Article 4 — Hillside Performance Standards

The City of Walnut Creek is situated among a series of major and minor hills. These hills are a highly valued natural topographical feature of the community because they visually define the City's boundaries and public open spaces, and/or public trails, because they provide a sense of the community's indigenous history, and because they provide visual stress relief to all persons traveling our highly traveled freeways, major arterials, and/or scenic corridors in and around the City.

The City's General Plan recognizes the intrinsic value and sensitive nature of these hillside areas by listing numerous policies and programs especially designed to minimize the negative impacts that may otherwise be associated with developing in hillside areas.

It is the intent of this article to implement the policies and programs of the City's General Plan relative to residentially zoned hillside areas and minimize visual impacts by promoting orderly development, preserving ridgelines and other significant natural topographical features of hillside areas, minimizing grading and regulating the placement of structures and other aesthetic qualities of development. This article is also intended to limit development which will result in high levels of risk of property damage and personal injury. (§4, Ord. 2239, eff. 7/5/24)

The terms used in this article shall have the following meanings:

A. Creek: Any natural watercourse noted on the most recent United States Geological Survey (USGS) Blue Line Survey Maps available for viewing in the Community Development Department, City of Walnut Creek.

B. Development: Any improvement of real property which requires the issuance of a permit from the City which permit is subject to review pursuant to Section 3-8.05, or Chapter 1 (Subdivisions) or 2 (Planning and Zoning) of Title 10, a building permit or a grading permit.

C. Highly Protected Tree: Any highly protected tree as defined in the City's Tree Preservation Ordinance. (Chapter 8 of Title 3 of the Municipal Code)

D. High Risk Area: Any portion of a site which, if developed, would subject persons or property to a high level of risk for personal injury or property damage due to its proximity to a known hazard, including, but not limited to, any portion of a site within fifty feet of a cliff or fault line, within an unrepaired slide area or in a ravine.

E. Hillside Area: Any property or portion of a property subject to this ordinance with an average slope of fifteen (15) percent or greater as defined by one of the density determination methods described in Sec. 10-2.3.406. below.

F. Net Site Area: Total site area minus high risk areas, and areas designated as undevelopable.

G. Net Lot Area: Total lot area minus existing and proposed roads, road easements, road rights-of-way, flags of flag lots, high risk areas and areas designated as undevelopable.

H. Ridgeline: The ground line located at the highest elevation of the ridge running parallel to the long axis of the ridge.

I. Rossmoor: The lands within the gated community of Rossmoor which are governed by P-D 1483 and its subsequent amendments.

J. Undevelopable Areas: All portions of the site determined to be high risk areas as defined in D. above shall be designated undevelopable and shall automatically be excluded from density calculations. Those portions of a site where the slope is above 30%, and slopes within a 100 foot vertical drop of the ridgeline of any visually prominent ridge may be designated undevelopable and may be excluded at the discretion of the applicant (see also Sec. 10-2.3.407.D.). Areas designated undevelopable must be excluded from further calculations of net site area, minimum lot size and density.

K. Visually Prominent Ridge: The highest hill or series of hills located within each of the Potential Ridge Areas indicated on the Zoning Map. (§20, Ord. 2070, eff. 6/20/2008; §4, Ord. 2239, eff. 7/5/24)

Except as exempted in Sec. 10-2.3.405, any development of any residentially zoned properties or portions of same properties within the City's boundaries, excluding the Core Area and Rossmoor, which have an average slope of fifteen (15) percent or greater as defined herein shall be subject to the provisions of this article. Where there is a conflict between this article and other provisions of the Municipal Code, the most restrictive provisions shall apply.

Unless exempted in Section 10-2.3.405, no new development shall be permitted on any property or portion of a property that is subject to this article unless said development is found to be consistent with this article. This determination shall be made by the reviewing body with the highest authority over any regular development application being sought. Other reviewing bodies in advisory roles on the application shall provide comments and recommendation to the final decision making body on the development's consistency with this article. When the application being sought does not normally require discretionary approval by the Community Development Director, the Planning Commission or the City Council, the discretionary authority for determining consistency shall be given to the Zoning Administrator. Where public notice is not normally required for an application, the noticing requirements of Section 10-2.4.302 shall apply. (§4, Ord. 2239, eff. 7/5/24)

The following items are exempt from the provisions of this article:

A. Additions to existing homes, where the addition does not exceed ten percent (10%) of the original house size before construction of the addition.

B. Accessory dwelling units.

• C. Urban lot splits.

D. The construction of new SB 9 dwelling units.

E. Any other minor change to the current conditions of the site which the Community Development Director finds will not be inconsistent with the intent and purpose of this article and for which the required findings and development standards are either not applicable or are met without any changes to the submitted plans. (§12, Ord. 2188, eff. 3/8/19; §12, Ord. 2234, eff. 11/17/23; §4, Ord. 2239, eff. 7/5/24)

The maximum density permitted on any property subject to this article shall be determined by using the density determination table shown below where the average slope is calculated as follows:

A. Average Slope Calculation for Sites or Portions of Sites Generally Rectangular in Shape and Sloping Uniformally in One Direction:

Compute the difference between the top elevation (T) and the bottom elevation (B) of the site or portion of the site in question. Divide that number (rise) by the horizontal distance between the top and bottom elevations (run). This distance is to be calculated using a line drawn perpendicular to the contour lines at a representative location within the parcel as determined by the Zoning Administrator. Multiply the resulting number by 100 to get the average slope (S) of the site or portions of the site in question.

B. Average Slope Calculation for Sites Not Described in A. above:

Measure the length of each contour (L1, L2, L3 ...) on the site in feet. Measure only those areas which are potentially developable (see definition of "undevelopable" in the definition section of this ordinance. Add them together (L). Multiply that number (L) by the contour interval of the map (I), then multiply that number by .0023. Divide the resulting number by the net site area (N) in acres. The resulting number shall be known as the average slope (S) of the site.

Algebraic equation: (((L1 + L2 + L3 + ...) x I) x .0023) ÷ N = S

C. Density Determination Table

• This does not prevent one single-family detached home from being built on any legal lot existing at the time this ordinance becomes effective regardless of its size, provided it complies with the other development standards of this article, the grading ordinance and those of the underlying zone. Where provisions may conflict, the most restrictive shall apply.

• The Planning Commission may grant exceptions to these maximum density standards under Section 102.2.1702 of Article 17 (Planned Development District) or upon making all of the following three findings:

1. The site is physically suitable for additional units in that it contains additional natural building sites on the property.

2. The addition of such units will not create environmental damage nor pose public health, safety, or welfare problems.

3. The development meets all the property development standards described in Section 10-2.3.407 below and the Planning Commission can still make all the findings required in Section 10-2.3.409, even with the additional units.

The following development standards shall apply to any development governed by this article.

A. Cluster Design vs. Minimum Lot Area:

Infill projects in established single family areas shall be designed with detached single family homes on separate lots according to the minimum lot size of the underlying zone. The lots shall be designed and the houses sited in such a manner as to minimize environmental and visual impacts.

Multiple Family projects and large scale projects (projects encompassing fifty or more acres) which are located on the periphery of the City shall be encouraged to cluster homes in areas with the least environmental and visual impacts in lieu of meeting a minimum lot size requirement

B. Tree Preservation: There shall be no grading or construction of any kind within the area surrounding any highly protected tree for a distance of one and one-half times the distance from the trunk to the dripline except that an exception for minor grading may be granted consistent with Section 3-8.05(b) of Chapter 8 (Tree Preservation Ordinance) of Title 3 (Public Safety) of the Walnut Creek Municipal Code.

C. Grading: Grading of the property shall be designed to minimize disruption of the natural topography. Grading is discouraged on the site except for roads; driveways; garage pads; cuts under the house; cuts on the uphill side of the house which are screened from public view by the house or existing vegetation; site distance requirements; drainage; and soil stability purposes. All approved grading shall be done in such a manner that it presents a finished look of rounded slopes. All exposed graded areas shall be hydroseeded/relandscaped to minimize erosion. Roads should follow contour lines, where feasible, to minimize grading.

D. Hillside/Ridge Preservation. No buildings or structures of any kind shall be constructed which encroach within a 100 foot vertical drop from the ridgeline of any visually prominent ridge or in such a manner that it breaks the skyline of any visually prominent ridge as viewed continuously for more than 1000 feet from any freeway, arterial, or scenic corridor within the City limits. No buildings or structures of any kind shall be constructed upon portions of any site where the true slope is above 30%. NOTWITHSTANDING the foregoing, development may be permitted when (1) the structure will be constructed on an existing lot which is accessed by an existing road

which traverses the top of the ridge and placing the house lower on the hill would either increase grading on the site or prevent a gravity flow sewer connection; or (2) the proposed construction will be screened from public view from below due to existing mature vegetation; or (3) the existing lot depth is not adequate to construct a home elsewhere on the site.

E. Rock Outcroppings: Significantly visible rock outcroppings shall be preserved and incorporated into any approved landscape/site plan to the greatest degree possible.

F. Yards and Lot Coverage: Minimum yards and maximum lot coverage shall be determined as part of the hillside development review process taking into account the need to preserve natural features on the site, minimize shadows on adjacent properties and preserve views, but in no case shall they be less than that required by the underlying zone.

G. Creek, Landslide, and Fault-Line Setbacks: No structures shall be built within 50 feet of a fault line, within 50 feet of the top of a creek bank or within that setback from a known landslide area recommended in a soils report prepared for the proposed development. Where significant riparian vegetation exists beyond the limits required above for creek setbacks, the setback line shall be extended to include such areas.

H. Exclusions: Any area of the site which has been excluded from density calculations shall be precluded from further residential development by a scenic easement, dedication of open space, deed of development rights or other appropriate method.

I. Antennas: Receiving and/or transmitting antennas shall be sited on the site in such a manner that the base is screened from public view and the top of the antenna does not break the skyline any more than is reasonably necessary to function properly

J. Drainage: Any increased runoff from the site due to proposed improvements to the site shall be collected and conveyed off the property in a manner that does not negatively impact downstream properties.

K. Screening of Mechanical Equipment: All mechanical equipment on site shall be screened from view off site, where feasible.

L. Exterior Lighting: Exterior lighting shall be designed and installed in such a manner that the light source is shielded from view off the site unless a finding is made that such lighting is necessary for safety reasons.

M. Pools: The siting and design of pools and pool-related structures shall be subject to review and approval of the Community Development Director. (§4, Ord. 2239, eff. 7/5/24)

In the recommendation for approval and in the approval of a project submitted under this ordinance, conditions may be imposed which are deemed necessary to implement the General Plan and/or make the findings listed below.

A. The proposed development complies with the purpose and intent of the Hillside Performance Standards as well as the specific property development standards required therein.

B. The proposed development, as conditioned, minimizes disruption of the natural topography, preserves the appearance of scenic ridgelines, and protects natural features on the site in their natural state such as heritage quality trees, creeks, riparian corridors, stock ponds, hillslopes, knolls, ridgelines, outcroppings and natural habitat areas to the greatest degree possible.

C. The proposed infill development, as conditioned, maintains a high quality residential design while reflecting existing residential patterns and character.

D. The proposed development, as conditioned, minimizes the impact of new residential development, to the extent feasible, upon existing residents' views.

E. Drainage systems, such as detention basins, have been considered, where applicable to preserve natural creek channels.

F. Open space lands within the proposed development have been left in private ownership, unless public ownership or access is desirable or necessary.

G. The proposed development has been reviewed against the seismic and slope instability hazard maps and the Association of Bay Area Governments (ABAG) Ground Shaking and Damage Potential maps, after which a geotechnical analysis was made and designated high risk areas have been designated as undevelopable on the approved plans.

H. The homes have been sited in such a manner as to protect natural features of the site, minimize grading, preserve the appearance of scenic vistas, minimize the risk of property damage and personal injury due to seismic hazards and slope instability and minimize shadows on adjacent properties, where practicable.

I. The design of the homes including massing, roof lines, exterior materials, colors, and decking have been designed to complement the terrain.

J. Proposed landscaping, as conditioned, preserves the natural character of the area while minimizing erosion and fire hazard risks to persons and property.

K. The project is consistent with the City's General Plan.

L. The project, as conditioned, protects the public health, safety, and general welfare of persons residing in and around the area as well as the community at large.