The County of Santa Cruz’ ADU Design Guide

Santa Cruz County has recently implemented new, more relaxed development standards intended to make building an Accessory Dwelling Unit (ADU) easier and more affordable. Towards this end it’s published three guidebook resources, Santa Cruz County ADU Basics, ADU Financing Guide, and ADU Design Guide. This article outlines the County’s ADU Design Guide.

ADU Types
For any homeowner on any property their design option will fall into one of four (4) categories, or types, as follows:
• ADUs within the Urban Services Line
• ADUs outside the Urban Services Line
• Conversion ADUs
• Remodel ADUs
ADU types affected by the Urban Services Line (USL) fall into three subcategories, namely: 1). Detached New Construction, 2). New Construction above a Detached Garage, and, 3). Attached New Construction.

What is the Urban Services Line?
The Urban Services Line (USL) is defined as the “boundary line defining those areas planned to accommodate urban densities of development as based on the pattern of existing urban services.” Basically, it’s a mapping designation determining whether your property is in the urban area vs. outlying rural portions of the County.

In general terms, within the USL the new development standards are geared to encourage smaller, lower profile units. Conversely, outside the USL larger, taller units are permitted.

Detached New Construction
For constructing a new, from-the-ground-up Accessory Unit detached from the main residence located within the USL the height limit is set at 17 feet maximum and maximum one-story in height. The size of the unit is set proportional to the area of the lot, up to a maximum of 800 sq. ft.
The same unit outside the USL is allowed to be built to an overall height of 28 feet and two-stories and, depending on the parcel size, from 800 up to a maximum of 1,200 sq. ft.

New Construction above a Detached Garage
Inside of the USL, for ADUs built above an existing detached garage are allowed to encroach to within five feet (5’) of rear and/or side property lines. The overall height of the building is set at 24 feet maximum. The size of the ADU proper, exclusive of the garage, is the same as for detached new construction up to a maximum of 800 sq. ft.

For ADU’s constructed above an existing detached garage outside the USL two height options are available. The first is to locate the garage+ADU building in conformance with district standard setbacks in which case a 28 ft. height limit pertains. Alternatively, setbacks can be reduced to five feet (5’) of rear and/or side property lines in which case the height limit is 24 ft. Building area is set the same as for new construction, ranging from 800-1,200 sq. ft. depending on the size of the parcel.

Attached New Construction
An ADU addition to an existing home inside the USL, setbacks can be reduced to 5 ft. of rear and/or side property lines if the height of the addition is limited to 24 ft. If district standard setbacks are conformed to, the addition’s height may be increased to 28 ft. The square footage of the ADU addition is governed the same as for detached new construction, namely proportioned to lot area up to a maximum of 800 sq. ft.

For an ADU addition (“attached new construction”) outside the USL district standard setbacks applicable to the parcel also apply to the new addition. The addition may be one story or two, up to a maximum height limit of 28 ft. Again, the area of the addition is the same as that for new construction, namely ranging from 800-1,200 sq. ft., relative to the parcel’s size.

Conversion ADUs
This type consists of conversion of an existing interior space or existing garage in an ADU. To meet the requirements they must be remodeled so as to provide a full kitchen, and their own entrance separate from the main entrance to the house. One consideration in a garage or basement conversion is head height, which may require floor excavation in order to meet Building Code requirements.

Remodel Alternative
Remodel alternatives are offered as a way for homeowners to make improvements resulting in more flexible use of the home resulting in, for example, more “rentable” space for housemates. The provisions allow construction of a kitchenette within the remodeled space. This option allows underused basements, attics, or spare bedrooms to be converted to rentable square footage.

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