Petaluma Municipal Code Ch. 16 Hillside Protection

Sections:

16.010 Purpose.

16.020 Objectives.

16.030 Applicability.

16.040 De9nitions.

16.050 General Provisions.

16.060 Single Lot Development.

16.070 Hillside Subdivisions.

This chapter establishes the regulations for development and alteration of properties in hillside and ridgeline

areas in order to preserve the essential scenic and natural resources that deOne the character of Petaluma, and to

implement the following General Plan goals and policies:

A. General Plan: Land Use, Growth Management and the Built Environment Element.

1. Preserve the essential scenic and natural resources of the open ridgelines and hillsides that help deOne

the character of Petaluma. Goal 2-G-2

2. Allow development in hillside areas that preserve ridgelines and are site sensitive. Policy 2-P-16

a. Protect unique natural features, including landforms, mature trees and their surrounding habitat,

and ridgelines, by requiring location of structures away from these assets.

b. Requiring architectural design that rePects the natural form of the hillside setting in order to

minimize visual and environmental impacts.

c. Prevent the signiOcant alteration of hillside topography through grading and paving.

d. Use visually unobtrusive building materials.

3. Retain ridgelines and prominent hillsides as open space through appropriate clustering and/or transfer

of density to other parts of a development site. Policy 2-P-17

B. General Plan: Community Design, Character and Sustainable Building Element.

1. Allow for clustering of residential units in the hills, permitting smaller lot sizes where clustering and

common space is maintained and proposed development corresponds to stipulated density ranges. Policy

3-P-71

2. Reinforce the existing character of the hillside neighborhoods, preserving topography and ridgelines.

Goal 3-G-12

3. Minimize grading, to all extent possible, stepping development into and with the natural topography.

Policy 3-P-80

4. Preserve trees and enhance the natural woodland ecology of the South Hills subarea. Policy 3-P-81

C. General Plan: Health and Safety Element.

1. On sites with slopes greater than 30 percent, require all development to be clustered outside of the 30

percent slope areas (and preferably on land less than 15 percent in slope) where possible. Policy 10-P-1

2. Ensure that new development on hillsides is constructed to reduce erosion and landslide hazards and in

compliance with any hillside regulations, including but not limited to: Policy 10-P-2

a. Limit cut slopes to 3:1, except where an engineering geologist can establish that a steeper slope

would perform satisfactorily over the long term.

b. Encourage the use of retaining walls or rock-Olled crib walls as an alternative to high cut slopes.

c. Ensure revegetation of cut-and-Oll slopes to control erosion. Plant materials for revegetation should

not be limited to hydro-seeding and mulching with annual grasses. Trees add structure to the soil and

take up moisture while adding color and diversity.

d. Ensure blending of cut-and-Oll slopes within existing contours, and provision of horizontal variation,

in order to mitigate the artiOcial appearance of engineered slopes.

e. Ensure structural integrity of sites previously Olled before approving redevelopment.

The following objectives are intended to ensure that all hillside development is in compliance with the goals,

policies, and implementing strategies of Petaluma’s General Plan.

A. Ensure high quality projects.

B. Ensure that projects are designed to Ot with and avoid site constraints.

C. Minimize the potential for geologic failures, Ores, and Poods that result from or adversely impact new

development.

D. Maintain the natural, open space character of the hillsides.

E. Promote public enjoyment of the hillsides, including the creation of hillside hiking/biking trails and open

space.

F. Maintain consistent visual character of Petaluma's hillside backdrop, for the community as a whole, by

discouraging developments of excessive visual prominence.

G. Ensure that development does not dominate, but rather visually blends and achieves harmony between the

natural and built environment.

H. Conserve the natural features of the site such as topography, natural drainage, vegetation (including native

and signiOcant trees), wildlife habitats, movement corridors, and other physical features.

I. Promote sustainability.

This chapter applies to properties zoned RR, R1, R2, R3, R4, R5, and P.U.D. that are covered by the provisions of

this Chapter. Section 16.060(B) prescribes the applicability of this Chapter to property proposed for New

Development, as deOned by the Chapter. Section 16.070(B) prescribes the applicability of this Chapter to property

proposed for subdivision.

The following deOnitions apply to this chapter. Where there is a conPict between other deOnitions in this

Ordinance and the deOnitions in this section, the deOnitions in this section shall apply to this Chapter.

A. Contour. A line drawn on a plan which connects points of equal elevation.

B. Cut. The mechanical removal of earth material.

C. Cut and 8ll. The excavating of earth material in one place and the depositing of it as Oll in an adjacent place.

D. Demolition. The removal of 50% or more of the exterior walls of a building or structure. Demolition includes

the relocation of a building from one parcel of land to another, and also includes the raising of an existing

structure beyond what is required for a new foundation.

E. Density. The number of dwelling units per net acre.

F. Fill. A deposit of earth material placed by artiOcial means.

G. Grading. To bring an existing surface to a designed form by excavating, Olling, or smoothing operations.

H. Major Subdivision. The subdivision of a parcel into more than four (4) parcels.

I. Minor Subdivision. The subdivision of a parcel of land into 4 or fewer parcels or 4 parcels and a remainder

parcel.

J. Natural Grade. The contour of the ground surface before grading.

K. New Development. Includes the development of a vacant parcel, new construction of a primary building on a

developed parcel, and the construction of a primary building when the primary building on a parcel has been

demolished.

L. Opportunities and Constraints Map. A graphic characterization of the parcel and the immediately adjacent

properties that includes the physical and natural amenities and limitations of the site including, but not limited to,

unique natural site features, landforms, woodlands, landslides, drainage patterns, creeks, mature trees and their

surrounding habitat, ridgelines, areas with a slope of more than 30 %, roads or trails, structures, and property

lines and a topographic description of the site using contours at 1’, 2’ or 5’ intervals as appropriate.

M. Ridgeline. A line connecting the highest points along a ridge separating drainage basins or small scale

drainage systems from one another.

N. Slope. An inclined ground surface, the inclination of which is expressed as a ratio of the vertical distance (rise),

or change in elevation, to the horizontal distance (run). The percent of any given slope is determined by dividing

the rise by the run, multiplied by one hundred.

O. Slope density formula. The size of lots allowed in a new subdivision based on a formula that increases the

minimum lot size allowed as the slope of the site increases.

P. South Hills. The South Hills is the area identiOed as the South Hills subarea on the General Plan Subareas Map

(General Plan Figure 2-1, Planning Subareas).

Q. View Platform. The following speciOc locations selected as vantage points from which Oeld observations are

made to assess the visual impact of development within the City:

? B Street easternmost (nearest the Petaluma River) terminus

? C Street easternmost (nearest Petaluma River) terminus

? D Street at the Petaluma River Drawbridge

? Lakeville Street at the Rail Depot

? CaulOeld Lane Overpass

? Corona Road Overpass

? Bodega Avenue from the City limit to the urban growth boundary

? D Street in the vicinity of the City limit/urban growth boundary

? I Street from the City limit to the urban growth boundary

? Penry Park

? Schollenberger Park

? Steamer Landing Park

? Roof of the “C” Street parking garage

? Terminated Vistas as identiOed in the Central Petaluma SpeciOc Plan (shown on SMART Code

Thoroughfare Map)

R. Visual Analysis. A visual representation of the proposed project that includes the modiOcations and

improvements to the site that would result from the project. The visual analysis is prepared from the vantage

point of an identiOed view platform. A visual analysis may be prepared using the following methods:

? Photographic exhibit

? Computer simulation

? Story poles

? Street elevations or other means of graphic representation that takes into account enough of the

neighboring structures or site characteristics to provide a sense of massing and scale.

? Other methods may be approved by the decision making authority.

S. West Hills. The West Hills is the area identiOed as the West Hills subarea on the General Plan Subareas Map

(General Plan Figure 2-1, Planning Subareas).

A. Purpose. The purpose of this Section is to provide design direction for hillside projects in order to create

development that is compatible with and appropriate for the hillside setting, and is consistent with the objectives

of this chapter and the goals and policies of the General Plan.

B. Applicability. Section 16.050 applies to new development as deOned by this Chapter and the subdivision of

property subject to the requirements of this Chapter. Section 16.060 provides speciOc requirements that apply to

Single Lot Development. Section 16.070 provides speciOc requirements that apply to Hillside Subdivisions.

C. Opportunities and Constraints Map. An Opportunities and Constraints Map should be prepared prior to siting

any proposed improvements (structures, roads, driveways, utilities, fencing, etc.). An opportunity and constraints

map includes, but is not limited to, the location of landslides, drainage patterns, creeks, trees with a trunk diameter of 4" or more and their surrounding habitat, ridgelines, existing roads and/or trails, structures, areas

with a slope of more than 30%, and property lines. The purpose of the Map is to assist in the following:

? Identifying the site features that should be preserved and retained;

? Determining the best location for the building(s);

? Determining the location for the road and/or driveway;

? Determining how best to site improvements to work with the natural topography and reduce grading;

and

? Determining the best use of retaining walls to reduce the amount of grading.

D. Visual Analysis. The purpose of the visual analysis is to simulate the impact of the proposed project within the

context of its surroundings. When siting and designing the improvements for the project, consideration should be

given to the potential visual impact of the project on community views of hillsides and ridgelines. In order to

evaluate the potential impact of a project on community views, speciOc view platforms have been identiOed. When

selecting a view platform(s) for the visual analysis, priority should be given to those platforms that provide the

greatest community view of the project. Depending on the location and visibility of the project, a visual analysis

may need to be prepared from more than one view platform. A visual analysis includes site improvements

(structures, roads, driveways, etc.) and site modiOcations (tree removal, grading, retaining walls, fences, etc.).

E. Site Design. The following should be considered in order to minimize grading, reduce the potential visual

impact, and to maintain the existing features of the site.

1. Site buildings and other improvements (i.e., roads and driveways) to conform to topography and take

advantage of existing site features (see Figures 16.1 and 16.2).

2. Limit building pads to the area immediately beneath buildings or driveways, or as required by the

   geotechnical report or Building Code.

   3. Reduce the visual prominence of development as viewed from identiOed community “viewing platforms.”

   4. Site buildings to allow adequate space for tree plantings or other screening.

   5. Avoid fence lines that daylight ridgelines, are highly visible from a distance, and/or separate

development parcels from open space (see Figure 16.3). Fences should be transparent (wire mesh, deer

fencing, etc.). If chain link or wire mesh Oner than 4" is used, it should be Onished with a dark colored coating

material.

Figure 16.1 Recommended

Figure 16.2 Recommended

Figure 16.3 Not Recommended

F. Grading and Retaining Walls. The following should be considered in order to minimize grading and to preserve

the natural topography of the site.

1. Design grading to conserve natural topographic features and appearances by minimizing the amount of

cut and Oll and by means of land form grading to blend graded slopes and benches with the natural

topography; straight graded cut and Oll slopes are discouraged.

2. Design grading to retain major natural topographic features (i.e., canyons, knolls, ridgelines, and

prominent landmarks rock outcroppings, and drainage ways).

3. Discourage building pads created on Oll (see Figure 16.5). Cut pads are preferred (see Figure 16.3).

4. Utilize grading to help set structures and roads into the hillside, not to create elevated pads (see Figures

16.1 and 16.2).

5. The limited use of retaining walls may be allowed when it can be demonstrated that their use will

substantially reduce the amount of grading.

6. Retaining walls should not be used to create large, Pat yard areas.

7. Retaining walls should blend with the natural topography, follow existing contours, and be curvilinear to

the greatest extent possible.

8. Retaining walls should not be higher than Ove feet. Where an additional retained portion is necessary

due to unusual or extreme conditions (e.g., lot conOguration, steep slope, or road design), the use of multiple-

terraced, lower retaining structures is preferred.

9. Terraced retaining walls should be separated by at least a three foot planting pocket and should include

appropriate landscaping.

10. Retaining walls that are visible from a public street should have a veneer of natural stone, stained

concrete, or earth toned textured surface to help blend the wall with the natural hillside environment and to

promote a rural character.

G. Roads and Driveways.

1. Roads should be designed to minimize excessive cutting.

2. Driveway lengths should be minimized and common driveways should be planned for in subdivision and

single lot site planning.

3. Roads should be pedestrian-friendly where feasible, with trails to open spaces at ridgetops, so long as

the sidewalk or improvement does not create excessive grading or conPict with Fire Department or Public

Works requirements.

H. Landscape Planting and Tree Preservation.

1. Compliance with Chapter 17 (Tree Preservation).

2. Submittal of an arborist’s report and/or tree preservation and protection plan as required by Section

17.055 (Project Arborist Requirements).

3. Provide landscape planting adjacent to retaining walls. Such planting should include a combination of

non-invasive trees, shrubs, and vines to screen the wall.

4. Avoid the use of invasive species.

5. Utilize plant materials to screen structures, frame views, disguise building edges and understories, break

up expansive walls, connect structures to the land and reduce the apparent bulk of structures.

6. Shade potentially rePective surfaces with tree canopies where appropriate, except when needed as solar

access for rooftop solar panels

7. Revegetate cut and Oll slopes.

8. Encourage the planting of water conserving and erosion control plant materials.

A. Purpose. To ensure that the development of parcels subject to the requirements of this Chapter is consistent

with the General Plan goals and policies related to hillside development, and is not visually prominent when

viewed from a community “viewing platform”.

B. Applicability. Section 16.060 applies to New Development, as deOned by this chapter, on any parcel located in

the South Hills and West Hills, as deOned by this Chapter.

C. Site Plan and Architectural Review. Planning Commission approval is required for new development in the

South Hills and West Hills.

D. Development Standards. Any parcel subject to this Chapter is also subject to the requirements of the zoning

district in which the parcel is located. Where the requirements of the underlying zoning district conPict with the

requirements of this chapter, the requirements of this Chapter shall control.

1. Building Height. 30 vertical feet from grade to the uppermost point of the roof as calculated below (see

Figures 16.3, 16.4 and 16.5). No point of any structure shall be more than 30’ above the grade directly

beneath that point.

Figure 16.3 Height Limit when Graded for Foundation Only

Figure 16.4 Height Limit when Graded for Flat Pad

Figure 16.5 Height Limit when Adding Fill

2. Setbacks. As prescribed by the underlying zoning district in Tables 4.6 through 4.9.

E. Exception to Required Setback. An exception to the setback required by the underlying zoning district may be

provided for as follows:

1. Primary Structure. A primary structure may encroach into a required setback for a distance of not more

than one-half of the required setback, subject to approval by the Planning Commission, if it can be found that

the decrease minimizes the impact of hillside development and grading and is consistent with the guidelines

contained in this chapter. If such a reduction is granted, a compensating increase in setback is required in the

opposing setback. For example, a Ove-foot (5’) reduction in a front setback would increase the rear setback by

Ove feet (5’).

2. Required Covered Parking. Required covered parking may encroach into a required front and/or side yard

setback if the decrease minimizes the impact of hillside development and grading and is consistent with the

guidelines contained in this chapter.

Findings Required.When the Planning Commission approves a reduction in the required setback, Ondings to

support the granting of the exception shall be provided.

F. Additional Setback Required. In order to protect signiOcant natural resources or to reduce visual prominence of

a proposed development, the Planning Commission may require building setback(s) that exceed(s) the required

setback of the underlying zoning district.

G. Exception to Retaining Wall Height (Section 13.050). For projects subject to Section 16.060, a maximum exposed

retaining wall height of Ove feet (5’) may be permitted with Planning Commission approval.

H. Site Design. The following site design guidelines shall be taken into consideration and incorporated into the

design of a hillside lot whenever possible. Conformance with these guidelines will be determined by the Planning

Commission.

1. Development patterns that form visually protruding or steeply cut slopes for roads or lots should be

avoided.

2. Building pads, including spaces leveled for foundations and the grading for driveways and yards, should

be as small as possible.

3. Building construction and related site grading should not signiOcantly disturb any ephemeral or

perennial watercourse on the site.

4. Buildings should be located to take advantage of existing vegetation for screening.

I. Architectural Design. The following architectural design guidelines shall be taken into consideration and

incorporated into the design of a hillside lot whenever possible. Conformance with these guidelines will be

determined by Planning Commission as part of project review.

1. Design buildings to conform to the natural topography and hillside setting of the site; to follow the

contours of the site; and to blend with the existing terrain in order to reduce bulk and mass.

2. Scale structures to Ot the surroundings, and not visually dominate the landscape. The apparent size of

exterior wall surfaces visible from oR site may be minimized through the use of single story elements, split

level foundations, varying setbacks and structure heights, and landscaping, all designed to break up massive

forms.

3. Design buildings to minimize bulk, mass and volume.

4. Bulk and Mass. Bulk and mass should be minimized when developing a hillside parcel. The following

methods may be used to minimize the bulk and mass of a building.

a. Keep building forms simple (see Figures 16.1 and 16.2).

b. Avoid architectural styles that are inherently viewed as massive and bulky.

c. Utilize grading cuts, rather than Olls, to create building pads.

d. Excavate or use below-grade rooms to reduce eRective bulk. The visual area of the building can be

minimized through a combined use of grading and landscaping techniques. Earth sheltered buildings

and “living roofs” are encouraged.

e. Exposed understory stem walls should not exceed 5’ and should be Onished with visually recessive,

earth-toned materials.

f. Step the building foundation and roofs with the natural slope (see Figures 16.1 and 16.2).

g. Use horizontal and vertical building components to reduce bulk.

h. Avoid two story wall planes.

i. Step back the second story so the diRerence in wall planes is visible from a distance.

j. Vary elevations, such as stepping back second stories, to conform with topography.

k. Avoid overhanging decks, large staircases, and patios formed by retaining walls that make buildings

appear more massive (see Figure 16.3).

l. Avoid use of solid wall railings that add to the mass of the design.

m. Create light and shadow by providing modest overhangs, projections, alcoves, and plane oRsets.

n. Use a combination of siding materials and articulate walls to reduce expansive, continuous planes.

o. Use vaulted ceilings rather than high walls and ceilings to attics above to achieve a feeling of

volume.

5. Colors and Materials. The following methods may be used to reduce the visibility of hillside development:

a. Use subdued and unobtrusive exterior Onish materials and colors for all structures.

b. Minimize the use of rePective material.

c. Earth tones and colors that occur naturally in the Petaluma hills are encouraged.

d. Structures should not call undue attention to themselves when viewed from a public vantage point.

6. Roofs.

a. Break roof forms and rooPines into smaller building components to rePect the irregular forms of

surrounding natural features (see Figures 16.1 and 16.2).

b. Generally orient the slope of the main roof in the same direction as the natural slope of the terrain

(see Figures 16.1 and 16.2).

c. Avoid large gable ends on downhill elevations.

d. Light colored and rePective rooOng materials are discouraged.

J. Process. As prescribed by Section 24.050 (Site Plan and Architectural Review).

K. Findings. In addition to the considerations for review identiOed in Section 24.050(E) (Standards for Review of

Applications), the following Ondings, where applicable, are also required:

1. The project meets or exceeds the objectives, standards, and guidelines of the Hillside Ordinance.

2. The design, scale, massing, height and siting of development is compatible and complementary with the

character and scale of the surrounding, developed neighborhood.

3. The design and site layout of the hillside project is respective of and protects the natural environment to

the maximum extent feasible.

4. Site grading has been designed to be as minimal as possible to achieve sensitive hillside design, minimize

tree removal and provide safe site access and required parking.

L. Submittal Documents. In addition to the submittal requirements identiOed on the Development Permit

Application Submittal Requirements Matrix the following shall be provided as indicated:

1. Opportunities and Constraints Map/Site Analysis is required for all projects.

2. Visual Analysis as required at the discretion of Planning staR or the decision making authority.

3. Arborist Report and/or Tree Preservation and Protection Plan as required by Section 17.055. (Ord. 2811

§ 4, 2022.)

A. Purpose. To create appropriately sized, located, and conOgured parcels that can be developed in a manner

consistent with this chapter and the General Plan goals and policies related to hillsides and ridgelines.

B. Applicability. Section 16.070 applies to any subdivision of property proposed for a parcel or group of parcels

located in the South Hills and West Hills, as deOned by this Chapter, and any parcel of land located within the City

that has an average slope of 10% or greater as determined using the Average Slope Formula contained in Section

16.070 (C1).

C. Minimum Parcel Size. The minimum parcel size shall be determined by the underlying zoning district or as

calculated by the slope density formula and/or table contained in Section 16.070(C2), whichever is greater.

1. Average Slope Formula. The average slope of the parcel shall be computed on the natural slope of the site

before grading, as calculated using the following formula:

I. The contour interval measured in feet.

The sum of the length of all contour lines contained within a

L. subject parcel measured in scale feet.

A. The area of the parcel in acres.

The average cross slope of a speciOc parcel of land expressed

S. in percent as determined by the “Average Slope” formula.

2. Slope Density Formula. The minimum parcel size shall be determined by the following formula, or the

table below:

Table 16.1

MINIMUM MINIMUM
SLOPE LOT SIZE SLOPE LOT SIZE

(SQ. FT.) (SQ. FT.)

10% 6,000 18% 11,092

11% 6,636 19% 12,410

12% 6,776 20% 14,083

13% 7,246 21% 16,278

14% 7.786 22% 19,283

15% 8,413 23% 23,648

16% 9,149 24% 30,568

17% 10,028 25% 43,560

3. Above 25% slope, one additional acre or portion thereof per dwelling unit will be required for each

additional 5% increase in slope.

4. Calculations of the average slope and the minimum parcel size shall be calculated by a registered civil

engineer or a licensed land surveyor using the formulas provided in Section 16.070(C1 and C2).

5. Modi8cations to Minimum Parcel Size. In a residential Planned Unit District (PUD), the minimum parcel size

may be Pexible in order to respond to site conditions and to comply with General Plan goals and policies

related to the clustering of development. The maximum number of dwelling units or lots shall remain as

prescribed in Section 16.070(D).

D. Density. The maximum number of dwelling units or lots is calculated by dividing the size of the lot to be

subdivided by the minimum parcel size required by Section 16.070 (C2). No project is guaranteed the maximum

density. The actual density yield shall be determined by the decision making authority. When calculating density,

any fraction shall be rounded down to the next whole unit. The density shall be consistent with the General Plan

density range for the site and the density as calculated by this section.

E. Development Standards. Any parcel subject to this Chapter is also subject to the requirements of the zoning

district in which the parcel is located. Where the requirements of the underlying zoning district conPict with the

requirements of this chapter, the requirements of this chapter shall control.

1. Exception to Retaining Wall Height (Section 13.050). For projects subject to Section 16.070, a maximum

exposed retaining wall height of 5 feet (5’) may be permitted with approval of the review authority.

F. Process. The process for the subdivision of land shall be as prescribed in the City’s Subdivision Ordinance

(Municipal Code Title 20).

G. Submittal Documents. In addition to the submittal requirements identiOed on the Development Permit

Application Submittal Requirements Matrix the following are required as part of an application for a subdivision of

land:

1. Topographic Survey

2. Opportunities and Constraints Map/Site Analysis

3. Slope Analysis: at a minimum delineating areas with slopes of 0-10%, 10%-15%, 15%-30%, >30%

4. Soils Report

5. If Buildings are proposed with subdivision, include the following:

a. Architectural drawings

b. Visual analysis

c. Landscape planting plans for common areas, tree mitigations, cut/Oll slope revegetation, and typical

front yards

H. Appeal. As prescribed in the City Subdivision Ordinance (Municipal Code Title 20).

The Petaluma Implementing Zoning Ordinance is current through Ordinance 2907, passed September 8,

Disclaimer: The city clerk’s oQce has the oQcial version of the Petaluma Implementing Zoning Ordinance. Users

should contact the city clerk’s oQce for ordinances passed subsequent to the ordinance cited above.

City Website: cityofpetaluma.net

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