Short answer: Plan for 8-14 months total from first design meeting to move-in day. The construction itself takes 4-6 months for most ADUs, but permits and planning add another 4-8 months on the front end.

Here's the real timeline breakdown based on projects we've completed in LA County.

The Full ADU Timeline

Phase 1: Design & Planning (4-8 weeks)

Before you can pull permits, you need plans. This phase includes:

• Initial consultation and site assessment — 1-2 weeks
• Architectural design and revisions — 3-6 weeks
• Engineering (structural, Title 24 energy calcs) — 2-3 weeks (often overlaps with design)

If you're doing a simple garage conversion with a standard layout, you might get through design in 4 weeks. A custom detached ADU with complex site conditions? Closer to 8 weeks.

Pro tip: Don't rush the design phase trying to save time. Changes during construction cost 10x more than changes on paper.

Phase 2: Permitting (6-12 weeks)

This is where most projects stall. LADBS (LA Department of Building and Safety) permit timelines vary wildly depending on:

• Plan check backlog (changes seasonally)
• Completeness of your submittal
• Whether you need corrections
• Expedited vs. standard review

Realistic LADBS timelines in 2026:

• Plan check: 4-8 weeks
• Corrections and resubmittal: 2-4 weeks (if needed)
• Permit issuance: 1 week

We covered permits in detail in our ADU Permit Timeline guide — worth reading if you're in the planning stages.

Phase 3: Construction (4-6 months)

Once permits are in hand, actual construction breaks down like this:

Garage Conversion ADU (400-600 SF): 3-4 months

• Demo and foundation work: 1-2 weeks
• Framing and structural: 2-3 weeks
• Rough MEP (mechanical, electrical, plumbing): 2-3 weeks
• Insulation and drywall: 2 weeks
• Finishes (flooring, cabinets, fixtures): 3-4 weeks
• Final inspections and punch list: 1-2 weeks

Detached ADU (600-1,200 SF): 4-6 months

• Site prep and foundation: 2-4 weeks
• Framing and roof: 3-4 weeks
• Rough MEP: 2-3 weeks
• Exterior (siding, windows, doors): 2-3 weeks
• Insulation and drywall: 2-3 weeks
• Finishes: 4-6 weeks
• Final inspections and punch list: 2 weeks

What slows construction down:

• Inspection delays (LADBS inspectors are busy)
• Material lead times (custom windows, cabinets)
• Weather (rain stops exterior work)
• Utility connections (LADWP, SoCalGas)
• Change orders (scope creep)

Phase 4: Final Inspections & Occupancy (2-4 weeks)

You're not done when construction finishes. Final steps include:

• Building department final inspection
• Fire department sign-off (if required)
• Utility meter installations
• Certificate of Occupancy

LADWP meter installation alone can take 2-4 weeks after you request it. Plan accordingly.

Total Timeline Summary

How to Speed Up Your ADU Project

1. Hire an experienced ADU contractor — We know what LADBS wants and submit clean plans the first time
2. Make decisions early — Pick your finishes, fixtures, and appliances before construction starts. Waiting on selections is the #1 cause of delays.
3. Use standard sizes — Custom windows take 6-8 weeks. Stock sizes ship in days.
4. Stay responsive — When your contractor asks a question, answer within 24 hours. Decisions that take a week to make can delay the project by a month.
5. Budget for contingency — Rushed decisions to save time usually cost more money

What Affects Your Specific Timeline?

Every project is different. Factors that can add time:

• Hillside or sloped lot — Additional engineering, special foundations
• Historic district — HPOZ review adds 4-8 weeks
• HOA approval — Variable, sometimes months
• Soil conditions — Bad soil = deeper foundations
• Easements or setback issues — May require variances

Ready to Start Your ADU?

At ZMA Legacy Builders, we handle ADU projects from design through final inspection. We'll give you a realistic timeline based on your specific property and help you avoid the common delays that frustrate LA homeowners.

Get a free site assessment — Call us at (213) 375-4958 or visit zmalegacybuilders.com/contact to schedule.

ZMA Legacy Builders is a licensed general contractor (CSLB #1137900) building ADUs throughout Los Angeles County. Updated March 2026.