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Cost Estimates by ADU Type
| ADU Type | Low Estimate | Mid Estimate | High Estimate | Per Sq Ft |
|---|---|---|---|---|
| Detached ADU (800 sq ft) | $150,000 | $225,000 | $350,000 | $190-$440 |
| Attached ADU (600 sq ft) | $100,000 | $165,000 | $250,000 | $165-$415 |
| Garage Conversion (400 sq ft) | $60,000 | $110,000 | $180,000 | $150-$450 |
| Basement ADU (500 sq ft) | $50,000 | $90,000 | $150,000 | $100-$300 |
| JADU (400 sq ft) | $30,000 | $50,000 | $80,000 | $75-$200 |
| Prefab ADU (500 sq ft) | $80,000 | $150,000 | $250,000 | $160-$500 |
Cost Breakdown
Here is where your ADU budget typically goes:
| Category | % of Total | Typical Range |
|---|---|---|
| Construction / Labor | 50-60% | $75,000-$210,000 |
| Materials | 20-30% | $30,000-$105,000 |
| Design & Architecture | 8-12% | $8,000-$35,000 |
| Permits & Fees | 5-10% | $5,000-$30,000 |
| Utility Connections | 3-8% | $5,000-$25,000 |
| Contingency | 10-15% | $15,000-$50,000 |
Hidden Costs to Watch For
- Sewer/water connection fees (can be $5,000-$15,000+)
- School impact fees (waived 750 sq ft or less of interior livable space in CA)
- Tree removal or site grading
- Upgraded electrical panel for main house
- Landscaping restoration after construction
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Costs by City
Construction costs vary significantly by location. Here are average ADU build costs for popular California cities:
| City | Avg Build Cost | Cost/Sq Ft | Permit Fees |
|---|---|---|---|
| Los Angeles | $150,000-$350,000 | $200-$400 | $4,000-$15,000 depending on size and type (plus 10% General Plan Maintenance Surcharge on permit fees as of June 9, 2026) |
| San Francisco | $200,000-$450,000 | $300-$500 | Replace the guessed range with SF's own published figures. DBI's own estimate: 'City fees range from 6-9% of construction costs' (and architects/engineers about 10%; at least $125,000 in material and labor for a new unit). PLANNING development application fee (Fee Schedule eff. 8/29/2025, rev. 6/15/2026) — New Construction: $3,502 flat under $100k; $3,504 base + 3.855% of cost above $100,000 in the $100k-499,999 band; $19,226 + 1.230% above $500,000. Alteration/Change of Use (garage or interior conversion): $504 under $10k; $516 + 5.274% above $10,000; $3,838 + 3.524% above $50,000; $5,638 + 3.855% above $100,000. Neighborhood notification $121 + $4.25/envelope; permit-revision back check $366. DBI building permit fees are TWO separate charges under SF Building Code Table 1A-A (amended Ord. 112-26, eff. 7/12/2026) — Plan Review: $1,671 + $15.60 per $1,000 over $50,000 ($50k-200k band), $4,011 + $13.31 per $1,000 over $200,000 ($200k-500k band); Permit Issuance: $677 + $4.83 per $1,000 ($50k-200k), $1,402 + $4.21 per $1,000 ($200k-500k). Table 1A-A note 1 states these exclude Public Works, Planning, Fire, Public Health and plumbing/electrical/mechanical permit fees. Add SFUSD school facility fees (calculated by DBI staff), SFPUC and Public Works right-of-way permits. OUR WORKED EXAMPLE (label as our calculation, not a published number): a $300,000 detached ADU = Planning $11,214 + DBI plan review $5,342 + DBI issuance $1,823, roughly $18,400 before trade permits and school fees — about 6% of construction cost, consistent with DBI's 6-9%. FEE WAIVER: building permit fees are waived for permits granting legal status to dwelling units built without permits, for activities prior to 1/1/2020 (Board Ord. 150571). |
| San Diego | $120,000-$300,000 | $180-$350 | $3,500-$12,000 |
| San Jose | $180,000-$400,000 | $250-$450 | City building permit fees, FY 2026-27 Building and Structure Permits Fee Schedule, effective August 10, 2026. ADU 0-750 sq ft: permit issuance $422, plan review $1,137, inspection $1,732 (total $3,291). ADU 751-1,200 sq ft: permit issuance $633, plan review $1,950, inspection $2,520 (total $5,103). Permit issuance includes addressing assignment for the unit; inspection includes the meter release inspection. Modular fees are 10% lower for plan review and 20% lower for inspections. Separately, an optional preliminary virtual meeting with a planner is billed at the Planning Division's hourly rate of $398/hour with a 30-minute minimum (i.e. $199). These are city permit fees only and exclude school/parkland impact fees, construction taxes, and construction cost. |
| Sacramento | $100,000-$250,000 | $150-$300 | Replace the guessed range with the city's OWN published figures. Form CDD-0419, 'Accessory Dwelling Unit (ADU) Fee Estimate (New Construction)', revised 07-12-2026, at a $170.80/sq ft valuation: 749 sq ft = $5,271.90 total; 750 sq ft = $10,624.40; 1,200 sq ft = $14,842.50. Representative line items at 1,200 sq ft: building permit $1,790.36, building plan review $751.95, fire dept administrative $176, fire inspection $294 ($0.11/sq ft, $294 minimum), fire plan review $260, planning inspection $526, planning review $263, public works review $205 deposit + hourly, utilities $205 deposit + hourly, construction excise tax $945.60, general plan fee $533 ($2.60 per $1,000 valuation), residential construction tax $315, technology fee $254.23. NOT included and additional: school district impact fees (calculated and collected by the district, form CDD-0226), Regional Sanitation and Sewer Development fees (the form says 'Check with County'), and possible sewer/water tap, housing and project-area impact fees. The optional ADU Zoning Review is now $0 (the $117 fee was waived). An optional building permit fee estimate service costs $164 (form CDD-0278). Additional review time bills at $216/hr building, $263/hr planning. The city's own caveat: 'This is only an estimate. The actual fees can vary based on project scope, location, fee changes, etc.' |
| Oakland | $160,000-$380,000 | $250-$420 | Published Oakland figures, not a guess. PLANNING/ZONING PERMIT (Design Review Exemption - Secondary Units/ADU), FY2025-26 grand totals including the 7.2% General Plan Update and 12.70% Technology/Records surcharges: Category I, II & III $593.95 (base report fee $491.62); Category IV $892.54 (base $738.77); Amnesty Program $1,779.79 (base $1,473.16). PERMIT APPLICATION INTAKE: $201.49 at the counter, $112.83 online. BUILDING PERMIT (Master Fee Schedule effective 8/28/2025, R3 residential): new construction $10.60 per $1,000 of construction valuation for plan review plus $8.00 per $1,000 for inspection (each with a $335.81 minimum); repairs/additions/alterations $17.08 plus $26.11 per $1,000. The City's own summary guidance is 'Building Permit Fees: Usually 4-6% of project value.' Plus a 12.70% Records Management & Technology Enhancement fee on all Building Services fees. ZONING INSPECTION for a building permit up to $200,000 valuation: $537.29. NEW SEWER LATERAL CONNECTION (the schedule expressly includes ADUs): $1,867.40. OUSD SCHOOL FEE collected by Planning & Building on the district's behalf: $5.17 per sq ft residential. Note: the widely circulated City 'Secondary Units' handout quoting a $464.89 planning permit fee and 5-6 week building permits was last updated 10/10/2019 and is obsolete - do not cite it. |
| Long Beach | $120,000-$280,000 | $180-$330 | Replace the guessed range with the city's published figures. Long Beach's own guidance: 'For most construction projects, you could expect to spend about 2% of your building costs on plan checks, permits, inspections and other agency fees.' Published components (Building Permit & Plan Check Fees, effective 5/20/2026): Building Permit fee by valuation — $1,264 for the first $100,000 plus $6 per additional $1,000 in the $100,001-$1,000,000 band; Combination Building Permit (Group R-3, includes electrical, plumbing, mechanical) = 150% of the Building Permit fee, minimum $164; Combination Plan Check = 85% of the Building Permit fee, minimum $154; Zoning Plan Check = 0.5% of project valuation for valuations up to $750,000, minimum $310, capped at 95% of the building standard plan check fee; NPDES permit = $2 per $1,000 of valuation with plan check at 75% of that; Expedited plan check = 2x standard. Add a $115.00 processing fee to EACH plan check and permit application, plus a 6% Technology Surcharge and a 6% General Plan Surcharge on all applicable fees. Worked from those published formulas, a $150,000-valuation ADU lands near $5,800 in permit and plan-check fees before impact fees — I am labelling that figure as DERIVED from the published schedule, not published by the city. |
| Fresno | $80,000-$200,000 | $120-$250 | City-published figures for a pre-approved-plan ADU: Plans FREE, Plan Check FREE, Building Permit 'Up to $2,400', School Impact Fee varies by sq ft (school fee is the district's, not the city's). Underlying Master Fee Schedule rates (fees effective 07/01/2025): R-3 One or Two-Family Production/Repeat/Standard Plan Infill = $34.89 plan check base + $1,279.35 inspection base at the 1,000 sq ft threshold. A custom-designed ADU instead uses R-3 (Custom): $580.69 plan check + $1,884.77 inspection at the same threshold. A CBSC surcharge of $1-$4 by valuation also applies. Do not publish a single range without splitting standard-plan vs custom. |
| Santa Ana | $130,000-$300,000 | $200-$360 | REPLACE THE GUESS WITH PUBLISHED FIGURES. Planning Division FY 2026-2027 Fee Schedule: Accessory Dwelling Unit Review $1,940.00; ADU Over-the-Counter Review $594.00; ADU Pre-Approved Plan Review $524.00. Certain applications also carry a 7% technology fee per transaction, and from July 1, 2026 a 2.5% credit/debit card processing fee. These are PLANNING fees only — building permit fees are additional and the city does not publish them ('Building permit fees vary according to the scope of work'; Permit Counter (714) 647-5800). |
| Anaheim | $130,000-$290,000 | $195-$350 | $3,500-$12,000 |
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