Backyard Homes in California: ADUs and Ownership

Updated October 2026

A backyard home lets you add a second household without buying a second lot. In California, the legal form is usually an ADU, and state law now makes one possible on almost every residential lot.

The short version

• Most single-family lots can add an ADU plus a JADU.
• Detached ADUs go up to 1,200 sf, with side and rear setbacks capped at 4 ft.
• Cities must decide a complete application within 60 days.
• You don’t have to live on site to build an ADU (AB 976). JADUs still require it.
• A backyard home can house family, earn rent, or both.

Three ways to build one

• Detached cottage: one or two stories, with the most privacy.
• Attached unit: an addition with its own entrance.
• Garage conversion: the fastest path, using a structure you already have.

Each one is a complete home: its own kitchen, bath and entrance. Tiny houses on wheels and trailers are a separate category with their own rules. Conversions usually cost the least per square foot. Detached cottages cost the most but give both households the most room to breathe.

Why owners do it

• Family: parents close by, adult children with their own door.
• Income: long-term rent can help carry the mortgage. Check your city’s short-term rental rules before planning on Airbnb.
• Value: a permitted second unit adds usable, legal square footage.

Decide the use before you design. A rental needs durable finishes and a separate path to the street. A unit for a parent needs a no-step entry and a bathroom that works with a walker.

What to watch out for

• Utilities. Sewer and power capacity often set the real budget.
• Size. Impact fees begin at 750 sf.
• Design. A backyard home should fit the main house and keep light and privacy for both.
• The bigger picture. On a large or vacant lot, SB 684 and SB 1123 can create separate, sellable homes, which is a different path to ownership than a rental unit.

How we use it

Foothill Residence stacks a home and a second household on one lot. Mariposa Complex in Altadena gives each of three SB 1123 homes an attached ground-floor ADU. See our small-lot subdivision work.