How Much Does an ADU Cost in San Francisco, CA?

Construction Cost Breakdown

Building an ADU in San Francisco costs between $300,000-$550,000 for new construction, with per-square-foot costs averaging $350-$650. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $120,000-$300,000, while prefab/modular ADUs fall in between at $180,000-$350,000.

Permit Costs & Timeline

Permit fees in San Francisco are Planning Department building-permit review (Fee Schedule effective August 29, 2025, revised June 15, 2026): new construction $3,502 under $100,000; $3,504 plus 3.855% of cost above $100,000 up to $499,999; $19,226 plus 1.230% above $500,000. Alteration or conversion: $504 under $10,000; $516 plus 5.274% above $10,000; $3,838 plus 3.524% above $50,000; $5,638 plus 3.855% above $100,000; back-check $366. DBI building permit (Building Code Table 1A-A, permits issued on or after July 12, 2026): plan review $1,617 plus $15.60 per $1,000 over $50,000, or $4,011 plus $13.31 per $1,000 over $200,000; permit issuance $677 plus $4.83 per $1,000 over $50,000, or $1,402 plus $4.21 per $1,000 over $200,000; plumbing, electrical, mechanical, Fire, Public Works and Public Health fees are extra (Table 1A-A note 1). SFUSD school facility fee $3.79 per sq ft of added habitable area (2026 Impact Fee Register). Worked example (our calculation, not a published figure): a $300,000 detached ADU pays about $11,214 to Planning plus $5,342 and $1,823 to DBI, roughly $18,400 before trade permits and school fees; DBI says City fees typically run 6-9% of construction cost. Fees are waived for permits that legalize units built without permits before January 1, 2020. The review timeline is 60 days from a complete application under Gov. Code 66317 (SB 543, January 2026: deemed approved if the City does not act). DBI requires every ADU applicant to sign an Application Processing Time Tolling Declaration choosing either to pause the 60-day clock while revising plans or to keep it running, in which case DBI may deny the application if code compliance is not shown within 60 days and revised plans are due at least 10 business days before the deadline. Local-program projects add the 15-day tenant notice, a 30-day Rent Board objection window (up to 90 days more if a tenant objects) and Planning in-house review before the building permit is filed; DBI states that State-program full permits generally have a shorter review and issuance timeline than the Local program. The City publishes no average issuance times, with plan check: Electronic plan review in Bluebeam Revu with a required Back Check page. Plans must be stamped by a licensed design professional unless the home is wood-frame, under 2 stories plus basement, under 25 ft wide between bearing walls and under 25 ft tall (Information Sheet G-01). An ADU must be at least 220 sq ft with 7.5-ft ceilings in living and sleeping rooms, its own entrance, a rescue window in every bedroom and an exit path of no more than 125 ft to the street. Buildings with 3 or more units and a rear-yard sleeping room may need a fire alarm and ground-floor sprinklers; a fire flow study is required for new floor area, and street tree, Public Works right-of-way, Maher soil and construction-waste requirements can apply. Impact fees are None for a State-program ADU or JADU under 750 sq ft of gross floor area, and none of any size on a lot with 3 existing units or fewer (Planning Code 207.2(j)); a larger ADU on a lot with 4 or more units pays impact fees in proportion to the primary unit's gross floor area at the rates in the Impact Fee Register (indexed 2% on January 1, 2026). Section 207.1 contains no parallel exemption for Local-program ADUs; confirm with the Planning Division. SFPUC water and wastewater capacity charges apply only if a new or larger meter is needed (5/8-inch meter: $2,288 water, $6,006 wastewater, FY2025-26 rates); a single-family home adding one ADU usually needs no added water capacity. Pre-approved plans: DBI runs a Pre-approved ADU Plans program in which building designers submit detached-ADU designs for a $2,408 flat review fee; approved designs are meant to be posted on DBI's site for owners to choose and have the designer adapt to their lot. As of September 19, 2026 DBI's page lists no approved designs. Pre-approved plans are drawn for 25-ft lots, are valid only for the current code cycle, cannot be used in slope-protection, landslide, liquefaction, Maher or flood zones, and still need site-specific plan check of Planning Code compliance, soils, fire separation, foundation and SFUSD fees; a separate tolling form applies to permits that use a pre-approved plan.

Rental Income & ROI

A typical ADU in San Francisco generates approximately $43,200 per year in rental income based on average 1-bedroom rents. At an average construction cost of $425,000, the estimated payback period is 9.8 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in San Francisco and varies by market (often less than build cost).

Ways to Reduce ADU Costs in San Francisco