What Is an ADU Contractor?

Key takeaways

• An ADU contractor is the licensed business that builds your unit.
• "ADU builder" is a sales name. The license is what counts.
• In California, a new ADU is usually a Class B general building job ¹.
• Every ADU needs a building permit, so the small-job license exemption never applies ².
• California contractors must keep a $25,000 bond on file ⁵. That is a small safety net, not full cover.
• Down payments on home improvement contracts are capped at $1,000 or 10%, whichever is less ⁶.

What an ADU contractor is, in plain English

An ADU is a small second home on your lot. The ADU contractor is the company you hire to build it.

The contractor signs the main contract with you. That is called the prime contract. They then do the work with their own crew, or hire other trades. Those trades are called subcontractors, or "subs". Electricians and plumbers are common subs.

The contractor runs the schedule, orders materials, books inspections and fixes defects. You pay them, and they pay the subs.

Why the choice of contractor matters to you

The contractor holds most of your money for months. If they slow down, run short of cash, or close, your project stalls.

A license is the floor, not the ceiling. It shows the business met state rules. It does not show it builds ADUs well.

Our builder attrition research looks at how many builders stop operating. That is why track record and payment terms matter as much as price.

Builder, general contractor or design-build

California's contractor license rules for ADUs

Business and Professions Code 7057 defines a general building contractor (Class B) as one whose principal business is structures that require at least two unrelated building trades or crafts, or who superintends the whole or part of that work.

A Class B contractor may not take a prime contract for other trades unless it requires at least two unrelated trades other than framing or carpentry, unless it holds the right specialty license or subcontracts to a licensed specialty contractor.

A new ADU, with foundation, framing, plumbing and electrical, is the textbook Class B job.

Under Section 7048, the license law does not apply to work under $1,000 in total, but only if the job also needs no building permit and is not split up to evade the limit. Every ADU needs a building permit, so whoever contracts to build it must be licensed.

The consequence of hiring an unlicensed contractor falls on both sides. Section 7031 bars an unlicensed contractor from suing to collect for licensed work, and Section 7031(b) lets the person who hired them sue to recover all compensation paid.

That is a remedy, not protection: money already spent may be hard to recover. Other states license contractors differently; see ADU laws by state.

Sources: [1] [2] [3]

What a contractor license proves, and what it does not

How to check an ADU contractor

1. Get the license number in writing and look it up on the CSLB license check. Match the business name and address exactly.
2. Confirm the classification is B (or the right specialty for the work) and the status is active.
3. Read any disciplinary actions and complaint history on the record.
4. Ask for proof of workers' compensation coverage, or a written explanation if the firm says it has no employees.
5. Ask for addresses of finished ADUs and check them against city permit records; HyreADU's permit contractor index shows how.
6. Compare at least two written bids on the same plan set with the bid comparison tool.

CSLB's online lookup was unavailable to HyreADU on 7 October 2026, so this page describes the check without quoting the page.

Where the contractor shows up in your paperwork

• Permit application: the contractor's license number, or an owner-builder declaration if you build it yourself.
• Contract: scope, payment schedule tied to completed work, change-order process and the license number.
• Bid: what is excluded, such as utility upgrades, fees and the site plan work.
• Financing: construction lenders typically review the contractor; see ADU financing.

Misconceptions

Myth "ADU specialist" means a special license.

Reality No ADU-specific license exists in California; the classification is the ordinary Class B general building license ¹.

Myth Small jobs never need a license.

Reality The under-$1,000 exemption ends once a building permit is needed, and every ADU needs one ².

Research and next steps

• Find a professionalShortlisting ADU builders
• California ADU buildersWho is building ADUs, from permit data
• ADU contractor enforcementLicensing actions in the ADU market
• ADU builder attritionHow many builders stop operating
• ADU construction hubThe build from start to finish

How an ADU build runs with a contractor

1. Bid. The contractor prices your approved plans. Read what is left out.
2. Contract. You sign a written contract with a payment schedule tied to work done ⁶.
3. Permit pull. The contractor’s license number goes on the permit, or you sign as an owner-builder.
4. Site work and foundation. Grading, trenches for utilities, then the slab or footings.
5. Framing and rough trades. Walls, roof, then rough plumbing, wiring and ducts. The city inspects each stage.
6. Close-in and finishes. Insulation, drywall, cabinets, fixtures and paint.
7. Final inspection and punch list. The city signs off. You list small fixes, called the punch list, and the contractor completes them.

Worked example: the down-payment cap

Hypothetical contract amounts, for arithmetic only. California caps the down payment on a home improvement contract at $1,000 or 10% of the contract, whichever is less ⁶. The formula shows the rule; the table runs it on three amounts.

For almost any ADU, the cap is $1,000. A builder who asks for a large deposit before work starts is a warning sign. Later payments may not run ahead of the work done or materials delivered ⁶. Ask a lawyer or the state board how the rule fits your contract.

The contractor bond: what it covers, and how far

California requires every licensed contractor to keep a contractor’s bond of $25,000 on file ⁵. A bond is a promise by an insurance-type company, called a surety, to pay valid claims.

The bond is shared by everyone with a claim. Claims from anyone other than the workers named in the law are capped at $7,500 in total ⁵. On an ADU contract, that is a small fraction of what you pay.

So treat the bond as a last resort. Your real protection is a careful contract, payments that follow the work, and a builder with a record you have checked. The three figures below are the state limits that frame that protection.

Sources: [5]

The paper trail a contractor leaves, stage by stage

• Bid: line items, allowances and exclusions.
• Contract: license number, price, schedule of payments.
• Building permit: the contractor of record.
• Inspection cards: sign-offs for each stage.
• Lien releases: papers showing subs and suppliers were paid.
• Loan draws: a construction lender pays out as stages finish. See ADU construction loan.

What drives an ADU contractor’s price

HyreADU does not publish a typical contractor price on this page. Costs vary by lot, city and plan. See ADU cost statistics for sourced figures.

What moves a bid most: site work, such as grading, long utility trenches and access; the foundation; the size and number of bathrooms and kitchens; and finish level.

Watch the allowances. An allowance is a placeholder amount for items not yet chosen, like tile or fixtures. Low allowances make a bid look cheap, then rise later.

Compare bids on the same plan set. The bid comparison tool lines them up.

Hiring a GC vs being your own builder

Contractor vs architect vs design-build

What to ask an ADU contractor before you sign

• What is your license number and classification?
• How many ADUs have you finished in this city? Which permit numbers?
• Who will run my job day to day?
• Which trades do you subcontract, and are they licensed?
• What is excluded from this bid?
• What are the allowances, item by item?
• How are change orders priced and approved?
• Will you give lien releases with each payment?

Checklist: hiring your ADU contractor

1. Get approved or near-final plans first, so all bids price the same thing.
2. Collect at least two written bids.
3. Look up each license on the state board site.
4. Check finished ADU addresses against city permit records.
5. Confirm workers’ compensation or a written reason for none.
6. Check the deposit and payment schedule against the limits ⁶.
7. Read the change-order and warranty terms.
8. Keep every lien release and inspection card.

Related terms

ADU Design-Build

ADU design-build is a way of delivering an accessory dwelling unit in which one firm is responsible for both designing the unit and building it, usually under one contract or a design agreement that rolls into a construction contract.

ADU Architect

An ADU architect is a state-licensed architect who designs an accessory dwelling unit and prepares the drawings the building department reviews, often managing plan-check corrections as well.

ADU Permit

An ADU permit is the building permit a city or county issues to allow construction of an accessory dwelling unit, after checking the plans against local zoning standards and the building code.

ADU Hard Costs

ADU hard costs are the money spent physically building an accessory dwelling unit: site preparation, foundation, framing, roofing, windows, mechanical, electrical and plumbing systems, finishes, and the trenching that brings utilities to the unit, together with the contractor’s labor, overhead and profit.

Construction Loan

A construction loan is a short-term loan that pays for building or rehabilitating a home, releasing the money in a series of advances, often called draws, as construction progresses rather than as one lump sum.

Prefab ADU

A prefab ADU is an accessory dwelling unit whose walls, floors or whole room modules are built in a factory and then shipped to the lot, where a crew sets them on a foundation and connects utilities.

ADU Cost Estimate

An ADU cost estimate is a written, itemized prediction of what it will cost to build a specific accessory dwelling unit on a specific lot, listing the work, materials, allowances, exclusions and assumptions behind the total.

ADU Construction

Building an ADU, from site work and foundation through framing, systems, finishes and final inspection.

Also referenced from: Prefab ADU, Permit Expediting, ADU Electrical Panel, ADU Site Preparation, ADU Framing, ADU Roofing, Construction Loan, ADU Architect, ADU Engineer