Yes, existing accessory structures can be converted to an ADU. Some important considerations to keep in mind are:
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Yes, provided the structure was legally constructed with building permits and the structure can be upgraded to meet the current building code requirements for a living unit. When an existing garage or other accessory structure is converted to an Accessory Home, no additional building setback verification is required. The Accessory Home must have independent exterior access from the existing residence.
Yes, provided the garage was legally constructed with building permits, the structure can be upgraded to meet the building code requirements for a second story and a living unit. An Accessory Home constructed above a garage must meet the setbacks required by zoning.
Fire separation will need to comply with tables R302.1(1) and R302.1(2) of the California Residential Code. ADUs equipped with automatic sprinklers require a 1-hour rated exterior wall if constructed within 3’ of a property line or 6’ from an adjacent sprinklered structure on the same lot. ADUs not equipped with fire sprinklers require a 1-hour rated exterior wall if constructed within 5’ of a property line or 10’ of an adjacent building on the same lot. For ADUs that are attached to a primary dwelling, 1-hour rated wall and/or floor assemblies are required to separate the dwelling units. See CRC R302 for additional information. Fire separation requirements do not apply to JADUs that are built within the walls of an existing dwelling.
Per R313.2, ADUs are exempt from automatic fire sprinkler system requirements if ALL the following are met:
ADU egress will need to comply with R311. Below is a list of some (but not all) applicable code requirements:
No. CMC 311.4 prohibits the transfer of air between adjacent dwelling units. Separate HVAC systems are required for each dwelling unit.
ADUs are eligible for, but do not require individual utility meters. If you are planning on extending utility connections from the primary dwelling to the ADU, you will need to demonstrate that the existing utilities are adequate to serve the proposed ADU. (Example: gas line sizing diagram, electrical load calculations, drainage fixture unit calculations, etc).
For new construction, the CA Energy Code 150.1 typically requires a new PV solar system to be installed to meet the prescriptive or performance energy design for the ADU. There are some exceptions, such as (but not limited to) participation in a shared solar electric generation system (CEC 150.1(b)(1), exception), and limited solar access (CEC 150.1(C)14, exception 1). Solar is not required for attached ADUs or conversions of existing space, including existing permitted attached and detached garages.
If your project is located within any Fire Hazard Severity Zone or Wildland Urban Interface Fire Area, then it will need to comply with the materials and construction methods outlined in CA Residential Code R337, as amended by Placer County. The requirements of R337 apply to new construction and to significant additions/remodels where the roofing, siding, and windows are all replaced within (1) year of building permit issuance per Placer County Code 15.04.270.