Planning an Attached ADU in California
Thinking about a unit connected to your existing home? Here's what planning and permitting an attached ADU generally involves.
What Is an Attached ADU?
An attached ADU is a unit connected to the existing house — for example, built onto the side or rear of the home, or created within an addition. Because it shares a wall or structure with the main house, an attached ADU typically involves different structural and design considerations than a fully detached unit, including how it connects to existing systems and how it affects the existing structure.
Legal ADU Pro helps California homeowners understand what planning an attached ADU typically involves and coordinate the plans, documentation, and professionals a project needs.
Design & Structural Considerations
- How the addition connects to the existing home's structure and systems
- Zoning rules and lot coverage limits that apply to the expanded footprint
- Design requirements for how the addition relates to the existing house
- Utility connections shared with or separated from the main home
An individual review helps clarify what's realistic for your specific property before you invest in plans.
General Process Overview
While every project and jurisdiction is different, planning an attached ADU generally involves: an initial review of the existing home and property, coordinating plans that account for the connection to the existing structure, submitting for the appropriate permits, responding to any plan check corrections, and completing inspections during and after construction.
Because the project connects to an existing structure, plans typically need to address how the addition interacts with existing framing, systems, and egress.
Plan Your Attached ADU
Legal ADU Pro can help you understand what an attached ADU project on your property typically involves.
Request a Property Review →Explore planning options for detached, garage conversion, and other new ADU projects.
View New ADU Services →Once plans are underway, see what's involved in coordinating permit submittal for a new ADU.
ADU Permit Coordination →If the addition already exists and wasn't permitted, this isn't the right page — see Unpermitted Addition Legalization instead.
Unpermitted Addition Legalization →What an Attached ADU Typically Needs
Most attached ADU projects need some combination of a site plan, floor plan, and elevations before they can be submitted for permits — see our ADU plans, drafting & design coordination guide for what's typically involved and when a licensed professional is required.
Questions About Planning an Attached ADU
An attached ADU shares a wall or structure with the main house, while a detached ADU is a fully standalone structure. Attached projects generally involve different structural and design considerations related to the connection with the existing home. See our Detached ADU guide for comparison.
It depends on your home's layout, zoning, and local requirements. An individual review is needed to understand what's realistic for your specific property.
Often, yes, particularly because the project connects to an existing structure. Legal ADU Pro helps identify when licensed professionals are likely needed and can help coordinate with them.
Ready to Plan Your Attached ADU?
Request an initial property review and understand what planning an attached ADU on your property typically involves.
Request a Property Review → Call 310-570-2885