An attached ADU and a JADU are different projects.
An attached ADU creates an accessory dwelling connected to the main home. A junior accessory dwelling unit is a distinct regulatory category with its own requirements and limitations. Do not select a label simply because the proposed space is small or shares a wall.
Have the design team and City confirm the applicable category for your layout, facilities, and existing structure. That classification affects the drawings, project obligations, and the decisions that need to be resolved. Our Costa Mesa ADU permit guide links to the official local starting point.
The meeting point needs careful construction planning.
Where new work touches the existing home, examine the roof, walls, foundations, drainage, and service connections. An addition can affect a room you intend to keep, an existing window, or the route through the house. These changes belong in the scope from the start.
If the home remains occupied, discuss dust separation, temporary protection, entry routes, and any planned interruptions to services. Access to the work area should be understood by the homeowner and construction team before the job begins.
Plan two households, not just extra floor area.
Independent living depends on more than a doorway. Think through acoustic separation, lighting, bathroom arrangements, kitchen use, outdoor access, and the location of laundry. Put the daily routines of each household on the plan.
Ask where deliveries arrive, how visitors find the entrance, and what is visible from each living area. If someone needs privacy while another household is active, the plan needs to support that without relying on everyone having the same schedule.
Include the work the main house needs.
A proposal for attached living space should make the existing-home changes visible. Finishing a new unit may also require modifying adjacent rooms, rerouting services, restoring surfaces, or coordinating work across the original structure.
Compare the whole scope with a detached ADU or garage conversion. The option using the least new floor area does not automatically involve the least construction.
Bring the right information into the first discussion.
Gather an existing floor plan if available, photos of the rooms involved, your intended use, and the areas of the main home that need to remain functional. List your privacy and accessibility priorities. These facts make a ADU project brief more useful than an isolated room-size target.
Local source: City of Costa Mesa ADU resources. Check the current City instructions for your address and proposed work.