Looking for an ADU builder in San Francisco, CA? Describe your project once and up to three licensed ADU builders who work in San Francisco and San Francisco County get back to you with a quote. It's free and there is no obligation.
San Francisco is home to about 827,526 people (2024 Census Bureau estimate), a shrinking community (−5.8% since 2020). With 17,726 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.
San Francisco at a glance
- Population (Census Bureau estimate, 2024)
- 827,526 (−5.8% since 2020)
- Rank in California
- 4th of 482 cities and towns
- Land area
- 47 sq mi
- Population density
- 17,726 people per sq mi (densely built-up)
- Type
- City (San Francisco city)
- Main county
- San Francisco County
What to check before hiring in San Francisco
- Rules: ADU rules are set by the state and the city; check San Francisco'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 San Francisco
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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 San Francisco
How much does an ADU cost in San Francisco, CA?
It depends on the type of unit, its size, the finishes and the utilities. Describe your project: builders who serve San Francisco 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 San Francisco 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.