Attached ADU design-build in Los Angeles
A new living unit built onto your house, with its own entrance, kitchen and bathroom.
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What is an attached ADU?
An attached ADU is a new living unit built onto the main house. It shares at least one wall with it and has its own entrance, kitchen and bathroom. It suits lots where a separate building does not fit behind the house. Siboni Development & Design designs, permits and builds it with one team.
How big can an attached ADU be?
Under state law, an attached ADU cannot exceed 50 percent of the floor area of the existing main house. A city cannot set its own maximum below 850 square feet, or 1,000 square feet for a unit with more than one bedroom, and must always allow a unit of at least 800 square feet.
| Topic | Rule | Source |
|---|---|---|
| Maximum size | 50 percent of the existing main house | Gov. Code § 66314(d)(4) |
| Lowest cap a city may set | 850 sq ft, or 1,000 sq ft with more than one bedroom | Gov. Code § 66321(b)(2) |
| Always allowed | At least 800 sq ft with four-foot side and rear setbacks | Gov. Code § 66321(b)(3) |
| Height | 25 feet, or the height limit of the main house if lower | Gov. Code § 66321(b)(4) |
| Setbacks | No more than four feet from the side and rear lot lines | Gov. Code § 66314(d)(7) |
How much does an attached ADU cost?
We do not publish a price range for attached ADUs: the cost depends on the size of the unit, the structure of the existing house where the two connect, and the distance to the utility connections. Every project starts with a free 45-minute site assessment, and the fixed price that follows includes design, permits, utilities, finishes and landscaping.
How does the process work?
Five steps, one contract, one point of contact. We handle the site assessment and feasibility, design with 3D renderings of your exact backyard, the entire city permit process (average approval: 6 weeks), construction with a dedicated project manager and a weekly photo report, then turnkey delivery once the final inspection has passed.
Sources
- California Government Code § 66314
- California Government Code § 66321
- California Department of Housing and Community Development, Accessory Dwelling Unit Handbook (March 2026)
Sources checked on . General information, not legal or financial advice. Rules change and each city applies its own standards: we confirm what applies to your lot during the free site assessment.
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