What is an attached ADU?
It is a separate dwelling built as an addition to your house. It shares at least one wall with the main home but has its own entrance, kitchen and bathroom, and there is usually no open door between the two.
How big can an attached ADU be?
As of October 2026, state law lets a city limit an attached ADU to 50 percent of the main home's floor area, but never below 850 sq ft, or 1,000 sq ft with more than one bedroom (Government Code §§66314(d)(4) and 66321(b)(2)). Fresno's own limits are set in Municipal Code §15-2754, and we check them for your address.
How tall can it be?
Up to 25 feet, or the height limit of your zone, whichever is lower, under Government Code §66321(b)(4)(D). That can allow a second story above part of the house where the structure and building code allow it.
Why choose attached over detached?
- Shorter utility runs. Water, sewer and power are right next door.
- Less yard used. Useful when the backyard is shallow or holds a pool.
- Closeness. Helpful for a relative who needs someone nearby.
What makes attached ADUs harder?
Tying new framing and roofing into an older house takes care. Where the two units meet, the wall must be fire-rated and should limit sound. Older homes may also need electrical upgrades before they can carry a second kitchen and its cooling load.
Will an attached ADU cost less than a detached one?
It depends on the roof tie-in and the condition of the house. Short utility runs save money, but matching an existing roof or reworking a wall can use those savings up. Published 2026 Sacramento figures from Block Renovation put attached ADUs at $100,000 to $300,000, as of October 2026. We price your version in writing.
Related
As of October 2026. Sources: HCD ADU Handbook (March 2026); California Government Code §§66314 and 66321; Block Renovation, Sacramento ADU Costs 2026.
Find out if an addition fits
Send the address. We check side yard space, the zone height limit and the electrical service before design starts.