Looking for an ADU builder in Fontana, CA? Describe your project once and up to three licensed ADU builders who work in Fontana and San Bernardino County get back to you with a quote. It's free and there is no obligation.
Fontana is home to about 218,455 people (2024 Census Bureau estimate), a growing community (+4.8% since 2020). With 5,047 people per sq mi, it is a densely built-up area. Homeowners here add accessory dwelling units for rental income, family members or a home office.
Fontana at a glance
- Population (Census Bureau estimate, 2024)
- 218,455 (+4.8% since 2020)
- Rank in California
- 20th of 482 cities and towns
- Land area
- 43 sq mi
- Population density
- 5,047 people per sq mi (densely built-up)
- Type
- City (Fontana city)
- Main county
- San Bernardino County
What to check before hiring in Fontana
- Rules: ADU rules are set by the state and the city; check Fontana's planning department for size, setback and parking limits.
- License and permit: in California, ADUs are built by licensed contractors under a building permit.
- Utilities: water, sewer and electrical capacity can drive the cost as much as the unit itself.
- Compare: ask for references and photos of ADUs each builder has completed.
Useful official resources
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HUD User
Federal housing research, including ADUs.
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ICC: International Code Council
Publisher of the building codes most states and cities adopt.
Services available in Fontana
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Detached ADU
Design and construction of a detached backyard unit, site-built or prefab, with the permit and utilities.
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Garage or interior conversion
Conversion of a garage, basement or part of the house into a legal accessory dwelling unit.
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ADU plans and permit
Feasibility, plans and permit application for an ADU before choosing a builder.
Frequently asked questions in Fontana
How much does an ADU cost in Fontana, CA?
It depends on the type of unit, its size, the finishes and the utilities. Describe your project: builders who serve Fontana reply with a quote.
How long does an ADU take?
Often several months for permits and a few more for construction; conversions and prefabs can be faster.
Do I need an architect?
Not always: designers, builders with in-house design or prefab companies can prepare the permit set, depending on local rules.
Which licensed ADU builders will contact me?
Up to three independent licensed ADU builders who serve Fontana and the surrounding area, chosen for the service you need. Your details are shared only with your consent.
Source: U.S. Census Bureau, Population Estimates Program (Vintage 2024) and Gazetteer Files (public domain), imported on 10/31/2026. Figures describe the incorporated place or county as published; they are shown for information only.