ADU (Accessory Dwelling Unit) Cost in Ontario, CA (2026)
A ADU remodel in Ontario typically costs between $62,500 and $312,000, with most homeowners spending around $135,000. Here's the local breakdown and what drives it.
Where the money goes
Typical split of a $135,000 ADU remodel in Ontario.
What affects your Ontario price
FAQ
How much does a ADU remodel cost in Ontario?
In Ontario, California, a ADU remodel typically runs $62,500 to $312,000 in 2026, with most projects near $135,000. Local labor and material costs put Ontario at about 104% of the US average.
What's included in that price?
A detached or attached secondary unit — foundation to finishes, plus utilities and permits.
Why is Ontario different from the national average?
Construction labor rates, permit fees, and material delivery costs vary by metro. Ontario's cost index is 1.04× the US baseline, which we apply to national ADU ranges.
How do I get an exact number for my project?
Use the free Reno estimate tool — describe your project (or upload a photo) and get a line-item estimate tied to your ZIP code, then share it with vetted local contractors.
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ADU (Accessory Dwelling Unit) cost in other cities
Other remodels in Ontario
Ranges are 2026 market estimates based on national ADU costs adjusted by Ontario's local construction cost index. Your actual cost depends on scope, finishes, and contractor. Get a project-specific estimate above.