Licensing · contracts · bids
How to Choose an ADU Builder in Walnut Creek
Hire a licensed B – General Building contractor, sign a written home improvement contract, and keep the down payment at $1,000 or less (CSLB FastFacts: ADU). Then compare bids line by line: design, permits, utility fees, site work, finishes and schedule.
CSLB ADU basics
- B – General Building contractors can build ADUs
- Written home improvement contract required
- Down payment: $1,000 maximum
- Never let payments get ahead of the work
- Change orders in writing
- 3-day right to cancel (5 days if 65+)
Delivery models
Three ways to get an ADU built
| Model | How it works | Good for | Watch for |
|---|---|---|---|
| Design-build ADU firm | One company designs, permits and builds | One contract, early pricing, fewer handoffs | Design range limited to what they build; compare at least two |
| Architect or designer + general contractor | You hire a designer, then bid the drawings to contractors | Custom designs, hillside lots, competitive bids | More coordination; budget surprises if bids come in high |
| Prefab company + local contractor | Factory unit plus local foundation, utilities and set | Standard layouts with good access | What the "all-in" price excludes; crane access |
Bid checklist
What every ADU bid should spell out
- Design, structural engineering and Title 24 energy work
- Who prepares and submits permits, and who pays plan-check fees
- Sewer route and Central San fees; water meter or capacity charges
- Electrical: subpanel, service or panel upgrade, PG&E coordination
- Site work: grading, retaining, drainage, tree protection, hauling
- Finish level, with allowances in dollars
- Schedule with milestones tied to payments
- Warranty terms and who handles punch-list items
- License number, insurance and workers' compensation
Red flags
Walk away when you see
- A deposit request over $1,000, or payments ahead of completed work
- Offers to build an unpermitted "garage studio" or "pool house"
- No license number on the contract, or a license that doesn't match the name
- Large upfront charges for plans or permits you can't verify with the building department
- Grants or rebates promised as guaranteed
- Pressure to sign the same day
Ask for addresses of ADUs the builder has permitted locally and confirm them with the city or County building department's permit records.
Questions
Questions to ask before you sign
- How many ADUs have you permitted in this city or the County?
- Will you design to a pre-approved plan or custom?
- What is excluded from this price?
- Who is on site day to day?
- How do change orders get priced and approved?
- What happens if the sewer route or soils differ from the plan?
FAQ
What license does an ADU builder need?
A B – General Building license, according to the CSLB. Specialty contractors (electrical, plumbing) work under their own licenses. Check every license, its status and its workers' compensation coverage at cslb.ca.gov.
How much deposit should I pay an ADU builder?
No more than $1,000. The CSLB says ADU construction is home improvement, the down payment cannot exceed $1,000, and progress payments should never get ahead of the work completed.
Should I hire a design-build firm or an architect and a contractor?
Design-build gives one point of responsibility and earlier pricing. An architect plus a separately bid contractor gives more design control and competitive bids but more coordination. Prefab companies handle the unit; you may still need a local contractor for site work.
Talk it through
Call to discuss your lot, budget and timeline with a local ADU builder.
Next step
Talk to a local ADU builder
Share your lot and goals. A local ADU builder can review feasibility and give you a quote.