How Much Does It Cost to Build an ADU? (By City)

ADU Cost Overview: Why Prices Vary So Dramatically

The total cost to build an ADU in 2026 ranges from roughly $80,000 for a simple garage conversion in a low-cost market to over $500,000 for a new detached structure in San Francisco. The variation is not random — it is driven by four primary factors: permit fees and impact fees charged by local governments, construction labor costs in your local market, land and site conditions, and the type of ADU you choose to build. Permit fees are the most transparently trackable cost component because they are published by city governments and documented in ordinances. PropertyZoned compiles these from official municipal sources for each of the 100 cities in our database. Impact fees — development charges for transportation, parks, water/sewer infrastructure — are the most variable permit cost component. California cities waive impact fees for ADUs under 750 square feet under state law (AB 881), while Portland, Oregon charges $10,000 to $25,000 in System Development Charges (SDCs) for new detached ADUs. Dallas charges no impact fees at all. Construction labor is the dominant cost driver — it accounts for 60-70 percent of total ADU project cost. Labor rates in San Francisco can be 3x the rates in Nashville or Charlotte. The same detached ADU design costs fundamentally different amounts to build depending on local labor market conditions. ADU type is the most controllable cost variable. Detached new construction ADUs are the most expensive. Attached ADUs (room additions) are typically less expensive. Garage conversions — converting existing enclosed space to habitable use — are significantly less expensive because the structure already exists. Interior conversions (basements, attics, in-law suites) are often the lowest-cost option. Understanding which ADU type is right for your lot, your budget, and your goals is the first step in accurate cost planning.

Permit Fees by City: What You Will Actually Pay

All permit fee figures below are sourced directly from city data compiled on PropertyZoned. These reflect actual published fee schedules as of 2026. Los Angeles (California): plan check $500-$3,000; building permit $1,500-$5,000; impact fees waived under 750 sqft (AB 881). Total permit fees: $2,000-$8,000. School fees waived under 750 sqft. This is one of the most favorable fee environments among major California cities. San Francisco (California): plan check $800-$3,500; building permit $2,000-$6,000; impact fees waived under 750 sqft. Total permit fees: $3,000-$10,000. SF DBI fee schedule reflects higher property valuations. School fees waived under 750 sqft. San Diego (California): plan check $600-$2,500; building permit $1,500-$5,500; impact fees waived under 750 sqft. Total permit fees: $2,500-$9,000. San Diego offers a Standard ADU Plan Program that can reduce plan check fees and timeline. Sacramento (California): plan check $500-$2,200; building permit $1,200-$4,500; impact fees waived under 750 sqft. Total permit fees: $2,000-$7,500. Sacramento generally has the lowest fees of major California cities. Austin (Texas): plan check $300-$2,000; building permit $1,000-$4,000; impact fees vary but can include significant Water/Wastewater and Transportation impact fees ($3,000-$8,000 additional). Total permit fees including impact fees: $3,000-$15,000. Austin's impact fees are notable. Dallas (Texas): plan check $300-$1,800; building permit $1,000-$4,500; no impact fees. Total permit fees: $2,000-$8,000. Dallas notably charges no impact fees for residential development — a meaningful cost advantage versus Austin. Portland (Oregon): plan check $1,500-$4,000; building permit $1,200-$3,500; System Development Charges (SDCs) for transportation, parks, water/sewer: typically $10,000-$25,000 for new detached ADU. Total costs: $3,000-$8,000 in base permit fees plus $10,000-$25,000 in SDCs. Denver (Colorado): plan check $1,500-$4,500; building permit $1,200-$3,500; school impact fees $3,000-$6,000 for new residential units. Total permit and impact fees: $3,000-$10,000 base plus $3,000-$6,000 school fees. Seattle (Washington): plan check $2,000-$5,000; building permit $1,500-$4,000; school impact fees $3,700 per attached ADU, $7,400 per detached ADU. Total permit fees: $4,000-$12,000 base plus school impact fees. Boise (Idaho): plan check $300-$1,500; building permit $800-$3,500. Total permit fees: $1,500-$6,000. Among the most affordable permit environments in our database. Nashville (Tennessee): plan check $200-$1,200; building permit $800-$3,500. Total permit fees: $2,000-$9,000 including water/wastewater tap fees. Salt Lake City (Utah): plan check $300-$1,500; building permit $800-$3,500. Total permit fees: $1,500-$6,000. Charlotte (North Carolina): plan check $300-$1,500; building permit $1,000-$4,000. Total permit fees: $1,500-$6,000.

Construction Costs by Region

Construction labor costs vary dramatically by region and are the primary driver of total ADU project cost. Here is a breakdown of regional construction cost ranges for new detached ADUs in 2026, based on prevailing residential construction rates. Pacific Coast (San Francisco, Los Angeles, San Diego, Seattle, Portland): $350-$700 per square foot of finished living area. A 600-square-foot detached ADU costs $210,000 to $420,000 in construction alone before design, permits, and site work. San Francisco is at the high end of this range. Los Angeles, San Diego, and Seattle are in the middle. Portland is at the lower end of this range but above Inland West cities. Mountain West (Denver, Salt Lake City, Boise): $220-$380 per square foot. A 600-square-foot detached ADU runs $132,000 to $228,000 in construction. Denver is at the high end; Boise is at the low end. The Mountain West has seen construction cost inflation from population growth, but remains materially less expensive than coastal markets. Southern Sunbelt (Austin, Dallas, Nashville, Charlotte): $180-$320 per square foot. A 600-square-foot detached ADU runs $108,000 to $192,000 in construction. Nashville and Charlotte are at the lower end; Austin has seen cost increases from rapid growth. New York City: $400-$700 per square foot for residential construction. NYC is comparable to San Francisco in construction cost. Garage conversions are less expensive per square foot because you are not building from scratch. Expect $150-$350 per square foot for garage conversion work depending on the level of renovation required. Basement conversions similarly run $80-$250 per square foot depending on ceiling height issues, waterproofing requirements, and egress work needed. Prefabricated or modular ADU units from manufacturers like Mighty Buildings, Abodu, Villa, and Dweller have grown popular in California, Oregon, and Washington. These factory-built units typically cost $100,000 to $220,000 fully installed — inclusive of foundation, delivery, and setup — representing significant savings versus custom construction in high-cost coastal markets.

Hidden Costs That Budget Busters Overlook

Many first-time ADU builders focus on construction quotes and permit fees while overlooking a range of additional costs that collectively can add 20-40 percent to total project cost. Architectural and engineering fees typically run 8-15 percent of construction cost. For a $200,000 ADU, this means $16,000 to $30,000 in design fees alone. In California and other states requiring stamped architectural plans, these fees are not optional. Engineering fees for structural, civil, or geotechnical work add an additional layer. Site work costs — grading, drainage, utilities, concrete work — are highly variable and depend on your specific lot conditions. A flat rear yard with existing utility access might add $5,000 to $15,000 in site work. A sloped hillside lot requiring retaining walls and significant grading might add $30,000 to $80,000 in site work costs alone. Utility connection fees: in cities without impact fee waivers, connecting a new ADU to water, sewer, and electrical service requires new meter connections and associated fees. Portland's SDCs include water and sewer system charges. Austin charges Water/Wastewater impact fees separately. Even in cities without formal impact fees, utility connection fees can add $3,000 to $15,000. Underpinning and ceiling height: in New York City and other markets where basement conversions are common, raising ceiling height often requires underpinning the foundation — a structural process costing $30,000 to $80,000 in some cases. Seismic and geotechnical requirements in earthquake-prone markets (San Francisco, Seattle, Los Angeles) may require geotechnical reports ($3,000 to $8,000) and structural engineering upgrades to meet current seismic standards. Construction loan interest: most ADU projects require financing during construction. A 12-month construction loan on a $200,000 ADU project at current rates adds $12,000 to $20,000 in interest costs that must be factored into feasibility. Landscaping restoration: after construction crews access the rear yard, landscaping restoration is typically needed. Budget $2,000 to $10,000 depending on existing yard conditions.

Ways to Reduce ADU Construction Costs

Experienced ADU developers have identified several strategies to reduce total project cost without compromising quality. The choices you make at the planning stage have the largest impact on ultimate cost. Choose garage conversion over new construction. A detached garage conversion to ADU typically costs $60,000 to $150,000 all-in — compared to $150,000 to $400,000 for a new detached ADU. You get the same living space, often with the same rental income potential, at dramatically lower cost. The existing structure handles foundation, framing, and roofing — you are essentially finishing interior space and adding utilities. Use pre-approved standard plans where available. San Diego's Standard ADU Plan Program, Portland's BDS standard plans, and similar programs in other cities offer pre-designed ADU plans reviewed and approved by the planning department. Using a standard plan typically reduces architectural fees by 30-50 percent and reduces plan check review time. Keep size under 750 square feet in California. State law waives impact fees and school fees for ADUs under 750 square feet. Designing to 749 square feet captures the full impact fee waiver benefit in California cities. Build attached rather than detached. Attached ADUs (room additions) typically cost 15-25 percent less per square foot than detached structures because they share at least one wall with the existing dwelling. The shared wall reduces framing, insulation, and siding costs. Avoid hillside sites. ADU projects on sloped lots routinely face $20,000 to $60,000 in additional site work costs compared to flat lots. If you have a choice between properties, a flat or gently sloping lot is significantly more ADU-cost-efficient. Consider prefabricated units in high-cost markets. In California and Pacific Northwest markets, prefab ADU manufacturers offer cost savings compared to custom construction. Get at least three contractor bids. ADU construction pricing varies considerably between contractors. Three competitive bids on the same plans often reveal a 15-25 percent spread in total construction cost.

City-by-City Cost Comparison: Total All-In Estimates

These total all-in estimates combine permit fees, impact fees, construction costs (using regional averages), design fees, and site work for a representative 600-square-foot new detached ADU. All permit and fee figures are sourced from city JSON data on PropertyZoned. San Francisco: permit fees $3,000-$10,000; construction $210,000-$420,000; design fees $20,000-$40,000; site work $10,000-$25,000. Total all-in: $250,000-$500,000+. San Francisco is consistently the most expensive ADU market in the US. Los Angeles: permit fees $2,000-$8,000; construction $150,000-$300,000; design fees $15,000-$30,000; site work $8,000-$20,000. Total all-in: $175,000-$360,000. LA is expensive but notably less than SF. San Jose: permit fees $2,500-$8,500; construction $160,000-$320,000; design fees $15,000-$30,000; site work $8,000-$20,000. Total all-in: $190,000-$380,000. Portland (Oregon): permit fees $3,000-$8,000 base plus $10,000-$25,000 in SDCs; construction $120,000-$240,000; design fees $12,000-$25,000; site work $8,000-$18,000. Total all-in: $155,000-$315,000. Note: SDCs significantly inflate Portland's total compared to its construction cost level. Seattle: permit fees $4,000-$12,000 plus school impact fees $7,400; construction $130,000-$250,000; design fees $12,000-$25,000; site work $8,000-$18,000. Total all-in: $165,000-$315,000. Denver: permit fees $3,000-$10,000 plus school impact fees $3,000-$6,000; construction $100,000-$200,000; design fees $10,000-$22,000; site work $6,000-$15,000. Total all-in: $125,000-$255,000. Austin: permit fees $3,000-$15,000; construction $90,000-$180,000; design fees $9,000-$20,000; site work $6,000-$15,000. Total all-in: $110,000-$230,000. Dallas: permit fees $2,000-$8,000 (no impact fees); construction $80,000-$160,000; design fees $8,000-$18,000; site work $5,000-$12,000. Total all-in: $100,000-$200,000. Nashville: permit fees $2,000-$9,000; construction $80,000-$150,000; design fees $8,000-$18,000; site work $5,000-$12,000. Total all-in: $100,000-$190,000. Boise: permit fees $1,500-$6,000; construction $75,000-$150,000; design fees $7,500-$15,000; site work $5,000-$12,000. Total all-in: $90,000-$185,000. Charlotte: permit fees $1,500-$6,000; construction $75,000-$145,000; design fees $7,500-$15,000; site work $5,000-$12,000. Total all-in: $90,000-$180,000. Salt Lake City: permit fees $1,500-$6,000; construction $80,000-$150,000; design fees $8,000-$15,000; site work $5,000-$12,000. Total all-in: $95,000-$185,000.

Financing Options Overview

ADU construction is a significant capital investment. Most homeowners cannot self-fund a $150,000 to $400,000 project from savings alone. Several financing pathways exist, each with different cost structures and qualification requirements. Home Equity Line of Credit (HELOC): the most common ADU financing tool. A HELOC draws on accumulated home equity, typically at a lower rate than construction loans. Requires sufficient equity (usually 80% LTV or better after the draw). Rates vary with prime rate — plan for 7-10% variable rates in the current environment. HELOCs are flexible (draw as needed during construction) and have relatively low closing costs. Construction-to-permanent loan: a specialized loan that converts from a construction draw structure to a permanent mortgage after the ADU is complete. Often used when you need to finance both construction and a significant portion of the land value. Higher closing costs but long-term fixed rate. California ADU financing programs: the California Housing Finance Agency (CalHFA) ADU Grant Program has offered grants of up to $40,000 for owner-occupied properties meeting income limits. Check CalHFA's current program availability as funding is released in rounds. Some California cities also offer ADU pre-development loans or forgivable loans tied to affordability covenants. Cash-out refinance: if current rates are competitive with your existing mortgage, a cash-out refinance can fund ADU construction with a single first mortgage. Requires lender appraisal of current property value. Portland SDC deferral: for Portland homeowners, System Development Charges can be deferred for ADUs rented at affordable rates under Portland's SDC deferral program — reducing upfront cash requirements. Renovation loan (FHA 203k or Fannie Mae HomeStyle): these loans combine purchase or refinance of the primary home with construction funds, potentially allowing ADU financing bundled into a mortgage product. More complex to execute but useful in some scenarios.

Getting Started: Building Your ADU Budget

A rigorous ADU feasibility analysis before you hire any professionals saves money and time. Here is the recommended process for building an accurate ADU budget. Step 1: Use PropertyZoned's ADU Feasibility Checker to get a preliminary feasibility assessment based on your city, lot, and zone. This gives you a baseline of what types and sizes of ADU are permitted before you invest in design fees. Step 2: Look up your city's permit fee schedule. PropertyZoned's city pages compile current permit fees from official sources. Get your city's ADU-specific fee schedule directly from your building department for current rates. Step 3: Research impact fees and SDCs. For California cities, confirm the 750 sqft threshold for fee waivers. For Portland, get a current SDC estimate before committing to new construction. For Austin, get a Water/Wastewater impact fee estimate from Austin Water. For Seattle, verify current school impact fees with SDCI. Step 4: Get three design fee proposals. Contact three architects familiar with ADU work in your city. Request fixed-fee proposals for ADU design services including permit drawings. Design fees vary considerably and are negotiable. Step 5: Evaluate garage conversion potential. If you have a detached garage in good condition, conversion is likely the most cost-effective ADU path. Get a contractor estimate for garage conversion before committing to new construction. Step 6: Build your cost model. Use the city-by-city ranges above as a starting point. Add your city-specific permit fees, regional construction costs, design fee proposals, and site-specific site work estimates. This gives you a project-specific range. Step 7: Assess financing options. Consult with a lender familiar with ADU financing in your city. CalHFA programs, HELOCs, and construction loans have different qualification criteria and costs. ADU construction is a major investment that typically takes 18-24 months from initial research to certificate of occupancy. Thorough upfront planning dramatically improves outcomes.

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