ADU Cost in San Jose - Plans, Permits & Build, One Fixed Price

How Much Does an ADU Cost in San Jose?

An accessory dwelling unit (ADU) in San Jose typically costs between $190,000 and $420,000 for a detached unit, while garage conversions run $140,000 to $210,000 and attached units land between $160,000 and $260,000. That’s the full build cost, including permits, design, site work, and finishes. Expect permit fees alone to add $12,000 to $25,000 to any San Jose ADU project, depending on school district fees, park fees, and utility connection charges.

Those numbers reflect what we see across Willow Glen, Cambrian, Evergreen, Berryessa, and the rest of San Jose in 2026. If you’re just starting to research, a ballpark of $250,000 for a typical detached one-bedroom ADU is a solid planning number. But there are big swings up and down from there, and that’s what this guide walks through.

What you’ll notice right away: San Jose is not a cheap place to build. The city’s ADU permit process is one of the more involved in the Bay Area, and labor rates here are higher than most of the country. But there are ways to keep costs down without cutting corners, and we’ll get into those too.

The home page for Lodgewick ADU San Jose has more on how we approach projects, but for now, let’s get into the actual dollars.

ADU Cost Breakdown (2026)

Here’s a line-by-line look at where the money goes on a typical detached ADU in San Jose. These figures are based on 2026 pricing for a 600-square-foot, one-bedroom, one-bath unit built to current California Building Code standards.

Cost Component	Typical Range (San Jose, 2026)	Notes
Design & Architecture	$8,000 – $18,000	Site-specific plans, Title 24 energy calculations, structural drawings
City Permits & Fees	$12,000 – $25,000	Building permit, school impact fees, sewer/water connection fees, park fees
Site Preparation	$10,000 – $30,000	Tree removal, grading, utility trenching, foundation excavation
Foundation	$25,000 – $45,000	Slab-on-grade for a 600 sq ft unit; increases with soil conditions
Framing & Shell	$40,000 – $70,000	Walls, roof structure, windows, exterior doors, roofing
Plumbing	$15,000 – $28,000	Full bathroom, kitchenette, water heater, sewer line connection
Electrical	$12,000 – $22,000	New subpanel, wiring, fixtures, smoke/CO detectors, solar-ready conduit
HVAC	$8,000 – $16,000	Mini-split system is standard; ducted systems cost more
Insulation & Drywall	$10,000 – $18,000	Title 24 insulation requirements, board, tape, texture
Interior Finishes	$25,000 – $55,000	Flooring, cabinets, counters, paint, trim, bathroom tile, fixtures
Appliances	$4,000 – $10,000	Range, refrigerator, dishwasher, washer/dryer hookups
Exterior Finish & Paint	$8,000 – $18,000	Siding, exterior paint, gutters, weatherproofing
Landscaping & Cleanup	$3,000 – $8,000	Basic regrading, gravel or path, haul-away
General Contractor Overhead & Profit	15 – 25% of hard costs	Project management, scheduling, warranties, coordination
Total – Detached ADU	$190,000 – $420,000	600 sq ft to 1,200 sq ft typical buildout

A few things worth knowing about those numbers. First, garage conversions run lower on average because the foundation, framing, and roof already exist. You’re paying for interior work, utility connections, and exterior upgrades rather than a full ground-up build. Second, attached ADUs (also called addition ADUs) land in the middle because you’re tying into the existing home’s roofline and utilities, which cuts some foundation and roof costs but adds complexity around the connection point.

JADU Costs in San Jose

A Junior ADU (JADU) is a smaller conversion inside the existing home footprint, usually 500 square feet or less, often converted from a bedroom, den, or attached garage. These run $70,000 to $120,000 in San Jose. The lower cost comes from no new foundation and minimal site work. Permits are also cheaper, typically $4,000 to $8,000. The tradeoff is that a JADU usually shares some facilities with the main house, which limits rental independence.

What Affects ADU Pricing in San Jose

Every lot is different, and San Jose’s size makes that especially true. A Cambrian backyard with good soil and a flat grade is a different project than an Almaden Valley hillside lot or an older Willow Glen property with mature trees and a tight setback. Here’s what moves the price most.

• Lot slope and soil conditions. San Jose has a mix of flat valley floor and hillside terrain. Hillside lots in Almaden Valley, Evergreen’s eastern edges, or Silver Creek often need retaining walls, deeper footings, or pier-and-grade-beam foundations, adding $20,000 to $60,000.
• Utility distance and capacity. The farther the ADU sits from the main panel and sewer line, the more trenching and pipe you need. A 40-foot underground electrical run might cost $4,000; a 120-foot run could hit $12,000. Older homes may also need a main panel upgrade ($3,500 – $6,000) before the ADU can even be approved.
• Tree removal and protection. San Jose has strict tree protection ordinances. Removing a heritage-sized tree or working around protected oaks can add $5,000 to $15,000 and add weeks to the permit process.
• Attached vs. detached. Detached ADUs cost the most per square foot because they need their own foundation, roof, and exterior envelope. Attached ADUs share a wall and sometimes utilities, cutting cost by roughly 10 – 15%.
• Finish level. Builder-grade cabinets and standard tile might total $25,000 for interior finishes on a 600-square-foot unit. Semi-custom cabinetry, quartz counters, and upgraded flooring push that to $45,000 or more. The ceiling is really set by the homeowner’s choices.
• Prefab vs. site-built. This is a bigger factor than most people expect. Prefab ADUs from manufacturers like Abodu, Cover, and Dvele can come in 20 – 35% under site-built costs on the construction side, but the site work, permits, and utility connections stay roughly the same. We work with these brands regularly and can help you compare an Abodu 600-square-foot model against a traditional build on the same lot. We also work with Mighty Buildings, Boxabl, Plant Prefab, Tuff Shed (for detached studios), and James Hardie siding materials.

How Much Does a Garage Conversion Cost in San Jose?

A garage conversion to an ADU in San Jose typically runs $140,000 to $210,000 for a one-bedroom unit of about 400 to 500 square feet. That includes everything from engineering and permits to a finished living space with a kitchenette and full bathroom.

Garage conversions are popular in San Jose because the structure already exists. The framing, roof, and foundation are already there, which saves $40,000 to $80,000 compared to a detached build. What you’re paying for is mostly interior work: insulation, drywall, plumbing, electrical, flooring, windows, and the conversion of the garage door opening into a proper wall or entry.

A few San Jose-specific realities: many garages in Cambrian and Willow Glen were built before current seismic codes, so expect some structural retrofit work, typically $8,000 to $20,000. Also, converting a garage means giving up covered parking, which matters if you’re in a neighborhood with tight street parking or an HOA that has rules about on-street vehicles.

How Much Does a Detached ADU Cost per Square Foot in San Jose?

Detached ADUs in San Jose run $380 to $560 per square foot for the full project in 2026. At the lower end, that’s a simple design, standard finishes, and a straightforward lot. At the upper end, you’re looking at premium finishes, a complicated site, or a larger unit where economies of scale haven’t kicked in for the fixed costs like permits.

Here’s the nuance: smaller units have a higher cost per square foot because the fixed expenses (permits, design, utility connections, project management) are spread across fewer square feet. A 400-square-foot studio at $200,000 is $500 per square foot. A 1,000-square-foot two-bedroom at $380,000 is $380 per square foot. Both are realistic San Jose projects.

2026 San Jose ADU Permit Costs

San Jose’s permit fees for an ADU land between $12,000 and $25,000, and they’re a line item homeowners often underestimate. The breakdown looks like this:

• Building permit: $3,000 – $8,000 depending on project valuation
• School impact fees: $4,000 – $10,000 for detached ADUs (garage conversions and JADUs under 750 sq ft are often exempt under current state law)
• Sewer and water connection fees: $2,500 – $6,000
• Park and traffic fees: $1,000 – $3,000
• Plan check and inspection fees: $1,500 – $4,000

California state law has made some of these more predictable. SB 9 and the ADU streamlining provisions require San Jose to review ADU permit applications within 60 days, and state law caps some impact fees for ADUs under 750 square feet. But the city still enforces its own school district fees and park fees, which is why the range above is wide. Every project includes the full permit fee disclosure in the written contract before work starts. That’s part of the Kingswell Guarantee, and it’s not something we treat as optional.

How to Save on an ADU in San Jose

The biggest lever on cost is choosing the right type of unit for your lot. That’s a conversation worth having before you commit to a design. Here’s what moves the needle in San Jose specifically.

Start with a garage conversion if the garage is in decent shape. If your garage has a serviceable slab, straight walls, and a roof that doesn’t need replacing, you’re already ahead by tens of thousands of dollars compared to ground-up construction.

Look at a JADU if the rental use is for family. A JADU can’t be sold separately and may have occupancy rules tied to the main house, but if you’re building for an aging parent or adult child, a $90,000 JADU beats a $250,000 detached unit.

Consider prefab, but account for the whole project cost. Prefab manufacturers like Abodu and Cover produce high-quality modules in a factory, which reduces on-site labor time and weather delays. The construction portion of a prefab ADU can be $50,000 to $80,000 below site-built, but site work, permits, and utilities remain full cost. We’ve built with these brands and can give you a realistic all-in number for your specific lot.

Avoid mid-project change orders. The single most common cause of budget overrun in San Jose is the homeowner changing finishes after framing starts. A written scope of work and a fixed price before demolition begins is the most reliable cost-control tool. That’s why our process under The Kingswell Guarantee includes a written price before any work starts, with no price changes at the door.

Keep the kitchenette modest. A full kitchen with a four-burner range, hood, and dishwasher adds $8,000 to $15,000 versus an efficiency kitchen with a two-burner cooktop and under-counter fridge. If you’re building for a tenant, many renters don’t need a full kitchen if the unit is near transit, downtown, or a commercial district. If you’re building for family, a modest efficiency kitchen still works fine for most daily use.

If you want to get a real number for your specific lot and scope, call (669) 266-4319. Estimates are free, and you’ll get a written number in your hands, not a verbal ballpark that changes later.

Hourly Rates and Cost to Hire an ADU Contractor in San Jose

Most San Jose ADU contractors bid the project as a fixed-price contract, not hourly. But behind that fixed price are labor rates that shape the bid. Here’s what labor costs look like in San Jose in 2026:

• General contractor: $85 – $140 per hour (owner-operator rates; larger firms charge more)
• Framing carpenter: $65 – $95 per hour
• Electrician: $90 – $135 per hour
• Plumber: $85 – $130 per hour
• HVAC technician: $80 – $120 per hour
• Painter/drywall finisher: $50 – $75 per hour
• Designer/architect: $90 – $150 per hour for custom work

When you see a $300,000 bid for a detached ADU, roughly $110,000 to $140,000 of that is labor. That’s the San Jose reality. Bay Area wages are high, and the contractors who do ADU work well are busy enough that they’ll simply walk away from a job that’s priced too low to sustain quality work.

How Long Does an ADU Take in San Jose?

From first design meeting to move-in, a detached ADU in San Jose takes 9 to 14 months. The phases break down like this:

• Design and engineering: 4 – 8 weeks for plans, structural calcs, Title 24 energy reports
• Permit review: 6 – 10 weeks under San Jose’s current ADU streamlining. The city is better than most Bay Area jurisdictions, but don’t plan around 60 days exactly. We’ve seen 45-day reviews on clean applications and 12-week reviews when plan checkers request structural revisions on hillside lots. Then add 4 – 6 weeks for any revisions and re-submittal.
• Site prep and foundation: 3 – 6 weeks depending on soil, utility trenching, and weather
• Framing, roofing, and exterior close-in: 4 – 8 weeks
• Rough-in (plumbing, electrical, HVAC): 3 – 5 weeks
• Insulation, drywall, finishes: 6 – 10 weeks
• Final inspection and occupancy approval: 1 – 2 weeks

Prefab projects compress the middle of that timeline. An Abodu or Cover unit can go from crane-set to finish in 6 – 8 weeks on top of roughly the same permitting window. If speed matters more than custom design, that’s worth exploring.

Is an ADU a Good Investment in San Jose?

For most San Jose homeowners, the answer is yes, but the math matters more than the marketing would have you believe. A $250,000 one-bedroom ADU in a good West San Jose or Cambrian neighborhood rents for $1,800 to $2,400 a month in 2026. That’s a gross yield of 8.6% to 11.5%, which is strong by Bay Area standards. But subtract property taxes (which rise with the added tax assessment for the improvement), insurance, maintenance, and vacancy, and the net yield lands closer to 6% to 8%.

The other consideration: ADUs add to your property’s assessed value, which triggers a supplemental property tax bill in the first year and higher property taxes after that. Figure roughly 1.0% to 1.2% of the ADU cost per year in additional property taxes. On a $250,000 ADU, that’s $2,500 to $3,000 a year. It’s real money, and it changes the investment picture.

There’s also the non-financial value that doesn’t show up in a spreadsheet: keeping aging parents close, giving an adult child a low-rent start in an expensive city, or creating a home office that’s actually separate from your living space. Many of our San Jose clients aren’t building primarily for rental income. They’re building because the lodge concept (a small house on a larger property) solves a family problem that no other option can.

How Much Does a Prefab ADU Cost in San Jose?

Prefab ADUs from brands like Abodu, Cover, and Dvele run $160,000 to $300,000 all-in for a one-bedroom unit in San Jose, including delivery, crane set, utility connections, and finishes. The factory-built portion runs $110,000 to $200,000 depending on the model, and site work, foundation, and permits make up the rest. Boxabl and Mighty Buildings tend to run at the lower end of that range, while Dvele and Plant Prefab sit at the higher end because of their premium materials and finish packages.

Tuff Shed is a different category entirely. Their backyard studios start around $25,000 to $60,000, but they are not habitable ADUs without major additional investment in insulation, electrical, plumbing, and permitting. If someone quotes you a $40,000 Tuff Shed and calls it an ADU, that number doesn’t include what’s actually required for legal occupancy in San Jose.

San Jose ADU Rules That Affect Cost

San Jose follows California’s statewide ADU standards, which are among the most permissive in the country, with some local specifics:

• Lot size: No minimum lot size for ADUs under current state law. If you have a single-family home, you can likely build an ADU.
• Setbacks: 4-foot side and rear setbacks for detached ADUs, matching state law, though corner lots and lots facing two streets may have additional restrictions.
• Height limits: 16 feet for detached ADUs, or 18 feet if within a half-mile of transit. Two-story ADUs are allowed if the lot zoning and setbacks permit it.
• Square footage caps: 850 sq ft for a one-bedroom ADU, 1,000 sq ft for a two-bedroom, or 50% of the primary home’s living area, whichever is less. The state law sets these, and San Jose follows them.
• Parking: No additional parking required if the ADU is within a half-mile of transit, in a historic district, or if the ADU is a conversion of existing space. This matters in San Jose because many neighborhoods near Stevens Creek Boulevard, Santa Clara Street, and the light rail lines qualify.
• JADU rules: JADUs must be within the existing structure or attached garage, and the property owner must live in one of the units. That owner-occupancy rule trips up some homeowners planning to move away and rent both units.

These rules shape what’s possible and therefore what it costs. A 1,000-square-foot two-bedroom ADU on a half-acre Evergreen lot is very doable. That same 1,000-square-foot two-bedroom on a 5,000-square-foot Willow Glen lot probably isn’t, because of the 50% of primary home rule. We’ll tell you what’s actually buildable on your lot before you spend money on design.

What’s the Cheapest Way to Build an ADU in San Jose?

The cheapest habitable ADU in San Jose is a JADU conversion at $70,000 to $120,000. After that, a garage conversion at $140,000 to $210,000 is the next tier. A detached studio from a prefab manufacturer might land around $160,000 all-in on a simple, flat lot with good utility access.

Be careful with the cheapest options, though. The $70,000 JADU assumes an existing space that’s in sound condition and close to existing plumbing. If your garage slab is cracked or the framing has termite damage from San Jose’s damp winters and dry summers, the “cheap” conversion can turn into an expensive rebuild. We inspect before we quote, and the written price reflects what we actually find, not a hopeful guess.

How to Choose an ADU Contractor in San Jose

An ADU is a six-figure investment, and the contractor you choose determines whether that money becomes a good building or a source of regret. Here’s what to look for in the San Jose market:

A written price before the work starts. Not a proposal with allowances and disclaimers. A price. If a contractor can’t put a number in writing, you can’t trust the number they’ll give you later. Our contracts include a written price before any work begins, every time. That’s not a marketing line. It’s how The Kingswell Way works.

A real arrival window. ADU projects are long, but the daily arrival behavior still matters. If the crew says they’ll be there Tuesday morning and shows up Thursday afternoon without a call, you have a communication problem that will repeat itself for 12 months. We give a defined arrival window and keep it.

A clean job site. A backyard construction site is disruptive by nature, but it doesn’t need to be a debris field. Respect for the site is a predictor of respect for the work.

A written guarantee. Ask what happens if something fails in year one. A contractor who hesitates or says “call me if anything comes up” hasn’t thought through the commitment. Our 365-Day Done Right Promise is written into every contract: if the work isn’t right, we come back and make it right, free, within the guarantee period.

Background-checked crews. These people are on your property for months. Uniformed, background-checked technicians are standard on every Lodgewick job site, so you always know who belongs there.

A live person on the phone. If you call at 7 a.m. on a Saturday with a question and hit a voicemail, that’s your answer about how the company handles questions after the contract is signed. A live person answers every call at (669) 266-4319, 24 hours a day, 7 days a week.

Russ Delmar leads Lodgewick ADU San Jose, and the standard for communication, cleanliness, and written commitments is set from the top. That’s not a platitude. It’s how projects actually run on the ground.

FAQs – San Jose ADU Cost

How much does a 1-bedroom ADU cost in San Jose?

A one-bedroom detached ADU in San Jose costs $190,000 to $320,000 for a 500 to 700 square-foot unit in 2026. Garage conversions for a one-bedroom layout run $140,000 to $190,000. The wide range comes mostly from site conditions and finish choices. Call (669) 266-4319 for a written quote on your specific lot.

How much does a 2-bedroom ADU cost in San Jose?

A two-bedroom detached ADU (700 to 1,000 square feet) runs $280,000 to $420,000 in San Jose. Two-bedroom units require more square footage, which drives up nearly every cost line, and the larger footprint often requires more site work and utility capacity. Expect permits for a two-bedroom ADU to hit the $15,000 to $25,000 range.

Is it cheaper to build an ADU or convert a garage?

Converting a garage is cheaper, typically $140,000 to $210,000 compared to $190,000 to $320,000 for a comparable one-bedroom detached ADU. The garage already has a foundation, walls, and a roof, which eliminates $40,000 to $80,000 in construction costs. The downside is losing your garage, which matters if you need the storage or parking.

Can you build an ADU in San Jose for under $150,000?

Yes, but with significant limits. A JADU conversion under 500 square feet can come in at $70,000 to $120,000, and a very basic garage conversion in a structurally sound garage might land at $140,000 to $150,000. For a new detached ADU, under $150,000 is not realistic in San Jose in 2026 unless you’re doing substantial work yourself, which most homeowners shouldn’t attempt for structural, utility, and permitting work.

How much does an ADU permit cost in San Jose?

San Jose ADU permit fees run $12,000 to $25,000 depending on unit size, type, and school district fees. Garage conversions and JADUs under 750 square feet may be exempt from school impact fees under current California law, which is a significant savings. Every Lodgewick contract includes the exact permit cost in the written price. Call (669) 266-4319 for details on your project.

How fast can an ADU be built in San Jose?

The fastest realistic timeline is 6 to 8 months from design start to move-in if you use a prefab unit from Abodu or Cover and your lot is simple. Site-built ADUs run 9 to 14 months. The permitting phase is rarely the bottleneck with San Jose’s current ADU processing times; site work and utility connections are.

Does an ADU increase property value in San Jose?

Yes. Market data for San Jose in 2025 and 2026 shows ADUs adding $150,000 to $350,000 in resale value, roughly in line with construction cost but with the added benefit of rental income during ownership. Appraisers in the Bay Area increasingly use the income approach for ADU-adjacent valuations, which rewards well-built units in strong rental neighborhoods.

Do you need a permit for an ADU in San Jose?

Yes. All ADUs and JADUs in San Jose require city building permits, and unpermitted ADUs cannot legally be rented and can complicate a future home sale. The permit process is manageable with a contractor who knows it well, which is one reason to choose a company that handles San Jose ADU permitting as standard practice rather than as an add-on service.

Get a Written Price for Your San Jose ADU

If you’re ready to turn your backyard or garage into livable space, start with a real number, not a guess. Call (669) 266-4319 and we’ll set up a site visit at your San Jose property. You’ll get a written price before any work starts, with the permit costs, site work, and finishes clearly broken out. No allowances that can balloon later, no scope gaps discovered mid-project, and no pressure. Just a straight answer about what the project will cost on your lot.

What you get with Lodgewick ADU San Jose: a written price first, a defined arrival window on every scheduled day, a clean job site from framing to paint, and a written guarantee on every project. If the work isn’t right within the 365-day period, we come back and make it right. That’s The Kingswell Guarantee, and it’s in writing before the first nail goes in.

Russ Delmar and the crew here know San Jose’s lots, its permit desk, and its neighborhoods. We’re not the cheapest option in town, and we’re not trying to be. We’re the option that puts the price, the promise, and the plan in writing.

Pricing reflects the San Jose market as of 2026. Lodgewick ADU San Jose offers free estimates – call (669) 266-4319.