Sonoma County Municipal Code § 25-43 Optional design and improvement standards

(a) The street and highway layout of each subdivision shall be based on the section of the streets and highways master plan, if such plan has been adopted for the portion of the county within which the subdivision lies. Where no such plan has been adopted, such subdivision layout shall conform to the suggestions of the planning commission and the requirements of this chapter.

Public roads parcels which front onto a county road or state highway and which have a density of five (5) acres/unit or greater shall meet all county standards for roads, including those as required pursuant to Section 25-57.

Rights-of-way shall be a minimum of fifty (50) feet unless deviation is duly approved.

(b) Widths of streets and highways shall conform to all county road standards including those as required pursuant to Section 25-57.

(c) Reserved strips controlling the access to public ways, or which will not prove taxable for special improvements, shall not be approved unless such strips are necessary for the protection of the public welfare or substantial property rights, or both, and in no case except in which the control and disposal of the land comprising such strips is placed definitely within the jurisdiction of the county under conditions approved by the planning commission.

(d) All streets shall, as far as practicable, be in alignment with existing adjacent streets by continuations of the centerlines thereof, or by adjustments by curves, and shall be in general conformity with the plans made for the most advantageous development of the area in which the subdivision lies.

(e) Streets shall be required to intersect one another at an angle as near to a right angle as is practicable in each specific case.

(f) Where a subdivision adjoins acreage, provision shall be made for adequate street access thereto.

(g) Wherever a dead-end street is permitted, an adequate turning area shall be provided.

(h) All streets shall be named, and such names shall be subject to the approval of the commission. Duplication of existing names shall not be allowed unless the streets are obviously in alignment with existing streets and not so far removed as to be confusing.

(i) Grades shall not exceed six percent (6%) on arterial or collector highways, ten percent (10%) on minor highways or fifteen percent (15%) on any street. Centerline radii shall not be less than five hundred feet (500') on highways, except in mountainous areas, where the radius may be reduced to not less than two hundred feet (200'); and on all other streets the centerline radii shall not be less than seventy-five feet (75'). Lesser radii and greater grades may be used in cases in which sufficient evidence is presented to show that the above requirements are not practicable; grades shall not, however, exceed twenty percent (20%) in any case.

(Ord. Nos. 965 § 4, 1139 § 4.)

(j) Note: All road base and surfacing standards are considered minimum. The equivalent of class I sub-base may be substituted for the class II base subject to the planning commission or zoning administrator approval.

Private roads—Projects with a density of one (1) unit /acre or less for which an applicant requires and the planning commission or zoning administrator approves private road status shall be developed in accordance with the following:

(1) An eighteen feet (18&prime); width roadway with six inch (6″) class II base, two inch (2″) A. C. pavement.

(2) Shoulders and A. C. dikes optional except as required for drainage control.

(3) Road for projects consisting of ten (10) lots or fewer or where "feeder" roads within a larger project contain ten (10) lots or fewer and where further divisions are not possible may, if approved by the planning commission or zoning administrator, be only twelve feet (12′) in width with six inch (6″) class II base, two inch (2″) A. C. pavement. A six foot (6′) cleared lane shall adjoin the twelve foot (12′) paved section for additional fire access; said section need not be surfaced or based.

(4) Rights-of-way shall be a minimum of twenty feet (20') unless altered by the planning commission or zoning administrator.

(5) Where speed on proposed roadways is deemed to be a concern, traffic control devices such as signing, and especially road design may be utilized as mitigating measures.

(6) For projects which assure long term road maintenance through the use of legal entities (such as homeowner's associations), private road standards may allow the use of "seal coat" for surfacing; width and base standards are to be consistent with subsections (j) (1) and (j) (3) where applicable. Seal coat shall consist of one and one-half inch (1½") layer of #4 rock; one (1) layer of RS-l sealing oil, and three-eighth inch (⅜″) of #6 rock.

(7) Where roadway grade is ten percent (10%) or less, the seal coat described in subsection (6) may be substituted for the two inch (2″) A. C. pavement.

(8) Where private roads require bridges, said bridges shall conform to regulation H-15 of the state department of transportation relating to bridge weight requirements.

(9) When half-width rights-of-way are proposed, improvements shall be in the minimum width of twelve inches (12″) with six inch (6″) class II base and two inch (2″) A. C. pavement.

(10) Civil engineered drainage plans shall be provided for all roads and driveways of all subdivisions.

(11) Grades shall not exceed fifteen percent (15%) but with the planning commission or zoning administrator approval may not exceed twenty percent (20%) for short distances.

(12) Roads for parcels greater than forty (40) acres shall meet county grade and alignment standards; width and surfacing standards to be determined by the planning commission or zoning administrator if deemed necessary.

(13) Driveways (defined as private roads serving two (2) lots or less) off subdivision roads shall meet county grade standards for private roads and may be required by the planning commission or zoning administrator to be improved depending on terrain, grade, length, and other factors.

(Ord. No. 6308, § I, 6-9-2020; Ord. No. 2510 §§ 15, l6.)

(Ord. No. 6523, § VII(Exh. D), 6-3-2025)

Footnotes:

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As to highways, roads and bridges generally, see Chapter 15 of this code.

(a) Long blocks shall be provided adjacent to main thoroughfares for the purpose of reducing the number of intersections; however, blocks shall not exceed twelve hundred feet in length unless existing conditions justify a variation from this requirement thereto upon their own volition or upon written request of the subdivider.

(b) Pedestrian ways ten feet in width may be required through the middle of blocks over one thousand feet in length to connect dead end streets, or to provide access to stream, lake, bay or ocean frontage, or such park or playground areas as may be indicated.

(c) At street intersections, the block corners shall be rounded at the property line by a radius of not less than twenty-five feet, or such other radius as will provide one hundred feet sight distance.

(d) Sidewalks may be required along all streets in a subdivision where the average area of the lots is less than fifteen thousand square feet.

(Ord. Nos. 965 § 4, 1137 § 4.)

(a) Minimum lot sizes shall conform to the standards established by the county zoning regulations and any additional requirements which may be adopted by formal resolution of the Board of Supervisors. Copies of such resolutions, when adopted, shall be maintained on file in the office of the clerk of the Board of Supervisors and the County Planning Commission, where they shall be available for public inspection; provided that nothing in this chapter shall be deemed to reduce any minimum parcel size requirements imposed upon any real property by agricultural preserve regulations and Williamson Act agreements or contracts. Moreover, if real property is subject to a Williamson Act agreement or contract and the minimum parcel size requirements for the agricultural preserve conflict with zoning regulations, the larger minimum parcel size requirement shall govern.

(Ord. No. 1651 § 8.)

(b) In no case shall lot width be less than sixty feet on the building setback line, nor the depth less than that necessary to provide the minimum lot size required nor shall the depth be less than eighty-five feet, nor greater than three times the width, exclusive of rights of way or easements necessary for road purposes; provided, that the Planning Commission may approve lots exceeding those minimums where lots are located on or adjacent to steep hillsides, rivers or creeks, or where property is to be used for business or industrial purposes.

(c) Lots without frontage on a street shall not be permitted.

(d) The side lines of lots shall run at right angles to the street upon which the lot faces, as far as practicable.

(e) Double frontage lots of less than two hundred feet in depth shall be avoided, except where essential to provide separation of residential development from traffic arteries, or where required by unusual or excessive topographic conditions. When double frontage lots are permitted or required, vehicular access rights shall be dedicated to the county along that street designated by the Planning Commission. The subdivider may be required to construct walls or fences and improve a planting strip adjacent thereto with approved landscaping.

(f) Corner lots shall be increased in width to not less than seventy feet on building setback line.

(g) All residential lots shall have a minimum twenty foot building setback line. Such setback shall be maintained on all street frontages on corner lots. A building setback line shall also be provided adjacent to streams and measured from the toe of the stream bank outward at a slope of 2.5:1 plus thirty feet or thirty feet outward from the top of bank, whichever is greater, or, where stream bank conditions do not reasonably allow such measurement because of the natural topography, bank erosion or other factors, a width shall be determined to reasonably meet the goals of this chapter.

(h) Corridor lots (flag lots) may be permitted in hillside development or difficult topography and unusual land shape or when lots back up to traffic arteries with the approval of the Planning Commission if the lot area conforms to the requirements of the zoning district excluding any area necessary for corridor access and the corridor has a minimum width of twenty feet for one lot and forty feet combined width for two lots. The access corridor on lots less than 1.5 acres in area shall be paved with asphalt or equivalent to a width of twelve feet for its entire length on a single lot and to a combined width of sixteen feet on two lots.

Corridors of excessive length shall not be permitted.

(Ord. Nos. 965 § 4, 1137 § 4.)

Should a subdivider elect to utilize development concepts such as cluster, townhouse, condominium or combinations thereof, whereby areas of permanent open space would be provided within the subdivision, he may petition the planning commission to reduce the standards established in this article by compliance with each of the following:

(a) Improve the subdivision design by density control and better community environment; the standards set out in this article concerning streets and lots may be varied only when the gross density of an area is not increased and open common area is created; provided, that the design has the approval of the planning commission, and where in their opinion the deviation will:

(1) Produce a more desirable and livable community.

(2) Create better community environment through dedication of public areas, scenic easements, open spaces or reforestation of barren areas.

(3) Reduce the danger of erosion.

(b) As an incentive to creating better overall communities, the planning commission may authorize deviations of up to seventy-five percent reduction in lot size but with no increase in density in the overall development; provided, that an area equivalent to the decrease is set aside as common usable open space in aggregates of at least one acre.

(c) Before any deviation based on improved design shall be authorized, the subdivider shall present a preliminary map of the development to the planning commission for approval prior to filing a tentative subdivision map. This map shall show lot arrangement, shape and size, street pattern along with cross sections of proposed roads, area of all common open space and other such information as the planning commission may feel necessary to make their findings. The proposed exceptions shall be approved by the planning commission, upon a finding that the variation as authorized will result in a community which is a substantial improvement over the community which could have been developed by following the requirements set out in this article.

(d) Where permanent open space or scenic easements are to be provided, the county shall be named as a party to any deed restrictions or alternate methods to forever preclude a use other than open space within those areas designated in the subdivision.

(Ord. No. 1137 § 5.)

(a) The subdivider shall provide sufficient easements or construction, or both, to provide adequate capacity for storm drainage, ensure reasonable channel stability, and provide adequate access for maintenance.

(b) The construction and maintenance of wells and individual sewage disposal systems shall meet the applicable standards or ordinances of the county.

(c) All deed restrictions shall run with the land and be enforceable by any owners of property lying within the subdivision.

(d) In all respects, the subdivision will be considered in relation to the master plan of the county or preliminary plans made in anticipation thereof.

(e) In all cases, the planning commission shall suggest to the subdivider such measures as will preserve and enhance the scenic values of the county and the conditions making for excellence of residential, commercial or industrial development.

(f) Failure of the subdivider to make adequate provision for required streets, highways, schools, drainage, and other planned public facilities, shall be reason to disapprove the tentative map.

(g) Where technical changes occur within the zoning regulations creating land use standards accommodating innovative planning concepts, such as cluster subdivisions, row housing, condominium, scenic easements, open space plans, and mobile home park subdivisions, they shall be considered as a supplement to this chapter.

(h) Repealed.

(i) Where projects are determined to warrant further geological investigation, a geologist's report shall be required which summarizes and illustrates the following categories:

(1) Areas where standard foundation and other conventional construction techniques are satisfactory;

(2) Areas where geological hazards may exist but which in the opinion of the geologist can be mitigated, i.e., foundation design;

(3) Areas where geologic suitability is uncertain without additional geotechnical and/or subsurface investigation.

(j) (1)

In areas such as ridges, hilltops, and other key areas judged to be extremely exposed from public roads or other critically visible offsite locations, development shall be prohibited unless adequate mitigation measures are available. In areas of eroding slopes and near drainage ways, development shall be prohibited unless adequate mitigating measures are available.

(2) Grading for development (building pads, leachfield areas, driveways) shall maximize retention of natural land forms such as rolling hills, ridgetops, areas of extensive vegetation and water courses. Grading shall not produce large flat planes or sharp angles or intersection with the natural terrain. Slopes shall be rounded and contoured to blend with existing terrain. Extensive terracing shall be prohibited.

(3) Development shall be encouraged to use the form of the land and vegetation to insure separation of building areas and minimal exposure from roads and other building areas.

(4) The solar exposure of building sites should allow for, at the minimum, basic passive solar heating and cooling design elements consistent with other applicable standards.

(5) The use of plantings (generally trees) consistent and compatible with those of the area may be required to mitigate the extent of exposure of the development area in conjunction with land forms, existing vegetation and other features. Screening required for shielding of development areas (not necessarily the immediate house site) shall consist of natural materials of the area, preferably using natural vegetation or land form modification similar in form to the natural terrain.

(6) Developments exceeding a total of fifty (50) lots and with a density greater than one (1) dwelling unit per acre may:

(a) Provide on-site open space areas for active and passive recreation (active defined as spaces for field and group activities such as football, soccer, baseball, tot lots, playgrounds, etc.; passive defined as areas used for sitting, walking, and project form). Said areas, where applicable, may be used for storm water retention, recharge areas, project form, or other multiple uses. Need and size of such areas shall be determined by the planning director taking into account number of units, size and shape of site, drainage, information derived from an EIR, environmental reconnaissance, or other documentation or site characteristics;

(b) Where a recreation agency (district, department, etc.) exists, a dedication of land in lieu of developing project related recreational facilities may be approved by the planning commission or zoning administrator, such approval shall be based on the following:

(i) Dedication shall consist of a minimum of four hundred (400) square feet per lot,

(ii) There shall be a demonstrated lack of need for additional recreational facilities at the time of development of the proposed project.

(7) Projects shall be analyzed for their relationship to the general plan open space plan and specific plan open space plans, and, where necessary, any adverse impacts mitigated.

(8) Building envelopes and building setback lines may be required by the planning commission or zoning administrator to achieve consistency with the standards listed in subsections (j)(1) through (j)(9) of this section.

(9) All roads shall be sited in conformity with subsections (j)(1), (j)(2), (j)(3) and (j)(5) cited above.

(k) (1)

Projects consisting of ten (10) lots or more shall provide a minimum of two thousand (2,000) gallons storage per lot either in the form of a pressurized distribution system with storage, said storage at the building site, or centralized storage equipped to accommodate emergency equipment. In any method used, water flow rates shall be five hundred (500) g.p.m. Total storage need not exceed forty thousand (40,000) gallons plus daily flow. Storage may consist not only in tanks but also in ponds, lakes, pools, etc., which are accessible for use by emergency equipment.

(2) For projects consisting of ten (10) lots or fewer, the planning commission or zoning administrator, after consultation with the local fire district/California Department of Forestry (CDF), may require a note placed on the parcel map/final map stating that a minimum of two thousand (2,000) gallon storage facility for fire protection shall be required at the time of building permit issuance for new dwellings.

(3) A fire management plan shall be prepared and submitted with the subdivision application that includes (but is not limited to) identification of fire hazards on the site, the development's relationship to these constraints, necessary protection measures, and provision for maintenance of any water system for the project.

(4) Where projects are proposing a "tie-in" with existing public or mutual water systems, the storage requirement may be adjusted based on the capability and/or storage capacity of the existing system.

(5) A design for the cleared area at the building site for a two hundred and thirty-six inch (236″) wheelbase vehicle shall be required to insure adequate emergency vehicle circulation.

(6) Access for fire protection purposes shall be provided consistent with Section 25-17(j); where deemed necessary by the planning commission or zoning administrator, additional emergency access may be required. The extent and improvement of same shall depend on the circumstances of each case as deemed necessary by the planning commission or zoning administrator in consultation with the local fire district or California Department of Forestry.

(l) (1)

Development and creation of impervious surfaces in a natural recharge area shall be subject to soils investigation and mitigation of potential recharge reduction. Should adequate mitigation not be possible, the project shall be denied.

(2) In order to reduce the offsite peak storm flow generated by projects with a density greater than one (1) dwelling unit per acre, retention ponds, drainage swales, or the use of check dams shall be utilized where deemed necessary by the planning commission or zoning administrator based on density, size of site, shape of site, and topography.

(3) Drainage improvements for runoff from all roadways and other impervious surfaces shall be engineered to minimize erosion through the use of rocked culvert inlets and outfalls, energy reducers, proper location of culverts, reseeding of exposed slopes, and minimizing the use of artificial slopes.

(m) Development allowed under the general plan in designated resource areas shall be permitted subject to the following design/siting requirements.

(1) Design of projects shall recognize the environmental and resource characteristics of the site and be designed in such a manner which allows for the preservation and continued production of the particular resource.

(2) Design of projects in resource areas shall utilize the least productive portion of the site, leaving the productive areas intact where possible. The design of projects shall be consistent with other applicable development standards.

(3) Development shall not adversely affect the natural course or riparian habitat of any stream. Mitigation measures shall be required of the project where development may result in impacts to such areas.

(4) Development shall not adversely affect tidal marshes, freshwater marshes, estuaries or marine waters. Impacts upon these areas by a project shall be mitigated.

(5) Development shall not adversely affect areas identified as significant wildlife habitat, and impacts upon these areas by a project shall be mitigated.

(6) Extensive changes or removal of vegetation shall demonstrate minimal adverse impacts on micro-climate conditions. Erosion protection and revegetation shall be required in all cases of vegetation removal.

(7) Whenever there is reason to suspect significant archaeological or paleontological sites (as noted in the initial study process) within the project area, an appropriate survey by qualified professionals shall be required as part of any environmental review and suggested mitigation measures implemented prior to development of the site.

(8) Development shall not adversely affect the existing volume of any water body, substantially increase chemical or nutrient pollution, or otherwise contribute to the deterioration of the quality and quantity of water in any water body.

(n) (1)

Utility lines shall be placed underground on projects with a density greater than one (1) unit/three (3) acres; the planning commission or zoning administrator, after consideration of the visual characteristics of the project site and development plan, may require undergrounding for projects with a density between one (1) unit/three (3) acres to one (1) unit/fifteen (15) acres; projects with a density less than one (1) unit/fifteen (15) acres shall not require undergrounding. Undergrounding shall be in accordance with the rules of public utility and state public utilities commission.

(2) Where new main utility lines are required, these lines and service lines to the building areas shall be undergrounded where densities require undergrounding; where main lines already exist, only service lines to the building areas shall be undergrounded.

(o) Projects shall be subject to Section 26-88-015 of the county code.

(p) Protect and encourage agricultural production by establishing a buffer between agricultural production on lands either designated in one (1) of the three (3) agricultural land use categories in the general plan or lands included within the "AR" zoning district, where any such lands abut a nonagricultural land use conducted on land outside the three (3) general plan land use categories. Generally, buffers shall be defined as a physical separation of one hundred feet (100′) to two hundred feet (200′). These may be modified based upon topographic feature, a substantial tree stand, water course or similar existing feature. In some circumstances, a landscaped berm or other manmade feature may enhance the buffer. The requirement for buffer may be modified after hearing by the advisory agency following a written recommendation by the agricultural commissioner.

Notwithstanding the provisions Chapter 26, of Article XXX (nonconforming uses) where the imposition of the buffer creates a nonconforming condition, expansion or modification of such use may be permitted provided that encroachment into the setback does not exceed that of the existing structure.

Agricultural production as used herein means either an existing agricultural operation or an agricultural operation that would be a reasonably anticipated use. No buffer or setback shall be created by the acquisition of a portion of a parcel devoted to an agricultural operation.

(q) The design guidelines set out in Section 26-90-050 of this code (the Taylor Mountain/Sonoma Mountain development guidelines) shall be utilized in addition to the provisions of this section in evaluating subdivision applications for parcels located within the subject area. Building envelopes and related map notations consistent with the provisions of Section 26-90-050 of this code shall be required for each lot.

(Ord. No. 6478, § V(Exh. B), 4-30-2024; Ord. No. 5130 § 2, 1999: Ord. No. 4981 § 7, 1996; Ord. No. 4101, 1989: Ord. No. 4014, 1989: Ord. No. 2510 §§ 17—21: Ord. 1137 § 6: Ord. No. 965 § 4.)

(Ord. No. 6523, § VII(Exh. D), 6-3-2025)