18.28.070   Additional OS District Regulations
   The following additional regulations shall apply in the OS district:
   (a)   Accessory Dwelling Units and Junior Accessory Dwelling Units
      Accessory Dwelling Units and Junior Accessory Dwelling Units are subject to the regulations set forth in Section 18.42.040.
   (b)   Site and Design Approval
      All sites in the OS district shall be subject to the Site Design and Review Combining District (D) as provided in Chapter 18.30(G) of the Zoning Ordinance, subject to the following modifications:
      (1)   Minor Site and Design Review: For minor projects (e.g., fences, landscape changes to an approved project, trash enclosures, accessory buildings 200 square feet or less, etc.), the review process shall follow the Minor Architectural Review (staff level) procedures as outlined in Section 18.77.070. To qualify as a minor project, the project shall have less than 10 cubic yards of excavation and or grading and be Categorically Exempt from the California Environmental Quality Act (CEQA).
      (2)   Major Site and Design Review: For all other projects not reviewed as Minor Site and Design Review, the project will be forwarded to the Planning and Transportation Commission for review and recommendation and then placed on the Council Consent agenda for final action, as prescribed for staff actions outlined in Section 18.77.060 (Standard Staff Review Process). Provided, however, that the following projects may be forwarded directly to the City Council Consent agenda by staff, without review by the Planning and Transportation Commission, where all of the following conditions apply:
         a.   The project is not a second dwelling unit; and
         b.   The project would comprise less than 1,000 square feet of floor area, less than 1,000 square feet of impervious cover, and less than 100 cubic yards of excavation and/or grading; and
         c.   The proposed floor area or impervious cover would not exceed 50% of the allowable for the site; and
         d.   The project and any prior projects within the prior five years would not cumulatively exceed these thresholds.
   (c)   Geological Soils Investigation and Report
      (1)   All applications for site and design approval shall be accompanied by a combined in-depth geologic and soils investigation and report prepared by a registered geologist certified by the state of California as an engineering geologist, and by a licensed civil engineer qualified in soil mechanics. Such report shall be based on surface, subsurface, and laboratory investigations and examinations and shall fully and clearly present:
         (A)   All pertinent data, interpretations, and evaluations;
         (B)   The significance of the data, interpretations, and evaluations with respect to the actual development or implementation of the intended land uses, and with respect to the effect upon future geological processes both on and off the site;
         (C)   Recommendations for any additional investigations that should be made. All costs and expenses incurred as a result of the requirements of this section, including the costs and expense of an independent review of the material submitted under this chapter by qualified persons retained by the city, shall be borne by the applicant.
      (2)   The requirement of subsection (1) may be waived by the city engineer for accessory facilities and landscaping where such improvements, in his opinion, would pose no potential hazard to life or property on the subject or surrounding properties.
   (d)   Landscaping
   The existing natural vegetation and land formations shall remain in a natural state unless modification is found to be necessary for a specific use allowed in this chapter through the site and design approval procedure. Reduction or elimination of fire hazards will be required where heavy concentrations of flammable vegetation occur. Landscaping as may be necessary and required shall be consistent with the purpose of this chapter.
      (1)   Landscaping shall be designed and installed consistent with the requirements and guidelines of Section 18.40.130 (Landscaping) of the Zoning Ordinance, and in particular with subsection 18.40.130(c) regarding landscaping in Natural Areas, as well as with the relevant Comprehensive Plan policies outlined in subsection (o) below. Exceptions to tree removal restrictions may be made for invasive species such as eucalyptus trees.
      (2)   A follow-up arborist and/or landscape report shall be required five years after the final sign-off of the project completion. This report shall evaluate the health of trees and significant landscape that were required for screen planting or and/or were designated as protected plantings on the approved plans for the project. The specifications of the report shall be provided in the conditions of approval of the project. This requirement also applies to sites that receive bonus floor area ratio (FAR) for maintaining specific percentages of the site as undisturbed native or restored. Any subsequent owner(s) shall also be obligated to replace any trees that die with trees of the same size and species stated on the approved planning and building permit plans.
   (e)   Fencing Restriction
   No barbed wire, or similar fencing having a cutting edge, may be installed except:
      (1)   To protect a vegetative community or wildlife habitat until it is fully established, subject to the imposition of reasonable time limits through site and design review pursuant to Chapter 18.30; and
      (2)   To enclose utility facilities, including, but not limited to, water or sewage pumps, storage tanks, and wells.
   (f)   Trash Enclosures
   Trash/recycle enclosures shall be permitted, with staff-level design review, within the front setback, including Special Setbacks, providing the enclosure is not more than six (6) feet tall, is covered, is fitted with self closing gates, and is screened. The access to the enclosure shall not be located on the side facing the street. The design of the enclosure shall be the minimum size needed to accomplish the purpose of enclosing and screening the containers.
   (g)   Tree Removal
   Removal of live trees shall be permitted only as provided in Title 8.
   (h)   Access to Remote Areas
   Roads, tracks, driveways, trails, or runways for automobiles, trucks, buses, or motorcycles or other wheeled vehicles shall not be developed except upon the securing of site and design approval. No such approval shall be granted except upon finding that the purpose for which the roads, tracks, driveways, trails, or runways are proposed is essential for the establishment or maintenance of a use which is expressly permitted in this chapter and that the design and location of the proposed roads, tracks, driveways, trails, or runways will be compatible with the terrain. The use of all roads, tracks, driveways, trails, or runways existing at the time of the adoption of this chapter which are nonconforming or have been established without proper approvals shall be terminated and shall be returned to natural terrain unless given approval in accordance with the regulations set forth in this chapter.
   (i)   Grading
   No grading for which a grading permit is required shall be authorized except upon the securing of site and design approval. No such approval shall be granted except upon a finding that the purpose for which the grading is proposed is essential for the establishment or maintenance of a use which is expressly permitted in this chapter and that the design, scope, and location of the grading proposed will be compatible with adjacent areas and will result in the least disturbance of the terrain and natural land features. All grading for which no permits or approvals are required shall be subject to the provisions set forth in this chapter.
   (j)   Soil Erosion and Land Management
   No site and design plan shall be approved unless it includes soil erosion and sediment control measures in accordance with any adopted procedures, technical standards, and specifications of the planning commission. No approval will be granted unless all needed erosion control measures have been completed or substantially provided for in accordance with said standards and specifications. The applicant shall bear the final responsibility for the installation and construction of all required erosion control measures according to the provisions of said standards and specifications.
   (k)   Subdivision
   All divisions of land into four or more parcels shall be designed on the cluster principle and shall be designed to minimize roads; to minimize cut, fill, and grading operations; to locate development in less rather than more conspicuous areas; and to achieve the purpose of this chapter.
   (l)   Substandard Lots
   Any parcel of land not meeting the area or dimension requirements of this chapter is a lawful building site if such parcel was a lawful building site on July 5, 1972. All other requirements of this chapter shall apply to any such parcel.
   (m)   Impervious Coverage
   The intent of limiting impervious cover is to minimize runoff, enhance infiltration to the soil, and provide a semi-rural appearance compatible with the OS district. Impervious coverage allowances are prescribed in Section 18.28.050(b) and shall be calculated as outlined below to include all building coverage, plus paved surfaces including but not limited to driveways, parking areas, sports or tennis courts, swimming pools, patios or decks, subject to exceptions and provisions as follows:
      (1)   All paved surfaces shall be classified as 100%, 75%, 50%, or 25% impervious, based upon the material that is to be used and the proposed design and installation. Determinations shall be made by the Planning Director based on permeability information provided by the applicant, and the Director may consult with the Public Works Department when necessary to determine the extent of the permeability. The applicant may provide information in the soils report to outline the baseline permeability of the specific areas proposed for coverage, and the baseline may be considered in determining the permeability of the material.
      (2)   A primary driveway composed of gravel or decomposed granite shall not be counted as impervious up to a width of 20 feet, where approved for use by the Public Works and Fire Departments.
      (3)   The portions of a primary driveway located in the 200 scenic setback shall be designed to have a natural appearance and shall not be counted as impervious up to a width of 20 feet (assuming the primary residence is located beyond the 200 setback).
      (4)   A primary driveway is one that extends from the nearest access road to the garage or carport providing the required parking for the main residence.
      (5)   The proposed pervious paving materials for the primary driveway shall only be permitted if acceptable to the Palo Alto Fire Department.
      (6)   The water surface area for in-ground pools and hot tubs shall not be counted as impervious. The Fire Department may require additional specifications for the pool in order to utilize the water more effectively for emergency response.
      (7)   The areas excluded from impervious coverage pursuant to approvals granted prior to July 1, 2007 shall remain excluded from impervious coverage calculations, unless the surfacing material is altered to a less permeable material.
   (n)   Light and Glare
   Exterior lighting should be low-intensity and shielded from view so it is not directly visible from off-site. The light emitted from skylights shall be minimal during the night hours. Utilizing treatments such as translucent glass, shading systems, and interior light placement can reduce the night glare. Skylights shall not use white glass.
   (o)   Story Poles and Other Visual Review Aids
   Story poles (with associated taping or flagging) shall be erected for projects involving new residences or other structures, or for substantial additions to new residences, for the purpose of providing a better understanding of the visual impacts of a proposal in the OS district. Story poles shall accurately outline the perimeter and key and highest rooflines of the proposed structure(s) and shall be durable and sturdy enough to be visible from distant views. Story poles shall be constructed to the satisfaction of the director prior to notice of a hearing and shall remain in place through the public hearing date. Erection of story poles prior to public hearing notice may be required by the director to allow for staff and neighbors to view the project. Other aids, such as taping the perimeter of other development (structures, pools, sport courts, etc.) on the site and identifying trees to be removed, may also be required by the director. Story poles shall be removed upon final action on a project or upon the direction of the director.
   (p)   Open Space Review Criteria
   In addition to the above provisions and development standards in Table 2, the following criteria shall be considered in the Site and Design review of all development of land in the OS district, as outlined in the Conservation Element of the Comprehensive Plan:
      (1)   The development should not be visually intrusive from public roadways and public parklands. As much as possible, development should be sited so it is hidden from view.
      (2)   Development should be located away from hilltops and designed to not extend above the nearest ridge line.
      (3)   Site and structure design should take into consideration impacts on privacy and views of neighboring property.
      (4)   Development should be clustered, or closely grouped, in relation to the area surrounding it to make it less conspicuous, minimize access roads, and reduce fragmentation of natural habitats.
      (5)   Built forms and landscape forms should mimic the natural topography. Building lines should follow the lines of the terrain, and trees and bushes should appear natural from a distance.
      (6)   Existing trees with a circumference of 37.5 inches, measured 4.5 feet above the ground level, should be preserved and integrated into the site design. Existing vegetation should be retained as much as possible.
      (7)   Cut is encouraged when it is necessary for geotechnical stability and to enable the development to blend into the natural topography. Fill is generally discouraged and should never be distributed within the driplines of existing trees. Locate development to minimize the need for grading.
      (8)   To reduce the need for cut and fill and to reduce potential runoff, large, flat expanses of impervious surfaces should be avoided.
      (9)   Buildings should use natural materials and earthtone or subdued colors.
      (10)   Landscaping should be native species that require little or no irrigation. Immediately adjacent to structures, fire retardant plants should be used as a fire prevention technique.
      (11)   Exterior lighting should be low-intensity and shielded from view so it is not directly visible from off-site.
      (12)   Access roads should be of a rural rather than urban character. (Standard curb, gutter, and concrete sidewalk are usually inconsistent with the foothills environment.)
   (q)   Standard Conditions of Approval
   The director shall maintain a list of standard project conditions for projects in the OS district that reflect the intent of the OS criteria. Conditions may address, but are not limited to, landscaping, tree protection, planting, and maintenance, lighting, roofing materials, grading, construction staging, and fire protection.
   (r)   Development Standards Exception
   Pursuant to a 1978 Settlement Agreement, nine designated lots less than 10 acres in size, located on page 54, book 182 of the Assessor’s Parcel Maps (182-54-xxx) are entitled to be developed as if they complied with the 10 acre minimum lot size for the OS zone. Owners of these nine lots may choose to comply with the parameters of the 1978 Agreement or the standard development regulations as described in this Chapter. A site shall utilize either the 1978 Agreement standards or the regulations described in this Chapter, but cannot use both.
(Ord. 5432 § 9, 2018: Ord. 5412 § 19, 2017: Ord. 5062 § 4, 2009: Ord. 4964 § 4 (part), 2007)