Can I get an ADU permit at the same time as a new house or a full rebuild?

Yes. California lets you apply for an ADU together with a new single-family or multifamily home, and the ADU must still be reviewed ministerially, without a hearing. The trade-off is that the agency may hold its decision on the ADU until it decides the house, and some fee and occupancy rules change when the ADU is built with a new home.

How concurrent review works

• Timing. Government Code section 66317(a)(3) requires a decision on a complete ADU application within 60 days when there is an existing dwelling on the lot. When the ADU application is submitted with an application for a new house, the agency may delay the ADU decision until it approves or denies the house. JADUs follow the same rule under section 66335.
• Still ministerial. Even when delayed, the ADU application must be considered without discretionary review or a hearing.
• Proposed homes count. State law allows ADUs on lots with a proposed or existing primary dwelling, and the state-protected ADU combinations in section 66323 apply to lots with a proposed single-family home.

What changes when the ADU is built with a new home

• Utility charges. Section 66311.5 says an ADU or JADU is not treated as a new residential use for utility connection fees or capacity charges unless it is constructed with a new single-family dwelling. Building both together can therefore open the door to those charges.
• Parking. Section 66322(a)(6) bars parking requirements for an ADU submitted with a new-home application only if the ADU or parcel also meets one of the other parking exemptions, such as being within one-half mile walking distance of public transit.
• Occupancy. Section 66328(a) generally bars a certificate of occupancy for the ADU before the main house receives one. Limited disaster exceptions exist, including for homes lost in the January 2025 Los Angeles fires.

What this means for your MEP plans and permit set

Designing both buildings at once lets you plan utilities for the whole site. One load calculation can size a service for the house and ADU together, or show where a separate service makes more sense. The sewer lateral, water service and any gas service can be sized and routed for both from the start, and Title 24 compliance must be documented for each new dwelling. Coordinate the two MEP sets so equipment, meter locations and trenches do not conflict on the site plan. See separate service versus subpanel, electrical load calculations, and the California ADU permit guide. Confirm how your jurisdiction sequences combined applications with your planning and building departments.

Sources: leginfo.legislature.ca.gov, leginfo.legislature.ca.gov, leginfo.legislature.ca.gov, leginfo.legislature.ca.gov, leginfo.legislature.ca.gov.