Hiring an ADU Contractor in California
An ADU bid is easier to judge when you know what it includes. Before choosing a builder, establish the project scope, verify the business you will contract with, and compare the same work across bids. A license record is a starting point, not evidence of ADU experience.
Start With the Property and the Plans
Write a short project brief: detached unit, addition or conversion; intended use; approximate size; existing plans; access constraints; and your budget range. Ask your local planning and building departments which requirements apply to the property. Use the California HCD ADU handbook as a state-level reference alongside that discussion.
A contractor's estimate is not permit approval. Ask which assumptions remain unresolved and who will check them. Keep early feasibility estimates separate from bids based on completed plans.
Verify the Business, Then Check Relevant Experience
Which license should an ADU builder hold? CSLB says a B – General Building contractor can build or install an ADU. A C-47 contractor can install a manufactured-home ADU built off site. Individual specialty licenses do not generally cover managing the whole build. Check the license against your actual project, not just the word “ADU” in an advertisement. See CSLB's ADU fact sheet.
- Match the identity. Ask for the legal business name and license number that will appear on your agreement. Check the current CSLB record, including status, classifications and restrictions.
- Review coverage and scope. Ask how the license covers the proposed work, who performs specialty work, and how bond and insurance information can be confirmed. Follow our license verification checklist.
- Ask for comparable projects. A garage conversion and a detached new build can present different challenges. Request references for similar work and permission to contact those owners.
- Identify the working team. Who estimates, designs, supervises the site and answers questions? Ask which work will be subcontracted and how changes are approved.
Our directory contains archived licensing information. It does not certify an ADU specialist, inspect completed projects or guarantee a contractor's performance. Verify current information directly with CSLB.
Verify a Contractor's License Now
Ask Every Bidder the Same Questions
- Plans and professional services: Are design, engineering, surveys or soil investigations included? Who owns and supplies the final documents?
- Site preparation: What is assumed about demolition, grading, foundations, drainage and access for equipment?
- Utilities: Does the price include trenching, connections and any electrical, water or sewer upgrades? Which costs require confirmation from the utility provider?
- Permits and fees: Who submits applications, answers plan-check comments, pays agency charges and arranges inspections?
- Finishes and equipment: Which products are specified? Which are allowances, and what happens if your selections exceed them?
- Exclusions: Are landscaping, fencing, paving repairs, appliances or cleanup outside the price? Ask for an explicit list.
- Schedule: What must happen before work starts? How are inspection, utility or material delays handled?
- Handover: Who obtains final sign-offs and supplies warranties, manuals and a list of unresolved items?
Compare Scope Before Comparing Totals
Use the printable three-bid worksheet. Mark each item as included, excluded, an allowance or still unknown. Ask bidders to resolve differences in writing before ranking their prices.
For example, one proposal might include utility trenching while another leaves it to the owner. Those totals do not describe the same job. An unknown cost is not zero, and a larger quote is not necessarily more complete. This is a comparison method, not an ADU cost estimate.
Agree on Payments and Changes Before Signing
CSLB's ADU fact sheet treats ADU construction as home improvement and calls for a written home-improvement contract. Agree on payment milestones and written change orders. Progress payments should follow completed work or delivered materials. Read our deposit calculator and payment guide for the ordinary limits and exceptions; do not assume a large advance is acceptable because the project is an ADU.
Keep a copy of the signed scope and exclusions. Agree on how you will receive progress updates and who can authorize extra work. Resolve vague phrases such as “utilities by owner” before they become a surprise invoice.
Before You Choose
Call references with specific questions: What changed from the original bid? How were unexpected conditions handled? Who communicated delays? Was the project completed and signed off? Combine those answers with your license checks and written proposal comparison.
If you want additional options, Angi offers a general project-request service. Confirm whether a responding professional handles your particular ADU scope; we have not verified ADU-specific matching or availability.
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Updated September 19, 2026. This checklist helps organize hiring decisions; property-specific approvals come from the relevant authorities. References: HCD ADU handbook and CSLB hiring guidance.