ADU Construction
Add square footage. Add rental income. Add real value.
Permitted, code-compliant ADU construction in Northern California: custom design, full construction, and garage conversions with permits and inspections managed in-house.
An accessory dwelling unit (ADU) is the highest-value square footage you can add to a Northern California property — for rental income, multigenerational living, or a home office. A1 Designing handles the full ADU project: design, permits, foundation, framing, MEP, finishes, and final inspection.
Most detached ADUs in our area cost $250,000–$450,000 turnkey; garage conversions are far less at $90,000–$180,000. We handle the entire city or county permit process so you don't have to navigate it.
What you need to know.
Detached ADUs in Northern California typically cost $250,000–$450,000 turnkey; garage conversions run $90,000–$180,000.
From design start to certificate of occupancy, expect 8–14 months for a new detached ADU in Solano, Yolo, Napa, or Sacramento counties.
California SB-9 and SB-13 streamlined permit pathways apply to most residential lots and can reduce permit timelines from 4 months to 60 days.
Every project, end to end.
- Custom ADU design and layout
- Site planning and survey coordination
- Permit applications + plan checks (city/county)
- Foundation and framing
- Electrical, plumbing, mechanical (MEP)
- Interior finishes, cabinetry, flooring
- Final inspection and certificate of occupancy
- Optional: rental-ready furnishing and staging
Real ranges, not online averages.
Garage conversion (400–600 sq ft)
4–7 months total
$90,000 – $180,000
Detached ADU — standard finishes (600–800 sq ft)
8–12 months total
$250,000 – $350,000
Detached ADU — premium finishes (800–1,200 sq ft)
10–14 months total
$380,000 – $550,000
How a adu construction project runs with us.
Site visit + feasibility
We walk your lot, review setbacks, utility access, and any HOA or city overlay rules to confirm what's buildable.
Design + budget alignment
We produce a layout that matches your goal (rental, family, office) and an itemized budget before any permit work starts.
Permits + plan check
We submit drawings, manage plan check revisions, and coordinate with city or county staff. Typical timeline: 2–4 months.
Construction
Foundation, framing, MEP rough-in, inspections, finishes — typically 5–8 months with weekly client updates.
Final inspection + certificate of occupancy
We coordinate the final inspection and hand over your certificate of occupancy. The unit is move-in or rental-ready.
Tell us about your project.
We'll come on-site, walk through the project together, and have a written quote in your inbox the same day. No pressure, no fluff.
- Free, no-obligation on-site consultation
- Written, itemized quote — same day
- Licensed, bonded, and insured
Questions, answered.
Don't see your question? Call us at (707) 999-6211 or use the form above.
A detached ADU in Northern California typically costs $250,000–$450,000 depending on size, finish level, and site conditions. Garage conversions run $90,000–$180,000. SB-9 lot splits and bonus density rules can reduce cost-per-unit substantially.
From design start to certificate of occupancy, expect 8–14 months. Permits run 2–4 months, construction runs 5–8 months. California SB-9 and SB-13 streamline the process for qualifying lots.
Yes — every California ADU requires a building permit. We handle the entire permit submittal, plan checks, and inspections so you don't navigate the city or county process alone.
Yes — both the on-site consultation and the written, itemized quote are 100% free with no obligation. We come to you, walk the project together, and email the quote the same day.
Yes. A1 Designing is a licensed California general contractor, fully bonded and insured. We are happy to share our CSLB license number and certificate of insurance at the start of any consultation.
ADU Construction across Northern California.
We're based in Vacaville and run jobs throughout Solano, Yolo, Napa, Sonoma, and Sacramento counties. Pick your city for local pricing, lead times, and recent projects.
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