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Cost to build an ADU at your address

We check your site conditions, square footage and finish level, and show you a precise estimate.

Enter your address for attached ADU costs near you.

Attached ADUs, San Francisco · single-unit · 75 projects · 23 completed

Attached: a new unit that expands the building.

Declared on permits: $131k–$285k · median $206,888

$163k–$356k estimated total

1 year 6 months to build.

Builders’ bids, Bay Area 2026: $150k–$350k (400–800 sq ft, construction only; Custom Home)

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Average cost to build an ADU in San Francisco

Estimated total · single-unit projects

  • Converted · 729 projects · 1 year 1 month to build
    $97k–$232kmedian $160k
  • Detached · 51 projects · 1 year 5 months to build
    $172k–$344kmedian $240k
  • Attached · 75 projects · 1 year 6 months to build
    $163k–$356kmedian $259k
  • Junior ADU · 13 projects · 10 months to build
    $122k–$211kmedian $188k

How we get these numbers. Each is the value declared on the building permit, divided by 0.8. Permits list construction cost only. Design adds about 10% and permit fees 6 to 9% (sf.gov). At the minimum, the declared permit value is about 80% of the total.

Why it is a range. Square footage, site conditions, foundation and utility work, finishes, and whether the unit is new or converted all move the price. The range covers the middle half of projects.

Get a precise estimate for your address. We check your site conditions, square footage and finish level, and give you a precise estimate before builders bid.