ADU builders: how to choose, check and compare bids

Five checks before you sign with any ADU builder

1. License. Active, in the right class, in the name on your contract. Look it up on the CSLB site, or read who can legally build an ADU.
2. ADU permits on record. Finished ADUs in your city, not just remodels. Our permit contractor index covers five California jurisdictions.
3. Insurance. Certificates issued to you that you confirm with the insurer.
4. An itemized bid on the same drawings. Compare bids line by line in the ADU bid comparison.
5. A fair payment schedule. A deposit within the California cap of $1,000 or 10 percent, whichever is less (Bus. & Prof. Code § 7159), then payments tied to finished work.

The full walk-through is how to find a good ADU contractor. Before a first meeting, read the questions to ask an ADU builder and how to check a contractor license.

Choosing who builds it

• ADU contractor: who can legally build one. An ADU contractor in California is a contractor licensed by the CSLB to build the whole unit.
• How to find a good ADU contractor. How to find a good ADU contractor comes down to five checks, done in order: an active license in the right class, ADU permits in their name in your city, insurance you can confirm, an itemized bid on the same drawings as the others, and payments tied to finished work..
• ADU construction company: what one actually does. An ADU construction company is a builder that focuses on accessory dwelling units.
• Custom ADU builders: when a custom design fits. Custom ADU builders design and build a unit for your lot instead of repeating a stock plan.
• ADU design-build: one contract for design and construction. ADU design-build means one firm both designs and builds your unit under one contract.
• ADU general contractor vs ADU builder company. An ADU general contractor and an ADU builder company hold the same license in California: a B General Building license.
• Affordable ADU contractor: where the real savings are. An affordable ADU contractor is one whose itemized bid is low because the project is simpler, not because lines are missing.

Design, engineering and studies

• ADU architect: when you need one. An ADU architect is not required for most ADUs in California.
• ADU designer: what a drafter delivers. An ADU designer, sometimes called a drafter, prepares the drawings your city reviews and your builder prices.
• ADU permit expediter: what one can and cannot do. An ADU permit expediter manages your application: the forms, the submittal, the plan check comments and the back-and-forth with the city.
• Structural engineer for an ADU: when you need one. A structural engineer for an ADU is needed when the design leaves conventional wood framing.
• ADU feasibility study: what it should cover. An ADU feasibility study answers one question before you pay for drawings: can this lot take an ADU, and what will make it hard? A good study covers zoning, setbacks and lot coverage, utility routes, access for equipment, hazard overlays and the fees that apply.
• Land survey for an ADU: when you need one. A land survey for an ADU locates your lot lines and, if needed, the slope of the ground.
• Soils report for an ADU: when it is required. A soils report for an ADU, also called a geotechnical report, tests the ground the foundation will sit on.
• Title 24 energy consultant for an ADU. A Title 24 energy consultant prepares the forms that show your ADU meets California’s Energy Code (Title 24, Part 6).

Building each kind of ADU

• Detached ADU construction: what the build takes. Detached ADU construction means building a new, separate unit, usually in the rear yard.
• Attached ADU: the rules and what to ask a builder. An attached ADU shares at least one wall with the main house and has its own entrance.
• Modular ADU: which law the unit is built to. A modular ADU is built in sections in a factory and set on a foundation on your lot.
• Two-story ADU: height rules and who builds it. A two-story ADU fits more floor area on a small footprint.
• Backyard cottage builders: what to check. A backyard cottage is a detached ADU by another name.

Utilities, energy and safety systems

• ADU solar installation: is it required?. ADU solar installation is required in California only when the ADU is a newly constructed building under the Energy Code, which in practice means a new detached unit.
• ADU utility connection: who does what. An ADU utility connection brings water, sewer and power to the unit.
• ADU sewer lateral: share the line or run a new one?. The sewer lateral is the pipe from your house to the public sewer.
• ADU electrical panel upgrade: do you need one?. An ADU electrical panel upgrade is needed only if a load calculation says the existing service cannot carry the house and the ADU together.
• ADU fire sprinklers: when they are required. ADU fire sprinklers are not required in California unless the main house is required to have them.

Finishing, legalizing and running it

• Unpermitted ADU legalization in California. Unpermitted ADU legalization in California rests on Gov.
• ADU interior design: small-space choices that matter. ADU interior design is about making a small floor plan feel and work larger.
• ADU landscaping: the rules and who does it. ADU landscaping restores the yard after construction and shapes privacy, drainage and access between the two homes.
• ADU property management: rules and licensing. ADU property management means someone handles tenants, rent and repairs for your unit.

Before you sign: checklists

• Questions to ask an ADU builder before you sign. Questions to ask an ADU builder fall into six groups: license and insurance, ADU experience in your city, what the bid includes, how payments and change orders work, the schedule, and the warranty.
• ADU contract checklist: what to check before you sign. An ADU contract checklist starts with what California law requires in a home improvement contract: the contractor’s name, address and license number, the contract price, a payment schedule in dollars tied to work, a down payment within the legal cap, approximate start and completion dates, and the rules for change orders.
• ADU bid red flags to spot before you sign. ADU bid red flags are signs that a price is incomplete or a builder is risky: one lump sum with no lines, no site work or utility connections, very low allowances, a deposit above the legal cap, payment ahead of work, no license number, cash-only terms, or pressure to sign today.
• ADU payment schedule: deposit and progress payments. An ADU payment schedule should start with a small down payment and tie every later payment to finished, inspected work.
• ADU warranty: what to get in writing. An ADU warranty usually has layers: the builder’s written warranty on workmanship, manufacturer warranties on equipment such as the water heater, heat pump and windows, and for a factory-built unit, the manufacturer’s warranty on the unit.
• ADU change orders: how they should work. ADU change orders are written changes to the contract’s scope, price or schedule.
• Check an ADU contractor license in five minutes. To check an ADU contractor license in California, search the CSLB’s Check a License tool by license number, business name or personnel name.

Why there is no list of companies here

A ranked list of ADU builders needs a published method and evidence behind each place. We have the public record, not a method, so we publish the record and leave the choice to you.

HyreADU is a publisher: it does not design, permit or build ADUs, it has no partner builders, and professional matching is not live yet. Our vetting standard says what we will check when it is.