ADU builders
ADU warranty: what to get in writing
By the HyreADU research desk. Last checked .
The short answer
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.
Ask for each in writing before you sign, with what is covered, for how long, and how to make a claim.
The layers of warranty
- Builder workmanship: defects in the work the builder did. Ask for the length and scope in writing.
- Equipment: water heater, heating and cooling, appliances and windows, from each manufacturer. Some need registration.
- Factory-built unit: the manufacturer’s warranty, and who handles claims for set-up and site work.
- Roofing and other materials: manufacturer warranties that may depend on approved installation.
What to ask for in writing
- What is covered and what is excluded.
- How long each part lasts, and when it starts.
- How to report a defect and how fast the builder must respond.
- Whether the warranty transfers to a buyer.
- Copies of all manufacturer warranties and manuals at handover.
Protect your claim
Keep photos of walls before they were closed, the approved plans, the final inspection and every invoice. Report defects in writing, promptly. Statutes on construction defects and claim periods are legal matters; we give no legal advice. Check the builder’s license history before you sign with how to check an ADU contractor license.
What to do next: read the questions to ask an ADU builder, check what decides ADU cost, then tell us about your project. Matching is not live yet, so we reply with information, not a quote.
Get ADU optionsQuestions
Is a builder required to give a warranty?
Practice varies; ask for a written warranty and put it in the contract.
Does a warranty cover settlement cracks?
Read the exclusions. Many warranties treat minor cracks differently from structural defects.
Who handles a prefab unit warranty?
The manufacturer for the unit, the site contractor for site work. Ask who coordinates.
Does registering equipment matter?
Some manufacturers require registration for the full warranty.
Sources
- FTC, How to avoid a home improvement scam. Checked September 5, 2026.
- CSLB Check a License (search by license number, business name, personnel name or HIS registration). Checked October 27, 2026.
- California HCD, Factory-Built Housing program. Checked September 5, 2026.
HyreADU is a publisher. It does not design, permit or build ADUs, has no partner builders, and gives no legal, tax or engineering advice. Rules vary by state and city; California rules are labeled as such.