Timeline & Process
How Long Does It Take to Build an ADU? (California Timeline)
A factory-built ADU in California is typically delivered in 4 to 9 months from contract signing, about 4 to 5 months for our smaller homes and 7 to 9 for the largest. A custom site-built ADU, by comparison, usually takes 16 to 24 months. The difference isn’t magic; it’s sequencing.
Site-built construction is linear: you wait for the permit, then every trade works one after another, on your property, for over a year. Factory building runs the home and the permitting/foundation in parallel, a mechanism Harvard’s Joint Center for Housing Studies points to as a key reason modular delivery times beat traditional site-built timelines, so by the time your foundation is ready, the home is nearly finished and delivery is a single crane day.
The short version: 4 to 9 months for a factory-built ADU vs. 16 to 24 for site-built. The time saver is building the home off-site while permits and the foundation move at the same time, not faster construction, smarter sequencing.
A realistic week-by-week timeline
| Phase | Time | What’s happening |
|---|---|---|
| Property analysis + factory tour | Week 1 | Confirm the lot works; walk a finished home |
| Site visit + feasibility study | Weeks 2 to 4 | Scope access/utilities; soils, setbacks, permits researched |
| Review + customize | Weeks 5 to 6 | Lock model, style, finishes; sign contract |
| Permit review + foundation | Weeks 7 to 14 | City plan check (state 60-day rule) while the home is built in the factory |
| Factory build | Weeks 7 to 20 | Runs in parallel with permitting + foundation |
| Delivery + final inspection | 1 day + sign-off | Crane set, utility hookups, final inspection, keys |
The exact numbers shift with model size and your city’s plan-check speed, but the shape holds: most of the “waiting” overlaps with the building.
Why factory building is faster
- No weather delays. Climate-controlled construction doesn’t stop for rain.
- Parallel work. The foundation and the home are built at the same time, not one after the other.
- Proven models. The same crews build the same models repeatedly, so there’s no figuring-it-out-on-site.
- One delivery day. The finished home is craned onto the foundation and hooked up in a day, not six more months of trades on your property.
See the full 7-step process for what each phase looks like.
What can slow it down
Honest answer: a few things. Incomplete permit applications trigger resubmittals (we avoid this by drafting plans the way local departments want them). Utility upgrades, a new sewer connection or electrical service, can add time. And the largest 1,200-square-foot homes simply take longer to build than a studio. A feasibility study flags any of these for your specific lot up front, so the timeline is predictable.
The fastest path
If speed matters most, our smaller models, the 450 studio and 660 one-bedroom, deliver in roughly 4 to 5 months. Choosing a proven model over a custom design also keeps the schedule tight.
Frequently asked questions
What is the fastest an ADU can be finished?
Our smallest models can be delivered in roughly 4 to 5 months from start to finish, best case. That depends on clean permitting, which is the one step nobody fully controls.
Which phase takes the longest?
Usually permitting, commonly 60 to 90 days. The factory build runs in parallel with it, which is why the total stays in months instead of stacking sequentially.
How does that compare with building on site?
A typical site-built ADU takes 16 to 24 months because design, permits, and construction happen one after another, with weather and subcontractor scheduling in between.
Want a real timeline for your address? Start with a free property analysis, we’ll map out the dates for your specific build.