Summary

This brochure explains how to calculate the maximum density of new dwelling groups, multi-family dwellings and land divisions. Density calculations differ between urban and rural areas.

Urban

Within the urban services line (USL) and rural services line (RSL), the number of allowable dwelling units or new parcels is based on the land area and the zoning. In urban areas, most residential zone districts are single-family (R-1) or multi-family (RM). Each zone district includes a number that indicates how many thousand square feet are required for each new lot or dwelling unit. For example: “R-1-6” or RM-6 means a minimum land area of 6,000 square feet per parcel or per dwelling unit. Accessory dwelling units are not counted in density calculations.

The area of the parcel used for density calculation is the “gross site area,” which includes all of the land in the lot, including rights of way, corridor access, slopes, floodplains, riparian corridors – most everything. This is a change from previous zoning ordinance policies. However, where parcels include coastal bluffs, the gross site area does not include the bluff area, beach, or any tideland areas. This applies both to parcels at the top of the bluff and parcels at the base of the bluff. But in urban areas away from the coast in R-1 and RM districts, the minimum land area for lots or primary dwellings is simply based on the gross land area divided by the required minimum size indicated by the zoning.

Within the residential agriculture (RA) and rural residential zone districts (RR) inside the RSL (or USL if applicable), the minimum parcel size is one acre, based on gross site area.

The maximum number of accessory dwelling units (ADUs) and junior accessory dwelling units (JADUs) is based primarily on the number of primary or multi-family dwellings on a parcel. Usually, one ADU and one JADU are allowed per single-family dwelling. However, on sites with multiple dwellings, whether dwelling groups, townhouses or multifamily dwellings, please contact the Planning Department, as the type of permit required may depend on the number of proposed ADUs and the density of the primary dwelling units.

The County GISWEB, also linked off of the Planning Dept. homepage, provides a map of the urban and rural services lines (Land Use Layer). The GIS also states where any given parcel is located – check the Land Use tab displayed below the parcel map.

Code references are 13.10.323(B) Site Area for the Creation of New Sites; 13.10.700-S, Site area, gross; and 13.10.700-D, Density.

Rural

Land area for density calculations outside the USL / RSL is based on net developable site area. (See SCCC 13.10.700-D for “Developable Land,” and 13.10.-700-S for “site area, net developable”). The following lands are considered undevelopable and are deducted from the gross site area:

• Rights-of-way designated for vehicle access.
• Slopes greater than 30%. (Note: A density credit is given for lands with 30%-50% slopes. Effectively, only lands greater than 50% are deducted.)
• Geologic hazard areas described in SCCC 16.10.080, including the following:
  • Floodplains and Coastal Inundation Areas
  • 50’ on either side of an earthquake fault
  • Landslides, unless stable and safe for development as documented by a geologic report
• Sensitive habitats and buffers as described in SCCC Chapter 16.32 (may require biotic report). Sensitive sandhills habitat, Special Forest areas and grasslands are mapped (approximately) in the GIS.
• Lakes, marshes, sloughs and wetlands and buffers (SCCC chapters 16.30 and 16.32)
• Riparian corridors and riparian buffer zones as described in SCCC 16.30.040. In rural areas, riparian corridors extend 50’ to either side of a perennial stream, 30’ on each side of an intermittent stream and include any lands containing riparian vegetation (e.g., willow, alder, cottonwood, dogwood).
• Any other areas unsuitable for development as described in SCCC Title 16.

In the RA and RR zone districts outside the USL / RSL, the required land area per dwelling unit is based on the rural residential density determination matrix (Chapter 13.14 SCCC), which establishes density within a range provided by the General Plan land use designation (table below), using a point system based on resources and constraints. The minimum parcel size (in net developable acres) within the R-M classification is always at least 10 acres, never more than 40 acres; in the R-R designation, at least 2.5 acres and never more than 20 acres; in the R-S designation, at least 1 acre, never more than 5 acres. Note: Overriding Minimums in the General Plan may also apply. Overriding Minimums may relate to water supply watersheds, groundwater protection, fire safety, secondary access, fault zones and other constraint factors. Throughout much of the San Lorenzo Valley, for example, the overriding minimum established by the County General Plan is 10 acres in order to protect the water supply watershed

Minimum Density in Urban Areas

The minimum density of dwellings, or maximum parcel size, is determined in urban areas by the density range provided by the General Plan designation. The maximum parcel size allowed within the urban General Plan designations is indicated in the table below.

SB9 Lot Splits and Dwelling Groups

Many parcels within the Census Urbanized Area are potentially eligible for SB9 lot splits or 2-unit dwelling groups (see the SB9 webpage). The minimum gross land area (minus bluffs / beaches) for new lots outside the Coastal Zone is 1,200 sq.ft. under SB9. Where an exception from a site or structural standard is required on a given lot, the associated new dwellings are limited to 800 sq.ft. (Inside the Coastal Zone, current standards must be met until the LCP is amended to add SB9 ordinance provisions.) More information about SB9 eligibility criteria, objective standards and application forms is located on the SB9 webpage.