Attached ADUs with their own front door.

An attached ADU is a complete dwelling joined to your house, either as new construction off the side or rear of the home or by converting attached space such as a garage.

Attaching to the main house can shorten utility runs and use yard space efficiently, and it suits lots without room for a freestanding unit. It also means building against an existing structure, so the roof tie-in, the foundation connection, fire-rated separation between units and sound control all need careful detailing.

Example: an attached-garage conversion

One Oxnard ADU started as an attached garage. The sewer was located, the slab was cut for waste lines, the floor was leveled with a new pour, a new roof was built over the existing walls and the unit got its own separate entrance. The main house was reroofed at the same time so the two read as one building.

Size and design

Many cities limit attached ADUs to 50 percent of the existing home's floor area, but state law still guarantees at least 800 square feet on a qualifying lot. Height limits for attached units are more generous than for detached ones in many cases. See the ADU rules guide for current standards.

Living side by side

Entries, windows and outdoor space should be planned so both households have privacy, and the shared wall and floor or ceiling assemblies detailed for fire separation and sound. Decide on separate or shared utilities, mailboxes and parking up front.