How Long Does It Take to Build an ADU? Realistic Timeline Breakdown
Jaime Costilla ·
The Honest Truth About ADU Timelines
Let's skip the sugar-coating. Most contractors will tell you 4-6 months. The reality? Plan for 6-12 months for a new construction ADU and 4-6 months for a garage conversion. Here's why, and how to move faster.
Phase 1: Design & Engineering (4-10 Weeks)
What happens: Your architect creates plans, structural engineer reviews, and Title 24 energy calculations are completed.
What causes delays:
- Changing your mind on layout (every revision adds 1-2 weeks)
- Complex lots requiring additional engineering (hillside, soil issues)
- Waiting for survey or soil reports
How to speed it up: Make design decisions early and stick with them. Use pre-approved plans if your city offers them — the City of San Diego and Chula Vista both have pre-approved ADU plan libraries.
Phase 2: Permitting (4-12 Weeks)
What happens: Plans submitted to the city for review. Building, planning, fire, and utility departments all review.
What causes delays:
- Plan check corrections (the #1 delay — happens in 60% of projects)
- Incomplete applications
- City backlog (larger cities can take 8-12 weeks; smaller San Diego cities often 4-6 weeks)
How to speed it up: Work with a builder like Vision ADU who handles permitting daily. We know exactly what each city wants to see, reducing correction cycles.
Phase 3: Construction (8-24 Weeks)
Garage Conversion: 8-12 weeks
- Demo & rough-in: 2-3 weeks
- Framing modifications: 1-2 weeks
- MEP (mechanical, electrical, plumbing): 2-3 weeks
- Insulation, drywall, finish: 3-4 weeks
New Construction: 16-24 weeks
- Site prep & foundation: 3-4 weeks
- Framing: 2-3 weeks
- Roof: 1-2 weeks
- MEP rough-in: 2-3 weeks
- Insulation & drywall: 2-3 weeks
- Finishes (flooring, cabinets, fixtures): 3-4 weeks
- Exterior (stucco, paint, landscaping): 2-3 weeks
What causes delays:
- Rain (Southern California averages 35 rain days/year, mostly Nov-Mar)
- Material supply chain issues
- Inspection scheduling
- Subcontractor availability
Phase 4: Final Inspections & Certificate of Occupancy (1-3 Weeks)
What happens: City inspectors verify everything meets code. You receive your Certificate of Occupancy.
What causes delays:
- Failed inspections requiring corrections
- Utility company delays for final connections
Realistic Total Timelines
| Project Type | Best Case | Average | Worst Case |
|---|---|---|---|
| Garage Conversion | 3.5 months | 5 months | 7 months |
| New Construction (small) | 6 months | 8 months | 12 months |
| New Construction (large) | 8 months | 10 months | 14 months |
| Junior ADU | 2.5 months | 4 months | 6 months |
Planning Your Vision ADU Project
These phase durations are planning estimates, not promises. Permit review depends on the city and is not guaranteed. Vision ADU sets the construction schedule in a written agreement and has missed one deadline in total.
Ready to get started? Book your free consultation and we'll provide a custom timeline for your project.