How Long Does It Take to Build an ADU in Los Angeles? (2026)

Q: How long does a garage conversion take?

A garage conversion usually takes about 3 to 4 months to build, plus design and permitting time.

Q: How long does ADU permitting take in Los Angeles?

Permitting typically takes 8 to 12 weeks, though simple flat lots can clear in about 4 weeks and hillside lots can take 3 to 4 months.

Short answer: Most ADU projects in Los Angeles take 6 to 12 months from start to finish — about 2–6 weeks for design, 8–12 weeks for permitting, and 3–8 months for construction. A small, pre-designed garage conversion can be done in about 6 months; a large detached ADU averages around 9 months; hillside or complex builds can take 12+ months. Starting with permit-ready plans is the single biggest time-saver.

ADU timeline overview

Phase	Typical duration
Design & plans	2–6 weeks (about 1 week with a pre-designed plan)
Permitting (plan check + clearances)	8–12 weeks
Construction	3–8 months
Total	6–12 months

Construction time by ADU type

ADU type	Construction time
Garage conversion (300–500 sq ft)	3–4 months
Small detached ADU (400–600 sq ft)	3–4 months
Large detached ADU (800–1,200 sq ft)	6–8 months

Phase by phase

Design & plans (2–6 weeks): a pre-designed plan set can be ready to submit in about a week; a fully custom design takes 4–6 weeks.
Permitting (8–12 weeks): initial plan check (2–4 weeks), corrections, and agency clearances. Simple flat lots can clear in as little as 4 weeks; hillside lots take 3–4 months.
Construction (3–8 months): site prep and foundation, framing, rough trades, drywall, then finishes and final inspections.

How to build your ADU faster

Start with a permit-ready plan set — pre-designed plans can cut permitting time roughly in half.
Have survey, title, and utility information ready early.
Respond quickly to design and plan-check questions — each delay can add about a week.
Work with an ADU-experienced design and build team.

Frequently asked questions