Remodels can be substantially cheaper than construction of a full, independent dwelling unit. Remodeling to create greater separation between living spaces while not creating a separate dwelling unit can accommodate the needs of many households.

A second area for limited food prep that does not include a full stove or oven is allowed in addition to the kitchen in an existing home. Essentially, a sink, refrigerator, counter space, and any small appliances that plug into a standard 110V wall outlet can be added to a bedroom or den to create a separate living space in the main home. The separate space must maintain an interior connection to the rest of the home, since it is not a fully independent ADU.

If there is existing habitable space in your home or an outbuilding that is suitable to be converted to an ADU, both construction and permitting costs are substantially reduced. In order to be a full ADU, the finished space must have a full bathroom, full kitchen, separate entrance, separate heat source, and sound and fire-wall separation from the primary home.

Do you have space to relocate your existing required parking space(s) outside the garage and use the garage as an ADU? Parking spaces can be replaced with uncovered parking in tandem or triple tandem (2 or 3 cars parked behind one another) to accommodate an ADU on your lot. See parking requirements below.

You may want to consult with a contractor regarding the condition and quality of the existing structure to see if converting is financially more feasible than new construction.

Additions to existing homes, depending on the age of the existing structure, can also be a more cost effective approach to creating an ADU, especially for smaller units, than new detached construction.

Additions under 500 sf are exempted from certain permit reviews and fees (such as school fees, affordable housing impact fee and soils report review, etc. ), creating the potential for considerable cost savings.

Example pre-fab Accessory Dwelling Unit

If detached new construction is the style of ADU that works best for your needs, consider whether a manufactured home or a prefab home would work on your site. Factory-built housing is legal to use as an ADU so long as it is attached to all required utilities and permanently mounted to an appropriate foundation. These units can represent significant construction cost savings in many locations, and require fewer building inspections for a quicker timeline to occupancy.

See a list of Resources for links to manufactured and pre-fab home dealers.

Once you’ve settled on a style of construction, consider site planning to minimize costs:

If you use a septic system, consider its location and elevation relative to a new ADU, and what additional costs this could create. Consult with County Environmental Health Services (scceh.com or 454-2022 for septic evaluation) early in your process.

ADUs that are built as free-standing New Construction trigger a requirement of 1 parking space, which must be accommodated on site.

In order to add any type of ADU, the main home on the property must meet current requirements for parking spaces in a garage, carport, or driveway; OR If the existing home does not meet current parking requirements, and the ADU does not trigger a requirement for a new parking space, the existing number of parking spaces must be maintained. As long as there is no net loss of off-street parking spaces on the property, spaces can be relocated and reconfigured in any manner that will fit on the parcel, including in tandem or triple tandem (three cars parked behind one another). There is no requirement that any of the parking spaces be covered by a carport or garage.

ADUs created as Conversions, or which are attached to the existing home or garage do not trigger a parking requirement, and therefore also do not trigger transportation-related fees.

On parcels of 6,000 sf or smaller, the County allows a 2% bonus above the standard lot coverage and floor area ratio limits in order to accommodate an ADU.