Golden State ADUs is a full-service design-build accessory dwelling unit (ADU) specialist located in Roseville, serving Vacaville homeowners along the Interstate 80 corridor, roughly 51 to 53 road miles west of our office. Architecture, structural and civil engineering, permitting and construction all come from one team, which is how we keep miscommunication and delays out of your ADU project. We are licensed and bonded (LIS. #1125656), we back every build with a 10-year structural integrity warranty and a 1-year fit-and-finish warranty, and we have been trusted by 100+ happy customers.
Building an accessory dwelling unit remains one of the most effective ways to create real additional living space on property you already own, without the disruption of gutting and remodeling the house you live in. The easiest first step is a free consultation: a 1-hour walkthrough where we look at your lot, discuss your goals and tell you honestly what it can support.
Book a Consultation or call (916) 909-2387.
Accessory Dwelling Unit Design, Permitting and ADU Construction Services in Vacaville
We design, engineer, permit and build ADUs of every type a Vacaville CA property can hold. The City’s own pre-reviewed detached plans come in 375, 550, 743 and 908 square feet, which gives you useful size anchors as you decide how much space you actually need.
Detached ADUs and Backyard Cottages
Detached ADUs are standalone dwellings with their own entrance, full kitchen, bathroom and laundry. This is the strongest option for privacy, for rental income, and for keeping family close without sharing walls.
- Studio through three-bedroom footprints
- Full kitchens, bathrooms and in-unit laundry
- Private entry, patio and a comfortable distance from the main house
Attached ADUs and Home Additions
An attached unit shares a wall with your main home and often costs less to tie into existing utilities. We design the addition so the roofline, siding and window proportions match the style of the original house rather than reading as remodeling bolted onto the back.
Garage Conversions and Junior ADUs
A garage conversion is remodeling with a purpose: an existing structure becomes finished living space with insulation, egress windows, a full bathroom and a code-compliant kitchen. Junior accessory dwelling units carve a small, self-contained unit out of the existing house, usually with its own exterior door. Garage conversions and JADUs are typically the lowest-cost paths to a legal second dwelling, and both still require permits, inspections and compliance with current regulations.
Custom ADUs: Studio, 1, 2 and 3 Bedroom Layouts
Custom ADUs are designed around your lot, your lifestyle and your purpose, at any size and layout the property allows. A quiet studio office, a two-bedroom rental unit, a guest house with a full kitchen and bath to accommodate guests year round: the plan follows the use, not a catalog. This is where your dream ADU stops being an idea and becomes a drawing set.
Retirement and Multigenerational ADUs
We create senior-friendly ADUs with ADA-compliant features such as zero-threshold entries, wider doorways, a curbless shower in the bathroom and single-level circulation. For families bringing parents home, this is the version of an accessory dwelling unit that changes daily life, not just the balance sheet.
Design, Engineering and Permits: The Entire Process Handled for You
You will not hire a separate architect, a separate engineer or a separate builder, and no one is drawing the ADU separately from the engineering that has to hold it up. Architectural design, structural and civil engineering come from our in-house arm, Golden State Design and Engineering, and permits, paperwork and compliance are done for you. You keep one point of contact through the entire process, from the first sketch to the final inspection card.
Why Vacaville Homeowners Choose Golden State ADUs as Their ADU Builder
One accountable team carries your ADU from concept to final inspection, so there is never a question about whose responsibility a problem is. Our company exists to build high quality ADUs and deliver exceptional service from the first walkthrough to the last inspection. Homeowners shopping for trusted ADU builders tend to ask the same questions, so here is the checklist we would use to vet any ADU builder, and how we answer it.
- One contract, one team. Design, engineering, permitting and ADU construction under a single agreement through Golden State Design and Engineering.
- Local code and permitting knowledge. We work to the City’s current rules, including the replacement ADU ordinance adopted as Ordinance 2011 on February 10, 2026, which is exactly the kind of detail that causes correction cycles when it is missed.
- Verifiable licensing. Licensed and bonded, LIS. #1125656. Verify any builder’s CSLB license before you sign, and know that California limits how large a down payment a builder may take on a construction contract.
- Written, itemized scope. Request an itemized written bid from every company based on the same plans. That is the only honest way to compare bids, and it is how we present ours.
- Fair and transparent pricing. Value engineering happens in the open, with assumptions, allowances and exclusions on the page.
- Responsiveness. We answer calls and emails quickly and send regular updates on progress without being chased.
- Warranties in writing. 10-year structural integrity, 1-year fit and finish.
- Quality you can inspect. 100+ happy customers and 18 Google reviews. Ask to see our portfolio and the actual warranty language when you contact us for your walkthrough.
We will be straight with you about one thing: our office is in Roseville, not Vacaville, and we serve the city via I-80. Driving distance has never been the thing that sinks an ADU project; unclear scope and slow communication are. Ask any ADU builder you are considering, including us, about their direct experience in Vacaville and Solano County, and expect a direct answer.
Talk to an ADU specialist and ask for the portfolio.
How We Build an ADU in Vacaville: Your Construction Project in 5 Steps
Every Vacaville ADU we build follows the same construction process, so you always know where your construction project stands and what comes next.
- Free consultation and feasibility review. In one hour on site we look at parcel dimensions, setbacks, your property layout, the distance between structures, utility locations, equipment access, grading and any HOA questions. We provide recommendations on placement and size, and you leave with a realistic picture of the possibilities, a preliminary budget and a working timeline.
- Design and engineering. Site measurements, architectural design, structural and civil engineering, and interior selections, developed collaboratively until the space fits how you actually live.
- Permit submittal. We prepare and submit the permit application to the City of Vacaville Building Division at 650 Merchant Street, respond to corrections and manage compliance through issuance. If you use the City’s pre-reviewed plans, property-specific plot plans, drainage information, mechanical plans, truss calculations and energy calculations may still be required, and we handle those too.
- Construction. On-site project management, quality materials and expert craftsmanship, with scheduled City inspections through foundation, framing, electrical, mechanical and plumbing.
- Finals and handover. Planning final and building final inspections, warranty handover and post-project construction administration.
Typical timing runs 3 to 5 months for design and permit plans and 3 to 4 months for construction. Those are typical ranges, not guarantees, and complex sites move slower.
Building an ADU in Vacaville: Permits, Neighborhoods and Site Conditions
Permits and the City
Every ADU in Vacaville requires a building permit, and inside city limits the City of Vacaville Building Division, not Solano County, reviews and inspects the work. The Building Division sits at 650 Merchant Street, (707) 449-5152, with an inspection line at (707) 317-1070.
Plan on a minimum of 15 business days for the first plan review and five business days for subsequent reviews, subject to complexity, with complete qualifying applications generally approved or denied within 60 days. Permits are estimated through the City’s ADU permit type in e-TRAKiT and priced at approval, so no one can quote you a flat number in advance. Under the 2026 ordinance materials, an accessory dwelling unit with 750 square feet or less of interior livable space is exempt from development impact fees.
State law opens the door to ADUs, but the City enforces the specifics, including parking expectations and how the new unit relates in design to the primary building on the lot. Those are property-by-property questions we confirm before design begins.
Neighborhoods and housing stock
Vacaville’s housing varies enough that an ADU strategy in one neighborhood makes no sense in another.
- The historic core. Contributing buildings on the 100, 200 and 300 blocks of Buck Avenue, plus historic groupings on East Monte Vista Avenue and Bush Street, Kendal Street and Kentucky Street. Exterior design here deserves real care, and historic status should be confirmed early.
- Leisure Town. Plans were approved by the City Council in 1962, and the homeowners association maintains an architectural-approval process. Compact single-story houses and a retirement-ADU fit that is hard to beat.
- Rice-McMurtry along Browns Valley Road. For example, a portion of this development has lots from 12,000 to 17,510 square feet, which is generous room for a detached unit.
- Newer planned areas. North Village, bounded by Midway Road, Leisure Town Road, Vaca Valley Parkway and Interstate 505; Southtown, approved in 2004 with 918 developed single-family homes; Brighton Landing, 767 planned detached homes at Leisure Town Road and Elmira Road; and Roberts’ Ranch, 785 planned homes at Leisure Town Road and Fry Road.
Climate, soils and terrain
Vacaville’s hot, dry summers and mild, wetter winters shape the design. We plan shading, insulation, glazing and correctly sized cooling for summer heat, and we schedule excavation and dry-in work around the November through March rainy stretch wherever the calendar allows.
Soils here include silty, sandy and clay loams, and some clay-rich soils are susceptible to expansion, so we confirm the foundation approach after site and soils review rather than promising a slab detail up front. This part of Solano County contains both foothill terrain and flatter alluvial plains, and the City publishes local fire-hazard severity information based on fuel, slope, fire weather and wind. Grading, drainage and access all follow from where your property sits.
Frequently Asked Questions
How much does ADU construction cost in Vacaville?
Cost depends on size, site conditions, utilities and finishes, so we provide an itemized written estimate after a walkthrough rather than a flat price. Soils, utility connections, demolition, site access and finish quality move the number more than square footage alone, which is why an itemized scope tells you far more than a per-square-foot figure. The lowest-cost paths are usually a garage conversion, smaller footprints and standardized layouts, and units of 750 square feet or less are exempt from development impact fees under the 2026 ordinance materials.
Do I need a permit to build an ADU in Vacaville?
Yes. Every ADU requires a building permit, reviewed and inspected by the City of Vacaville Building Division at 650 Merchant Street, and the work must comply with local zoning and building codes. We prepare and submit the application, respond to corrections and coordinate inspections. Permits are estimated through the City’s ADU permit type in e-TRAKiT and finalized at approval.
How long does a Vacaville ADU permit and build take?
Plan on roughly 4 to 8 months including permitting for a typical project: 3 to 5 months for design and permit plans and 3 to 4 months for construction. The City calls for a minimum of 15 business days for the first plan review and five business days for subsequent reviews, with complete qualifying applications generally approved or denied within 60 days. Those are review standards, not guarantees.
Does Vacaville have pre-approved ADU plans I can use?
Yes. The City offers pre-reviewed detached plans at 375, 550, 743 and 908 square feet. Property-specific plot plans, drainage information, mechanical plans, truss calculations and energy calculations may still be your responsibility, and a custom design often fits the lot or the intended use better.
What about the $40,000 California ADU grant?
State ADU grant funding has been offered through California programs in the past, availability changes, and we never assume grant money in an estimate. Contact the state housing finance agency and your local planning department to verify current program status before you budget around it.
Do you serve my part of Vacaville, including Leisure Town and other HOA neighborhoods?
Yes. We serve Vacaville CA from our Roseville office via I-80, a distance of roughly 51 to 53 road miles city to city. City approval and HOA architectural approval are separate workstreams, and the Leisure Town association maintains its own architectural review process, so we help you understand both paths without offering legal advice.
Ready to Start Your Vacaville ADU Project?
Start with the free consultation. In one hour on your lot we cover placement, feasibility, the permit path and a preliminary budget before you commit to a single sheet of plans, so you can see exactly how an ADU would enhance the property and the way your family lives on it.
Design and permits run 3 to 5 months, so starting the conversation now puts your ADU construction in the drier months rather than the November to March rain.
Call (916) 909-2387, contact us at office@gsadus.com, or visit us at 1001 Enterprise Way #100 in Roseville. Book a Consultation and let’s see what your backyard can do.
