ADU Construction in Southern California & the Bay Area
Quick answer
In Southern California, a garage-conversion ADU typically costs $120,000–$220,000 and a detached ADU of about 500 sq ft costs $180,000–$300,000; larger detached units run $280,000–$450,000. Most projects take about 6–12 months from design to move-in. California law requires cities to approve or deny a complete ADU application within 60 days.
5.0 from 47 reviews on Houzz · CSLB Lic. #1040337 · Class B
What our adu construction service includes
Garage conversions and detached accessory dwelling units, managed from feasibility and plans through permits, utilities and move-in.
MDG Builders sells, designs and manages your project; the work is performed by licensed, insured subcontractors.
- Feasibility and site review
- Design and plan-check coordination
- Foundations, framing and utilities
- Kitchen, bath and finishes
- Final inspection and certificate of occupancy
ADU Construction cost in California
| Scope | Typical installed range |
|---|---|
| Garage conversion ADU | $120,000 – $220,000 |
| Detached ADU, about 500 sq ft | $180,000 – $300,000 |
| Detached ADU, 800–1,000 sq ft | $280,000 – $450,000 |
Cost factors
- Conversion versus new detached construction
- Size, bedrooms and bathrooms
- Utility trenching distance, sewer and panel upgrade
- Soil, slope and fire-zone requirements
- Finish level
- City plan-check timing
How long it takes
About 6–12 months from first meeting to move-in, driven by design, plan check, construction and utility connections. Conversions are usually faster than detached builds.
Permits
ADUs require a building permit. Under California law the agency must approve or deny a complete application within 60 days, or it is deemed approved. Cities cannot require replacement parking when a garage is converted to an ADU.
| Garage conversion | Detached ADU | |
|---|---|---|
| Typical cost | $120,000–$220,000 | $180,000–$300,000 (about 500 sq ft) |
| Structure | Reuses existing garage when sound | All-new foundation and framing |
| Yard impact | Minimal | Uses yard space |
| Replacement parking | Not required by state law | Depends on site |
How your adu construction project works
Consultation
Call (888) 666-8224 or send the form to share goals, timing and budget range.
Site visit
We measure, assess existing conditions and discuss options in person.
Written proposal
You receive a written scope and price; typical ranges are a guide, not a quote.
Permits and scheduling
We coordinate permits where required and schedule licensed, insured subcontractors.
Construction and walkthrough
Our team manages the work through final inspection and walkthrough.
What clients say about MDG Builders
We had no idea where to start, we had a large project with so many moving parts can be very challenging for novices like us. From the very beginning, Emil was responsive, helpful, timely with any questions, night and day. Since this was a gut job we were even more nervous. We were astonished on just how easy the whole process was with no hiccups at all. Less than 3 weeks and we had a wonderful spa. His workers were responsible, timely, responsive and did an amazing job down to the little details. Even our friends were surprised we had such an easy time with the job. Book them for any job because you will not be disappointed.
We couldn't be happier with My Design Guide Inc. We hired them to gut our basement and remove a few dead trees. He showed up when he said he was going to, respected our space, worked hard, completed the project on time for the cost that he quoted, and left the space as clean as possible. It is so rare to find any contractor these days who do what they say they are going to do, so this company is a real diamond in the rough. Highly recommend!
From the beginning, we had a great experience with the team at My Design Guide Inc! We wanted to upgrade our patio but we weren't creative enough to know what to do. David was full of great suggestions to make the patio a true conversation piece while still honoring our budget and we couldn't be happier with the result! The quality of work and professionalism is the best I have seen in this business, and they really do take pride in their work. David communicated with us throughout the process and was meticulous in ensuring our yard was still taken care of during the construction period. We have received so many compliments on our new paver patio, fire pit with seating, and built-in outdoor counter. I highly recommend going with them. I would go with them again a hundred times over!
Verbatim Houzz reviews of MDG Builders; some describe projects other than adu construction.
ADU Construction questions, answered
Related services:
Cost guides:
How much does an ADU cost in Southern California?
Typical ranges: $120,000–$220,000 for a garage conversion, $180,000–$300,000 for a detached unit of about 500 sq ft, and $280,000–$450,000 for 800–1,000 sq ft.
How long does it take to build an ADU?
About 6–12 months from first meeting to move-in, depending on design, plan check and utilities.
How long does ADU permit approval take in California?
Cities must approve or deny a complete application within 60 days under state law. Reaching a complete application can take additional time.
Do I need replacement parking if I convert my garage?
No. State law prohibits requiring replacement parking when a garage is converted to an ADU.
Is a garage conversion cheaper than a detached ADU?
Usually, because the structure exists. Slab, footing, sewer and panel conditions can narrow the gap.
Can I rent out my ADU?
ADUs are commonly rented long-term; check your city's rules on short-term rentals.
What is the difference between an ADU and a JADU?
A junior ADU (JADU) is created within the existing home and is limited in size; an ADU can be attached, detached or a conversion.
Who actually does the work on my project?
MDG Builders (My Design Guide Inc, CSLB #1040337, Class B) sells, plans and manages your project from start to finish. The hands-on work is performed by licensed, insured subcontractors in each trade, scheduled and supervised by our team so you have one point of contact.
Is MDG Builders licensed in California?
Yes. My Design Guide Inc holds California Contractors State License Board license #1040337, Class B (General Building). You can look up any license on the CSLB website.
What areas do you serve?
Southern California from Lancaster to San Diego, plus the San Francisco Bay Area.
How do I get an estimate?
Call (888) 666-8224, email info@mydesignguide.com or send the estimate form. We discuss your goals, schedule a site visit and send a written proposal. Office hours are Monday to Thursday 8 AM to 5 PM and Friday 8 AM to 2 PM.
Planning a adu construction project?
Free estimates. A real person answers — call or send the form and we'll follow up to schedule a site visit.
MDG Builders at a glance
- Who
- My Design Guide Inc dba MDG Builders, a licensed general contractor that sells, designs and manages remodeling and construction projects
- License
- CSLB #1040337, Class B (General Building)
- Where
- Based in Tarzana, CA; serving Southern California (Lancaster to San Diego) and the San Francisco Bay Area
- Phone & email
- (888) 666-8224 · info@mydesignguide.com
- Hours
- Mon–Thu 8:00 AM–5:00 PM · Fri 8:00 AM–2:00 PM · Sat–Sun closed
- Rating
- 5.0 from 47 reviews on Houzz