125. The Approval Authority may
require proposed parking lots, spaces, or driveways to be arranged
as collective private driveways, shared parking areas, and on-street
parallel parking bays where topography, special traffic, building,
grading, or other circumstances necessitate additional regulation
to minimize land and soil disturbance and minimize impervious surface
areas.
(Ord. 6465, 11/20/2023)
Additional fire protection requirements may be required in hillside
development areas which are considered vegetated areas subject to
wildfires as determined by the Fire Marshal.
(A)
All buildings with a gross area in excess of 1,500 square feet shall
be constructed within 50 feet of an approved fire lane or public street.
Fire apparatus access shall be provided to within 50 feet of the building
(this may mean modifying the driveway designs for width, grade and
construction material in order to meet fire lane requirements). Installation
of a residential fire sprinkler system will be considered as an alternative
to the requirement to be within 50 feet of a fire lane or street.
(B)
The developer shall specify in the recorded Covenants, Conditions
and Restrictions that a wildfire defense plan for each lot/parcel,
approved by the Fire Marshal, will be required prior to the issuance
of a Building Permit.
(C)
All buildings located in or adjacent to vegetated areas subject to
wildfires shall have Class A or B roofing as specified in the Oregon
State Structural Specialty Code.
