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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 |
| Size | Typical total cost | What it usually fits |
|---|---|---|
| 400 sq ft | $100,000–$160,000 | A studio or compact one-bedroom; the usual garage-conversion footprint. |
| 500 sq ft | $125,000–$200,000 | A comfortable one-bedroom. The most-quoted size in cost searches. |
| 600 sq ft | $150,000–$240,000 | One bedroom with a separate living area, or a tight two-bedroom. |
| 750 sq ft | $188,000–$300,000 | Two bedrooms. In California, staying at 750 sq ft or less exempts you from impact fees. |
| 1,000 sq ft | $250,000–$400,000 | A full two-bedroom. At or near the cap in many cities. |
| 1,200 sq ft | $300,000–$480,000 | The statutory maximum in much of California and a common cap elsewhere. |
Rounded to the nearest $1,000. A garage conversion at the same square footage generally lands 30–50% below these figures because the shell, slab and roof already exist; a prefab unit lands lower on construction and higher on delivery and craning.
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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ADU Cost per Square Foot by City
Construction costs vary more by location than by anything else you choose. Every figure below is the same one on that city's own rules page, and the permit fee is the one its building department publishes.
| City | Avg Build Cost | Cost/Sq Ft | Permit Fees |
|---|---|---|---|
| New York City, NY | $150,000-$450,000 | $300-$580 | DOB filing fee (Admin. Code 28-112.1): a detached ADU filed as a New Building pays $0.06 per sq ft with a $100 minimum, so $100 for 800 sq ft; an interior conversion filed as an Alt-CO pays $170 for the first $5,000 of work plus $2.60 per $1,000 above that (about $550 on a $150,000 job). |
| Los Angeles, CA | $220,000-$400,000 | $300-$500 | No flat ADU fee. The LADBS building permit fee is set by construction valuation under LAMC 91.107 Table 1-A: for a valuation between $100,000 and $500,000 the codified base is $395 plus $3.50 per $1,000 (about $1,445 on $300,000, or about $2,384 as a combined building-mechanical permit at 165% of that figure), plus plan check at 90% of the permit fee (91.107.3.1.1), a 2% plan-maintenance fee (91.107.4.3), a fire-hydrant fee of 0.22% of valuation on jobs of $50,000 or more (91.107.4.4), state seismic and green-code surcharges, and the City Planning General Plan Maintenance Surcharge, raised from 7% to 10% on June 9, 2026 (CF 09-0969-S4). Table 1-A amounts are indexed to CPI every July 1 (91.107.1.1), so run the LADBS Permit Fee Calculator for the current total. LAUSD developer fees of $5.38 per sq ft apply to an ADU larger than 500 sq ft from August 11, 2026 (about $4,300 on 800 sq ft) |
| Chicago, IL | $150,000-$350,000 | $200-$400 | $2,525-$3,050 for a new coach house in 2026 permit records (DOB building permit fee minimum $2,450 for new residential construction in Table 14A-12-1204.3(3), plus a $75 zoning review fee on most permits; a few paid $1,500 zoning fees). $1,875-$3,150 for a conversion unit (minimum $1,800 for a permit that adds a dwelling unit, Table 14A-12-1204.3(4), plus zoning). The formula is construction factor x review factor x floor area (14A-4-412.2.2.1; $0.44 per sq ft x 0.75 for a wood-frame Group R coach house), so the minimums govern any ADU-sized project. A $300 deposit is paid at application (14A-12-1204.1). DOH lists no pre-certification fee; an affordable ADU costs $500 to register |
| Houston, TX | $140,000-$260,000 | $225-$350 | Set by the City Fee Schedule (CPI increase of 1.391% on Jan 1, 2026): minimum building permit $91.06, minimum plumbing permit $97.56, administrative fee $33.56; the full residential fee formula was not readable this pass, so price your project with HPC's Fee Calculator. |
| Phoenix, AZ | $150,000-$280,000 | $200-$350 | Valuation-based (PDD Fee Schedule, Ordinance G-7465, effective January 20, 2026, Table A): permit fee $703 on the first $50,000 plus $9 per $1,000 up to $200,000, then $2,053 plus $9 per $1,000; residential plan review is 80% of the permit fee when valuation exceeds $50,000 (100%, minimum $195, at or below); plot plan review $98; each extra utility meter $98. Examples: a $150,000 valuation is about $1,603 permit + $1,282 plan review + $98 = $2,983; $250,000 is about $2,503 + $2,002 + $98 = $4,603. Valuation is the higher of the city's square-foot valuation table or your contract price. Re-inspections after the first are $195 each |
| San Antonio, TX | $125,000-$320,000 | $225-$400 | FY2026 DSD fee schedule (rev. Oct 2025), new residential construction by size: $988 total basic permit fees for 501-1,000 sq ft, $1,022 for 1,001-1,250 and $1,201 for 1,251-1,500 sq ft (building, trade and sewer permits plus a $200 plan review). 100% waivable for income-qualified ADUs. |
| San Diego, CA | $250,000-$450,000 | $375-$600 | IB-501 (August 2026), Table 501A: a detached ADU of 500 sq ft or less, or an attached ADU or JADU up to 1,100 sq ft, pays $3,512.92 plan check plus $2,228.29 inspection for the first 500 sq ft ($5,741.21) and $6.98 + $4.46 per sq ft above that (about $9,173 for an 800 sq ft attached unit). A detached ADU over 500 sq ft is billed at the single-dwelling-unit rate: $8,085.26 plan check plus $8,401.90 inspection ($16,487.16 flat up to 3,000 sq ft including attached accessory structures). Every project also pays the $737 General Plan Maintenance Fee, a $12.16 mapping fee, a 2.5-hour DIF-calculation review (about $442 at the $176.84 hourly rate), $529.71 per new address, water/sewer plan check of $176.57 (no meter change) or $353.13 (new meter), and state seismic and building-standards fees. School district fees apply to any ADU of 500 sq ft or more (IB-146). Express plan check costs $793.95 plus 1.5x the regular plan check fee |
| Dallas, TX | $130,000-$320,000 | $250-$400 | $1,200-$1,400 building permit for a 600-1,000 sq ft unit: Table A-I ($1.07 per sq ft up to 700 sq ft; $0.34569 per sq ft plus $300 above) plus $577 plan review, $25 handling and $15 technology fee (fee schedule of July 1, 2025); Board of Adjustment special exception $600 (Ch. 52 Sec. 303.12.1.4). |
| San Jose, CA | $200,000-$450,000 | $300-$500 | FY 2026-27 Building Fee Schedule (effective Aug 10, 2026): ADU 0-750 sq ft $422 issuance + $1,137 plan review + $1,732 inspection = $3,291; 751-1,200 sq ft $633 + $1,950 + $2,520 = $5,103. Excludes construction taxes, school and parkland fees and any planner meeting ($398/hour). |
| Austin, TX | $150,000-$350,000 | $250-$450 | About $1,850-$2,150 in DSD fees for an 800-1,200 sq ft unit (FY2025-26 residential schedule, eff. Oct 1, 2025): $106.72 processing + $896.50-$1,220 plan review + roughly $840-$885 in building, electrical, mechanical, plumbing and energy permits; Austin Energy adds $220-$440. |
| Jacksonville, FL | $150,000-$300,000 | $150-$360 | Building permit fees are set by Ordinance Code Chapter 320 on the gross floor area under roof, plus separate electrical, plumbing and mechanical permit fees; the city publishes no ADU-specific figure, so price it in JaxEPICS or with the Building Inspection Division (904-255-8500). |
| Fort Worth, TX | $130,000-$320,000 | $250-$400 | $300-$900 building permit for a 500-1,200 sq ft unit. FY2027 Table 1-C-3 (R use groups, fee ordinance on the Sept 15, 2026 Council budget agenda, effective Oct 1, 2026): an R-3 unit up to 500 sq ft pays $61.01 plus $0.45 per sq ft over 65; 65-700 sq ft $102 plus $0.74 per sq ft over 65; 700-1,400 sq ft $570 plus $0.53 per sq ft over 700. Worked: 500 sq ft about $257, 800 sq ft $623, 1,000 sq ft $729, 1,200 sq ft $835, plus a $33.08 application fee and $16.87 technology fee; no plan-review deposit for R-3 accessory structures. Until Sept 30, 2026 the FY2025-26 table (Ord. 27191-09-2024) applies: 500 sq ft $240.80, 800 sq ft $592.44, 1,000 sq ft $692.44, plus $31.50 and $16.87. A garage conversion is a residential remodel at $119 per trade ($595 for five trades, FY2027). Third-party plan review and inspection reduce the permit fee to 70%, 55% or 35% |
| Charlotte, NC | $115,000-$230,000 | $135-$270 | $900-$1,700 county building permit for a $100,000-$250,000 ADU (LUESA Fee Ordinance rev. July 1, 2026, Sec. II.A.1: $632.57 + $5.49 per $1,000 over $50,000, $907.12 + $5.93 per $1,000 over $100,000, $1,203.52 + $4.59 per $1,000 over $150,000) plus a $3 technology charge and the city LDIRL fee. |
| San Francisco, CA | $300,000-$550,000 | $350-$650 | 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 |
| Seattle, WA | $325,000-$550,000 | $400-$650 | $3,453 in plan-review and building-permit fees for a 500 sq ft DADU valued at $93,145, per SDCI's own 2026 fee example (up 18.7 percent from $2,908 in 2025). Fees are valuation-based (Fee Subtitle Table D-1); at SDCI's 2026 rate of $186.29 per sq ft for wood-frame R-3 construction, the 2026 Fee Estimator gives roughly $4,990 for a 1,000 sq ft DADU, 75 percent due at intake. Add a 5 percent technology fee, the $6.50 state surcharge, hourly reviews at the 2026 base rate of $292 per hour where triggered, plus separate electrical, plumbing and side sewer permits. A subject-to-field-inspection permit pays 40 percent of the plan-review fee, and a pre-approved standard-plan submittal gets a reduced plan-review fee (Tip 310) |
| Denver, CO | $200,000-$450,000 | $250-$500 | Building permit is valuation-based: $770 + $5.60 per $1,000 over $100,000 (about $1,330 at $200,000) plus a 50% plan-review fee; zoning permit $150 + $0.50 per $1,000; SUDP $425 application + $150 inspection; Denver Water ADU system development charge $2,170 (from Jul 1, 2026). |
| Nashville, TN | $200,000-$300,000 | $250-$475 | $5.00 per $1,000 of construction value (Metro Code 16.28.110.A.1) plus a $25 zoning exam fee and a 10% Codes tech fee; no plan-review fee for one- and two-family work. A 700 sq ft DADU valued on the ICC table at $169.09/sq ft (about $118,000) comes to roughly $675 before trade permits |
| Washington, DC | $150,000-$550,000 | $200-$500 | New construction: $0.03 per cu ft of building plus a 10% enhanced fee and a $0.002/sq ft Green Building Fee. Alterations such as a basement conversion: $30 + 2% of construction value plus 10%, and a 0.13% green fee; a 50% filing deposit is paid up front (DOB Building Permit Fee Schedule). |
| Boston, MA | $75,000-$350,000 | $150-$400 | Long-form building permit $50 plus $10 per $1,000 of estimated construction cost (ISD fee schedule dated May 15, 2023): about $950 on a $90,000 interior ADU, $3,050 on a $300,000 detached ADU; ZBA appeal $150 for a 1-3 family home. |
| Las Vegas, NV | $110,000-$230,000 | $180-$330 | Square-footage based (Building & Safety 2020 Building User Fees, Table 3-A, effective July 1, 2021 and still in force). The city's Permit Fee Estimator carries a "Single-Family Casita with Kitchen" line at the R-3 single-family rates: for a wood-frame (Type V) casita up to 1,000 sq ft, plan check $500 + inspection/permit $933 + $55 administration = $1,488; a 1,200 sq ft unit is about $1,676 and a 1,500 sq ft unit about $1,961 (plan check adds $0.467 and inspection $0.477 per sq ft over 1,000). Zoning fees arise only if a standard cannot be met: Administrative Deviation $300; Variance $300 plus $500 notification; Special Use Permit $500 plus $500 notification; Zoning Verification Letter $100 (Department of Planning Fee Schedule, Resolution R-21-2008). Contractors need a Nevada license and a city business license before a permit issues |
| Portland, OR | $180,000-$280,000 | $250-$400 | Building permit and plan-review fees are valuation-based under the Building and Other Permits Fee Schedule effective July 10, 2026 (no flat ADU fee); trade permits are separate. SDCs: Parks $7,941 (under 700 sq ft) or $11,878, Transportation $3,421, waived with the 10-year no-STR covenant |
| Detroit, MI | $90,000-$200,000 | $140-$240 | BSEED building permit (fee schedule modified 7/18/2025): $2,895.29 at $100,000 project cost plus $27.82 per $1,000 above that (about $4,286 at $150,000); trade permits and a 35% plan-review deposit are extra. Relevant only if the zoning changes. |
| Albuquerque, NM | $120,000-$240,000 | $160-$320 | Valuation-based (Plan Review and Building Permit Fees table, rev. April 2010, still posted): a $150,000-$250,000 casita pays about $640-$920 permit plus $415-$600 plan review (65%), $25 zoning, $50 hydrology and trade permits. Site Plan - Administrative fee: see the Planning General Fee Schedule. |
| Tucson, AZ | $150,000-$250,000 | $150-$300 | City fees are valuation-based (FY2027 Planning and Permitting Fee Schedule, effective July 1, 2026). Building permit for new construction: $1,038.05 plus $9.64 per $1,000 over $50,000, or $1,520.05 plus $8.25 per $1,000 over $100,000 (Section 4-02.4); building staff review (plan check) for residential is 50% of the permit fee (4-02.2.1); digital filing fee 1% (minimum $18.54). Worked example: a $120,000 valuation gives a $1,685.05 permit + $842.53 plan review + about $25 filing = roughly $2,550; at $200,000 it is about $3,550. Using an approved model plan waives the construction-document review and substitutes a $176.55 site-plan review (4-02.3.3), so the same $120,000 casita pays about $1,880. Valuation follows the ICC Building Valuation Data table; ask PDSD (pdsdinquiries@tucsonaz.gov) for the current per-square-foot figure. Setback relief via the Design Development Option costs $278.07 plus public-notice fees |
| Fresno, CA | $150,000-$320,000 | $200-$330 | Pre-approved plans: plans and plan check free; the city's Oct 2025 estimator puts the building permit at $2,344-$2,861 by plan. Custom ADU: Master Fee Schedule (eff. 7/1/2026) R-3 Custom = $599.56 plan check + $1,946.03 inspection at 1,000 sq ft, plus a 12.83% General Plan surcharge. |
| Sacramento, CA | $170,000-$400,000 | $250-$500 | City fee estimate form CDD-0419 (rev. 7/12/2026), at a $170.80 per sq ft valuation: about $5,272 total for a 749 sq ft new detached ADU, $10,624 at 750 sq ft and $14,843 at 1,200 sq ft. Line items at 1,200 sq ft: building permit $1,790.36, plan review $751.95, fire administrative $176, fire inspection $294 ($0.11 per sq ft, $294 minimum), fire plan review $260, planning inspection $526, planning review $263, public works and utilities review $205 deposit each plus hourly, construction excise tax $945.60, general plan fee $533 ($2.60 per $1,000 of valuation), residential construction tax $315, technology fee $254.23. Not included: school district fees (paid to the district, form CDD-0226), regional sanitation and county sewer fees, and any water or sewer tap, housing or project-area impact fees. Optional ADU Zoning Review: $0 (was $117 before July 2026). Optional written fee estimate: $164 (form CDD-0278). Extra review time bills at $216 per hour for Building and $263 per hour for Planning |
| Mesa, AZ | $150,000-$280,000 | $175-$350 | Valuation-based (Development Services Schedule of Fees, July 2026): $500 plus $6 per $1,000 of valuation over $25,000, up to $200,000; then $1,550 plus $9 per $1,000. A $150,000 ADU pays about $1,250 and a $250,000 unit about $2,000, plan review and trade permits included. |
| Kansas City, MO | $90,000-$200,000 | $150-$300 | Residential building permit = $483 + $1.41 per $1,000 of valuation over $100,000 (City fee calculator; Building Code Sec. 18-20): about $554 on a $150,000 ADU or $624 on $200,000, plus separate electrical, plumbing and mechanical permits. |
| Atlanta, GA | $120,000-$240,000 | $140-$280 | $1,700-$2,750 for a $150,000-$300,000 ADU: building permit $7 per $1,000 of construction cost (minimum $150) plus a $25 technology fee, three trade permits at $150 plus $25 each, and a $100 certificate of occupancy (Department of City Planning fee tables, checked Sept 2026). |
| Colorado Springs, CO | $185,000-$420,000 | $325-$650 | PPRBD permit is valuation-based ($45.65 per sq ft in 2025-26): about $345 for a 750 sq ft unit or $505 for 1,250 sq ft, plus a 28% plan-examination fee. City DRE plan review $180 (new structure) or $130 (addition) plus $25 IT fee (Res. 191-25, eff. Jan 1, 2026). No separate land-use application fee. |
| Raleigh, NC | $150,000-$400,000 | $300-$550 | About $950-$1,600 in building, trade and plan-review fees for a 600-1,000 sq ft ADU under the FY2027 Development Fee Guide (building permit = 0.38% of ICC-based construction value; trades and plan review are percentages of it). Facility and utility fees are extra. |
| Long Beach, CA | $215,000-$400,000 | $310-$450 | $5,500-$6,500 in city plan-check and permit fees for a 750-800 sq ft new ADU (derived from the Building Permit & Plan Check Fees effective 5/20/2026 and IB-077's $175.92 per sq ft R-3 valuation): combination building permit at 150% of the valuation-based permit fee ($1,264 for the first $100,000 of valuation plus $6 per $1,000 above, min $164), combination plan check at 85% of the permit fee (min $154), zoning plan check at 0.5% of valuation (min $310), NPDES at $2 per $1,000 plus 75% for plan check, a $115 processing fee per application, and 6% Technology and 6% General Plan surcharges on all applicable fees; expedited plan check costs 2x. The city's own guide: budget about 2% of construction cost for plan check, permits and inspections. Impact, school and sewer fees are extra |
| Miami, FL | $150,000-$320,000 | $250-$450 | About $2,200-$3,500 in city building fees on a $200,000-$350,000 unit: 0.50% of construction cost (min $110), $2.80 per $1,000 up-front, solid-waste $0.22 per $100 (max $600), energy $0.11/sq ft, CO $105 (Res. R-26-0200, 4/23/2026); zoning $250 up-front; impact fees extra. |
| Oakland, CA | $210,000-$400,000 | $250-$500 | Zoning: ADU Design Review Exemption (Categories I, II and III) $878.58 base, $1,061.45 total with the 7.2% General Plan Update and 12.70% Technology/Records surcharges; ADU Amnesty Program $1,765.74 total (Zoning Fee Schedule FY2026-27, loaded September 4, 2026). Permit application intake $134.32 online or $201.49 at the counter. Building permit (Master Fee Schedule effective July 1, 2026, R-3): new construction plan review $10.60 plus inspection $8.00 per $1,000 of construction value, each with a $335.81 minimum; alterations and additions $17.08 plus $26.11 per $1,000; electrical, plumbing and mechanical inspections $7.66, $4.79 and $4.36 per $1,000 of each trade's value; plus a 7.20% General Plan surcharge and a 12.70% Records Management and Technology fee on building fees; zoning inspection $537.28 on a new-construction residential permit. Our arithmetic for a $300,000 new detached ADU: about $6,700 in building plan-check and inspection fees plus $1,061.45 zoning, before trade permits. The City's own rule of thumb is 4-6% of project value. Separate: new sewer lateral connection permit $1,798.93 (Public Works schedule, expressly including ADUs) and the OUSD school fee of $5.17 per sq ft |
| Minneapolis, MN | $150,000-$465,000 | $180-$550 | $325 zoning application, plus a valuation-based building permit: about $3,200-$5,400 on $150,000-$300,000 of work (permit fee + 65% plan-review fee + 0.05% state surcharge, 2026 schedule). Plumbing, mechanical and electrical permits are separate. |
| Tampa, FL | $100,000-$250,000 | $170-$350 site-built | S-1 special use application for an ADU or EFR: $194 (current fee listed in the city's July 2026 fee study; a proposed rise to $445, then $695 and $945 over three years had not been adopted by Council as of September 2026). Zoning fees are set by Council resolution and charged in Accela. Building permit fees are valuation-based through the city's online Fee Estimator, plus the 2.5% Florida building permit surcharge |
| Anaheim, CA | $220,000-$450,000 | $300-$500 | Building Permit Fees schedule (Exhibit A, Tier 3 Type VB, Residential Category 1, Dwellings and Custom; posted Aug 2026): combined plan check and building permit of $1,677 for the first 500 sq ft plus $213 per extra 100 sq ft up to 1,000 sq ft (about $2,316 for an 800 sq ft ADU), then $2,741 at 1,001 sq ft plus $171 per 100 sq ft (about $3,083 for 1,200 sq ft). Add trade permits (electrical $26 for the first 100 sq ft plus $0.26 per sq ft; plumbing $49 per fixture; $188 minimum per trade permit), Zoning Plan Check $352 and a $114 address fee (Planning fee schedule, Aug 2025). Budget roughly $3,000-$4,500 in city fees for an 800-1,200 sq ft detached ADU before impact and school fees |
| Henderson, NV | $110,000-$260,000 | $180-$330 | No ADU line in the DSC fee schedule (eff. 10/1/2025). Closest rows: Accessory Building - Residential at 1,000 sq ft = $1,303 plan check + $1,266 inspection (MPE included); Single-Family Addition at 1,000 sq ft = $1,601 + $1,555. Confirm the fee category at intake. |
| Honolulu, HI | $150,000-$450,000 | $250-$550 | $0 for the ADU's plan review and building permit: ROH § 18-6.5 waives both fees for the creation of an accessory dwelling unit, extended through June 30, 2030 by Ordinance 25-12 (no waiver if work started without a permit). For scale, ROH 18-6.2 would otherwise charge $700 plus $10 per $1,000 of value above $100,000 (about $2,200 on a $250,000 job) plus a 20 percent plan-review fee. Grading, grubbing and stockpiling permit fees processed with an ADU permit are waived too (§ 18A-2.4). A zoning adjustment, if needed, costs $200 initial review plus $400 processing (DPP, November 2025) |
| Riverside, CA | $180,000-$320,000 | $180-$280 | Valuation-based, not flat: roughly $1,400-$1,500 in Building & Safety permit and plan-check fees for an 800 sq ft ADU on the FY2023-24 schedule ($100.04/sq ft valuation), plus Planning's $289 zoning check and surcharges; the city's 2022 workshop put all-in fees at $3,000-$9,000. |
| Irvine, CA | $185,000-$420,000 | $300-$525 | Planning ADU review is hourly at $217.64 against a $1,500 deposit; building plan check plus inspection is $0.68 + $0.56 per sq ft for a new detached unit ($0.86 + $1.33 for additions and conversions) plus 10% automation fee (Aug 15, 2026 schedules); roughly $2,700-$3,900 all-in for a 750 sq ft ADU |
| Saint Paul, MN | $125,000-$350,000 | $180-$400 | Valuation-based (Sec. 33.04; schedule effective 2/25/2023): $1,499 for the first $100,000 plus $8 per additional $1,000, a plan-check fee of 65% of that, and the 0.05% state surcharge — about $3,200 on a $150,000 ADU and $5,300 on $300,000, before trade permits and any SAC. |
| Santa Ana, CA | $180,000-$400,000 | $300-$500 | Planning Division FY2026-27 fee schedule (effective July 1, 2026): Accessory Dwelling Unit Review $1,940; ADU Over-the-Counter Review $594; ADU Pre-Approved Plan Review $524; Minor Exception (appeal of a denial) $3,579. A 7% technology fee is added to all Planning, Building and Public Works applications, plan checks and permits, and card payments carry a 2.5% processing fee. Building Safety has no ADU-specific line: the FY2026-27 fee schedule (Section X) charges structural plan check and inspection per sq ft by project type, for example $1.42/sq ft plan check for a single-story residential single-family structure ($3.14 two-story) plus $0.81/sq ft inspection, or $1.78 plus $1.42 per sq ft for a first-floor residential addition up to 500 sq ft, with electrical, plumbing and mechanical items priced separately; ask Building Safety at (714) 647-5800 which lines apply to your unit. Public Works: sewer connection fee $53 per plumbing fixture unit and a water capacity fee of $930 for a new 5/8-inch meter (FY2026-27 Public Works summary) |
| Orlando, FL | $150,000-$260,000 | $200-$260 | Building permit: $64.94 for the first $1,000 of construction cost plus $4.32 per additional $1,000, plus about 10% in surcharges (fee schedule eff. Jan 2023); the city says ADU building-permit fees typically total $450-$1,050. Electrical, plumbing and mechanical permits are extra. |
| Pittsburgh, PA | $135,000-$325,000 | $225-$375 | PLI 2026 schedule (eff. Jan 1, 2026): residential base permit fee $6.00 per $1,000 of construction value (min $130, max $8,000; 40% due at application) plus $4.50 SETF, $5 records fee and a $2-$25 technology fee; DCP residential zoning review $1.00 per $1,000 (min $50). |
ADU Cost Questions
How much does a 500 square foot ADU cost?
At the median cost across the 125 cities we track ($250–$400 per square foot), a 500 sq ft ADU runs $125,000 to $200,000 for the finished build — construction, materials, design and permits. A 500 sq ft garage conversion is typically 30–50% less because the shell, slab and roof already exist. Site work, a utility upgrade or poor access can add $5,000–$25,000 on top, and none of it shows up in an online estimate.
What is the cost per square foot to build an ADU?
$250–$400 per square foot is the median range across the 125 cities on this site, and the spread between cities is wider than the spread between ADU types: the cheapest markets we track start near $120/sq ft and the most expensive coastal ones reach $750. Look up your own city in the table above rather than using a national average.
How much does it cost to hire a full-service ADU builder?
A design-build firm that handles drawings, permitting and construction usually quotes one price for the whole job, and that price is what the per-square-foot figures above describe. Hiring the pieces separately — an architect at 8–12% of build cost, a permit expediter, then a general contractor — can come in lower on paper but moves the coordination risk onto you. Ask any builder to itemise design, permits and construction so you are comparing the same scope.
How accurate is an ADU cost calculator?
Treat any calculator, including this one, as a budgeting range rather than a quote. It knows your city, ADU type and size; it does not know your slope, soil, sewer depth, electrical panel, tree protection or how far the unit sits from the existing service. Those are what move a real bid, and they are why two identical ADUs on neighbouring lots can differ by $40,000. Use the estimate to decide whether to start; use a site visit to decide what to build.
What does an ADU cost estimate usually leave out?
The five that surprise people most: sewer and water connection fees ($5,000–$15,000 and up), a main-house electrical panel upgrade, site grading or tree removal, landscaping restoration after the build, and a contingency — budget 10–15%, because on a project this size something always comes up. School and other impact fees are a sixth, though in California an ADU of 750 sq ft or less of interior livable space is exempt from them.
Is a garage conversion cheaper than building a detached ADU?
Almost always, and usually by a wide margin, because the foundation, walls and roof already exist. The trade-offs are that you lose the garage, you inherit whatever is wrong with the existing slab and framing, and bringing an unconditioned structure up to habitable code — insulation, egress windows, ceiling height, moisture — sometimes costs more than the savings. Get both priced before you assume.
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