Buying Guide · 2026
Prefab ADUs in Northern California and the Bay Area
Shopping for a prefab ADU in Northern California really means shopping for three things: a home built to California code inside a factory, a builder close enough to truck it to your lot and set it by crane, and a price that covers the whole project, not just the box. Framework First is a family-owned modular builder that builds about 97% of each home in our own Salinas factory. We deliver across Santa Clara County (San Jose and the rest of the South Bay) plus Monterey, Santa Cruz and San Benito counties, with San Luis Obispo County case by case. Our 14 models run $199,000 to $599,000 all-inclusive, from 405 to 1,200 square feet.
The short version: “Prefab” covers several different products, so first ask which one you’re being quoted. A modular ADU built to California code, approved through the state’s factory-built housing program and set on a permanent foundation becomes real property, like a site-built home. Compare builders on the all-in price, the distance from their factory to your lot, and whether you can walk through a finished home before you sign.
On this page
What “prefab” means when you’re shopping
Four different products get sold as prefab:
- Modular. Whole sections are built and finished in a factory, trucked to your lot and set on a permanent foundation. This is what we build. Our homes are built to California’s residential building code and become real property once installed.
- Panelized. Wall and roof panels are built in a factory, then assembled and finished on your lot.
- Kit. Pre-cut materials that you or your contractor assemble on site, with permits, foundation and every trade still on you.
- Manufactured. Built to a federal manufactured-home code, typically on a steel chassis. State ADU law lets one count as an ADU, but it is a different product, often financed differently. Our homes are modular, not manufactured.
California’s housing department describes factory-built housing as a factory-constructed version of a site-built home, with no practical difference once it’s assembled on site. Start with what a prefab ADU is. More detail in ADU construction methods compared and prefab vs. modular vs. manufactured homes.
Where we build prefab ADUs in Northern California
| County | Example cities | Our coverage |
|---|---|---|
| Santa Clara | San Jose, Sunnyvale, Mountain View, Palo Alto, Los Gatos, Morgan Hill, Gilroy | Core service area |
| Santa Cruz | Santa Cruz, Aptos, Capitola, Scotts Valley, Watsonville | Core service area |
| Monterey | Salinas, Monterey, Carmel, Marina, Seaside | Core service area, home of our factory |
| San Benito | Hollister, San Juan Bautista | Core service area |
| San Luis Obispo | Paso Robles, Atascadero | Case by case |
| San Francisco, Alameda, Contra Costa, San Mateo, Marin, Sonoma, Napa | San Francisco, the East Bay, the Peninsula, the North Bay | Outside our regular service area |
| Sacramento, the Central Valley and the North State | Sacramento, Stockton, Fresno, Redding | Outside our service area |
Distance shapes a factory-built project in two ways. Every home makes the trip from our Salinas factory by truck, so a shorter route means fewer roads, turns and overhead lines to plan around on delivery day. And a factory within driving distance is one you can walk through before you sign. San Jose is about an hour from ours.
If you’re in San Francisco, the East Bay, the Peninsula north of Santa Clara County or the North Bay, reach out anyway and we’ll tell you honestly whether we can take your project on. Either way, the checklist below works with any builder.
How a factory-built ADU gets approved
There are two approvals: one from the state, one from your city or county.
The state approves the home itself. Under California’s factory-built housing program, run by the Department of Housing and Community Development (HCD), each design is plan-approved by an HCD-certified agency, an HCD-approved quality assurance agency inspects production in the factory, and an HCD insignia of approval goes on each unit before it ships. The standard is the same California Building Standards Code that site-built homes follow, as HCD’s Factory-Built Housing Handbook explains. That’s how our homes are inspected in Salinas before they leave.
Your city or county permits the ADU on your lot. Local rules still decide zoning, setbacks, design standards, the foundation, utilities and the installation, which the local building department inspects as it would any home. The city generally doesn’t re-review the state-approved construction plans for the unit itself.
The ADU permit itself follows California’s statewide ADU law: ministerial approval with no hearing, a completeness decision within 15 business days, and an approve-or-deny decision within 60 days of a complete application when there’s already a home on the lot. Every city and county also had to create a pre-approved ADU plan program by January 1, 2025, and a detached ADU using a pre-approved plan gets a decision within 30 days of a complete application. More in pre-approved ADU plans in California. In Santa Clara County’s program for unincorporated areas, you still submit a site-specific plan, and expedited review isn’t available in wildland urban interface, flood or geologic hazard zones. The fastest path for your parcel varies by city and is confirmed in the feasibility study.
What you are actually buying, and what it costs
A unit-only price covers a home leaving a factory. An all-inclusive price covers a finished, inspected home on your lot. A unit-only purchase still leaves the foundation, installation, utility hookups and inspections for you to hire out and coordinate. Use this checklist with every builder:
| Item | Question to ask | How Framework First handles it |
|---|---|---|
| Plans and Title 24 | Who prepares the site plan and energy report? | Prepared for you, in the price |
| Permitting | Is there a permitting budget, or is every fee extra? | A permitting budget is built into every price; actual permit costs are set by your city or county and confirmed in the feasibility study |
| Foundation | Is an engineered foundation part of the price? | Yes, poured while your home is built |
| Factory build | Are flooring, paint, fixtures and cabinets done before delivery? | Yes, finished in our factory |
| Delivery and crane | Are transport and the crane set separate lines? | Both in the price |
| Hookups | Who levels the home and connects it on site? | Our crews |
| Appliances | Which appliances are included? | Dishwasher, refrigerator, range, microwave and disposal |
| Final inspection | Who meets the inspector? | Our team |
Our 14 models run $199,000 to $599,000, from the Four Fifty studio to the three-bedroom Twelve Hundred U. Every price is on our pricing page and every floor plan on the models page. Skip price-per-square-foot math: every ADU needs a kitchen, a bathroom, a foundation and a delivery whatever its size.
What moves a project beyond the catalog price is property-specific work, such as a septic upgrade, a retaining wall or an electrical panel that needs more capacity. We do that work in-house, priced per property, so the project stays with one builder. Slope, soil, utility distances and delivery access also shape the plan. A feasibility study ($497 standard, $997 for an empty lot) confirms all of it for your parcel.
Delivery day and timeline on a Bay Area lot
Delivery is typically a single day: your home arrives by truck, and a crane sets it on the foundation poured while it was being built. On tight Bay Area lots the questions are about access. Can the truck and crane reach your street? Are trees, power lines or the main house in the lift path? Will the crane need part of the street? In San Jose, for example, crane work and temporary lane closures in the public right-of-way fall under a Public Works encroachment permit. Our site visit maps the route and the lift before delivery is scheduled. More in how crane delivery works.
Our model timelines run from the day your construction deposit lands to final inspection: about 4 months for the Four Fifty in the best case, 5 to 6 months for the 405 through the Seven Forty-Nine, 6 months for the 885 and 945 models, and 7 to 9 months for the Twelve Hundred models. Your home is built while permits and your foundation move in parallel. Permitting is the stage no builder fully controls, so local timelines vary by jurisdiction and are confirmed in your feasibility study.
How to compare prefab builders
- Check the license. Ask whether the home is built by a state-licensed modular home manufacturer. Ours is MFG #1595931.
- Ask about the state approval. Will the home be built under California’s factory-built housing program and carry the HCD insignia?
- Ask where the factory is, and how far the home travels to reach your lot.
- Tour a finished home. On our Salinas factory tour, you walk through completed homes and homes being built, and you’ll meet a member of our team, often Cathy herself.
- Get inclusions in writing, line by line, using the table above.
- Ask for references in your county, and whether they’ve permitted homes in your city.
Frequently asked questions
Do you build prefab ADUs in the Bay Area?
Yes, in Santa Clara County, which covers San Jose and the South Bay, plus Monterey, Santa Cruz and San Benito counties, with San Luis Obispo County case by case. San Francisco, the East Bay, the Peninsula north of Santa Clara County and the North Bay are outside our regular service area, though we’re glad to talk it through.
How much does a prefab ADU cost in Northern California?
Our 14 models run $199,000 to $599,000 all-inclusive, with a permitting budget, plans, foundation, factory build, delivery, hookups, appliances and final inspection in one number. Property-specific work like a septic upgrade is priced per property, and the feasibility study confirms permit costs for your address.
Is a prefab ADU permitted the same way as a site-built one?
Your city or county permits it as an ADU under the same state law, with a 60-day decision once the application is complete when there’s already a home on the lot. The difference is that the home is also plan-approved and inspected in the factory under the state program, so local review focuses on zoning, setbacks, the foundation, utilities and installation.
Can I see a prefab ADU before I buy?
Yes. Our free factory tour in Salinas runs about 90 minutes and is scheduled after your Online Property Analysis. You walk through completed homes, see others being built and meet our team.
How long does a prefab ADU take to build?
From the day your construction deposit lands to final inspection, about 4 months for the Four Fifty in the best case, up to 7 to 9 months for the Twelve Hundred models. Permitting time varies by jurisdiction and can shift any timeline.
Start with The ADU Designer by Framework First, where you can design and price your home on your own schedule. Submitting a design leads you to book a free Online Property Analysis, a 30-minute call where our team pulls your property records and tells you which models fit your lot. Then come see the homes in person at our Salinas factory.
