New Detached ADU Cost - Plans, Permits & Build, One Fixed Price

How Much Does New Detached ADU Cost in San Diego?

A new detached ADU in San Diego typically costs between $275,000 and $420,000 for a turnkey build in 2026, with most homeowners in neighborhoods like Clairemont, North Park, and Rancho Peñasquitos landing around $325,000 to $375,000 for a 700 to 900 square foot, one-bedroom unit. Prefab units from brands like Abodu or Cover tend to come in at the lower end of that spectrum, while fully custom builds with higher-end finishes push toward $500,000 or more. These numbers include construction, permits, utility connections, and standard interior finishes, but exclude major site work like slope remediation or retaining walls, which can add another $30,000 to $80,000 depending on your lot.

At Lodgewick ADU San Diego, we put a written price in your hands before any work begins, so you’re never guessing what the final bill will look like. If you want a firm number for your specific property, call us at (619) 376-2760 for a free estimate.

If you’re starting your research, our guide to New Detached ADU in San Diego walks through the full process from lot assessment to final inspection.

Key Takeaways: New Detached ADU Cost in San Diego

• Typical total cost: $275,000 – $420,000 for a standard one-bedroom detached unit in 2026
• Cost per square foot: $380 – $550, with prefab units starting near $300/sq ft
• Permits and fees: $18,000 – $35,000 depending on the jurisdiction and utility connection requirements
• Timeline: 8 – 16 months for custom builds; 5 – 10 months for prefab, start to move-in
• Biggest cost drivers: slope and soil conditions, foundation type, utility trenching distance, and finish level

New Detached ADU Cost Breakdown (2026)

Here’s where the money actually goes on a typical San Diego detached ADU project. These are real ranges based on the bids and builds we’ve managed across the county since 2010.

Cost Item	Typical Range (San Diego)	Notes
Architecture & engineering	$12,000 – $28,000	Site plan, structural drawings, Title 24 calcs, soil report if required
Permits & city fees	$18,000 – $35,000	Building, electrical, plumbing, mechanical permits; School fees; sewer and water connection fees
Site prep	$10,000 – $60,000	Demo, grading, trenching, tree removal, retaining walls if slope exceeds 4:1
Foundation	$25,000 – $60,000	Slab on grade is least expensive; raised or post-tension foundations cost more on expansive soils
Framing & structure	$40,000 – $90,000	Materials cost for lumber alone has ranged from $14 – $22 per sq ft since 2023
Electrical	$18,000 – $40,000	New subpanel, interior wiring, fixture installation, solar readiness if desired
Plumbing	$15,000 – $35,000	New sewer lateral, water supply line, interior rough-in, fixtures
HVAC	$8,000 – $20,000	Mini-split systems are the standard choice for ADUs in San Diego’s climate
Drywall, insulation & paint	$18,000 – $38,000	Insulation requirements are strict under California’s 2025 Energy Code (Title 24)
Flooring	$6,000 – $18,000	LVP and engineered hardwood are the most common choices we install
Kitchen	$20,000 – $50,000	Stock cabinets to semi-custom, mid-range appliances, stone or quartz countertops
Bathroom	$12,000 – $30,000	One full bath with tub or walk-in shower, mid-range fixtures
Windows & doors	$10,000 – $25,000	Dual-pane, low-E, Title 24 compliant
Roofing	$12,000 – $30,000	Composition shingle is most common; standing seam metal runs 30 – 50% higher
Exterior finish	$15,000 – $40,000	Stucco, fiber cement (James Hardie), or wood siding
Contractor overhead & project management	$30,000 – $60,000	Typically 12 – 18% of the total build cost

What drives the difference between a $300,000 build and a $420,000 build on a similar footprint? Three things: soil conditions, access, and finishes. If your backyard in Bay Ho has deep clay or requires a 60-foot trench to reach the sewer line, your site costs climb quickly. If the unit is a 900-square-foot two-bedroom rather than a 600-square-foot one-bedroom, everything scales up. And if you choose custom cabinetry, quartzite counters, and a standing-seam metal roof, the finish budget alone can double.

Prefab ADUs from brands we work with directly, including Abodu, Cover, Dvele, Mighty Buildings, Boxabl, and Plant Prefab, typically come in between $180,000 and $320,000 all-in, including installation and standard site work. The trade-off: less design flexibility, but faster timelines and fewer change-order surprises during the build.

What Affects New Detached ADU Pricing in San Diego

Every lot is different, and San Diego’s geography throws more variables at an ADU build than most homeowners expect. Here are the six factors that move your price the most.

1. Your lot’s slope and soil

A flat lot in Mira Mesa generally needs a simple slab-on-grade foundation. A hillside lot in Mission Hills or Bankers Hill often requires caissons, retaining walls, or a raised foundation system, which can add $25,000 to $70,000 before any vertical construction even starts. San Diego’s coastal mesas hide a lot of expansive clay and decomposed granite, and the difference between good soil and bad soil isn’t visible from the surface.

2. Trenching distance to utilities

If your ADU sits 20 feet from the main house’s sewer and electrical panel, connection costs stay modest. If it’s 90 feet from the nearest sewer lateral in a Tierrasanta backyard, the plumbing and electrical trenching line items can jump from $8,000 to $25,000. That’s pure distance, not material upgrades.

3. Unit size and bedroom count

A 500-square-foot studio ADU in City Heights might cost $210,000 all-in. A 1,000-square-foot two-bedroom in Scripps Ranch will land closer to $480,000. More square feet means more of everything: foundation, framing, electrical, drywall, finishes. And San Diego’s ADU ordinance allows detached units up to 1,200 square feet in most residential zones, so the upper end of that range is very much on the table.

4. Prefab vs. custom construction

Prefab ADU manufacturers set a base price for the module, but the total installed cost includes the foundation, utility connections, and site work. A 640-square-foot Abodu unit with a standard foundation and typical site conditions runs about $250,000 to $300,000 in San Diego. A comparable custom stick-built unit usually starts around $330,000. Prefab saves around 15 – 22% on average, mostly through construction-time efficiency.

5. Finish level

Mid-range finishes, what we’d call “rental-grade but nice,” cost roughly $45 – $60 per square foot for materials in the kitchen and bath. High-end finishes, custom cabinets, quartzite or marble, and designer lighting, run $110 – $160 per square foot. On a 750-square-foot unit, that’s a $50,000 to $80,000 swing.

6. Permitting jurisdiction

The City of San Diego has streamlined ADU permitting under state law SB 9 and the city’s ADU Bonus Program, but fees still vary by address. A typical permit package in the city runs $18,000 to $30,000 when you include school fees, park impact fees (waived for ADUs under 750 sq ft), and connection charges. Unincorporated San Diego County areas, like parts of Spring Valley or Lakeside, follow different fee schedules, and some jurisdictions add stormwater requirements that city builds don’t face.

Prefab vs. Custom Detached ADU Costs in San Diego

Homeowners weighing a new detached ADU often ask whether a prefab or custom build makes more sense for their budget. Here’s a quick side-by-side, based on the projects we’ve managed across San Diego County.

• Abodu (prefab): 500 – 890 sq ft, $210,000 – $390,000 installed. Timeline: 5 – 8 months. Best for flat lots with simple access.
• Cover (prefab, panelized): 600 – 1,200 sq ft, $260,000 – $520,000 installed. Timeline: 7 – 10 months. More design customization than a standard module.
• Dvele (prefab, high-performance): 400 – 1,600 sq ft, $290,000 – $700,000 installed. Timeline: 9 – 14 months. Top-tier energy efficiency and durability.
• Boxabl (casita-scale): 360 – 480 sq ft, $95,000 – $160,000 installed. Timeline: 4 – 7 months. Compact, efficient, but limited to studio and one-bedroom layouts.
• Custom stick-built: 500 – 1,200 sq ft, $275,000 – $550,000. Timeline: 10 – 16 months. Full design control, tailored to any lot condition.

The right answer depends on your lot, your budget, and how soon you need the unit occupied. We walk through those trade-offs on our New Detached ADU in San Diego page, and every estimate we provide includes a clear comparison of prefab versus custom options matched to your property.

How to Save on a New Detached ADU in San Diego

Building an ADU is a major investment, but there are legitimate ways to reduce the total without cutting corners on structure, safety, or livability.

Stay under 750 square feet

The City of San Diego waives certain impact fees for ADUs under 750 square feet. Depending on your address, that waiver can save $6,000 to $12,000 in city fees alone.

Choose a simple foundation

If your lot allows it, a slab-on-grade foundation is the least expensive option. Avoid raised foundations unless your slope or drainage situation genuinely requires it.

Use a prefab or panelized system

Prefab ADUs from brands like Cover and Abodu reduce on-site construction time by 40 – 60%, which means lower project management costs and fewer weather-related delays. On a $350,000 build, that efficiency can translate to $25,000 – $45,000 in savings.

Select mid-range finishes

Most of the money you’ll spend on finishes lives in the kitchen and bathroom. Stock cabinets, quartz counters, and standard tile will serve tenants and family members just as well as custom millwork, and they’ll save you $20,000 to $50,000 depending on the unit size.

Plan the utility route early

The single most avoidable cost driver we see is trenching distance rework. If you know where the ADU will go and route utilities along the shortest practical path before the septic or sewer connection is planned, you can keep that line item under $12,000 in most cases.

The best way to get a real number is to have us walk your property and give you a written estimate. There’s no charge for it, and you’ll have a number you can plan around. Call (619) 376-2760 to schedule one.

How We Price New Detached ADUs: The Kingswell Way

Lodgewick ADU Builders is the ADU company of the Kingswell family, and we’ve been building accessory dwelling units, garage conversions, and home additions in San Diego since 2010. The Kingswell Way is simple: say the price before the work begins, show up in the window we give you, leave the job site cleaner than we found it, put the guarantee in writing, and come back if anything fails.

Every project we take on operates under The Kingswell Guarantee. That means you get a written price before any work starts, no price changes at the door, a defined arrival window for every crew day, and a written guarantee on every build. If your ADU has a problem within the first year, we come back and make it right, covered by our 365-Day Done Right Promise. That commitment is written into every contract, not just referenced in a brochure.

Russ Delmar leads our San Diego team. He’s been managing residential construction in this county for over a decade, and he personally reviews every estimate that goes out the door. If a number doesn’t look right to him, it doesn’t leave our office.

We also work hands-on with the leading prefab ADU manufacturers, including Abodu, Cover, Dvele, Mighty Buildings, Boxabl, and Plant Prefab, as well as material suppliers like James Hardie and Tuff Shed. That means the pricing we quote reflects actual current costs from the brands we’ll be installing on your property, not generic square-foot averages from a national database.

And when you call us, a live person answers. Not a voicemail, not a chatbot. 24 hours a day, 7 days a week, at (619) 376-2760. If you have a question about your build, your guarantee, or the estimate you received, you’ll talk to a human being who knows what’s happening on your project.

If you’re just starting to research, our home page has an overview of our ADU services and the areas we cover across San Diego County.

FAQs – New Detached ADU Cost in San Diego

How much does a new detached ADU cost in San Diego in 2026?

A new detached ADU in San Diego typically costs $275,000 to $420,000 turnkey. Smaller prefab units from brands like Boxabl can come in under $200,000, while custom two-bedroom builds over 1,000 square feet often exceed $500,000. Call (619) 376-2760 for a written estimate specific to your lot and floor plan.

Is it cheaper to build a prefab ADU or a custom ADU in San Diego?

Prefab is usually cheaper. A 640-square-foot Abodu or Cover unit typically costs $210,000 to $320,000 installed, while a comparable custom stick-built unit runs $330,000 to $420,000. Prefab saves 15 – 22% on average due to shorter construction timelines and factory-controlled material costs.

How much do ADU permits cost in San Diego?

ADU permit fees in the City of San Diego typically run $18,000 to $35,000 including building, electrical, plumbing, and mechanical permits, school fees, and water/sewer connection charges. Fees in unincorporated county areas can vary by jurisdiction. Lodgewick handles the entire permitting process as part of every build.

How long does it take to build a new detached ADU in San Diego?

A prefab ADU from Abodu, Cover, or Boxabl can be move-in ready in 5 to 10 months from the date permits are submitted. A custom stick-built unit typically takes 10 to 16 months, depending on site conditions, design iterations, and inspection scheduling. Your written estimate includes a projected timeline, and our arrival window commitment keeps that schedule honest.

What’s the most expensive part of building a new detached ADU in San Diego?

Site preparation and foundation work are the most variable, ranging from $10,000 to $120,000 depending on slope, soil, tree removal, and utility trenching distance. On a typical flat lot, the foundation and site work account for about 12 – 16% of total cost. On a hillside lot in neighborhoods like Mission Hills or La Jolla, that share can exceed 25%.

Can I get a written price before I commit to building?

Yes. At Lodgewick ADU San Diego, every project begins with a written estimate provided before any work starts. That price is committed in writing, with no changes at the door. We also include a written guarantee on every build. Call (619) 376-2760 to schedule a free on-site assessment and get your number in writing.

What Your San Diego ADU Budget Should Plan For in 2026

If you’re setting a budget for a new detached ADU in San Diego, plan on $325,000 to $375,000 for a well-built one-bedroom unit with mid-range finishes on a typical flat lot. Set aside an additional 10 – 15% for contingencies, especially if your property has slope, access challenges, or older utility lines that may need replacement. And get the number committed in writing before you sign anything.

When we walk a property in Clairemont or Rancho Bernardo, we’re looking for the same things you’d look for: How far is the sewer line? What’s the soil doing? Is the electrical panel at capacity? Those are the details that determine whether your build stays under $350,000 or pushes past $450,000. A thorough site visit from someone who’s built ADUs in this county for years is the difference between a pleasant surprise and a painful one.

Lodgewick ADU San Diego provides free, no-pressure estimates for new detached ADUs, garage conversions, and home additions across San Diego County. Call us at (619) 376-2760 and ask for a site walk. You’ll get a written price, a realistic timeline, and a builder who stands behind the work with a written guarantee.

Pricing reflects the San Diego market as of 2026. Lodgewick ADU San Diego offers free estimates – call (619) 376-2760.

Written by Russ Delmar, Owner at Lodgewick ADU San Diego, serving San Diego County since 2010.